Journal of Applied Crystallography
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Journal of Applied Crystallography covers a wide range of crystallographic topics from the viewpoints of both techniques and theory. The journal presents articles on the application of crystallographic techniques and on the related apparatus and computer software. For many years, Journal of Applied Crystallography has been the main vehicle for the publication of small-angle scattering articles and powder diffraction techniques. The journal is the primary place where crystallographic computer program information is published.enCopyright (c) 2018 International Union of Crystallography2018-09-24International Union of CrystallographyInternational Union of Crystallographyhttp://journals.iucr.orgurn:issn:1600-5767Journal of Applied Crystallography covers a wide range of crystallographic topics from the viewpoints of both techniques and theory. The journal presents articles on the application of crystallographic techniques and on the related apparatus and computer software. For many years, Journal of Applied Crystallography has been the main vehicle for the publication of small-angle scattering articles and powder diffraction techniques. The journal is the primary place where crystallographic computer program information is published.text/htmlJournal of Applied Crystallography, Volume 51, Part 5, 2018textweekly62002-02-01T00:00+00:005512018-09-24Copyright (c) 2018 International Union of CrystallographyJournal of Applied Crystallography1262urn:issn:1600-5767med@iucr.orgSeptember 20182018-09-24Journal of Applied Crystallographyhttp://journals.iucr.org/logos/rss10j.gif
//journals.iucr.org/j/issues/2018/05/00/isscontsbdy.html
Still imageSerial electron crystallography for structure determination and phase analysis of nanocrystalline materials
http://scripts.iucr.org/cgi-bin/paper?yr5034
Serial electron crystallography has been developed as a fully automated method to collect diffraction data on polycrystalline materials using a transmission electron microscope. This enables useful data to be collected on materials that are sensitive to the electron beam and thus difficult to measure using the conventional methods that require long exposure of the same crystal. The data collection strategy combines goniometer translation with electron beam shift, which allows the entire sample stage to be probed. At each position of the goniometer, the locations of the crystals are identified using image recognition techniques. Diffraction data are then collected on each crystal using a quasi-parallel focused beam with a predefined size (usually 300–500 nm). It is shown that with a fast and sensitive Timepix hybrid pixel area detector it is possible to collect diffraction data of up to 3500 crystals per hour. These data can be indexed using a brute-force forward-projection algorithm. Results from several test samples show that 100–200 frames are enough for structure determination using direct methods or dual-space methods. The large number of crystals examined enables quantitative phase analysis and automatic screening of materials for known and unknown phases.Copyright (c) 2018 Smeets, Zou and Wanurn:issn:1600-5767Smeets, S.Zou, X.Wan, W.2018-08-09doi:10.1107/S1600576718009500International Union of CrystallographySerial crystallography using electron diffraction has been developed as a fully automated method for collecting electron diffraction data from a large number of crystals. It is demonstrated how the data can be used for structure determination and phase analysis.ENserial crystallographyelectron diffractionstructure determinationphase analysisSerial electron crystallography has been developed as a fully automated method to collect diffraction data on polycrystalline materials using a transmission electron microscope. This enables useful data to be collected on materials that are sensitive to the electron beam and thus difficult to measure using the conventional methods that require long exposure of the same crystal. The data collection strategy combines goniometer translation with electron beam shift, which allows the entire sample stage to be probed. At each position of the goniometer, the locations of the crystals are identified using image recognition techniques. Diffraction data are then collected on each crystal using a quasi-parallel focused beam with a predefined size (usually 300–500 nm). It is shown that with a fast and sensitive Timepix hybrid pixel area detector it is possible to collect diffraction data of up to 3500 crystals per hour. These data can be indexed using a brute-force forward-projection algorithm. Results from several test samples show that 100–200 frames are enough for structure determination using direct methods or dual-space methods. The large number of crystals examined enables quantitative phase analysis and automatic screening of materials for known and unknown phases.text/htmlSerial electron crystallography for structure determination and phase analysis of nanocrystalline materialstext5512018-08-09Copyright (c) 2018 Smeets, Zou and WanJournal of Applied Crystallographyresearch papers12621273Real-time study of transients during high-temperature creep of an Ni-base superalloy by far-field high-energy synchrotron X-ray diffraction
http://scripts.iucr.org/cgi-bin/paper?ks5585
The high-temperature mechanical behavior of single-crystal Ni-base superalloys has been formerly studied by in situ triple-crystal synchrotron X-ray diffractometry (TCD). However, the 1/300 s recording frequency does not allow real-time tests. It is shown here that real-time monitoring is possible with far-field diffractometry in transmission. The use of a far-field camera enables one to follow a diffraction spot with high angular precision and high recording speed. This technique allows measurement of the mechanical response of an AM1 Ni-base single-crystal superalloy following steep load jumps and relaxations during high-temperature creep tests. Local crystal misorientation is revealed and rafting (oriented coalescence) is examined. This new technique is compared with TCD, in order to highlight its benefits and drawbacks.Copyright (c) 2018 International Union of Crystallographyurn:issn:1600-5767Tréhorel, R.Ribarik, G.Schenk, T.Jacques, A.2018-08-09doi:10.1107/S1600576718010014International Union of CrystallographyA far-field double-crystal diffractometry technique using synchrotron X-rays was employed to record lattice parameters of an Ni-base single-crystal superalloy with a high frequency (every 7 s) during an in situ creep test. Diffraction scans reveal the presence of subgrains. This article describes this technique and the associated data processing to obtain results that open new scientific opportunities to follow crystalline materials in real time.ENX-ray diffractiontransmission geometryfar fieldmisfitNi-base superalloysThe high-temperature mechanical behavior of single-crystal Ni-base superalloys has been formerly studied by in situ triple-crystal synchrotron X-ray diffractometry (TCD). However, the 1/300 s recording frequency does not allow real-time tests. It is shown here that real-time monitoring is possible with far-field diffractometry in transmission. The use of a far-field camera enables one to follow a diffraction spot with high angular precision and high recording speed. This technique allows measurement of the mechanical response of an AM1 Ni-base single-crystal superalloy following steep load jumps and relaxations during high-temperature creep tests. Local crystal misorientation is revealed and rafting (oriented coalescence) is examined. This new technique is compared with TCD, in order to highlight its benefits and drawbacks.text/htmlReal-time study of transients during high-temperature creep of an Ni-base superalloy by far-field high-energy synchrotron X-ray diffractiontext5512018-08-09Copyright (c) 2018 International Union of CrystallographyJournal of Applied Crystallographyresearch papers12741282Local distortion and octahedral tilting in BaCexTi1−xO3 perovskite
http://scripts.iucr.org/cgi-bin/paper?po5133
Ceramics with perovskite structure and composition BaCexTi1−xO3 (x = 0.02–0.30) show a progressive evolution with increasing x, from the long-range polar order of ferroelectric BaTiO3 to the short-range polar order typical of relaxors. The ionic size mismatch between Ti4+ and Ce4+ determines strong local strains which have a significant impact on dielectric properties and phase transitions. The pair distribution function, coupled with transmission electron microscopy analysis, was applied to study the local structure. Because of the inner B-cation sizes, the superposition of rigid B—O octahedra with different volumes is not compatible with the construction of an ideal perovskite structure. In this light, local structure can be described by an original model which allows (i) different Ti—O and Ce—O distances and (ii) the typical distortions of the two end members: off-center displacement of Ti occurring in BaTiO3 and octahedral tilt in BaCeO3. The results show a clear difference, in terms of volumes, between oxygen octahedra with titanium and those related to cerium. In addition, the inclusion of cerium causes a tilt of its oxygen cage, as occurs in pure BaCeO3, creating contra-rotations and distortions of the octahedra containing titanium. This complex arrangement entails a substantial distortion, increasing as a function of cerium amount, which strongly influences the directions of titanium displacements, their local correlation and consequently their long-range cooperative effects.Copyright (c) 2018 International Union of Crystallographyurn:issn:1600-5767Confalonieri, G.Buscaglia, V.Capitani, G.Canu, G.Rotiroti, N.Bernasconi, A.Pavese, A.Dapiaggi, M.2018-08-24doi:10.1107/S1600576718010786International Union of CrystallographyA new hypothesis for the ferroelectric relaxor behavior variation in BaTiO3 synthetic perovskite doped with Ce4+ is presented. The pair distribution function is used to explore the local structure and to propose a new local structural model consisting of oxygen octahedron tilting coupled with titanium displacements.ENCe4+-doped BaTiO3perovskiteslocal disordered structurepair distribution functiontransmission electron microscopyTEMCeramics with perovskite structure and composition BaCexTi1−xO3 (x = 0.02–0.30) show a progressive evolution with increasing x, from the long-range polar order of ferroelectric BaTiO3 to the short-range polar order typical of relaxors. The ionic size mismatch between Ti4+ and Ce4+ determines strong local strains which have a significant impact on dielectric properties and phase transitions. The pair distribution function, coupled with transmission electron microscopy analysis, was applied to study the local structure. Because of the inner B-cation sizes, the superposition of rigid B—O octahedra with different volumes is not compatible with the construction of an ideal perovskite structure. In this light, local structure can be described by an original model which allows (i) different Ti—O and Ce—O distances and (ii) the typical distortions of the two end members: off-center displacement of Ti occurring in BaTiO3 and octahedral tilt in BaCeO3. The results show a clear difference, in terms of volumes, between oxygen octahedra with titanium and those related to cerium. In addition, the inclusion of cerium causes a tilt of its oxygen cage, as occurs in pure BaCeO3, creating contra-rotations and distortions of the octahedra containing titanium. This complex arrangement entails a substantial distortion, increasing as a function of cerium amount, which strongly influences the directions of titanium displacements, their local correlation and consequently their long-range cooperative effects.text/htmlLocal distortion and octahedral tilting in BaCexTi1−xO3 perovskitetext5512018-08-24Copyright (c) 2018 International Union of CrystallographyJournal of Applied Crystallographyresearch papers12831294Data-reduction procedure for correction of geometric factors in the analysis of specular X-ray reflectivity of small samples
http://scripts.iucr.org/cgi-bin/paper?rg5148
For small samples, the modification of the X-ray reflectivity (XRR) profile by the geometric factors due to the profile and size of the beam and the size of the sample is significant. These geometric factors extend the spill-over angle, which is often greater than the critical angle for small samples. To separate the geometric factors, it is necessary to know the spill-over angle. Since the geometric factors are smoothly varying functions and extend beyond the critical angle, it is impossible to determine the spill-over angle from the XRR profile of small samples. It is shown that the spill-over angle can be determined by comparing the normal XRR profile of a small sample with the XRR profile taken with a surface-contact knife edge on the same sample. Thus, a procedure has been developed for data reduction for small samples and validated with suitable experiments. Unlike the methods used hitherto, which have drawbacks, this is a self-consistent method for data reduction.Copyright (c) 2018 International Union of Crystallographyurn:issn:1600-5767Das, A.Singh, S.D.Choudhari, R.J.Rai, S.K.Ganguli, T.2018-08-24doi:10.1107/S1600576718010579International Union of CrystallographyA data-reduction procedure for the removal of the effect of geometric factors from the angle-dependent specular X-ray reflectivity profile of small samples is described.ENspecular X-ray reflectivitygeometric factorsdata reductionsmall samplesFor small samples, the modification of the X-ray reflectivity (XRR) profile by the geometric factors due to the profile and size of the beam and the size of the sample is significant. These geometric factors extend the spill-over angle, which is often greater than the critical angle for small samples. To separate the geometric factors, it is necessary to know the spill-over angle. Since the geometric factors are smoothly varying functions and extend beyond the critical angle, it is impossible to determine the spill-over angle from the XRR profile of small samples. It is shown that the spill-over angle can be determined by comparing the normal XRR profile of a small sample with the XRR profile taken with a surface-contact knife edge on the same sample. Thus, a procedure has been developed for data reduction for small samples and validated with suitable experiments. Unlike the methods used hitherto, which have drawbacks, this is a self-consistent method for data reduction.text/htmlData-reduction procedure for correction of geometric factors in the analysis of specular X-ray reflectivity of small samplestext5512018-08-24Copyright (c) 2018 International Union of CrystallographyJournal of Applied Crystallographyresearch papers12951303Operando powder X-ray diffraction study of P2-NaxNi0.3Mn0.7O2 cathode material during electrochemical cycling
http://scripts.iucr.org/cgi-bin/paper?kc5076
Layered transition metal oxides are of significant interest for applications in sodium-ion batteries. This article reports an operando powder X-ray diffraction study of the cathode material P2-NaxNi0.3Mn0.7O2 during electrochemical cycling. The structural changes are shown to be reversible over two full cycles, and refinement of sodium occupancies provides insight into the very complex ion movement during battery operation. The sodium loading progresses through a set of metastable compositions showing that the working battery is out of equilibrium on a structural level. Peak broadening caused by stacking faults is observed in the P2 structure at ∼4.0 V, prior to the ∼4.2 V phase transformation from P2 to the `Z' phaseCopyright (c) 2018 International Union of Crystallographyurn:issn:1600-5767Kjeldgaard, S.Birgisson, S.Kielland, A.G.Iversen, B.B.2018-08-24doi:10.1107/S1600576718010531International Union of CrystallographyOperando powder X-ray diffraction measurements on layered P2-NaxNi0.3Mn0.7O2 provide detailed insight into non-equilibrium structural changes in the cathode material during charge and discharge.ENoperando powder X-ray diffractionsodium-ion batterieslayered transition metal oxidesLayered transition metal oxides are of significant interest for applications in sodium-ion batteries. This article reports an operando powder X-ray diffraction study of the cathode material P2-NaxNi0.3Mn0.7O2 during electrochemical cycling. The structural changes are shown to be reversible over two full cycles, and refinement of sodium occupancies provides insight into the very complex ion movement during battery operation. The sodium loading progresses through a set of metastable compositions showing that the working battery is out of equilibrium on a structural level. Peak broadening caused by stacking faults is observed in the P2 structure at ∼4.0 V, prior to the ∼4.2 V phase transformation from P2 to the `Z' phasetext/htmlOperando powder X-ray diffraction study of P2-NaxNi0.3Mn0.7O2 cathode material during electrochemical cyclingtext5512018-08-24Copyright (c) 2018 International Union of CrystallographyJournal of Applied Crystallographyresearch papers13041310Influence of crystal structure defects on the small-angle neutron scattering/diffraction patterns of clay-rich porous media
http://scripts.iucr.org/cgi-bin/paper?vg5089
Analysing the structure and microstructure of compacted swelling clay minerals is important because of the applications of these minerals in engineering and environmental sciences. Given the typical sub-micrometre size of the particles and pores in clays, small-angle scattering techniques are well suited for such analysis. Interpretation of the intensity patterns, however, remains complex, especially in the intermediate region between the first Bragg peak and the small-angle range. In this study, theoretical small-angle neutron scattering and neutron diffraction patterns are calculated for three-dimensional virtual porous media representative of packed swelling clay particles (i.e. 0.1–0.2 µm size fraction of vermiculite). This packing represents the distribution of the size, shape and particle orientation of a bulk vermiculite sample, for which experimental scattering/diffraction patterns were also collected. It was found that a good fit between the experimental and calculated scattering/diffraction profiles can be obtained only if the presence of crystal-structure defects in the particles is considered. The existence of such defects was supported by transmission electron microscopy analysis. Their influence on power law exponents extracted from intensity profiles is assessed in detail. The analysis is further extended to the influence of mineral dehydration and particle orientation on the intensity profiles. This work shows that using virtual porous media as toy models makes it possible to evaluate the roles of different microstructural parameters in the extent of variation of power law exponents. Such knowledge can be used for better interpretation of small-angle scattering data of natural compacted swelling clay-rich media.Copyright (c) 2018 International Union of Crystallographyurn:issn:1600-5767Ferrage, E.Hubert, F.Baronnet, A.Grauby, O.Tertre, E.Delville, A.Bihannic, I.Prêt, D.Michot, L.J.Levitz, P.2018-08-24doi:10.1107/S160057671801052XInternational Union of CrystallographyThis paper describes use of a combination of experimental and calculated small-angle neutron scattering/neutron diffraction profiles for the analysis of power law exponent evolution with different typical changes in structure and microstructure properties of swelling clay minerals.ENsmall-angle neutron scatteringclay mineralsneutron diffractionporous mediacrystal defectsAnalysing the structure and microstructure of compacted swelling clay minerals is important because of the applications of these minerals in engineering and environmental sciences. Given the typical sub-micrometre size of the particles and pores in clays, small-angle scattering techniques are well suited for such analysis. Interpretation of the intensity patterns, however, remains complex, especially in the intermediate region between the first Bragg peak and the small-angle range. In this study, theoretical small-angle neutron scattering and neutron diffraction patterns are calculated for three-dimensional virtual porous media representative of packed swelling clay particles (i.e. 0.1–0.2 µm size fraction of vermiculite). This packing represents the distribution of the size, shape and particle orientation of a bulk vermiculite sample, for which experimental scattering/diffraction patterns were also collected. It was found that a good fit between the experimental and calculated scattering/diffraction profiles can be obtained only if the presence of crystal-structure defects in the particles is considered. The existence of such defects was supported by transmission electron microscopy analysis. Their influence on power law exponents extracted from intensity profiles is assessed in detail. The analysis is further extended to the influence of mineral dehydration and particle orientation on the intensity profiles. This work shows that using virtual porous media as toy models makes it possible to evaluate the roles of different microstructural parameters in the extent of variation of power law exponents. Such knowledge can be used for better interpretation of small-angle scattering data of natural compacted swelling clay-rich media.text/htmlInfluence of crystal structure defects on the small-angle neutron scattering/diffraction patterns of clay-rich porous mediatext5512018-08-24Copyright (c) 2018 International Union of CrystallographyJournal of Applied Crystallographyresearch papers13111322Glassy carbon, NIST Standard Reference Material (SRM 3600): hydrogen content, neutron vibrational density of states and heat capacity
http://scripts.iucr.org/cgi-bin/paper?po5124
Commercial glassy carbon plates being used as absolute intensity calibration standards in small-angle X-ray scattering applications (NIST SRM 3600) have been characterized in several recent publications. This contribution adds to the characterization by measuring the hydrogen content of a plate to be (4.8 ± 0.2) × 10−4 (mol H)/(mol C), and by measuring the vibrational spectrum by neutron inelastic scattering. The spectrum bears a strong resemblance to published measurements on graphite, allowing the identification of several spectral features. The measured spectrum is used to calculate the heat capacity of low-hydrogen-content glassy carbon for comparison with measurements reported here from 20 to 295 K.Copyright (c) 2018 Ronald L. Cappelletti et al.urn:issn:1600-5767Cappelletti, R.L.Udovic, T.J.Li, H.Paul, R.L.2018-08-24doi:10.1107/S1600576718010828International Union of CrystallographyCommercial glassy carbon plates (NIST SRM 3600) being used as absolute intensity calibration standards in small-angle X-ray scattering applications are further characterized in terms of hydrogen content, vibrational density of states and specific heat capacity.ENstandard reference materialsglassy carbonhydrogen contentneutron vibrational density of statesspecific heatgraphiteCommercial glassy carbon plates being used as absolute intensity calibration standards in small-angle X-ray scattering applications (NIST SRM 3600) have been characterized in several recent publications. This contribution adds to the characterization by measuring the hydrogen content of a plate to be (4.8 ± 0.2) × 10−4 (mol H)/(mol C), and by measuring the vibrational spectrum by neutron inelastic scattering. The spectrum bears a strong resemblance to published measurements on graphite, allowing the identification of several spectral features. The measured spectrum is used to calculate the heat capacity of low-hydrogen-content glassy carbon for comparison with measurements reported here from 20 to 295 K.text/htmlGlassy carbon, NIST Standard Reference Material (SRM 3600): hydrogen content, neutron vibrational density of states and heat capacitytext5512018-08-24Copyright (c) 2018 Ronald L. Cappelletti et al.Journal of Applied Crystallographyresearch papers13231328X-ray measurement of triaxial residual stress on machined surfaces by the cosα method using a two-dimensional detector
http://scripts.iucr.org/cgi-bin/paper?ks5603
In recent years, the cosα method has attracted engineers as a new method of X-ray stress measurement using the whole Debye–Scherrer (D–S) ring recorded on a two-dimensional detector. The principle of the cosα method was first proposed by Taira, Tanaka & Yamasaki [J. Soc. Mater. Sci. Jpn, (1978), 27, 251–256] for in-plane biaxial stress analysis and later extended by Sasaki and co-workers [Sasaki & Hirose (1995). Trans. Jpn Soc. Mech. Eng. Part A, 61, 2288–2295; Sasaki, Takahashi, Sasaki & Kobayashi (2009). Trans. Jpn Soc. Mech. Eng. Part A, 75, 219–227] to the triaxial state of stress. The method proposed by Sasaki and co-workers utilizes several D–S rings taken at different incident angles of X-rays in order to determine triaxial stresses. In the present paper, the cosα method was applied to measure triaxial residual stresses of uni-directionally machined surfaces of a carbon steel made by grinding, milling and planing. A recommended procedure for experimental measurements of in-plane normal and shear stresses and out-of-plane shear stress is proposed, together with a new method for determination of the out-of-plane normal stress. The tilt angle of X-ray incidence for stress determination is recommended to be larger than 35°, where the stress constant is low and the stress sensitivity is high. Normal incidence is recommended for the determination of out-of-plane shear stresses. The out-of-plane shear stress along the cutting direction was characteristic of uni-directionally machined surfaces and increased with cutting severity in the order of grinding, milling and planing. The in-plane normal stress was compressive for ground and milled surfaces, and the magnitude of compression was larger in the direction perpendicular to the cutting direction. On the basis of the stress values measured under different tilt angles, it is suggested that the magnitude of in-plane normal residual stress increases near the surface. The out-of-plane normal stress determined by the new method indicated a small compression.Copyright (c) 2018 International Union of Crystallographyurn:issn:1600-5767Tanaka, K.2018-09-10doi:10.1107/S1600576718011056International Union of CrystallographyThe cosα method was applied to measure triaxial residual stresses of uni-directionally machined surfaces of a carbon steel made by grinding, milling and planing. A recommended procedure for experimental measurements of in-plane normal and shear stresses and out-of-plane shear stresses is proposed, together with a new method for determination of the out-of-plane normal stress.ENX-ray stress measurementcosα methodtriaxial residual stressuni-directionally machined surfacesIn recent years, the cosα method has attracted engineers as a new method of X-ray stress measurement using the whole Debye–Scherrer (D–S) ring recorded on a two-dimensional detector. The principle of the cosα method was first proposed by Taira, Tanaka & Yamasaki [J. Soc. Mater. Sci. Jpn, (1978), 27, 251–256] for in-plane biaxial stress analysis and later extended by Sasaki and co-workers [Sasaki & Hirose (1995). Trans. Jpn Soc. Mech. Eng. Part A, 61, 2288–2295; Sasaki, Takahashi, Sasaki & Kobayashi (2009). Trans. Jpn Soc. Mech. Eng. Part A, 75, 219–227] to the triaxial state of stress. The method proposed by Sasaki and co-workers utilizes several D–S rings taken at different incident angles of X-rays in order to determine triaxial stresses. In the present paper, the cosα method was applied to measure triaxial residual stresses of uni-directionally machined surfaces of a carbon steel made by grinding, milling and planing. A recommended procedure for experimental measurements of in-plane normal and shear stresses and out-of-plane shear stress is proposed, together with a new method for determination of the out-of-plane normal stress. The tilt angle of X-ray incidence for stress determination is recommended to be larger than 35°, where the stress constant is low and the stress sensitivity is high. Normal incidence is recommended for the determination of out-of-plane shear stresses. The out-of-plane shear stress along the cutting direction was characteristic of uni-directionally machined surfaces and increased with cutting severity in the order of grinding, milling and planing. The in-plane normal stress was compressive for ground and milled surfaces, and the magnitude of compression was larger in the direction perpendicular to the cutting direction. On the basis of the stress values measured under different tilt angles, it is suggested that the magnitude of in-plane normal residual stress increases near the surface. The out-of-plane normal stress determined by the new method indicated a small compression.text/htmlX-ray measurement of triaxial residual stress on machined surfaces by the cosα method using a two-dimensional detectortext5512018-09-10Copyright (c) 2018 International Union of CrystallographyJournal of Applied Crystallographyresearch papers13291338Time-resolved X-ray absorption spectroscopy on Al–Cu alloys – from solute copper to stable precipitates
http://scripts.iucr.org/cgi-bin/paper?nb5226
Although binary aluminium alloys seem to be uninteresting and well known, some aspects of their precipitation sequence – especially the early stages immediately after quenching – are still not well understood. Since the Al–Cu system is the basis for many ternary and quaternary high-strength alloys with application in the aviation sector, it is important to understand this binary system in detail. This problem is here tackled by a unique combination of differential scanning calorimetry and X-ray absorption fine structure measurements, where relaxed atomic coordinates for simulation of the spectra have been obtained by ab initio calculations. Thereby, it is possible to attribute any exo- or endothermal peak to a certain type of precipitate, even though formation and dissolution regions have a large overlap in this system. This unique combination of experimental and numerical methods allows one to determine the local atomic environment around Cu atoms, thus following the formation and growth of Guinier–Preston zones, i.e. Cu platelets on {100} planes, during the precipitation process.Copyright (c) 2018 International Union of Crystallographyurn:issn:1600-5767Petschke, D.Lotter, F.Bläss, E.Staab, T.E.M.2018-09-10doi:10.1107/S1600576718011214International Union of CrystallographyTime-resolved X-ray absorption spectroscopy provides a powerful method to investigate the very early stages and precipitation sequence of the model system Al–Cu. Small changes in the local atomic structure of the probed element can be observed and verified by X-ray absorption fine structure simulations using ab initio calculated atomic coordinates as simulation input.ENX-ray absorption spectroscopyAl–Cu alloysdifferential scanning calorimetryab initio calculationAlthough binary aluminium alloys seem to be uninteresting and well known, some aspects of their precipitation sequence – especially the early stages immediately after quenching – are still not well understood. Since the Al–Cu system is the basis for many ternary and quaternary high-strength alloys with application in the aviation sector, it is important to understand this binary system in detail. This problem is here tackled by a unique combination of differential scanning calorimetry and X-ray absorption fine structure measurements, where relaxed atomic coordinates for simulation of the spectra have been obtained by ab initio calculations. Thereby, it is possible to attribute any exo- or endothermal peak to a certain type of precipitate, even though formation and dissolution regions have a large overlap in this system. This unique combination of experimental and numerical methods allows one to determine the local atomic environment around Cu atoms, thus following the formation and growth of Guinier–Preston zones, i.e. Cu platelets on {100} planes, during the precipitation process.text/htmlTime-resolved X-ray absorption spectroscopy on Al–Cu alloys – from solute copper to stable precipitatestext5512018-09-10Copyright (c) 2018 International Union of CrystallographyJournal of Applied Crystallographyresearch papers13391351A fast X-ray-diffraction-based method for the determination of crystal size distributions (FXD-CSD)
http://scripts.iucr.org/cgi-bin/paper?rg5152
A procedure for a fast X-ray-diffraction-based crystal size distribution analysis, named FXD-CSD, is presented. The method enables the user, with minimal sample preparation, to determine the crystal size distribution (CSD) of crystalline powders or polycrystalline materials, derived via an intensity scaling procedure from the diffraction intensities of single Bragg spots measured in spotty diffraction patterns with a two-dimensional detector. The method can be implemented on any single-crystal laboratory diffractometer and any synchrotron-based instrument with a fast-readout two-dimensional detector and a precise sample scanning axis. The intensity scaling is achieved via the measurement of a reference sample with known CSD under identical conditions; the only other prerequisite is that the structure (factors) of both sample and reference material must be known. The data analysis is done with a software package written in Python. A detailed account is given of each step of the procedure, including the measurement strategy and the demands on the spottiness of the diffraction rings, the data reduction and the intensity corrections needed, and the data evaluation and the requirements for the reference material. Using commercial laboratory X-ray equipment, several corundum crystal size fractions with precisely known CSD were measured and analysed to verify the accuracy and precision of the FXD-CSD method; a comparison of known and deduced CSDs shows good agreement both in mean size and in the shape of the size distribution. For the used material and diffractometer setup, the crystal size application range is one to several tens of micrometres; this range is highly material and X-ray source dependent and can easily be extended on synchrotron sources to cover the range from below 0.5 µm to over 100 µm. FXD-CSD has the potential to become a generally applicable method for CSD determination in the field of materials science and pharmaceutics, including development and quality management, as well as in various areas of fundamental research in physics, chemistry, chemical engineering, crystallography, the geological sciences and bio-crystallization. It can be used also under in situ conditions for studying crystal coarsening phenomena, and delivers precise and accurate CSDs, permitting experimental tests of various theories developed to predict their evolution.Copyright (c) 2018 International Union of Crystallographyurn:issn:1600-5767Neher, S.H.Klein, H.Kuhs, W.F.2018-09-10doi:10.1107/S1600576718010567International Union of CrystallographyA fast X-ray-diffraction-based procedure for measuring crystallite size distributions is presented. Unprecedented precision and accuracy is achieved with a data acquisition fast enough to permit in situ studies under non-ambient conditions.ENcrystal size distributionX-ray diffractionFXD-CSDspotty diffraction patternstwo-dimensional detectorsA procedure for a fast X-ray-diffraction-based crystal size distribution analysis, named FXD-CSD, is presented. The method enables the user, with minimal sample preparation, to determine the crystal size distribution (CSD) of crystalline powders or polycrystalline materials, derived via an intensity scaling procedure from the diffraction intensities of single Bragg spots measured in spotty diffraction patterns with a two-dimensional detector. The method can be implemented on any single-crystal laboratory diffractometer and any synchrotron-based instrument with a fast-readout two-dimensional detector and a precise sample scanning axis. The intensity scaling is achieved via the measurement of a reference sample with known CSD under identical conditions; the only other prerequisite is that the structure (factors) of both sample and reference material must be known. The data analysis is done with a software package written in Python. A detailed account is given of each step of the procedure, including the measurement strategy and the demands on the spottiness of the diffraction rings, the data reduction and the intensity corrections needed, and the data evaluation and the requirements for the reference material. Using commercial laboratory X-ray equipment, several corundum crystal size fractions with precisely known CSD were measured and analysed to verify the accuracy and precision of the FXD-CSD method; a comparison of known and deduced CSDs shows good agreement both in mean size and in the shape of the size distribution. For the used material and diffractometer setup, the crystal size application range is one to several tens of micrometres; this range is highly material and X-ray source dependent and can easily be extended on synchrotron sources to cover the range from below 0.5 µm to over 100 µm. FXD-CSD has the potential to become a generally applicable method for CSD determination in the field of materials science and pharmaceutics, including development and quality management, as well as in various areas of fundamental research in physics, chemistry, chemical engineering, crystallography, the geological sciences and bio-crystallization. It can be used also under in situ conditions for studying crystal coarsening phenomena, and delivers precise and accurate CSDs, permitting experimental tests of various theories developed to predict their evolution.text/htmlA fast X-ray-diffraction-based method for the determination of crystal size distributions (FXD-CSD)text5512018-09-10Copyright (c) 2018 International Union of CrystallographyJournal of Applied Crystallographyresearch papers13521371Stacking faults in β-Ga2O3 crystals observed by X-ray topography
http://scripts.iucr.org/cgi-bin/paper?vh5085
Planar defects in (\overline{2}01)-oriented β-Ga2O3 wafers were studied using X-ray topography. These planar defects were rectangular with dimensions of 50–150 µm, and the X-ray topography analysis revealed that they were stacking faults (SFs) enclosed by a single partial dislocation loop on the (\overline{2}01) plane. The SF formation was found to be supported by a unique structural feature of the (\overline{2}01) plane as a slip plane; the (\overline{2}01) plane consists of close-packed octahedral Ga and O layers, allowing slips to form SFs. Vacancy arrays along the b axis in the octahedral Ga layer reduce the self-energy of the edge component in the partial dislocation extending along the b axis. It is speculated that the SFs occur during the crystal growth process for unknown reasons and then recover owing to elastic instability after initially increasing in size as crystal growth proceeds. Based on this analysis, a structural model for the SFs is proposed.Copyright (c) 2018 Yamaguchi and Kuramataurn:issn:1600-5767Yamaguchi, H.Kuramata, A.2018-09-10doi:10.1107/S1600576718011093International Union of CrystallographyX-ray topography analysis reveals the presence of stacking faults in β-Ga2O3 wafers grown by the edge-defined film-fed growth method. These stacking faults are found to be associated with a Shockley-type partial dislocation loop on the basis of the contrast extinction rules determined by varying the value of the diffraction vector.ENX-ray topographystacking faultspartial dislocationsslip planesPlanar defects in (\overline{2}01)-oriented β-Ga2O3 wafers were studied using X-ray topography. These planar defects were rectangular with dimensions of 50–150 µm, and the X-ray topography analysis revealed that they were stacking faults (SFs) enclosed by a single partial dislocation loop on the (\overline{2}01) plane. The SF formation was found to be supported by a unique structural feature of the (\overline{2}01) plane as a slip plane; the (\overline{2}01) plane consists of close-packed octahedral Ga and O layers, allowing slips to form SFs. Vacancy arrays along the b axis in the octahedral Ga layer reduce the self-energy of the edge component in the partial dislocation extending along the b axis. It is speculated that the SFs occur during the crystal growth process for unknown reasons and then recover owing to elastic instability after initially increasing in size as crystal growth proceeds. Based on this analysis, a structural model for the SFs is proposed.text/htmlStacking faults in β-Ga2O3 crystals observed by X-ray topographytext5512018-09-10Copyright (c) 2018 Yamaguchi and KuramataJournal of Applied Crystallographyresearch papers13721377Model-free classification of X-ray scattering signals applied to image segmentation
http://scripts.iucr.org/cgi-bin/paper?ge5050
In most cases, the analysis of small-angle and wide-angle X-ray scattering (SAXS and WAXS, respectively) requires a theoretical model to describe the sample's scattering, complicating the interpretation of the scattering resulting from complex heterogeneous samples. This is the reason why, in general, the analysis of a large number of scattering patterns, such as are generated by time-resolved and scanning methods, remains challenging. Here, a model-free classification method to separate SAXS/WAXS signals on the basis of their inflection points is introduced and demonstrated. This article focuses on the segmentation of scanning SAXS/WAXS maps for which each pixel corresponds to an azimuthally integrated scattering curve. In such a way, the sample composition distribution can be segmented through signal classification without applying a model or previous sample knowledge. Dimensionality reduction and clustering algorithms are employed to classify SAXS/WAXS signals according to their similarity. The number of clusters, i.e. the main sample regions detected by SAXS/WAXS signal similarity, is automatically estimated. From each cluster, a main representative SAXS/WAXS signal is extracted to uncover the spatial distribution of the mixtures of phases that form the sample. As examples of applications, a mudrock sample and two breast tissue lesions are segmented.Copyright (c) 2018 International Union of Crystallographyurn:issn:1600-5767Lutz-Bueno, V.Arboleda, C.Leu, L.Blunt, M.J.Busch, A.Georgiadis, A.Bertier, P.Schmatz, J.Varga, Z.Villanueva-Perez, P.Wang, Z.Lebugle, M.David, C.Stampanoni, M.Diaz, A.Guizar-Sicairos, M.Menzel, A.2018-09-10doi:10.1107/S1600576718011032International Union of CrystallographyThis article describes a modeling framework to relate the molecular orientation of nanostructures to polarized resonant soft X-ray scattering measurements using the Born approximation and a full tensor treatment.ENpolarized resonant soft X-ray scatteringanisotropic nanostructureselectromagnetic modelingIn most cases, the analysis of small-angle and wide-angle X-ray scattering (SAXS and WAXS, respectively) requires a theoretical model to describe the sample's scattering, complicating the interpretation of the scattering resulting from complex heterogeneous samples. This is the reason why, in general, the analysis of a large number of scattering patterns, such as are generated by time-resolved and scanning methods, remains challenging. Here, a model-free classification method to separate SAXS/WAXS signals on the basis of their inflection points is introduced and demonstrated. This article focuses on the segmentation of scanning SAXS/WAXS maps for which each pixel corresponds to an azimuthally integrated scattering curve. In such a way, the sample composition distribution can be segmented through signal classification without applying a model or previous sample knowledge. Dimensionality reduction and clustering algorithms are employed to classify SAXS/WAXS signals according to their similarity. The number of clusters, i.e. the main sample regions detected by SAXS/WAXS signal similarity, is automatically estimated. From each cluster, a main representative SAXS/WAXS signal is extracted to uncover the spatial distribution of the mixtures of phases that form the sample. As examples of applications, a mudrock sample and two breast tissue lesions are segmented.text/htmlModel-free classification of X-ray scattering signals applied to image segmentationtext5512018-09-10Copyright (c) 2018 International Union of CrystallographyJournal of Applied Crystallographyresearch papers13781386Complete structural and strain analysis of single GaAs/(In,Ga)As/GaAs core–shell–shell nanowires by means of in-plane and out-of-plane X-ray nanodiffraction
http://scripts.iucr.org/cgi-bin/paper?rg5150
Typically, core–shell–shell semiconductor nanowires (NWs) made from III–V materials with low lattice mismatch grow pseudomorphically along the growth axis, i.e. the axial lattice parameters of the core and shell materials are the same. Therefore, both the structural composition and interface strain of the NWs are encoded along directions perpendicular to the growth axis. Owing to fluctuations in the supplied growth species during molecular beam epitaxy (MBE) growth, structural parameters such as local shell thickness, composition and strain may differ between NWs grown onto the same substrate. This requires structural analysis of single NWs instead of measuring NW ensembles. In this work, the complete structure of single GaAs/(In,Ga)As/GaAs core–shell–shell NW heterostructures is determined by means of X-ray nanodiffraction using synchrotron radiation. The NWs were grown by MBE on a prepatterned silicon (111) substrate with a core diameter of 50 nm and an (In,Ga)As shell thickness of 20 nm with a nominal indium concentration of 15%, capped by a 30 nm GaAs outer shell. In order to access single NWs with the X-ray nanobeam being incident parallel to the surface of the substrate, a single row of holes with a separation of 10 µm was defined by electron-beam lithography to act as nucleation centres for MBE NW growth. These well separated NWs were probed sequentially by X-ray nanodiffraction, recording three-dimensional reciprocal-space maps of Bragg reflections with scattering vectors parallel (out-of-plane) and perpendicular (in-plane) to the NW growth axis. From the out-of-plane 111 Bragg reflection, deviations from hexagonal symmetry were derived, together with the diameters of probed NWs grown under the same conditions. The radial NW composition and interface strain became accessible when measuring the two-dimensional scattering intensity distributions of the in-plane 2{\overline 2}0 and 22{\overline 4} reflections, exhibiting well pronounced thickness fringes perpendicular to the NW side planes (truncation rods, TRs). Quantitative values of thickness, composition and strain acting on the (In,Ga)As and GaAs shells were obtained via finite-element modelling of the core–shell–shell NWs and subsequent Fourier transform, simulating the TRs measured along the three different directions of the hexagonally shaped NWs simultaneously. Considering the experimental constraints of the current experiment, thicknesses and In content have been evaluated with uncertainties of ±2 nm and ±0.01, respectively. Comparing data taken from different single NWs, the shell thicknesses differ from one to another.Copyright (c) 2018 International Union of Crystallographyurn:issn:1600-5767Al Hassan, A.Davtyan, A.Küpers, H.Lewis, R.B.Bahrami, D.Bertram, F.Bussone, G.Richter, C.Geelhaar, L.Pietsch, U.2018-09-13doi:10.1107/S1600576718011287International Union of CrystallographyThe complete structure of single GaAs/(In,Ga)As/GaAs core–shell–shell nanowire heterostructures has been determined in the as-grown geometry. This has been done by probing in-plane Bragg reflections by means of X-ray nanodiffraction using synchrotron radiation and by nanowire modelling using finite-element methods.ENcore–shell semiconductor nanowiresin-plane and out-of-plane X-ray diffractionsynchrotron nanoprobesthickness determinationstrain determinationfinite-element modellingreciprocal-space mappingTypically, core–shell–shell semiconductor nanowires (NWs) made from III–V materials with low lattice mismatch grow pseudomorphically along the growth axis, i.e. the axial lattice parameters of the core and shell materials are the same. Therefore, both the structural composition and interface strain of the NWs are encoded along directions perpendicular to the growth axis. Owing to fluctuations in the supplied growth species during molecular beam epitaxy (MBE) growth, structural parameters such as local shell thickness, composition and strain may differ between NWs grown onto the same substrate. This requires structural analysis of single NWs instead of measuring NW ensembles. In this work, the complete structure of single GaAs/(In,Ga)As/GaAs core–shell–shell NW heterostructures is determined by means of X-ray nanodiffraction using synchrotron radiation. The NWs were grown by MBE on a prepatterned silicon (111) substrate with a core diameter of 50 nm and an (In,Ga)As shell thickness of 20 nm with a nominal indium concentration of 15%, capped by a 30 nm GaAs outer shell. In order to access single NWs with the X-ray nanobeam being incident parallel to the surface of the substrate, a single row of holes with a separation of 10 µm was defined by electron-beam lithography to act as nucleation centres for MBE NW growth. These well separated NWs were probed sequentially by X-ray nanodiffraction, recording three-dimensional reciprocal-space maps of Bragg reflections with scattering vectors parallel (out-of-plane) and perpendicular (in-plane) to the NW growth axis. From the out-of-plane 111 Bragg reflection, deviations from hexagonal symmetry were derived, together with the diameters of probed NWs grown under the same conditions. The radial NW composition and interface strain became accessible when measuring the two-dimensional scattering intensity distributions of the in-plane 2{\overline 2}0 and 22{\overline 4} reflections, exhibiting well pronounced thickness fringes perpendicular to the NW side planes (truncation rods, TRs). Quantitative values of thickness, composition and strain acting on the (In,Ga)As and GaAs shells were obtained via finite-element modelling of the core–shell–shell NWs and subsequent Fourier transform, simulating the TRs measured along the three different directions of the hexagonally shaped NWs simultaneously. Considering the experimental constraints of the current experiment, thicknesses and In content have been evaluated with uncertainties of ±2 nm and ±0.01, respectively. Comparing data taken from different single NWs, the shell thicknesses differ from one to another.text/htmlComplete structural and strain analysis of single GaAs/(In,Ga)As/GaAs core–shell–shell nanowires by means of in-plane and out-of-plane X-ray nanodiffractiontext5512018-09-13Copyright (c) 2018 International Union of CrystallographyJournal of Applied Crystallographyresearch papers13871395Probing the intrinsic and extrinsic origins of piezoelectricity in lead zirconate titanate single crystals
http://scripts.iucr.org/cgi-bin/paper?to5180
The physical origin of the piezoelectric effect has been the focus of much research work. While it is commonly accepted that the origins of piezoelectricity may be intrinsic (related to the change of lattice parameters) and extrinsic (related to the movement of domain walls), their separation is often a challenging experimental task. Here in situ high-resolution synchrotron X-ray diffraction has been combined with a new data analysis technique to characterize the change of the lattice parameters and domain microstructure of a PbZr1−xTixO3 (x = 0.45) crystal under an external electric field. It is shown how `effective piezoelectric coefficients' evolve upon the transition from purely `intrinsic' effects to `extrinsic' ones due to domain-wall motion. This technique and corresponding data analysis can be applied to broader classes of materials and provide important insights into the microscopic origin of their physical properties.Copyright (c) 2018 International Union of Crystallographyurn:issn:1600-5767Zhang, N.Gorfman, S.Choe, H.Vergentev, T.Dyadkin, V.Yokota, H.Chernyshov, D.Wang, B.Glazer, A.M.Ren, W.Ye, Z.-G.2018-09-13doi:10.1107/S1600576718011317International Union of CrystallographyA new X-ray-diffraction-based experiment and data analysis technique for probing the origins of the piezoelectric effect in multi-domain ferroelectric/ferroelastic single crystals is introduced. The technique has been demonstrated for PbZr1−xTixO3 (x = 0.45).ENpiezoelectricityferroelectricityin situ X-ray diffractionThe physical origin of the piezoelectric effect has been the focus of much research work. While it is commonly accepted that the origins of piezoelectricity may be intrinsic (related to the change of lattice parameters) and extrinsic (related to the movement of domain walls), their separation is often a challenging experimental task. Here in situ high-resolution synchrotron X-ray diffraction has been combined with a new data analysis technique to characterize the change of the lattice parameters and domain microstructure of a PbZr1−xTixO3 (x = 0.45) crystal under an external electric field. It is shown how `effective piezoelectric coefficients' evolve upon the transition from purely `intrinsic' effects to `extrinsic' ones due to domain-wall motion. This technique and corresponding data analysis can be applied to broader classes of materials and provide important insights into the microscopic origin of their physical properties.text/htmlProbing the intrinsic and extrinsic origins of piezoelectricity in lead zirconate titanate single crystalstext5512018-09-13Copyright (c) 2018 International Union of CrystallographyJournal of Applied Crystallographyresearch papers13961403On physical scattering density fluctuations of amorphous samples
http://scripts.iucr.org/cgi-bin/paper?ks5606
Using the rigorous results obtained by Wiener [Acta Math. (1930), 30, 118–242] on the Fourier integral of a bounded function and the condition that small-angle scattering intensities of amorphous samples are almost everywhere continuous, the conditions that must be obeyed by a function η(r) for this to be considered a physical scattering density fluctuation are obtained. These conditions can be recast in the following form: the V → ∞ limit of the modulus of the Fourier transform of η(r), evaluated over a cubic box of volume V and divided by V1/2, exists and its square obeys the Porod invariant relation. Some examples of one-dimensional scattering density functions obeying the aforesaid condition are numerically illustrated.Copyright (c) 2018 International Union of Crystallographyurn:issn:1600-5767Ciccariello, S.Riello, P.Benedetti, A.2018-09-13doi:10.1107/S1600576718011330International Union of CrystallographyA function can be considered a physical scattering density fluctuation if the modulus of its Fourier transform, evaluated over a finite volume V and divided by V1/2, tends to a bounded non-vanishing function as V → ∞ and if the squared limit obeys the Porod invariant relation.ENsmall-angle scattering intensityscattering density fluctuationgeneralized harmonic analysisUsing the rigorous results obtained by Wiener [Acta Math. (1930), 30, 118–242] on the Fourier integral of a bounded function and the condition that small-angle scattering intensities of amorphous samples are almost everywhere continuous, the conditions that must be obeyed by a function η(r) for this to be considered a physical scattering density fluctuation are obtained. These conditions can be recast in the following form: the V → ∞ limit of the modulus of the Fourier transform of η(r), evaluated over a cubic box of volume V and divided by V1/2, exists and its square obeys the Porod invariant relation. Some examples of one-dimensional scattering density functions obeying the aforesaid condition are numerically illustrated.text/htmlOn physical scattering density fluctuations of amorphous samplestext5512018-09-13Copyright (c) 2018 International Union of CrystallographyJournal of Applied Crystallographyresearch papers14041420Calibration of rotation axes for multi-axis goniometers in macromolecular crystallography
http://scripts.iucr.org/cgi-bin/paper?ap5028
The installation of multi-axis goniometers such as the ESRF/EMBL miniKappa goniometer system has allowed the increased use of sample reorientation in macromolecular crystallography. Old and newly appearing data collection methods require precision and accuracy in crystal reorientation. The proper use of such multi-axis systems has necessitated the development of rapid and easy to perform methods for establishing and evaluating device calibration. A new diffraction-based method meeting these criteria has been developed for the calibration of the motors responsible for rotational motion. This method takes advantage of crystal symmetry by comparing the orientations of a sample rotated about a given axis and checking that the magnitude of the real rotation fits the calculated angle between these two orientations. Hence, the accuracy and precision of rotational motion can be assessed. This rotation calibration procedure has been performed on several beamlines at the ESRF and other synchrotrons. Some resulting data are presented here for reference.Copyright (c) 2018 K. Ian White et al.urn:issn:1600-5767White, K.I.Bugris, V.McCarthy, A.A.Ravelli, R.B.G.Csankó, K.Cassetta, A.Brockhauser, S.2018-09-13doi:10.1107/S1600576718010956International Union of CrystallographyAn easy to perform rotation calibration procedure has been developed for miniKappa and/or other multi-axis goniometers used in macromolecular crystallography to enhance the precision of experiments involving crystal reorientations.ENkappa diffractometermacromolecular crystallographyreorientationcalibrationThe installation of multi-axis goniometers such as the ESRF/EMBL miniKappa goniometer system has allowed the increased use of sample reorientation in macromolecular crystallography. Old and newly appearing data collection methods require precision and accuracy in crystal reorientation. The proper use of such multi-axis systems has necessitated the development of rapid and easy to perform methods for establishing and evaluating device calibration. A new diffraction-based method meeting these criteria has been developed for the calibration of the motors responsible for rotational motion. This method takes advantage of crystal symmetry by comparing the orientations of a sample rotated about a given axis and checking that the magnitude of the real rotation fits the calculated angle between these two orientations. Hence, the accuracy and precision of rotational motion can be assessed. This rotation calibration procedure has been performed on several beamlines at the ESRF and other synchrotrons. Some resulting data are presented here for reference.text/htmlCalibration of rotation axes for multi-axis goniometers in macromolecular crystallographytext5512018-09-13Copyright (c) 2018 K. Ian White et al.Journal of Applied Crystallographyresearch papers14211427Reciprocal space mapping and strain scanning using X-ray diffraction microscopy
http://scripts.iucr.org/cgi-bin/paper?nb5230
Dark-field X-ray microscopy is a new full-field imaging technique for nondestructively mapping the structure of deeply embedded crystalline elements in three dimensions. Placing an objective in the diffracted beam generates a magnified projection image of a local volume. By placing a detector in the back focal plane, high-resolution reciprocal space maps are generated for the local volume. Geometrical optics is used to provide analytical expressions for the resolution and range of the reciprocal space maps and the associated field of view in the sample plane. To understand the effects of coherence a comparison is made with wavefront simulations using the fractional Fourier transform. Reciprocal space mapping is demonstrated experimentally at an X-ray energy of 15.6 keV. The resolution function exhibits suppressed streaks and an FWHM resolution in all directions of ΔQ/Q = 4 × 10−5 or better. It is demonstrated by simulations that scanning a square aperture in the back focal plane enables strain mapping with no loss in resolution to be combined with a spatial resolution of 100 nm.Copyright (c) 2018 International Union of Crystallographyurn:issn:1600-5767Poulsen, H.F.Cook, P.KLeemreize, H.Pedersen, A.F.Yildirim, C.Kutsal, M.Jakobsen, A.C.Trujillo, J.X.Ormstrup, J.Detlefs, C.2018-09-13doi:10.1107/S1600576718011378International Union of CrystallographyA method of high-resolution reciprocal space mapping and strain scanning using the back focal plane in dark-field X-ray microscopy is introduced.ENX-ray diffraction microscopydiffraction contrast tomographystructural characterizationsynchrotron radiationtomographydiffraction imagingDark-field X-ray microscopy is a new full-field imaging technique for nondestructively mapping the structure of deeply embedded crystalline elements in three dimensions. Placing an objective in the diffracted beam generates a magnified projection image of a local volume. By placing a detector in the back focal plane, high-resolution reciprocal space maps are generated for the local volume. Geometrical optics is used to provide analytical expressions for the resolution and range of the reciprocal space maps and the associated field of view in the sample plane. To understand the effects of coherence a comparison is made with wavefront simulations using the fractional Fourier transform. Reciprocal space mapping is demonstrated experimentally at an X-ray energy of 15.6 keV. The resolution function exhibits suppressed streaks and an FWHM resolution in all directions of ΔQ/Q = 4 × 10−5 or better. It is demonstrated by simulations that scanning a square aperture in the back focal plane enables strain mapping with no loss in resolution to be combined with a spatial resolution of 100 nm.text/htmlReciprocal space mapping and strain scanning using X-ray diffraction microscopytext5512018-09-13Copyright (c) 2018 International Union of CrystallographyJournal of Applied Crystallographyresearch papers14281436Differential evolution and Markov chain Monte Carlo analyses of layer disorder in nanosheet ensembles using total scattering
http://scripts.iucr.org/cgi-bin/paper?kc5081
Assemblies of nanosheets are often characterized by extensive layer-position disorder. Coupled with the often minute coherent scattering domain size and relaxation of the nanosheet structure itself, unambiguous interpretation of X-ray and neutron scattering data from such materials is non-trivial. This work demonstrates a general approach towards refinement of layer-disorder information from atomic pair distribution function (PDF) data for materials that span the gap between turbostratism and ordered stacking arrangements. X-ray total scattering data typical of a modern rapid-acquisition PDF instrument are simulated for a hypothetical graphene-like structure using the program DIFFaX, from which atomic PDFs are extracted. Small 1 × 1 × 20 supercell models representing the stacking of discrete layer types are combined to model a continuous distribution of layer-position disorder. Models optimized using the differential evolution algorithm demonstrate improved fit quality over 75 Å when a single mean layer-type model is replaced with a constrained 31-layer-type model. Posterior distribution analyses using the Markov chain Monte Carlo algorithm demonstrate that the influence of layer disorder and finite particle size are correlated. However, the refined mean stacking vectors match well with the generative parameter set.Copyright (c) 2018 International Union of Crystallographyurn:issn:1600-5767Metz, P.C.Koch, R.Misture, S.T.2018-09-20doi:10.1107/S1600576718011597International Union of CrystallographyThe structure of a hypothetical layer ensemble with stacking disorder is globally refined from simulated pair distribution function (PDF) data using hierarchically constrained models, highlighting the availability of interlayer atomic correlations within the PDF – information that is often non-trivial to obtain from powder diffraction data.ENpair distribution functionsstacking disorderdifferential evolution algorithmMarkov chain Monte Carlo algorithmnanosheetsAssemblies of nanosheets are often characterized by extensive layer-position disorder. Coupled with the often minute coherent scattering domain size and relaxation of the nanosheet structure itself, unambiguous interpretation of X-ray and neutron scattering data from such materials is non-trivial. This work demonstrates a general approach towards refinement of layer-disorder information from atomic pair distribution function (PDF) data for materials that span the gap between turbostratism and ordered stacking arrangements. X-ray total scattering data typical of a modern rapid-acquisition PDF instrument are simulated for a hypothetical graphene-like structure using the program DIFFaX, from which atomic PDFs are extracted. Small 1 × 1 × 20 supercell models representing the stacking of discrete layer types are combined to model a continuous distribution of layer-position disorder. Models optimized using the differential evolution algorithm demonstrate improved fit quality over 75 Å when a single mean layer-type model is replaced with a constrained 31-layer-type model. Posterior distribution analyses using the Markov chain Monte Carlo algorithm demonstrate that the influence of layer disorder and finite particle size are correlated. However, the refined mean stacking vectors match well with the generative parameter set.text/htmlDifferential evolution and Markov chain Monte Carlo analyses of layer disorder in nanosheet ensembles using total scatteringtext5512018-09-20Copyright (c) 2018 International Union of CrystallographyJournal of Applied Crystallographyresearch papers14371444Nanodomains and local structure in ternary alkaline-earth hexaborides
http://scripts.iucr.org/cgi-bin/paper?kc5077
The local structures of ternary alkaline-earth hexaborides (MB6, M = Ca0.5Sr0.5, Ca0.5Ba0.5 and Sr0.5Ba0.5) have been analysed using X-ray pair distribution function (PDF) analysis, Raman spectroscopy and transmission electron microscopy (TEM). The results show significant local deviations from the average cubic structure within the boron sub-lattice and support the conclusion that rapid synthesis processes lead to the formation of coherent nanodomains over length scales of about 10 nm. Reverse Monte Carlo fitting of the PDFs allows for quantification of the displacement disorder within the boron sub-lattice as a function of sample composition. Detailed Raman spectroscopy studies and high-resolution TEM support the models derived from X-ray scattering. The average magnitude of the static displacement disorder varies by sample composition and positively correlates with the cation radius ratios across the three compositions. The new models form a foundation for future computational and experimental studies aimed at understanding and predicting properties of hexaborides.Copyright (c) 2018 International Union of Crystallographyurn:issn:1600-5767Koch, R.Metz, P.C.Jaime, O.Vargas-Consuelos, C.I.Borja-Urby, R.Ko, J.Y.P.Cahill, J.T.Edwards, D.Vasquez, V.R.Graeve, O.A.Misture, S.T.2018-09-24doi:10.1107/S1600576718012657International Union of CrystallographyLocal symmetry reduction in several ternary metal hexaborides is shown through X-ray total scattering, Raman spectroscopy and high-resolution transmission electron microscopy.ENhexaboridesX-ray pair distribution functionlocal structureRaman spectroscopyreverse Monte CarloThe local structures of ternary alkaline-earth hexaborides (MB6, M = Ca0.5Sr0.5, Ca0.5Ba0.5 and Sr0.5Ba0.5) have been analysed using X-ray pair distribution function (PDF) analysis, Raman spectroscopy and transmission electron microscopy (TEM). The results show significant local deviations from the average cubic structure within the boron sub-lattice and support the conclusion that rapid synthesis processes lead to the formation of coherent nanodomains over length scales of about 10 nm. Reverse Monte Carlo fitting of the PDFs allows for quantification of the displacement disorder within the boron sub-lattice as a function of sample composition. Detailed Raman spectroscopy studies and high-resolution TEM support the models derived from X-ray scattering. The average magnitude of the static displacement disorder varies by sample composition and positively correlates with the cation radius ratios across the three compositions. The new models form a foundation for future computational and experimental studies aimed at understanding and predicting properties of hexaborides.text/htmlNanodomains and local structure in ternary alkaline-earth hexaboridestext5512018-09-24Copyright (c) 2018 International Union of CrystallographyJournal of Applied Crystallographyresearch papers14451454Effects of multiple scattering encountered for various small-angle scattering model functions
http://scripts.iucr.org/cgi-bin/paper?vg5087
In small-angle scattering theory and data modeling, it is generally assumed that each scattered ray – photon or neutron – is only scattered once on its path through the sample. This assumption greatly simplifies the interpretation of the data and is valid in many cases. However, it breaks down under conditions of high scattering power, increasing with sample concentration, scattering contrast, sample path length and ray wavelength. For samples with a significant scattering power, disregarding multiple scattering effects can lead to erroneous conclusions on the structure of the investigated sample. In this paper, the impact of multiple scattering effects on different types of scattering pattern are determined, and methods for assessing and addressing them are discussed, including the general implementation of multiple scattering effects in structural model fits. The modification of scattering patterns by multiple scattering is determined for the sphere scattering function and the Gaussian function, as well as for different Sabine-type functions, including the Debye–Andersen–Brumberger (DAB) model and the Lorentzian scattering function. The calculations are performed using the semi-analytical convolution method developed by Schelten & Schmatz [J. Appl. Cryst. (1980). 13, 385–390], facilitated by analytical expressions for intermediate functions, and checked with Monte Carlo simulations. The results show how a difference in the shape of the scattering function plotted versus momentum transfer q results in different multiple scattering effects at low q, where information on the particle mass and radius of gyration is contained.Copyright (c) 2018 Jensen and Barkerurn:issn:1600-5767Jensen, G.V.Barker, J.G.2018-09-20doi:10.1107/S1600576718010816International Union of CrystallographyThe means by which multiple scattering contributions in experimental small-angle scattering data can be estimated, and how they can be included in the data analysis, are reviewed and discussed. The multiple scattering effects for a range of relevant model scattering functions are calculated using semi-analytically derived solutions to Hankel transforms as well as Monte Carlo simulations.ENsmall-angle scatteringmultiple scattering effectsdata modelingIn small-angle scattering theory and data modeling, it is generally assumed that each scattered ray – photon or neutron – is only scattered once on its path through the sample. This assumption greatly simplifies the interpretation of the data and is valid in many cases. However, it breaks down under conditions of high scattering power, increasing with sample concentration, scattering contrast, sample path length and ray wavelength. For samples with a significant scattering power, disregarding multiple scattering effects can lead to erroneous conclusions on the structure of the investigated sample. In this paper, the impact of multiple scattering effects on different types of scattering pattern are determined, and methods for assessing and addressing them are discussed, including the general implementation of multiple scattering effects in structural model fits. The modification of scattering patterns by multiple scattering is determined for the sphere scattering function and the Gaussian function, as well as for different Sabine-type functions, including the Debye–Andersen–Brumberger (DAB) model and the Lorentzian scattering function. The calculations are performed using the semi-analytical convolution method developed by Schelten & Schmatz [J. Appl. Cryst. (1980). 13, 385–390], facilitated by analytical expressions for intermediate functions, and checked with Monte Carlo simulations. The results show how a difference in the shape of the scattering function plotted versus momentum transfer q results in different multiple scattering effects at low q, where information on the particle mass and radius of gyration is contained.text/htmlEffects of multiple scattering encountered for various small-angle scattering model functionstext5512018-09-20Copyright (c) 2018 Jensen and BarkerJournal of Applied Crystallographyresearch papers14551466Structure of crystallized particles in sputter-deposited amorphous germanium films
http://scripts.iucr.org/cgi-bin/paper?vh5086
Pristine thin films of amorphous Ge prepared by sputtering are unstable and form coarse crystalline particles of 100 nm in size upon crystallization by electron irradiation. These crystalline particles exhibit unusual diffraction patterns that cannot be understood from the diamond cubic structure. The structure has previously been assumed to be a metastable hexagonal form. In the present work, the structure of the coarse crystalline particles has been analysed in detail by transmission electron microscopy, considering the possibility that those diffraction patterns might occur with the diamond cubic structure if the particle consists of thin twin layers. By high-resolution lattice imaging the particles have been shown to be of the diamond cubic structure containing a high density of twins and stacking faults parallel to {111}. With such defects, diffraction patterns can be complex because of the following effects: superposition of two or more diffraction patterns of the same structure but of different orientations, double diffraction through twin crystals, and streaks parallel to the thin crystal which give rise to extra diffraction spots. It is found that diffraction patterns taken from various orientations can be explained in terms of these effects.Copyright (c) 2018 International Union of Crystallographyurn:issn:1600-5767Okugawa, M.Nakamura, R.Hirata, A.Ishimaru, M.Yasuda, H.Numakura, H.2018-09-20doi:10.1107/S1600576718012153International Union of CrystallographyThe structure of crystalline particles of submicrometre size formed in an amorphous thin-film matrix by electron irradiation has been re-analysed. It is found that the unusual diffraction patterns observed in earlier reports, which suggested a hexagonal structure, can be explained by the standard diamond cubic structure but with a complex microstructure: fine twins and dense stacking faults on {111} planes. High-resolution lattice images support this interpretation.ENcrystallized Ge thin filmstwinningstreaking effectsPristine thin films of amorphous Ge prepared by sputtering are unstable and form coarse crystalline particles of 100 nm in size upon crystallization by electron irradiation. These crystalline particles exhibit unusual diffraction patterns that cannot be understood from the diamond cubic structure. The structure has previously been assumed to be a metastable hexagonal form. In the present work, the structure of the coarse crystalline particles has been analysed in detail by transmission electron microscopy, considering the possibility that those diffraction patterns might occur with the diamond cubic structure if the particle consists of thin twin layers. By high-resolution lattice imaging the particles have been shown to be of the diamond cubic structure containing a high density of twins and stacking faults parallel to {111}. With such defects, diffraction patterns can be complex because of the following effects: superposition of two or more diffraction patterns of the same structure but of different orientations, double diffraction through twin crystals, and streaks parallel to the thin crystal which give rise to extra diffraction spots. It is found that diffraction patterns taken from various orientations can be explained in terms of these effects.text/htmlStructure of crystallized particles in sputter-deposited amorphous germanium filmstext5512018-09-20Copyright (c) 2018 International Union of CrystallographyJournal of Applied Crystallographyresearch papers14671473Crystal growth, a research-driven laboratory course
http://scripts.iucr.org/cgi-bin/paper?gj5204
The research-driven laboratory experiment described herein has at its core the individual development of students, combining core subject matter with the opportunity to explore, in a research environment, areas outside of traditional curricula; however, it maintains the pedagogical training for an undergraduate major degree in chemistry and sciences in general. The laboratory can feasibly be implemented in high schools to expose students to an engaging and intellectually fulfilling aspect of chemistry early in their career. This seven-week project is based on the growth and study of crystals and encourages students, from the outset, to conceive, propose, design, plan and carry out their own research on chemicals and conditions of their own choosing. The wide array of laboratory equipment, analytical instrumentation and techniques that the students are potentially exposed to, from micropipettes and optical microscopes to scanning electron microscopy and powder X-ray diffraction, puts these projects on a par with senior capstone research projects. The feedback from the students for the seven years this project has been in operation is almost unanimous in enthusiasm and praise.Copyright (c) 2018 International Union of Crystallographyurn:issn:1600-5767Whelan, J.Koussa, J.Chehade, I.Sabanovic, M.Chang, A.Carelli, D.An, Z.Zhang, L.Bernstein, J.Rabeh, W.M.2018-08-09doi:10.1107/S1600576718009573International Union of CrystallographyThe use of crystal growth as the basis for laboratory experimentation will train students majoring in sciences, but more importantly, it stimulates their interest in carrying out and maintaining a research project of their own.ENscience laboratoriesresearch experiencecrystal growthX-ray crystallographyeducationThe research-driven laboratory experiment described herein has at its core the individual development of students, combining core subject matter with the opportunity to explore, in a research environment, areas outside of traditional curricula; however, it maintains the pedagogical training for an undergraduate major degree in chemistry and sciences in general. The laboratory can feasibly be implemented in high schools to expose students to an engaging and intellectually fulfilling aspect of chemistry early in their career. This seven-week project is based on the growth and study of crystals and encourages students, from the outset, to conceive, propose, design, plan and carry out their own research on chemicals and conditions of their own choosing. The wide array of laboratory equipment, analytical instrumentation and techniques that the students are potentially exposed to, from micropipettes and optical microscopes to scanning electron microscopy and powder X-ray diffraction, puts these projects on a par with senior capstone research projects. The feedback from the students for the seven years this project has been in operation is almost unanimous in enthusiasm and praise.text/htmlCrystal growth, a research-driven laboratory coursetext5512018-08-09Copyright (c) 2018 International Union of CrystallographyJournal of Applied Crystallographyteaching and education14741480Crystallographic shelves: space-group hierarchy explained
http://scripts.iucr.org/cgi-bin/paper?in5013
Space groups are classified, according to different criteria, into types, classes, systems and families. Depending on the specific research topic, some of these concepts will be more relevant to the everyday crystallographer than others. Unfortunately, incorrect use of the classification terms often leads to misunderstandings. This article presents the rationale behind the different classification levels.Copyright (c) 2018 International Union of Crystallographyurn:issn:1600-5767Nespolo, M.Aroyo, M.I.Souvignier, B.2018-09-24doi:10.1107/S1600576718012724International Union of CrystallographyThe classification of space groups into types, classes, systems and families is explained.ENspace-group classificationcrystal classescrystal systemscrystal familiesBravais classeslattice systemsSpace groups are classified, according to different criteria, into types, classes, systems and families. Depending on the specific research topic, some of these concepts will be more relevant to the everyday crystallographer than others. Unfortunately, incorrect use of the classification terms often leads to misunderstandings. This article presents the rationale behind the different classification levels.text/htmlCrystallographic shelves: space-group hierarchy explainedtext5512018-09-24Copyright (c) 2018 International Union of CrystallographyJournal of Applied Crystallographyteaching and education14811491PDFgetN3: atomic pair distribution functions from neutron powder diffraction data using ad hoc corrections
http://scripts.iucr.org/cgi-bin/paper?po5132
PDFgetN3, a new software tool for the extraction of pair distribution functions (PDFs) from neutron powder diffraction intensity data, is described. Its use is demonstrated with constant-wavelength neutron data measured at the new powder diffractometer PEARL at the Delft University of Technology. PDFgetN3 uses an ad hoc data collection protocol similar to PDFgetX3. The quality of the resulting PDFs is assessed by structure refinement and by comparison with established results from synchrotron X-ray scattering.Copyright (c) 2018 International Union of Crystallographyurn:issn:1600-5767Juhás, P.Louwen, J.N.Eijck, L. vanVogt, E.T.C.Billinge, S.J.L.2018-08-09doi:10.1107/S1600576718010002International Union of CrystallographyPDFgetN3, a software program for obtaining pair distribution functions from constant-wavelength neutron powder diffraction data, is presented.ENneutron diffractionpair distribution functionsconstant-wavelength neutron instrumentscomputer programsPDFgetN3, a new software tool for the extraction of pair distribution functions (PDFs) from neutron powder diffraction intensity data, is described. Its use is demonstrated with constant-wavelength neutron data measured at the new powder diffractometer PEARL at the Delft University of Technology. PDFgetN3 uses an ad hoc data collection protocol similar to PDFgetX3. The quality of the resulting PDFs is assessed by structure refinement and by comparison with established results from synchrotron X-ray scattering.text/htmlPDFgetN3: atomic pair distribution functions from neutron powder diffraction data using ad hoc correctionstext5512018-08-09Copyright (c) 2018 International Union of CrystallographyJournal of Applied Crystallographycomputer programs14921497xINTERPDF: a graphical user interface for analyzing intermolecular pair distribution functions of organic compounds from X-ray total scattering data
http://scripts.iucr.org/cgi-bin/paper?po5127
A new software program, xINTERPDF, that analyzes the intermolecular correlations in organic compounds via measured X-ray total scattering data is described.Copyright (c) 2018 International Union of Crystallographyurn:issn:1600-5767Shi, C.2018-09-20doi:10.1107/S1600576718012359International Union of CrystallographyA new software program, xINTERPDF, that analyzes the intermolecular correlations in organic compounds via measured X-ray total scattering data is described.ENX-ray total scatteringpair distribution functionPython programminggraphical user interfacesA new software program, xINTERPDF, that analyzes the intermolecular correlations in organic compounds via measured X-ray total scattering data is described.text/htmlxINTERPDF: a graphical user interface for analyzing intermolecular pair distribution functions of organic compounds from X-ray total scattering datatext5512018-09-20Copyright (c) 2018 International Union of CrystallographyJournal of Applied Crystallographycomputer programs14981499reductus: a stateless Python data reduction service with a browser front end
http://scripts.iucr.org/cgi-bin/paper?po5131
The online data reduction service reductus transforms measurements in experimental science from laboratory coordinates into physically meaningful quantities with accurate estimation of uncertainties from instrumental settings and properties. This reduction process is based on a few well known transformations, but flexibility in the application of the transforms and algorithms supports flexibility in experiment design, enabling a broader range of measurements than a rigid reduction scheme for data. The user interface allows easy construction of arbitrary pipelines from well known data transforms using a visual data flow diagram. Source data are drawn from a networked, open data repository. The Python back end uses intelligent caching to store intermediate results of calculations for a highly responsive user experience. The reference implementation allows immediate reduction of measurements as they are recorded for the three neutron reflectometry instruments at the NIST Center for Neutron Research, without the need for visiting scientists to install additional software on their own computers.Copyright (c) 2018 International Union of Crystallographyurn:issn:1600-5767Maranville, B.Ratcliff, W. IIKienzle, P.2018-09-24doi:10.1107/S1600576718011974International Union of CrystallographyA web-based flexible scientific data reduction system is presented, which accesses published data stores and transforms raw measurements into interpretable data through data flow diagrams that are converted to advanced calculations on a Python 3 back end; the results are returned in real time through the web interface. The application was developed for handling neutron and X-ray reflectometry results at a user facility.ENneutron reflectometryX-ray reflectometrydata reductioncomputer programsThe online data reduction service reductus transforms measurements in experimental science from laboratory coordinates into physically meaningful quantities with accurate estimation of uncertainties from instrumental settings and properties. This reduction process is based on a few well known transformations, but flexibility in the application of the transforms and algorithms supports flexibility in experiment design, enabling a broader range of measurements than a rigid reduction scheme for data. The user interface allows easy construction of arbitrary pipelines from well known data transforms using a visual data flow diagram. Source data are drawn from a networked, open data repository. The Python back end uses intelligent caching to store intermediate results of calculations for a highly responsive user experience. The reference implementation allows immediate reduction of measurements as they are recorded for the three neutron reflectometry instruments at the NIST Center for Neutron Research, without the need for visiting scientists to install additional software on their own computers.text/htmlreductus: a stateless Python data reduction service with a browser front endtext5512018-09-24Copyright (c) 2018 International Union of CrystallographyJournal of Applied Crystallographycomputer programs15001506José Lima-de-Faria (1925–2018)
http://scripts.iucr.org/cgi-bin/paper?es5005
Copyright (c) 2018 International Union of Crystallographyurn:issn:1600-5767Ferraris, G.2018-09-20doi:10.1107/S1600576718013316International Union of CrystallographyObituary for José Lima-de-Faria.ENobituarytext/htmlJosé Lima-de-Faria (1925–2018)text5512018-09-20Copyright (c) 2018 International Union of CrystallographyJournal of Applied Crystallographycrystallographers15071508The Scientific Method: Reflections from a Practitioner. By Massimiliano di Ventra. Oxford University Press, 2018. Pp. 128. Price GBP 13.99. ISBN 9780198825623.
http://scripts.iucr.org/cgi-bin/paper?xo0126
Copyright (c) 2018 International Union of Crystallographyurn:issn:1600-5767Helliwell, J.R.2018-08-09doi:10.1107/S1600576718010919International Union of CrystallographyBook review.ENbook reviewstext/htmlThe Scientific Method: Reflections from a Practitioner. By Massimiliano di Ventra. Oxford University Press, 2018. Pp. 128. Price GBP 13.99. ISBN 9780198825623.text5512018-08-09Copyright (c) 2018 International Union of CrystallographyJournal of Applied Crystallographybook reviews15091510