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 Crystallography2018-03-21International 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 2, 2018textweekly62002-02-01T00:00+00:002512018-03-21Copyright (c) 2018 International Union of CrystallographyJournal of Applied Crystallography233urn:issn:1600-5767med@iucr.orgMarch 20182018-03-21Journal of Applied Crystallographyhttp://journals.iucr.org/logos/rss10j.gif
//journals.iucr.org/j/issues/2018/02/00/isscontsbdy.html
Still imageNeutron diffraction from aligned stacks of lipid bilayers using the WAND instrument
http://scripts.iucr.org/cgi-bin/paper?aj5306
Neutron diffraction from aligned stacks of lipid bilayers is examined using the Wide-Angle Neutron Diffractometer (WAND), located at the High Flux Isotope Reactor, Oak Ridge, Tennessee, USA. Data were collected at different levels of hydration and neutron contrast by varying the relative humidity (RH) and H2O/D2O ratio from multi-bilayers of dioleoylphosphatidylcholine and sunflower phosphatidylcholine extract aligned on single-crystal silicon substrates. This work highlights the capabilites of a newly fabricated sample hydration cell, which allows the lipid bilayers to be hydrated with varying H/D ratios from the RH generated by saturated salt solutions, and also demonstrates WAND's capability as an instrument suitable for the study of aligned lipid multi-bilayers.Copyright (c) 2018 International Union of Crystallographyurn:issn:1600-5767Marquardt, D.Frontzek, M.D.Zhao, Y.Chakoumakos, B.C.Katsaras, J.2018-02-06doi:10.1107/S1600576718001243International Union of CrystallographyThe implementation is described of neutron diffraction from aligned lipid bilayer stacks on the Wide-Angle Neutron Diffractometer (WAND), located at the High Flux Isotope Reactor, Oak Ridge, Tennessee, USA.ENneutron diffractionlipid bilayersrelative humiditydeuterationNeutron diffraction from aligned stacks of lipid bilayers is examined using the Wide-Angle Neutron Diffractometer (WAND), located at the High Flux Isotope Reactor, Oak Ridge, Tennessee, USA. Data were collected at different levels of hydration and neutron contrast by varying the relative humidity (RH) and H2O/D2O ratio from multi-bilayers of dioleoylphosphatidylcholine and sunflower phosphatidylcholine extract aligned on single-crystal silicon substrates. This work highlights the capabilites of a newly fabricated sample hydration cell, which allows the lipid bilayers to be hydrated with varying H/D ratios from the RH generated by saturated salt solutions, and also demonstrates WAND's capability as an instrument suitable for the study of aligned lipid multi-bilayers.text/htmlNeutron diffraction from aligned stacks of lipid bilayers using the WAND instrumenttext2512018-02-06Copyright (c) 2018 International Union of CrystallographyJournal of Applied Crystallographyresearch papers00The suite of small-angle neutron scattering instruments at Oak Ridge National Laboratory
http://scripts.iucr.org/cgi-bin/paper?aj5303
Oak Ridge National Laboratory is home to the High Flux Isotope Reactor (HFIR), a high-flux research reactor, and the Spallation Neutron Source (SNS), the world's most intense source of pulsed neutron beams. The unique co-localization of these two sources provided an opportunity to develop a suite of complementary small-angle neutron scattering instruments for studies of large-scale structures: the GP-SANS and Bio-SANS instruments at the HFIR and the EQ-SANS and TOF-USANS instruments at the SNS. This article provides an overview of the capabilities of the suite of instruments, with specific emphasis on how they complement each other. A description of the plans for future developments including greater integration of the suite into a single point of entry for neutron scattering studies of large-scale structures is also provided.Copyright (c) 2018 International Union of Crystallographyurn:issn:1600-5767Heller, W.T.Cuneo, M.Debeer-Schmitt, L.Do, C.He, L.Heroux, L.Littrell, K.Pingali, S.V.Qian, S.Stanley, C.Urban, V.S.Wu, B.Bras, W.2018-02-21doi:10.1107/S1600576718001231International Union of CrystallographyThe suite of small-angle neutron scattering instrumentation available at the High Flux Isotope Reactor and Spallation Neutron Source of Oak Ridge National Laboratory is presented.ENsmall-angle neutron scatteringscientific user facilitiesultra-small-angle neutron scatteringOak Ridge National LaboratoryORNLOak Ridge National Laboratory is home to the High Flux Isotope Reactor (HFIR), a high-flux research reactor, and the Spallation Neutron Source (SNS), the world's most intense source of pulsed neutron beams. The unique co-localization of these two sources provided an opportunity to develop a suite of complementary small-angle neutron scattering instruments for studies of large-scale structures: the GP-SANS and Bio-SANS instruments at the HFIR and the EQ-SANS and TOF-USANS instruments at the SNS. This article provides an overview of the capabilities of the suite of instruments, with specific emphasis on how they complement each other. A description of the plans for future developments including greater integration of the suite into a single point of entry for neutron scattering studies of large-scale structures is also provided.text/htmlThe suite of small-angle neutron scattering instruments at Oak Ridge National Laboratorytext2512018-02-21Copyright (c) 2018 International Union of CrystallographyJournal of Applied Crystallographyresearch papers00Recent upgrades of the neutron reflectometer D17 at ILL
http://scripts.iucr.org/cgi-bin/paper?uh5001
The vertical sample-plane reflectometer D17 at the Institut Laue–Langevin in Grenoble, France, has undergone several major upgrades since its commissioning, which are summarized in this article. The three major improvements are (i) a new focusing guide, increasing the usable flux on the sample by a factor of 2.5; (ii) a new beam polarizer and new spin flippers, allowing for the use of polarized neutrons in time-of-flight mode; and (iii) a new detector with a particularly uniform response under homogeneous exposure, improved stability and state-of-the-art detector electronics. The combination of these factors has paved the road to new possibilities in fast kinetic measurements, magnetism and off-specular scattering. Examples and scientific references for the new capabilities are presented.Copyright (c) 2018 International Union of Crystallographyurn:issn:1600-5767Saerbeck, T.Cubitt, R.Wildes, A.Manzin, G.Andersen, K.H.Gutfreund, P.2018-03-01doi:10.1107/S160057671800239XInternational Union of CrystallographyThe article describes recent upgrades of the polarized neutron reflectometer D17 at the Institut Laue–Langevin, Grenoble, France, and presents recent examples of scientific studies enabled with the new options.ENneutron reflectometrypolarized neutronsoff-specular scatteringD17The vertical sample-plane reflectometer D17 at the Institut Laue–Langevin in Grenoble, France, has undergone several major upgrades since its commissioning, which are summarized in this article. The three major improvements are (i) a new focusing guide, increasing the usable flux on the sample by a factor of 2.5; (ii) a new beam polarizer and new spin flippers, allowing for the use of polarized neutrons in time-of-flight mode; and (iii) a new detector with a particularly uniform response under homogeneous exposure, improved stability and state-of-the-art detector electronics. The combination of these factors has paved the road to new possibilities in fast kinetic measurements, magnetism and off-specular scattering. Examples and scientific references for the new capabilities are presented.text/htmlRecent upgrades of the neutron reflectometer D17 at ILLtext2512018-03-01Copyright (c) 2018 International Union of CrystallographyJournal of Applied Crystallographyresearch papers00RAINBOWS: refractive analysis of the incoming neutron beam over the white spectrum. A new fast neutron reflectometry technique exploiting a focusing prism
http://scripts.iucr.org/cgi-bin/paper?uj5003
Neutron reflectivity is a powerful technique for characterizing interfaces in many areas of science. The traditional method of time of flight for measuring the wavelength of neutrons in a white beam is extremely wasteful, as the vast majority of neutrons must be absorbed in the choppers in order to produce a pulsed beam. A prism operates continuously, with a transmission up to two orders of magnitude higher than choppers. The wavelength-dependent deflection of the beam by the prism, coupled with a high spatial resolution detector, results in excellent wavelength resolution. The theory of how the resolution is considerably enhanced by curving the surface of the prism is described in detail for a real experimental arrangement. It is demonstrated how this can be used for faster neutron reflectometry, including the merging of different angles and subtraction of background. The technique shows considerable promise for neutron reflectivity, opening up new areas of science particularly in the realms of kinetics and small samples.Copyright (c) 2018 International Union of Crystallographyurn:issn:1600-5767Cubitt, R.Segura Ruiz, J.Jark, W.2018-03-01doi:10.1107/S1600576718001528International Union of CrystallographyA new technique is described, exploiting a focusing prism to measure the wavelength of cold neutrons. The technique can be applied to neutron reflectivity, resulting in considerable gains in performance.ENneutron reflectometryinterface kineticsneutron opticsneutron prismsNeutron reflectivity is a powerful technique for characterizing interfaces in many areas of science. The traditional method of time of flight for measuring the wavelength of neutrons in a white beam is extremely wasteful, as the vast majority of neutrons must be absorbed in the choppers in order to produce a pulsed beam. A prism operates continuously, with a transmission up to two orders of magnitude higher than choppers. The wavelength-dependent deflection of the beam by the prism, coupled with a high spatial resolution detector, results in excellent wavelength resolution. The theory of how the resolution is considerably enhanced by curving the surface of the prism is described in detail for a real experimental arrangement. It is demonstrated how this can be used for faster neutron reflectometry, including the merging of different angles and subtraction of background. The technique shows considerable promise for neutron reflectivity, opening up new areas of science particularly in the realms of kinetics and small samples.text/htmlRAINBOWS: refractive analysis of the incoming neutron beam over the white spectrum. A new fast neutron reflectometry technique exploiting a focusing prismtext2512018-03-01Copyright (c) 2018 International Union of CrystallographyJournal of Applied Crystallographyresearch papers00Optimization of moderators and beam extraction at the ESS
http://scripts.iucr.org/cgi-bin/paper?uh5002
A global approach coupling the moderator to the beam extraction system has been applied for the design optimization of the thermal and cold moderators of the European Spallation Source (ESS), which will be the brightest neutron source in the world for condensed-matter studies. The design is based on the recently developed high-brightness low-dimensional moderator concepts. Para-hydrogen is used for the cold neutron source, while thermal neutrons are provided by moderation in water. The overall moderation configuration was chosen in order to satisfy a range of requirements on bispectral extraction, beamport configuration and instrument performance. All instruments are served by a single moderator assembly above the target, arranged in a `butterfly' geometry with a height of 3 cm. This was determined to be the optimal height for trade-off between high brightness and efficient guide illumination, by analysis of the performance of 23 instruments, based on the reference suite of the ESS Technical Design Report. The concept of `brilliance transfer' is introduced to quantify the performance of the neutron optical system from the source to the sample. The target monolith incorporates a grid of 42 neutron beamports with an average separation of 6°, allowing a free choice between cold and thermal neutron sources at all instrument positions. With the large number of beamports and the space below the target available for future moderators, ample opportunities are available for future upgrades.Copyright (c) 2018 Ken Holst Andersen et al.urn:issn:1600-5767Andersen, K.H.Bertelsen, M.Zanini, L.Klinkby, E.B.Schönfeldt, T.Bentley, P.M.Saroun, J.2018-03-12doi:10.1107/S1600576718002406International Union of CrystallographyAll instruments at the European Spallation Source (ESS), Lund, Sweden, are served by a carefully optimized moderator assembly, providing world-leading performance and excellent flexibility and upgradeability.ENwater moderatorspara-hydrogen moderatorslow-dimensional moderatorspancake moderatorsbutterfly moderatorsbrilliance transferneutron instrumentsA global approach coupling the moderator to the beam extraction system has been applied for the design optimization of the thermal and cold moderators of the European Spallation Source (ESS), which will be the brightest neutron source in the world for condensed-matter studies. The design is based on the recently developed high-brightness low-dimensional moderator concepts. Para-hydrogen is used for the cold neutron source, while thermal neutrons are provided by moderation in water. The overall moderation configuration was chosen in order to satisfy a range of requirements on bispectral extraction, beamport configuration and instrument performance. All instruments are served by a single moderator assembly above the target, arranged in a `butterfly' geometry with a height of 3 cm. This was determined to be the optimal height for trade-off between high brightness and efficient guide illumination, by analysis of the performance of 23 instruments, based on the reference suite of the ESS Technical Design Report. The concept of `brilliance transfer' is introduced to quantify the performance of the neutron optical system from the source to the sample. The target monolith incorporates a grid of 42 neutron beamports with an average separation of 6°, allowing a free choice between cold and thermal neutron sources at all instrument positions. With the large number of beamports and the space below the target available for future moderators, ample opportunities are available for future upgrades.text/htmlOptimization of moderators and beam extraction at the ESStext2512018-03-12Copyright (c) 2018 Ken Holst Andersen et al.Journal of Applied Crystallographyresearch papers00Conceptual design of CHESS, a new direct-geometry inelastic neutron spectrometer dedicated to studying small samples
http://scripts.iucr.org/cgi-bin/paper?ah5005
CHESS is a new direct-geometry inelastic spectrometer, which is planned for the Second Target Station (STS) at the Spallation Neutron Source (SNS) in Oak Ridge. It will take full advantage of the increased peak brilliance of the high-brightness STS coupled moderators and of recent advances in instrument design and technology to achieve unprecedented performance for inelastic scattering in the cold energy range. This paper presents a conceptual design that addresses key requirements and technical solutions which are derived directly from the science case and anticipated use of the instrument.Copyright (c) 2018 International Union of Crystallographyurn:issn:1600-5767Sala, G.Lin, J.Y.Y.Graves, V.B.Ehlers, G.2018-03-12doi:10.1107/S1600576718002224International Union of CrystallographyThis paper describes the conceptual design of a new direct-geometry inelastic spectrometer, called CHESS, which is planned for the Second Target Station at the Spallation Neutron Source in Oak Ridge, USA.ENCHESSneutron spectrometersconceptual designsmall samplesCHESS is a new direct-geometry inelastic spectrometer, which is planned for the Second Target Station (STS) at the Spallation Neutron Source (SNS) in Oak Ridge. It will take full advantage of the increased peak brilliance of the high-brightness STS coupled moderators and of recent advances in instrument design and technology to achieve unprecedented performance for inelastic scattering in the cold energy range. This paper presents a conceptual design that addresses key requirements and technical solutions which are derived directly from the science case and anticipated use of the instrument.text/htmlConceptual design of CHESS, a new direct-geometry inelastic neutron spectrometer dedicated to studying small samplestext2512018-03-12Copyright (c) 2018 International Union of CrystallographyJournal of Applied Crystallographyresearch papers00QUOKKA, the pinhole small-angle neutron scattering instrument at the OPAL Research Reactor, Australia: design, performance, operation and scientific highlights
http://scripts.iucr.org/cgi-bin/paper?uh5003
QUOKKA is a 40 m pinhole small-angle neutron scattering instrument in routine user operation at the OPAL research reactor at the Australian Nuclear Science and Technology Organisation. Operating with a neutron velocity selector enabling variable wavelength, QUOKKA has an adjustable collimation system providing source–sample distances of up to 20 m. Following the large-area sample position, a two-dimensional 1 m2 position-sensitive detector measures neutrons scattered from the sample over a secondary flight path of up to 20 m. Also offering incident beam polarization and analysis capability as well as lens focusing optics, QUOKKA has been designed as a general purpose SANS instrument to conduct research across a broad range of scientific disciplines, from structural biology to magnetism. As it has recently generated its first 100 publications through serving the needs of the domestic and international user communities, it is timely to detail a description of its as-built design, performance and operation as well as its scientific highlights. Scientific examples presented here reflect the Australian context, as do the industrial applications, many combined with innovative and unique sample environments.Copyright (c) 2018 International Union of Crystallographyurn:issn:1600-5767Wood, K.Mata, J.P.Garvey, C.J.Wu, C.-M.Hamilton, W.A.Abbeywick, P.Bartlett, D.Bartsch, F.Baxter, P.Booth, N.Brown, W.Christoforidis, J.Clowes, D.d'Adam, T.Darmann, F.Deura, M.Harrison, S.Hauser, N.Horton, G.Federici, D.Franceschini, F.Hanson, P.Imamovic, E.Imperia, P.Jones, M.Kennedy, S.Kim, S.Lam, T.Lee, W.T.Lesha, M.Mannicke, D.Noakes, T.Olsen, S.R.Osborn, J.C.Penny, D.Perry, M.Pullen, S.A.Robinson, R.A.Schulz, J.C.Xiong, N.Gilbert, E.P.2018-03-20doi:10.1107/S1600576718002534International Union of CrystallographyThe design, performance, operation and scientific highlights from the QUOKKA SANS instrument at the OPAL Research Reactor, Australia, are described.ENSANSQUOKKAneutron scattering instrumentsvariable wavelengthQUOKKA is a 40 m pinhole small-angle neutron scattering instrument in routine user operation at the OPAL research reactor at the Australian Nuclear Science and Technology Organisation. Operating with a neutron velocity selector enabling variable wavelength, QUOKKA has an adjustable collimation system providing source–sample distances of up to 20 m. Following the large-area sample position, a two-dimensional 1 m2 position-sensitive detector measures neutrons scattered from the sample over a secondary flight path of up to 20 m. Also offering incident beam polarization and analysis capability as well as lens focusing optics, QUOKKA has been designed as a general purpose SANS instrument to conduct research across a broad range of scientific disciplines, from structural biology to magnetism. As it has recently generated its first 100 publications through serving the needs of the domestic and international user communities, it is timely to detail a description of its as-built design, performance and operation as well as its scientific highlights. Scientific examples presented here reflect the Australian context, as do the industrial applications, many combined with innovative and unique sample environments.text/htmlQUOKKA, the pinhole small-angle neutron scattering instrument at the OPAL Research Reactor, Australia: design, performance, operation and scientific highlightstext2512018-03-20Copyright (c) 2018 International Union of CrystallographyJournal of Applied Crystallographyresearch papers00Structural evolution of a Ge-substituted SnSe thermoelectric material with low thermal conductivity
http://scripts.iucr.org/cgi-bin/paper?kc5067
Thermoelectric materials are expected to become new alternative sources of sustainable energy. Among them, the SnSe intermetallic alloy has been described as an excellent thermoelectric compound, characterized by an extremely low thermal conductivity with maximum performance at the onset of a structural phase transition at 800 K. Recently, novel SnSe derivatives with Ge substitution have been synthesized by a direct arc-melting technique. This produces nanostructured polycrystalline samples that exhibit a record high Seebeck coefficient, anticipating an excellent performance above room temperature. Here, the structural phase transition from a GeS-type structure (space group Pnma) to a TlI-type structure (space group Cmcm) is investigated in situ via neutron powder diffraction (NPD) in the temperature range 298–853 K for the selected composition Sn0.8Ge0.2Se. This transition takes place at 803 K, as shown by differential scanning calorimetry. The analysis from the NPD data shows a non-monotonic behaviour of the anisotropic displacement parameters upon entering the domain of the Cmcm structure. The energies of the atomic vibrations have been quantitatively analysed by fitting the temperature-dependent mean-square displacements to Einstein oscillators. The thermal conductivity of Sn0.8Ge0.2Se is as low as 0.35 W m−1 K−1 at 773 K, which mostly represents the lattice thermal contribution.Copyright (c) 2018 International Union of Crystallographyurn:issn:1600-5767Serrano-Sánchez, F.Nemes, N.M.Martínez, J.L.Juan-Dura, O.de la Torre, M.A.Fernández-Díaz, M.T.Alonso, J.A.2018-02-06doi:10.1107/S1600576718000808International Union of CrystallographyThe Sn1−xGexSe compounds constitute a novel family of high-performance thermoelectric materials. This in situ neutron diffraction study of Sn0.8Ge0.2Se across the structural transition helps in understanding the extremely low lattice thermal conductivity observed in this compound.ENthermoelectric materialsneutron powder diffractionnanostructureZT figure of meritlattice thermal conductivityphase transitionsThermoelectric materials are expected to become new alternative sources of sustainable energy. Among them, the SnSe intermetallic alloy has been described as an excellent thermoelectric compound, characterized by an extremely low thermal conductivity with maximum performance at the onset of a structural phase transition at 800 K. Recently, novel SnSe derivatives with Ge substitution have been synthesized by a direct arc-melting technique. This produces nanostructured polycrystalline samples that exhibit a record high Seebeck coefficient, anticipating an excellent performance above room temperature. Here, the structural phase transition from a GeS-type structure (space group Pnma) to a TlI-type structure (space group Cmcm) is investigated in situ via neutron powder diffraction (NPD) in the temperature range 298–853 K for the selected composition Sn0.8Ge0.2Se. This transition takes place at 803 K, as shown by differential scanning calorimetry. The analysis from the NPD data shows a non-monotonic behaviour of the anisotropic displacement parameters upon entering the domain of the Cmcm structure. The energies of the atomic vibrations have been quantitatively analysed by fitting the temperature-dependent mean-square displacements to Einstein oscillators. The thermal conductivity of Sn0.8Ge0.2Se is as low as 0.35 W m−1 K−1 at 773 K, which mostly represents the lattice thermal contribution.text/htmlStructural evolution of a Ge-substituted SnSe thermoelectric material with low thermal conductivitytext2512018-02-06Copyright (c) 2018 International Union of CrystallographyJournal of Applied Crystallographyresearch papers00Origin of the superstructure elucidated by atomic resolution HAADF-STEM and HREM in the Ce10W22O81 lanthanide tungstate phase
http://scripts.iucr.org/cgi-bin/paper?ks5584
The present paper provides new information on the attribution of the cationic sites of the orthorhombic Ce10W22O81 crystal phase prepared in the CeO2–Ce2O3–WO3 ternary system. Atomic resolution HAADF-STEM (high-angle annular dark-field scanning transmission electron microscopy) and HREM (high-resolution electron microscopy) investigations have highlighted the presence of two mixed columns of Ce and W cations along the a axis that were previously assigned to pure W cations in the asymmetric unit. This discovery explains the presence of a commensurate superstructure doubling the orthorhombic unit-cell length ao.Copyright (c) 2018 International Union of Crystallographyurn:issn:1600-5767Patout, L.Hallaoui, A.Neisius, T.Campos, A. P. C.Dominici, C.Alfonso, C.Charaï, A.2018-02-06doi:10.1107/S1600576718001103International Union of CrystallographyAtomic resolution high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) and high-resolution electron microscopy (HREM) are used to highlight partial chemical ordering of cations and superstructures in metal oxides.ENscheelite-like structurecommensurate superstructureshigh-resolution electron microscopyHREM projection symmetrieshigh-angle annular dark-field scanning transmission electron microscopyatomic resolution HAADF-STEM quantificationThe present paper provides new information on the attribution of the cationic sites of the orthorhombic Ce10W22O81 crystal phase prepared in the CeO2–Ce2O3–WO3 ternary system. Atomic resolution HAADF-STEM (high-angle annular dark-field scanning transmission electron microscopy) and HREM (high-resolution electron microscopy) investigations have highlighted the presence of two mixed columns of Ce and W cations along the a axis that were previously assigned to pure W cations in the asymmetric unit. This discovery explains the presence of a commensurate superstructure doubling the orthorhombic unit-cell length ao.text/htmlOrigin of the superstructure elucidated by atomic resolution HAADF-STEM and HREM in the Ce10W22O81 lanthanide tungstate phasetext2512018-02-06Copyright (c) 2018 International Union of CrystallographyJournal of Applied Crystallographyresearch papers00Single-crystal neutron diffraction in diamond anvil cells with hot neutrons
http://scripts.iucr.org/cgi-bin/paper?pd5100
It is demonstrated that it is possible to perform single-crystal measurements in diamond anvil cells (DACs) with a monochromatic beam at modern hot neutron sources that offer the benefit of short neutron wavelengths with high fluxes. A piston–cylinder DAC with conical Boehler–Almax diamonds that allows for a wide accessibility of the reciprocal space has been developed. The diffraction data collected in this cell using hot neutrons are of very good quality and can be used for a full and reliable structure refinement.Copyright (c) 2018 International Union of Crystallographyurn:issn:1600-5767Grzechnik, A.Meven, M.Friese, K.2018-02-21doi:10.1107/S1600576718000997International Union of CrystallographyIt is shown that it is possible to perform single-crystal measurements in diamond anvil cells with a monochromatic beam at modern hot neutron sources. The data are of very good quality and can be used for a full and reliable structure refinement.ENhot neutronssingle-crystal diffractiondiamond anvil cellshigh pressureIt is demonstrated that it is possible to perform single-crystal measurements in diamond anvil cells (DACs) with a monochromatic beam at modern hot neutron sources that offer the benefit of short neutron wavelengths with high fluxes. A piston–cylinder DAC with conical Boehler–Almax diamonds that allows for a wide accessibility of the reciprocal space has been developed. The diffraction data collected in this cell using hot neutrons are of very good quality and can be used for a full and reliable structure refinement.text/htmlSingle-crystal neutron diffraction in diamond anvil cells with hot neutronstext2512018-02-21Copyright (c) 2018 International Union of CrystallographyJournal of Applied Crystallographyresearch papers001817441Thermo-physical properties of a new UV nonlinear optical crystal: NaSr3Be3B3O9F4
http://scripts.iucr.org/cgi-bin/paper?gj5197
NaSr3Be3B3O9F4 (NSBBF) as a new UV nonlinear optical crystal has aroused great interest in recent years. This study investigates the thermo-physical properties of NSBBF, including thermal expansion, thermal diffusivity, thermal conductivity and specific heat, which are important parameters for applications. The specific heat of NSBBF is comparable to that of CsLiB6O10 (CLBO) and larger than that of β-BaB2O4 (β-BBO), indicating that NSBBF has a very high laser damage threshold. The thermal expansion coefficients of NSBBF are determined as αa = 1.05 × 10−5 K−1 and αc = 1.34 × 10−5 K−1, exhibiting much smaller anisotropy than those of CLBO and β-BBO. The thermal diffusivity and conductivity of NSBBF are also obtained in the temperature region from 323 to 573 K, showing comparable anisotropies to β-BBO. All these results show that NSBBF is suitable for high-power UV laser generation.Copyright (c) 2018 International Union of Crystallographyurn:issn:1600-5767Fang, Z.Liu, L.Wang, X.Chen, C.2018-02-21doi:10.1107/S1600576718001218International Union of CrystallographyCompared with other major UV nonlinear optical crystals, especially in the 266 nm region, the thermo-physical properties of NaSr3Be3B3O9F4 are rather competitive, indicating good crystal growth potential and high-power 266 nm laser generation ability.ENNaSr3Be3B3O9F4 (NSBBF)thermo-physical propertiesspecific heatthermal expansionthermal conductivitythermal diffusivityNaSr3Be3B3O9F4 (NSBBF) as a new UV nonlinear optical crystal has aroused great interest in recent years. This study investigates the thermo-physical properties of NSBBF, including thermal expansion, thermal diffusivity, thermal conductivity and specific heat, which are important parameters for applications. The specific heat of NSBBF is comparable to that of CsLiB6O10 (CLBO) and larger than that of β-BaB2O4 (β-BBO), indicating that NSBBF has a very high laser damage threshold. The thermal expansion coefficients of NSBBF are determined as αa = 1.05 × 10−5 K−1 and αc = 1.34 × 10−5 K−1, exhibiting much smaller anisotropy than those of CLBO and β-BBO. The thermal diffusivity and conductivity of NSBBF are also obtained in the temperature region from 323 to 573 K, showing comparable anisotropies to β-BBO. All these results show that NSBBF is suitable for high-power UV laser generation.text/htmlThermo-physical properties of a new UV nonlinear optical crystal: NaSr3Be3B3O9F4text2512018-02-21Copyright (c) 2018 International Union of CrystallographyJournal of Applied Crystallographyresearch papers00Low-angle boundaries in ZnGeP2 single crystals
http://scripts.iucr.org/cgi-bin/paper?ks5583
The structure of low-angle boundaries in ZnGeP2 crystals grown by the vertical Bridgman technique was studied using Borrmann X-ray topography. The slip systems of the dislocations in the boundaries were identified by studying the contrast rosettes generated by the Borrmann effect, in the region near the dislocation core. It was shown that the boundaries are of two types: type I consists of edge dislocations of the {1\overline{1}0}〈110〉 slip system, and type II of edge and mixed dislocations of the {010}〈100〉 slip system. The boundaries of both types, consisting of pure edge dislocations with lines along [001], are symmetrical tilt boundaries with [001] rotation axes. The misorientations generated by the boundaries were estimated to range between 2–20 and 1–40′′, respectively. Low-angle boundaries are thought to be formed by polygonization of dislocations, caused by thermoelastic stresses.Copyright (c) 2018 International Union of Crystallographyurn:issn:1600-5767Lei, Z.Okunev, A.Zhu, C.Verozubova, G.Yang, C.2018-02-21doi:10.1107/S1600576718001097International Union of CrystallographyThe structure of low-angle boundaries in ZnGeP2 crystals grown by the vertical Bridgman technique was studied using the Borrmann effect in X-ray topography. Two types of these boundaries were revealed, each comprising different dislocation slip systems.ENZnGeP2 single crystalsX-ray topographyBorrmann effectdislocationslow-angle boundariescontrast rosettesdiffraction image simulationThe structure of low-angle boundaries in ZnGeP2 crystals grown by the vertical Bridgman technique was studied using Borrmann X-ray topography. The slip systems of the dislocations in the boundaries were identified by studying the contrast rosettes generated by the Borrmann effect, in the region near the dislocation core. It was shown that the boundaries are of two types: type I consists of edge dislocations of the {1\overline{1}0}〈110〉 slip system, and type II of edge and mixed dislocations of the {010}〈100〉 slip system. The boundaries of both types, consisting of pure edge dislocations with lines along [001], are symmetrical tilt boundaries with [001] rotation axes. The misorientations generated by the boundaries were estimated to range between 2–20 and 1–40′′, respectively. Low-angle boundaries are thought to be formed by polygonization of dislocations, caused by thermoelastic stresses.text/htmlLow-angle boundaries in ZnGeP2 single crystalstext2512018-02-21Copyright (c) 2018 International Union of CrystallographyJournal of Applied Crystallographyresearch papers00Lattice tilt and strain mapped by X-ray scanning nanodiffraction in compositionally graded SiGe/Si microcrystals
http://scripts.iucr.org/cgi-bin/paper?rg5143
The scanning X-ray nanodiffraction technique is used to reconstruct the three-dimensional distribution of lattice strain and Ge concentration in compositionally graded Si1−xGex microcrystals grown epitaxially on Si pillars. The reconstructed crystal shape qualitatively agrees with scanning electron micrographs and the calculated three-dimensional distribution of lattice tilt quantitatively matches finite-element method simulations. The grading of the Ge content obtained from reciprocal-space maps corresponds to the nominal grading of the epitaxial growth recipe. The X-ray measurements confirm strain calculations, according to which the lattice curvature of the microcrystals is dominated by the misfit strain, while the thermal strain contributes negligibly. The nanodiffraction experiments also indicate that the strain in narrow microcrystals on 2 × 2 µm Si pillars is relaxed purely elastically, while in wider microcrystals on 5 × 5 µm Si pillars, plastic relaxation by means of dislocations sets in. This confirms previous work on these structures using transmission electron microscopy and defect etching.Copyright (c) 2018 International Union of Crystallographyurn:issn:1600-5767Meduňa, M.Isa, F.Jung, A.Marzegalli, A.Albani, M.Isella, G.Zweiacker, K.Miglio, L.Känel, H. von2018-03-01doi:10.1107/S1600576718001450International Union of CrystallographyThe high-resolution three-dimensional distribution of lattice tilt and shape in Ge compositionally graded SiGe microcrystals is reconstructed using scanning X-ray nanodiffraction. The obtained intensity reciprocal-space maps and tilt real-space maps prove the start of defect formation for various crystal sizes and Ge grading rates, in excellent agreement with previous observations using transmission electron microscopy and defect etching.ENscanning X-ray nanodiffractionlattice bendinggraded SiGe microcrystalsstrain relaxationThe scanning X-ray nanodiffraction technique is used to reconstruct the three-dimensional distribution of lattice strain and Ge concentration in compositionally graded Si1−xGex microcrystals grown epitaxially on Si pillars. The reconstructed crystal shape qualitatively agrees with scanning electron micrographs and the calculated three-dimensional distribution of lattice tilt quantitatively matches finite-element method simulations. The grading of the Ge content obtained from reciprocal-space maps corresponds to the nominal grading of the epitaxial growth recipe. The X-ray measurements confirm strain calculations, according to which the lattice curvature of the microcrystals is dominated by the misfit strain, while the thermal strain contributes negligibly. The nanodiffraction experiments also indicate that the strain in narrow microcrystals on 2 × 2 µm Si pillars is relaxed purely elastically, while in wider microcrystals on 5 × 5 µm Si pillars, plastic relaxation by means of dislocations sets in. This confirms previous work on these structures using transmission electron microscopy and defect etching.text/htmlLattice tilt and strain mapped by X-ray scanning nanodiffraction in compositionally graded SiGe/Si microcrystalstext2512018-03-01Copyright (c) 2018 International Union of CrystallographyJournal of Applied Crystallographyresearch papers00A Monte Carlo approach for scattering correction towards quantitative neutron imaging of polycrystals
http://scripts.iucr.org/cgi-bin/paper?po5111
The development of neutron imaging from a qualitative inspection tool towards a quantitative technique in materials science has increased the requirements for accuracy significantly. Quantifying the thickness or the density of polycrystalline samples with high accuracy using neutron imaging has two main problems: (i) the scattering from the sample creates artefacts on the image and (ii) there is a lack of specific reference attenuation coefficients. This work presents experimental and simulation results to explain and approach these problems. Firstly, a series of neutron radiography and tomography experiments of iron, copper and vanadium are performed and serve as a reference. These materials were selected because they attenuate neutrons mainly through coherent (Fe and Cu) and incoherent (V) scattering. Secondly, an ad hoc Monte Carlo model was developed, based on beamline, sample and detector parameters, in order to simulate experiments, understand the physics involved and interpret the experimental data. The model, developed in the McStas framework, uses a priori information about the sample geometry and crystalline structure, as well as beamline settings, such as spectrum, geometry and detector type. The validity of the simulations is then verified with experimental results for the two problems that motivated this work: (i) the scattering distribution in transmission imaging and (ii) the calculated attenuation coefficients.Copyright (c) 2018 M. Raventós et al.urn:issn:1600-5767Raventós, M.Lehmann, E.H.Boin, M.Morgano, M.Hovind, J.Harti, R.Valsecchi, J.Kaestner, A.Carminati, C.Boillat, P.Trtik, P.Schmid, F.Siegwart, M.Mannes, D.Strobl, M.Grünzweig, C.2018-03-01doi:10.1107/S1600576718001607International Union of CrystallographyThis article describes the development and application of a Monte Carlo tool to improve the quantification capabilities of neutron imaging applied to polycrystals. The combination of modelling and experimentation gives a better understanding of how scattering coming from polycrystalline samples affects neutron imaging experiments.ENneutron imagingquantificationneutron scatteringMonte Carlo methodsThe development of neutron imaging from a qualitative inspection tool towards a quantitative technique in materials science has increased the requirements for accuracy significantly. Quantifying the thickness or the density of polycrystalline samples with high accuracy using neutron imaging has two main problems: (i) the scattering from the sample creates artefacts on the image and (ii) there is a lack of specific reference attenuation coefficients. This work presents experimental and simulation results to explain and approach these problems. Firstly, a series of neutron radiography and tomography experiments of iron, copper and vanadium are performed and serve as a reference. These materials were selected because they attenuate neutrons mainly through coherent (Fe and Cu) and incoherent (V) scattering. Secondly, an ad hoc Monte Carlo model was developed, based on beamline, sample and detector parameters, in order to simulate experiments, understand the physics involved and interpret the experimental data. The model, developed in the McStas framework, uses a priori information about the sample geometry and crystalline structure, as well as beamline settings, such as spectrum, geometry and detector type. The validity of the simulations is then verified with experimental results for the two problems that motivated this work: (i) the scattering distribution in transmission imaging and (ii) the calculated attenuation coefficients.text/htmlA Monte Carlo approach for scattering correction towards quantitative neutron imaging of polycrystalstext2512018-03-01Copyright (c) 2018 M. Raventós et al.Journal of Applied Crystallographyresearch papers00In situ study of the kinetics of growth of Pb nanoparticles embedded in a PbO–B2O3 glass
http://scripts.iucr.org/cgi-bin/paper?rg5142
The process of growth of liquid Pb nanoparticles embedded in a lead borate glass was investigated by transmission electron microscopy (TEM) and by in situ small-angle X-ray scattering (SAXS) during isothermal annealing at different temperatures within the 649–679 K range. A TEM study at room temperature of the glass–Pb nanoparticle composite, previously subjected to isothermal annealing, showed the presence of a number of nearly spherical Pb nanocrystals with some size dispersion. The analysis of several series of experimental SAXS curves recorded in situ, for increasing periods of time of isothermal annealing at different temperatures, allowed the authors to determine time and temperature dependences of the radius distribution functions of the growing spherical Pb nanoparticles. Since all selected annealing temperatures were higher than the melting temperature of bulk Pb, the Pb nanoparticles were in all cases in the liquid state during the whole growth process. A fast increase in the total volume of Pb droplets was observed during the initial stages of annealing, which indicated that the Pb droplets grow because of the incorporation of Pb atoms dispersed in the glass matrix. For more advanced stages of droplet growth, when the concentration of Pb atoms becomes close to its equilibrium concentration, the time dependences of the average radius, number density and total volume of Pb droplets are those predicted by the classical theory of coarsening proposed by Lifshitz–Slyosov–Wagner. Furthermore, it has been established that the Pb nanodroplets preserve their spherical shape and their relative dispersion in size through the whole coarsening process and that the activation energy for diffusion of Pb atoms and growth of Pb droplets embedded in the studied glass is Ea = 2.65 ± 0.09 eV per atom.Copyright (c) 2018 International Union of Crystallographyurn:issn:1600-5767Gorgeski, A.Craievich, A.F.Corrêa, L.M.Montoro, L.A.Kellermann, G.2018-03-01doi:10.1107/S1600576718001462International Union of CrystallographyThe growth of Pb droplets in a lead borate glass was investigated by transmission electron microscopy and in situ small-angle X-ray scattering during isothermal annealing within the 649–679 K temperature range. At advanced stages of the process, the dependences on time of the average radius, number density and total volume of Pb droplets are in good agreement with the predictions of the theoretical LSW model proposed by Lifshitz–Slyosov–Wagner for the classical coarsening mechanism.ENglass–nanoparticle compositenanoparticle growthnanodropletssmall-angle X-ray scatteringSAXStransmission electron microscopyTEMThe process of growth of liquid Pb nanoparticles embedded in a lead borate glass was investigated by transmission electron microscopy (TEM) and by in situ small-angle X-ray scattering (SAXS) during isothermal annealing at different temperatures within the 649–679 K range. A TEM study at room temperature of the glass–Pb nanoparticle composite, previously subjected to isothermal annealing, showed the presence of a number of nearly spherical Pb nanocrystals with some size dispersion. The analysis of several series of experimental SAXS curves recorded in situ, for increasing periods of time of isothermal annealing at different temperatures, allowed the authors to determine time and temperature dependences of the radius distribution functions of the growing spherical Pb nanoparticles. Since all selected annealing temperatures were higher than the melting temperature of bulk Pb, the Pb nanoparticles were in all cases in the liquid state during the whole growth process. A fast increase in the total volume of Pb droplets was observed during the initial stages of annealing, which indicated that the Pb droplets grow because of the incorporation of Pb atoms dispersed in the glass matrix. For more advanced stages of droplet growth, when the concentration of Pb atoms becomes close to its equilibrium concentration, the time dependences of the average radius, number density and total volume of Pb droplets are those predicted by the classical theory of coarsening proposed by Lifshitz–Slyosov–Wagner. Furthermore, it has been established that the Pb nanodroplets preserve their spherical shape and their relative dispersion in size through the whole coarsening process and that the activation energy for diffusion of Pb atoms and growth of Pb droplets embedded in the studied glass is Ea = 2.65 ± 0.09 eV per atom.text/htmlIn situ study of the kinetics of growth of Pb nanoparticles embedded in a PbO–B2O3 glasstext2512018-03-01Copyright (c) 2018 International Union of CrystallographyJournal of Applied Crystallographyresearch papers00New applications of the X-ray rotation tilt technique
http://scripts.iucr.org/cgi-bin/paper?te5025
The piezoelectric materials langasite (LGS) and calcium tantalum gallium silicate (CTGS) have been investigated with the X-ray rotation tilt (XRRT) technique using a new evaluation method. The XRRT technique is a microdiffraction method where diffraction lines are registered on a two-dimensional detector. These lines can be described using conic sections analogous to Kossel lines. Their form and position depend upon the lattice parameters and orientation of the investigated crystal. They can, therefore, be used to obtain these parameters. The new evaluation method allows for an automatic indexing of XRRT and Kossel reflections without knowledge of the pattern centre and detector-to-sample distance. This enables the investigation of more complex crystal structures like LGS and CTGS, where in this work the lattice constants and orientation were measured at various points on the sample.Copyright (c) 2018 International Union of Crystallographyurn:issn:1600-5767Heckert, M.Enghardt, S.Bauch, J.2018-03-01doi:10.1107/S1600576718001632International Union of CrystallographyA high-precision lattice constant determination of piezoelectric langasite and calcium tantalum gallium silicate crystals using the X-ray rotation tilt technique combined with a new evaluation method is presented.ENmicrodiffractionX-ray rotation tilt techniquelattice constant determinationThe piezoelectric materials langasite (LGS) and calcium tantalum gallium silicate (CTGS) have been investigated with the X-ray rotation tilt (XRRT) technique using a new evaluation method. The XRRT technique is a microdiffraction method where diffraction lines are registered on a two-dimensional detector. These lines can be described using conic sections analogous to Kossel lines. Their form and position depend upon the lattice parameters and orientation of the investigated crystal. They can, therefore, be used to obtain these parameters. The new evaluation method allows for an automatic indexing of XRRT and Kossel reflections without knowledge of the pattern centre and detector-to-sample distance. This enables the investigation of more complex crystal structures like LGS and CTGS, where in this work the lattice constants and orientation were measured at various points on the sample.text/htmlNew applications of the X-ray rotation tilt techniquetext2512018-03-01Copyright (c) 2018 International Union of CrystallographyJournal of Applied Crystallographyresearch papers00Paracrystalline structure of gold, silver, palladium and platinum nanoparticles
http://scripts.iucr.org/cgi-bin/paper?po5115
Metallic nanoparticles are of great importance because of their unique physical, chemical, antimicrobial, diagnostic, therapeutic, biomedical, sensing, biosensing, catalytic and optical properties. Detailed knowledge of the atomic scale structure of these materials is essential for understanding their activities and for exploiting their potential. This paper reports structural studies of silica-supported silver, gold, palladium and platinum nanoparticles using X-ray diffraction and high-resolution transmission electron microscopy. Electron microscopy observation allowed the determination of nanoparticle sizes, which were estimated to be in the range of 45–470 Å, and their distribution. The obtained histograms exhibit a multimodal distribution of the investigated nanoparticle sizes. The X-ray diffraction data were analyzed using the Rietveld method in the form of Williamson–Hall plots, the PDFgui fitting procedure and model-based simulation. The Williamson–Hall plots provide evidence for the presence of strain in all investigated samples. The PDFgui fitting results indicate that the investigated nanoparticles consist of atomic clusters with different sizes and degrees of disorder as well as slightly different lattice parameters. The detailed structural characterization performed via model-based simulations proves that all samples exhibit a face-centered cubic type structure with paracrystalline distortion. The degree of disorder predicted by the paracrystalline theory is correlated with the sizes of the nanoparticles. The catalytic properties of the investigated noble metals are discussed in relation to their disordered structure.Copyright (c) 2018 International Union of Crystallographyurn:issn:1600-5767Jurkiewicz, K.Kamiński, M.Glajcar, W.Woźnica, N.Julienne, F.Bartczak, P.Polański, J.Lelątko, J.Zubko, M.Burian, A.2018-03-12doi:10.1107/S1600576718001723International Union of CrystallographySilica-supported Au, Ag, Pd and Pt nanoparticles have a face-centered cubic paracrystalline structure.ENmetal nanoparticlesX-ray diffractionpair distribution functionparacrystalline structureMetallic nanoparticles are of great importance because of their unique physical, chemical, antimicrobial, diagnostic, therapeutic, biomedical, sensing, biosensing, catalytic and optical properties. Detailed knowledge of the atomic scale structure of these materials is essential for understanding their activities and for exploiting their potential. This paper reports structural studies of silica-supported silver, gold, palladium and platinum nanoparticles using X-ray diffraction and high-resolution transmission electron microscopy. Electron microscopy observation allowed the determination of nanoparticle sizes, which were estimated to be in the range of 45–470 Å, and their distribution. The obtained histograms exhibit a multimodal distribution of the investigated nanoparticle sizes. The X-ray diffraction data were analyzed using the Rietveld method in the form of Williamson–Hall plots, the PDFgui fitting procedure and model-based simulation. The Williamson–Hall plots provide evidence for the presence of strain in all investigated samples. The PDFgui fitting results indicate that the investigated nanoparticles consist of atomic clusters with different sizes and degrees of disorder as well as slightly different lattice parameters. The detailed structural characterization performed via model-based simulations proves that all samples exhibit a face-centered cubic type structure with paracrystalline distortion. The degree of disorder predicted by the paracrystalline theory is correlated with the sizes of the nanoparticles. The catalytic properties of the investigated noble metals are discussed in relation to their disordered structure.text/htmlParacrystalline structure of gold, silver, palladium and platinum nanoparticlestext2512018-03-12Copyright (c) 2018 International Union of CrystallographyJournal of Applied Crystallographyresearch papers00Evidence of damage evolution during creep of Al–Mg alloy using synchrotron X-ray refraction
http://scripts.iucr.org/cgi-bin/paper?aj5299
In order to provide further evidence of damage mechanisms predicted by the recent solid-state transformation creep (SSTC) model, direct observation of damage accumulation during creep of Al–3.85Mg was made using synchrotron X-ray refraction. X-ray refraction techniques detect the internal specific surface (i.e. surface per unit volume) on a length scale comparable to the specimen size, but with microscopic sensitivity. A significant rise in the internal specific surface with increasing creep time was observed, providing evidence for the creation of a fine grain substructure, as predicted by the SSTC model. This substructure was also observed by scanning electron microscopy.Copyright (c) 2018 International Union of Crystallographyurn:issn:1600-5767Cabeza, S.Müller, B.R.Pereyra, R.Fernández, R.González-Doncel, G.Bruno, G.2018-03-12doi:10.1107/S1600576718001449International Union of CrystallographyDamage accumulation during creep of Al–3.85Mg was studied by synchrotron X-ray refraction. Evidence of a significant rise in damage was detected with accumulated creep time and deformation. This was explained by the creation of a fine grain substructure observed by electron microscopy, as predicted by current models.ENaluminium alloyscreepdamagesynchrotron X-ray refractionelectron microscopysubgrain structureIn order to provide further evidence of damage mechanisms predicted by the recent solid-state transformation creep (SSTC) model, direct observation of damage accumulation during creep of Al–3.85Mg was made using synchrotron X-ray refraction. X-ray refraction techniques detect the internal specific surface (i.e. surface per unit volume) on a length scale comparable to the specimen size, but with microscopic sensitivity. A significant rise in the internal specific surface with increasing creep time was observed, providing evidence for the creation of a fine grain substructure, as predicted by the SSTC model. This substructure was also observed by scanning electron microscopy.text/htmlEvidence of damage evolution during creep of Al–Mg alloy using synchrotron X-ray refractiontext2512018-03-12Copyright (c) 2018 International Union of CrystallographyJournal of Applied Crystallographyresearch papers00Optimum Levenberg–Marquardt constant determination for nonlinear least-squares
http://scripts.iucr.org/cgi-bin/paper?po5119
A new method for determining an approximate optimum value for the Levenberg–Marquardt constant has been shown to improve the convergence rate of nonlinear least-squares problems including complex X-ray powder diffraction and single-crystal structural refinements. In the Gauss–Newton method of nonlinear least squares, a lower value for the objective function is occasionally not realized after solving the matrix equation AΔp = b. This situation occurs when either the objective function is at a minimum or the A matrix is ill conditioned. Invariably the Levenberg–Marquardt method is used, where the matrix equation is reformulated to (A + λI)Δp = b and λ is the Levenberg–Marquardt constant. The values chosen for λ depend on whether the objective function increases or decreases. This paper describes a new method for setting the Levenberg–Marquardt constant, as implemented in the computer program TOPAS-Academic Version 7, which in general results in an increased rate of convergence and additionally a lowering of the objective function as a function of starting parameter values. The reduction in computation is problem dependent and ranges from 10% for typical crystallographic refinements to 50% for large refinements. In addition, the method can be applied to general functions including cases where the objective function comprises both the sum of squares and penalties including functions with discontinuities. Of significance is the trivial extra computational effort required in determining λ as well as the simplicity in carrying out the calculation; the latter should allow for easy implementation in refinement programs.Copyright (c) 2018 International Union of Crystallographyurn:issn:1600-5767Coelho, A.A.2018-03-20doi:10.1107/S1600576718001784International Union of CrystallographyA new method for determining an approximate optimum value for the Levenberg–Marquardt constant has been developed. The method increases the rate of convergence of nonlinear least-sqaures problems.ENLevenberg–Marquardt methodconjugate gradientsingle-crystal refinementRietveld refinementTOPAS-AcademicA new method for determining an approximate optimum value for the Levenberg–Marquardt constant has been shown to improve the convergence rate of nonlinear least-squares problems including complex X-ray powder diffraction and single-crystal structural refinements. In the Gauss–Newton method of nonlinear least squares, a lower value for the objective function is occasionally not realized after solving the matrix equation AΔp = b. This situation occurs when either the objective function is at a minimum or the A matrix is ill conditioned. Invariably the Levenberg–Marquardt method is used, where the matrix equation is reformulated to (A + λI)Δp = b and λ is the Levenberg–Marquardt constant. The values chosen for λ depend on whether the objective function increases or decreases. This paper describes a new method for setting the Levenberg–Marquardt constant, as implemented in the computer program TOPAS-Academic Version 7, which in general results in an increased rate of convergence and additionally a lowering of the objective function as a function of starting parameter values. The reduction in computation is problem dependent and ranges from 10% for typical crystallographic refinements to 50% for large refinements. In addition, the method can be applied to general functions including cases where the objective function comprises both the sum of squares and penalties including functions with discontinuities. Of significance is the trivial extra computational effort required in determining λ as well as the simplicity in carrying out the calculation; the latter should allow for easy implementation in refinement programs.text/htmlOptimum Levenberg–Marquardt constant determination for nonlinear least-squarestext2512018-03-20Copyright (c) 2018 International Union of CrystallographyJournal of Applied Crystallographyresearch papers00Anomalous grazing-incidence small-angle X-ray scattering of Ga2O3-based nanoparticles
http://scripts.iucr.org/cgi-bin/paper?rg5137
Grazing-incidence small-angle X-ray scattering (GISAXS) performed at several X-ray energies in the vicinity of the absorption edge of a considered element is called anomalous GISAXS (AGISAXS). This emerging technique takes advantage of the variation of the scattering factor near an absorption edge, allowing the morphology of multi-component nanomaterials to be unraveled. The selected model system for AGISAXS simulations is mainly an In2O3 layer containing Ga2O3-based nanoparticles. The transmission coefficients at the different X-ray energies near the Ga K edge are identical at one specific incident angle (near the critical angle). Hence, it could be relevant to perform AGISAXS at this incident angle in order to cancel the transmission modification as the X-ray energy changes. For buried nanoparticles, grazing-incidence effects are negligible with respect to the anomalous element-specific contribution provided that the experiments are performed at energies a few electronvolts below the absorption edge. Interestingly, AGISAXS has a clearly different intensity behavior versus X-ray energy for an embedded monodisperse spherical particle, a hole and a core–shell particle. Hence, AGISAXS can be used to unambiguously distinguish such embedded particles. Moreover, even for a dense layer of core–shell nanoparticles on a substrate, anomalous effects are much larger than grazing effects as the X-ray energy changes. Finally, it is shown that experimental anomalous scattering can be significant and can be satisfactorily simulated.Copyright (c) 2018 International Union of Crystallographyurn:issn:1600-5767Revenant, C.2018-03-20doi:10.1107/S1600576718001772International Union of CrystallographyAnomalous grazing-incidence small-angle X-ray scattering allows the determination of the morphology of multi-component nanomaterials.ENsynchrotron radiationresonant scatteringanomalous grazing-incidence small-angle X-ray scatteringcontrastgrazing-angle effectsGrazing-incidence small-angle X-ray scattering (GISAXS) performed at several X-ray energies in the vicinity of the absorption edge of a considered element is called anomalous GISAXS (AGISAXS). This emerging technique takes advantage of the variation of the scattering factor near an absorption edge, allowing the morphology of multi-component nanomaterials to be unraveled. The selected model system for AGISAXS simulations is mainly an In2O3 layer containing Ga2O3-based nanoparticles. The transmission coefficients at the different X-ray energies near the Ga K edge are identical at one specific incident angle (near the critical angle). Hence, it could be relevant to perform AGISAXS at this incident angle in order to cancel the transmission modification as the X-ray energy changes. For buried nanoparticles, grazing-incidence effects are negligible with respect to the anomalous element-specific contribution provided that the experiments are performed at energies a few electronvolts below the absorption edge. Interestingly, AGISAXS has a clearly different intensity behavior versus X-ray energy for an embedded monodisperse spherical particle, a hole and a core–shell particle. Hence, AGISAXS can be used to unambiguously distinguish such embedded particles. Moreover, even for a dense layer of core–shell nanoparticles on a substrate, anomalous effects are much larger than grazing effects as the X-ray energy changes. Finally, it is shown that experimental anomalous scattering can be significant and can be satisfactorily simulated.text/htmlAnomalous grazing-incidence small-angle X-ray scattering of Ga2O3-based nanoparticlestext2512018-03-20Copyright (c) 2018 International Union of CrystallographyJournal of Applied Crystallographyresearch papers00Direct derivation (DD) of weight fractions of individual crystalline phases from observed intensities and chemical composition data: incorporation of the DD method into the whole-powder-pattern fitting procedure
http://scripts.iucr.org/cgi-bin/paper?to5169
A formula for quantitative phase analysis (QPA), called the intensity–composition (IC) formula, can be used for deriving weight fractions of individual crystalline phases in a mixture from sets of observed integrated intensities, measured in a wide 2θ range, with chemical composition data [Toraya (2016). J. Appl. Cryst. 49, 1508–1516; Toraya (2017). J. Appl. Cryst. 50, 820–829]. In this study, the IC formula has been incorporated into the whole-powder-pattern fitting (WPPF) procedure to conduct QPA. The fitting function for calculating the profile intensity at each step of the scattering angle consists of three sub-functions that represent the individual component diffraction patterns. The first sub-function calculates the diffraction pattern using a set of integrated intensities, the parameter values of which are determined by the least-squares fitting of the whole-powder pattern as is usually done by the whole-powder-pattern decomposition (WPPD) method. The second sub-function uses a set of integrated intensity parameters, which are preliminarily prepared by WPPD or may be calculated from a crystal structure model. These intensity parameters, multiplied by a scale factor, are fixed at their original values while the scale factor is adjusted in WPPF. The third sub-function uses an observed or calculated diffraction pattern multiplied by a scale factor. This diffraction pattern can be fitted directly by adjusting the scale factor. Therefore, one can fit patterns consisting of heavily broadened and degraded diffraction lines, like those of clay minerals, without being concerned with the problem of peak overlap in decomposing the diffraction pattern. The IC formula uses the total sums of the intensities under the diffraction patterns of individual phases as observed data sets; therefore, it can equally treat these intensity data sets irrespective of differences in the profile models used by the three sub-functions. The three sub-functions can arbitrarily be chosen and linearly combined, and then they can simultaneously be fitted to the observed diffraction pattern of a target mixture. The capability of the above method has been demonstrated with QPA of mixtures consisting of α-quartz, albite and kaolinite. Theories of currently used QPA techniques are reviewed from a viewpoint of the present theory and they can be interpreted as being based on the same principle, whereby the total observed intensities of individual phases are divided by the standard reference intensity per unit weight.Copyright (c) 2018 International Union of Crystallographyurn:issn:1600-5767Toraya, H.2018-03-20doi:10.1107/S1600576718001474International Union of CrystallographyThe intensity–composition formula, which can be used for directly deriving weight fractions of individual crystalline phases from sets of observed integrated intensities and chemical composition data, has been incorporated into the whole-powder-pattern fitting procedure. Mixtures containing known structure, unknown structure, and high and low crystalline materials can be quantified by using the present procedure.ENX-ray powder diffractionquantitative phase analysisintensity–composition formulawhole-powder-pattern fitting techniquesunresolved diffraction patternsA formula for quantitative phase analysis (QPA), called the intensity–composition (IC) formula, can be used for deriving weight fractions of individual crystalline phases in a mixture from sets of observed integrated intensities, measured in a wide 2θ range, with chemical composition data [Toraya (2016). J. Appl. Cryst. 49, 1508–1516; Toraya (2017). J. Appl. Cryst. 50, 820–829]. In this study, the IC formula has been incorporated into the whole-powder-pattern fitting (WPPF) procedure to conduct QPA. The fitting function for calculating the profile intensity at each step of the scattering angle consists of three sub-functions that represent the individual component diffraction patterns. The first sub-function calculates the diffraction pattern using a set of integrated intensities, the parameter values of which are determined by the least-squares fitting of the whole-powder pattern as is usually done by the whole-powder-pattern decomposition (WPPD) method. The second sub-function uses a set of integrated intensity parameters, which are preliminarily prepared by WPPD or may be calculated from a crystal structure model. These intensity parameters, multiplied by a scale factor, are fixed at their original values while the scale factor is adjusted in WPPF. The third sub-function uses an observed or calculated diffraction pattern multiplied by a scale factor. This diffraction pattern can be fitted directly by adjusting the scale factor. Therefore, one can fit patterns consisting of heavily broadened and degraded diffraction lines, like those of clay minerals, without being concerned with the problem of peak overlap in decomposing the diffraction pattern. The IC formula uses the total sums of the intensities under the diffraction patterns of individual phases as observed data sets; therefore, it can equally treat these intensity data sets irrespective of differences in the profile models used by the three sub-functions. The three sub-functions can arbitrarily be chosen and linearly combined, and then they can simultaneously be fitted to the observed diffraction pattern of a target mixture. The capability of the above method has been demonstrated with QPA of mixtures consisting of α-quartz, albite and kaolinite. Theories of currently used QPA techniques are reviewed from a viewpoint of the present theory and they can be interpreted as being based on the same principle, whereby the total observed intensities of individual phases are divided by the standard reference intensity per unit weight.text/htmlDirect derivation (DD) of weight fractions of individual crystalline phases from observed intensities and chemical composition data: incorporation of the DD method into the whole-powder-pattern fitting proceduretext2512018-03-20Copyright (c) 2018 International Union of CrystallographyJournal of Applied Crystallographyresearch papers00Crystallographic patterns in Philippine indigenous textiles
http://scripts.iucr.org/cgi-bin/paper?gj5195
The aim of this study was to analyze a representative sample of Philippine indigenous textiles in order to capture the range of symmetries and color symmetries present. This paper examines the existence of symmetries in finite designs, and classifies the plane-group and frieze-group symmetry types of the repeated patterns in woven textiles. The tendency of a particular symmetry to be more or less common than another can indicate relationships between the symmetries and the weaving technique or the culture that produced them. This paper will also examine designs and patterns with color symmetry found in these textiles. The sample consisted of 588 repeated patterns and finite designs in textiles (389 plane, 166 frieze and 33 finite) culled from well known museums in the Philippines, personal collections of scholars, existing literature on Philippine textiles and field visits.Copyright (c) 2018 International Union of Crystallographyurn:issn:1600-5767De Las Peñas, M.L.A.N.Garciano, A.Verzosa, D.M.Taganap, E.2018-03-20doi:10.1107/S1600576718002182International Union of CrystallographyThis work discusses the symmetry and color-symmetry group structures of finite designs and repeated patterns present in Philippine indigenous textiles.ENsymmetrycolor symmetryPhilippine indigenous textilesThe aim of this study was to analyze a representative sample of Philippine indigenous textiles in order to capture the range of symmetries and color symmetries present. This paper examines the existence of symmetries in finite designs, and classifies the plane-group and frieze-group symmetry types of the repeated patterns in woven textiles. The tendency of a particular symmetry to be more or less common than another can indicate relationships between the symmetries and the weaving technique or the culture that produced them. This paper will also examine designs and patterns with color symmetry found in these textiles. The sample consisted of 588 repeated patterns and finite designs in textiles (389 plane, 166 frieze and 33 finite) culled from well known museums in the Philippines, personal collections of scholars, existing literature on Philippine textiles and field visits.text/htmlCrystallographic patterns in Philippine indigenous textilestext2512018-03-20Copyright (c) 2018 International Union of CrystallographyJournal of Applied Crystallographyresearch papers00How to distinguish between opposite faces of an a-plane sapphire wafer
http://scripts.iucr.org/cgi-bin/paper?vh5081
A method to distinguish between two symmetrically equivalent opposite (11{\overline 2}0) and ({\overline 1}{\overline 1}20) faces of an a-plane sapphire wafer is described. It is shown that use of conventional X-ray diffraction analysis makes it possible to determine the `sign' of the sapphire a face in contrast to the `sign' of the c, m or r faces. Correct determination of the a-plane wafer orientation is important for further growth and processing of heteroepitaxial structures.Copyright (c) 2018 International Union of Crystallographyurn:issn:1600-5767Yunin, P.A.Drozdov, Y.N.2018-02-06doi:10.1107/S1600576718001383International Union of CrystallographyA method to distinguish between opposite (11\overline 20) and (\overline 1\overline 120) faces of an a-plane sapphire wafer using X-ray diffractometry is described.ENa-plane sapphireX-ray diffractionA method to distinguish between two symmetrically equivalent opposite (11{\overline 2}0) and ({\overline 1}{\overline 1}20) faces of an a-plane sapphire wafer is described. It is shown that use of conventional X-ray diffraction analysis makes it possible to determine the `sign' of the sapphire a face in contrast to the `sign' of the c, m or r faces. Correct determination of the a-plane wafer orientation is important for further growth and processing of heteroepitaxial structures.text/htmlHow to distinguish between opposite faces of an a-plane sapphire wafertext2512018-02-06Copyright (c) 2018 International Union of CrystallographyJournal of Applied Crystallographyshort communications00System for in situ observation of three-dimensional structural changes in polymer films during uniaxial deformation. Corrigendum
http://scripts.iucr.org/cgi-bin/paper?fs5157
Ambiguities in the article by Miyazaki, Shimokita, Ogawa & Yamamoto [J. Appl. Cryst. (2015), 48, 1016–1022] are clarified.Copyright (c) 2018 International Union of Crystallographyurn:issn:1600-5767Miyazaki, T.Shimokita, K.Ogawa, H.Yamamoto, K.2018-02-06doi:10.1107/S1600576718001875International Union of CrystallographyCorrigendum to J. Appl. Cryst. (2015), 48, 1016–1022.ENsmall-angle X-ray scatteringwide-angle X-ray diffractionstress–strain relationshipsthree-dimensional structural evaluationAmbiguities in the article by Miyazaki, Shimokita, Ogawa & Yamamoto [J. Appl. Cryst. (2015), 48, 1016–1022] are clarified.text/htmlSystem for in situ observation of three-dimensional structural changes in polymer films during uniaxial deformation. Corrigendumtext2512018-02-06Copyright (c) 2018 International Union of CrystallographyJournal of Applied Crystallographyaddenda and errata00Multiscale Materials Modeling. Approaches to Full Multiscaling. Edited by Siegfried Schmauder and Immanuel Schäfer. De Gruyter, 2016. Pp. XX+326. Price (hardcover) EUR 119.95, USD 168.00, GBP 89.99. ISBN 978-3-11-041236-9.
http://scripts.iucr.org/cgi-bin/paper?xo0087
Copyright (c) 2018 International Union of Crystallographyurn:issn:1600-5767Fukushima, Y.2018-03-12doi:10.1107/S1600576718001899International Union of CrystallographyBook review.ENbook reviewsmultiscale materials modelingtext/htmlMultiscale Materials Modeling. Approaches to Full Multiscaling. Edited by Siegfried Schmauder and Immanuel Schäfer. De Gruyter, 2016. Pp. XX+326. Price (hardcover) EUR 119.95, USD 168.00, GBP 89.99. ISBN 978-3-11-041236-9.text2512018-03-12Copyright (c) 2018 International Union of CrystallographyJournal of Applied Crystallographybook reviews00Scientific Leadership. By J. W. (Hans) Niemantsverdriet and Jan-Karel Felderhof. De Gruyter, 2017. Pp. xv+171. Price (paperback) EUR 29.95, USD 34.99, GBP 24.99. ISBN 978-3-11-046888-5.
http://scripts.iucr.org/cgi-bin/paper?xo0115
Copyright (c) 2018 International Union of Crystallographyurn:issn:1600-5767Helliwell, J.R.2018-03-20doi:10.1107/S160057671800290XInternational Union of CrystallographyBook reviewENbook reviewsscientific leadershiptext/htmlScientific Leadership. By J. W. (Hans) Niemantsverdriet and Jan-Karel Felderhof. De Gruyter, 2017. Pp. xv+171. Price (paperback) EUR 29.95, USD 34.99, GBP 24.99. ISBN 978-3-11-046888-5.text2512018-03-20Copyright (c) 2018 International Union of CrystallographyJournal of Applied Crystallographybook reviews00