Acta Crystallographica Section A
http://journals.iucr.org/a/issues/2017/03/00/isscontsbdy.html
Acta Crystallographica Section A: Foundations and Advances covers theoretical and fundamental aspects of the structure of matter. The journal is the prime forum for research in diffraction physics and the theory of crystallographic structure determination by diffraction methods using X-rays, neutrons and electrons. The structures include periodic and aperiodic crystals, and non-periodic disordered materials, and the corresponding Bragg, satellite and diffuse scattering, thermal motion and symmetry aspects. Spatial resolutions range from the subatomic domain in charge-density studies to nanodimensional imperfections such as dislocations and twin walls. The chemistry encompasses metals, alloys, and inorganic, organic and biological materials. Structure prediction and properties such as the theory of phase transformations are also covered.enCopyright (c) 2017 International Union of Crystallography2017-05-01International Union of CrystallographyInternational Union of Crystallographyhttp://journals.iucr.orgurn:issn:2053-2733Acta Crystallographica Section A: Foundations and Advances covers theoretical and fundamental aspects of the structure of matter. The journal is the prime forum for research in diffraction physics and the theory of crystallographic structure determination by diffraction methods using X-rays, neutrons and electrons. The structures include periodic and aperiodic crystals, and non-periodic disordered materials, and the corresponding Bragg, satellite and diffuse scattering, thermal motion and symmetry aspects. Spatial resolutions range from the subatomic domain in charge-density studies to nanodimensional imperfections such as dislocations and twin walls. The chemistry encompasses metals, alloys, and inorganic, organic and biological materials. Structure prediction and properties such as the theory of phase transformations are also covered.text/htmlActa Crystallographica Section A: Foundations and Advances, Volume 73, Part 3, 2017textweekly62002-01-01T00:00+00:003732017-05-01Copyright (c) 2017 International Union of CrystallographyActa Crystallographica Section A: Foundations and Advances209urn:issn:2053-2733med@iucr.orgMay 20172017-05-01Acta Crystallographica Section Ahttp://journals.iucr.org/logos/rss10a.gif
http://journals.iucr.org/a/issues/2017/03/00/isscontsbdy.html
Still imageNon-crystallographic symmetry of liquid metal, flat crystallographic faults and polymorph transformation of the M7C3 carbide
http://scripts.iucr.org/cgi-bin/paper?lk5015
The fine lamellar fault structure of primary M7C3 carbide particles in the heat-resistant Fe–Cr–Ni–C alloy of the HP series (0.45C–25Cr–35Ni) in the cast condition has been revealed using transmission electron microscopy. The lamellar fault structure is regarded as an inheritance of the initial melt structure. A one-to-one correspondence between the crystal structures of M7C3, M5C2, M3C and M23C6 carbides and constructions of the projective 103 Desargues configuration and its subconfigurations is shown. Mutual mapping between 103 Desargues subconfigurations determines transformations of the ten-vertex equal-edged triangulated clusters appearing as building units of these carbides.Copyright (c) 2017 International Union of Crystallographyurn:issn:2053-2733Talis, A.L.Kraposhin, V.S.Kondrat'ev, S.Y.Nikolaichik, V.I.Svyatysheva, E.V.Everstov, A.A.2017-03-13doi:10.1107/S2053273317000936International Union of CrystallographyThe crystal structures of M7C3, M5C2, M3C and M23C6 carbides are determined by the finite projective geometry constructions, namely the Desargues configuration 103 and its subconfigurations. The unique mechanism of the liquid-crystal transition and in situ polymorph transformations between these carbides is described within the framework of the same approach.ENcarbide M7C3carbide M23C6carbide transformationsprojective geometryfinite projective groupsDesargues configurationheat-resistant Fe–Cr–Ni alloysThe fine lamellar fault structure of primary M7C3 carbide particles in the heat-resistant Fe–Cr–Ni–C alloy of the HP series (0.45C–25Cr–35Ni) in the cast condition has been revealed using transmission electron microscopy. The lamellar fault structure is regarded as an inheritance of the initial melt structure. A one-to-one correspondence between the crystal structures of M7C3, M5C2, M3C and M23C6 carbides and constructions of the projective 103 Desargues configuration and its subconfigurations is shown. Mutual mapping between 103 Desargues subconfigurations determines transformations of the ten-vertex equal-edged triangulated clusters appearing as building units of these carbides.text/htmlNon-crystallographic symmetry of liquid metal, flat crystallographic faults and polymorph transformation of the M7C3 carbidetext3732017-03-13Copyright (c) 2017 International Union of CrystallographyActa Crystallographica Section Aresearch papers209217The phantom derivative method when a structure model is available: about its theoretical basis
http://scripts.iucr.org/cgi-bin/paper?mq5050
This study clarifies why, in the phantom derivative (PhD) approach, randomly created structures can help in refining phases obtained by other methods. For this purpose the joint probability distribution of target, model, ancil and phantom derivative structure factors and its conditional distributions have been studied. Since PhD may use n phantom derivatives, with n ≥ 1, a more general distribution taking into account all the ancil and derivative structure factors has been considered, from which the conditional distribution of the target phase has been derived. The corresponding conclusive formula contains two components. The first is the classical Srinivasan & Ramachandran term, relating the phases of the target structure with the model phases. The second arises from the combination of two correlations: that between model and derivative (the first is a component of the second) and that between derivative and target. The second component mathematically codifies the information on the target phase arising from model and derivative electron-density maps. The result is new, and explains why a random structure, uncorrelated with the target structure, adds useful information on the target phases, provided a model structure is known. Some experimental tests aimed at checking if the second component really provides information on φ (the target phase) were performed; the favourable results confirm the correctness of the theoretical calculations and of the corresponding analysis.Copyright (c) 2017 International Union of Crystallographyurn:issn:2053-2733Burla, M.C.Cascarano, G.L.Giacovazzo, C.Polidori, G.2017-03-13doi:10.1107/S2053273317001334International Union of CrystallographyThe phantom derivative phasing method has been generalized via the study of joint probability distribution functions involving the prior knowledge of a model electron-density map or of a molecular model structure.ENphasingproteinsphantom derivative methodThis study clarifies why, in the phantom derivative (PhD) approach, randomly created structures can help in refining phases obtained by other methods. For this purpose the joint probability distribution of target, model, ancil and phantom derivative structure factors and its conditional distributions have been studied. Since PhD may use n phantom derivatives, with n ≥ 1, a more general distribution taking into account all the ancil and derivative structure factors has been considered, from which the conditional distribution of the target phase has been derived. The corresponding conclusive formula contains two components. The first is the classical Srinivasan & Ramachandran term, relating the phases of the target structure with the model phases. The second arises from the combination of two correlations: that between model and derivative (the first is a component of the second) and that between derivative and target. The second component mathematically codifies the information on the target phase arising from model and derivative electron-density maps. The result is new, and explains why a random structure, uncorrelated with the target structure, adds useful information on the target phases, provided a model structure is known. Some experimental tests aimed at checking if the second component really provides information on φ (the target phase) were performed; the favourable results confirm the correctness of the theoretical calculations and of the corresponding analysis.text/htmlThe phantom derivative method when a structure model is available: about its theoretical basistext3732017-03-13Copyright (c) 2017 International Union of CrystallographyActa Crystallographica Section Aresearch papers218226Edge-2-transitive trinodal polyhedra and 2-periodic tilings
http://scripts.iucr.org/cgi-bin/paper?eo5070
All trinodal, edge-2-transitive polyhedra and 2-periodic tilings are enumerated and described. These are of special interest for the design and synthesis of materials such as metal–organic polyhedra and frameworks.Copyright (c) 2017 International Union of Crystallographyurn:issn:2053-2733Delgado-Friedrichs, O.O'Keeffe, M.2017-03-27doi:10.1107/S2053273317001565International Union of CrystallographyAll trinodal, edge-2-transitive polyhedra and 2-periodic tilings are described.ENnetstilingsminimal transitivityAll trinodal, edge-2-transitive polyhedra and 2-periodic tilings are enumerated and described. These are of special interest for the design and synthesis of materials such as metal–organic polyhedra and frameworks.text/htmlEdge-2-transitive trinodal polyhedra and 2-periodic tilingstext3732017-03-27Copyright (c) 2017 International Union of CrystallographyActa Crystallographica Section Aresearch papers227230Diffuse single-crystal scattering corrected for molecular form factor effects
http://scripts.iucr.org/cgi-bin/paper?vk5016
This paper shows that chemical short-range order in two-component molecular crystals can be solved directly by separating the influence of the molecular form factor from the diffraction pattern. This novel technique is demonstrated by analysing the diffuse scattering of tris-tert-butyl-1,3,5-benzene tricarboxamide.Copyright (c) 2017 International Union of Crystallographyurn:issn:2053-2733Schmidt, E.Neder, R.B.2017-03-27doi:10.1107/S2053273317002297International Union of CrystallographyIt is shown that chemical short-range order in two-component molecular crystals can be solved directly by separating the influence of the molecular form factor.ENdiffuse scatteringmolecular form factorsThis paper shows that chemical short-range order in two-component molecular crystals can be solved directly by separating the influence of the molecular form factor from the diffraction pattern. This novel technique is demonstrated by analysing the diffuse scattering of tris-tert-butyl-1,3,5-benzene tricarboxamide.text/htmlDiffuse single-crystal scattering corrected for molecular form factor effectstext3732017-03-27Copyright (c) 2017 International Union of CrystallographyActa Crystallographica Section Aresearch papers231237Groupoids and labelled quotient graphs: a topological analysis of the modular structure in pyroxenes
http://scripts.iucr.org/cgi-bin/paper?kx5059
The analysis of the modular structure of pyroxenes, recently discussed in Nespolo & Aroyo [Eur. J. Mineral. (2016), 28, 189–203], has been performed on the respective labelled quotient graphs (LQGs). It is shown that the structure and maximum symmetry of the module, i.e. its layer group, can be determined directly from the LQG. Partial symmetry operations between different modules have been associated with automorphisms of the quotient graph that may not be consistent with net voltages over the respective cycles. These operations have been shown to generate the pyroxene groupoid structure.Copyright (c) 2017 International Union of Crystallographyurn:issn:2053-2733Eon, J.-G.2017-03-27doi:10.1107/S2053273317003333International Union of CrystallographyA signature of partial symmetry operations acting in orthoenstatite is evidenced in its labelled quotient graph.ENpyroxenesspace groupoidslabelled quotient graphsmodular structuresThe analysis of the modular structure of pyroxenes, recently discussed in Nespolo & Aroyo [Eur. J. Mineral. (2016), 28, 189–203], has been performed on the respective labelled quotient graphs (LQGs). It is shown that the structure and maximum symmetry of the module, i.e. its layer group, can be determined directly from the LQG. Partial symmetry operations between different modules have been associated with automorphisms of the quotient graph that may not be consistent with net voltages over the respective cycles. These operations have been shown to generate the pyroxene groupoid structure.text/htmlGroupoids and labelled quotient graphs: a topological analysis of the modular structure in pyroxenestext3732017-03-27Copyright (c) 2017 International Union of CrystallographyActa Crystallographica Section Aresearch papers238245On the Penrose and Taylor–Socolar hexagonal tilings
http://scripts.iucr.org/cgi-bin/paper?ae5032
The intimate relationship between the Penrose and the Taylor–Socolar tilings is studied, within both the context of double hexagon tiles and the algebraic context of hierarchical inverse sequences of triangular lattices. This unified approach produces both types of tilings together, clarifies their relationship and offers straightforward proofs of their basic properties.Copyright (c) 2017 Lee and Moodyurn:issn:2053-2733Lee, J.-Y.Moody, R.V.2017-05-07doi:10.1107/S2053273317003576International Union of CrystallographyA uniform geometric/algebraic approach to the Penrose and Taylor–Socolar hexagonal tilings is given, which clarifies their construction and the way in which they are inter-related.ENPenrose tilingTaylor–Socolar tilingdouble hexagon tilingnested triangularizationsinverse sequences of hierarchical latticesThe intimate relationship between the Penrose and the Taylor–Socolar tilings is studied, within both the context of double hexagon tiles and the algebraic context of hierarchical inverse sequences of triangular lattices. This unified approach produces both types of tilings together, clarifies their relationship and offers straightforward proofs of their basic properties.text/htmlOn the Penrose and Taylor–Socolar hexagonal tilingstext3732017-05-07Copyright (c) 2017 Lee and MoodyActa Crystallographica Section Aresearch papers246256Resonant and non-resonant magnetic scatterings with circularly polarized X-rays: magnetic scattering factor and electron density of gadolinium iron garnet
http://scripts.iucr.org/cgi-bin/paper?td5039
Theoretical and experimental studies on resonant magnetic scattering have been carried out using circularly polarized X-rays. Polarization dependence of the asymmetric ratio between right- and left-handed polarized scattering amplitudes has revealed that resonant and non-resonant magnetic scatterings can be observed simultaneously. In this study, synchrotron X-ray intensity experiments were conducted on Gd iron garnet (GdIG) at the pre-edge of the Fe K absorption edge. The asymmetric ratio between circular polarizations exhibited three peaks due to the resonant magnetic responses of Fe3+ in the Fe2 (24d) site. These magnetic responses are antiparallel and have apparently higher resolution than dispersive X-ray magnetic circular dichroism at the pre-edge region; this can be mainly attributed to electric dipole transitions from 1s to t2 energy levels of the 3d orbitals in the tetrahedral symmetry in an unstable state quenched at higher temperature. Resonant magnetic scattering factors f′m were estimated from the asymmetric ratios. Fourier analysis was conducted using the intensity differences among circularly polarized X-rays at an energy of E = 7.1085 keV. At this energy level, the characteristic distribution of magnetic electron density was clearly observed. This distribution was interpreted as a spin arrangement of Gd and Fe ions in GdIG. Also observed was the presence of hybridization of the magnetic electron orbitals as well as of the resonant magnetic Fe3+. The proposed method has the potential to be widely used in crystal structure analysis.Copyright (c) 2017 International Union of Crystallographyurn:issn:2053-2733Sasaki, Y.Okube, M.Sasaki, S.2017-04-27doi:10.1107/S2053273317003588International Union of CrystallographyThe energy dependence of resonant magnetic scattering factors revealed antiparallel magnetic moments within the t2 (3d) orbitals at the Fe K pre-edge. Circular polarization of X-rays is a powerful tool for examining magnetic electrons via both resonant and non-resonant magnetic scatterings simultaneously.ENresonant magnetic scatteringnon-resonant effectscircular polarizationGd iron garnetGd3Fe5O12Theoretical and experimental studies on resonant magnetic scattering have been carried out using circularly polarized X-rays. Polarization dependence of the asymmetric ratio between right- and left-handed polarized scattering amplitudes has revealed that resonant and non-resonant magnetic scatterings can be observed simultaneously. In this study, synchrotron X-ray intensity experiments were conducted on Gd iron garnet (GdIG) at the pre-edge of the Fe K absorption edge. The asymmetric ratio between circular polarizations exhibited three peaks due to the resonant magnetic responses of Fe3+ in the Fe2 (24d) site. These magnetic responses are antiparallel and have apparently higher resolution than dispersive X-ray magnetic circular dichroism at the pre-edge region; this can be mainly attributed to electric dipole transitions from 1s to t2 energy levels of the 3d orbitals in the tetrahedral symmetry in an unstable state quenched at higher temperature. Resonant magnetic scattering factors f′m were estimated from the asymmetric ratios. Fourier analysis was conducted using the intensity differences among circularly polarized X-rays at an energy of E = 7.1085 keV. At this energy level, the characteristic distribution of magnetic electron density was clearly observed. This distribution was interpreted as a spin arrangement of Gd and Fe ions in GdIG. Also observed was the presence of hybridization of the magnetic electron orbitals as well as of the resonant magnetic Fe3+. The proposed method has the potential to be widely used in crystal structure analysis.text/htmlResonant and non-resonant magnetic scatterings with circularly polarized X-rays: magnetic scattering factor and electron density of gadolinium iron garnettext3732017-04-27Copyright (c) 2017 International Union of CrystallographyActa Crystallographica Section Aresearch papers257270Convex polyhedra with minimum and maximum names
http://scripts.iucr.org/cgi-bin/paper?eo5071
The paper reports the combinatorial types of convex n-acra (i.e. n-vertex polyhedra) for which the minimum (min.) and maximum (max.) names are attained. Hence, min. and max. names can be independently found without generating the whole combinatorial variety of convex n-acra (e.g. by the routine recurrence Fedorov algorithm) and calculating names for each n-acron.Copyright (c) 2017 International Union of Crystallographyurn:issn:2053-2733Voytekhovsky, Y.L.2017-04-20doi:10.1107/S2053273317004053International Union of CrystallographyThe combinatorial types of convex n-acra with minimum and maximum names for any n ≥ 4 are found. Thus, the latter can be directly calculated from the adjacency matrices of their edge graphs.ENconvex polyhedraedge graphadjacency matrixminimum namemaximum nameThe paper reports the combinatorial types of convex n-acra (i.e. n-vertex polyhedra) for which the minimum (min.) and maximum (max.) names are attained. Hence, min. and max. names can be independently found without generating the whole combinatorial variety of convex n-acra (e.g. by the routine recurrence Fedorov algorithm) and calculating names for each n-acron.text/htmlConvex polyhedra with minimum and maximum namestext3732017-04-20Copyright (c) 2017 International Union of CrystallographyActa Crystallographica Section Ashort communications271273International Tables for Crystallography, Volume A, Space-group symmetry. 6th edition. Edited by Mois I. Aroyo. Wiley, 2016. Pp. xxi + 873. Price GBP 295.00, EUR 354.00 (hardcover). ISBN 978-0-470-97423-0.
http://scripts.iucr.org/cgi-bin/paper?xo0080
Copyright (c) 2017 International Union of Crystallographyurn:issn:2053-2733Nespolo, M.2017-04-20doi:10.1107/S2053273317005526International Union of CrystallographyENbook reviewInternational Tables for Crystallographyspace-group symmetrytext/htmlInternational Tables for Crystallography, Volume A, Space-group symmetry. 6th edition. Edited by Mois I. Aroyo. Wiley, 2016. Pp. xxi + 873. Price GBP 295.00, EUR 354.00 (hardcover). ISBN 978-0-470-97423-0.text3732017-04-20Copyright (c) 2017 International Union of CrystallographyActa Crystallographica Section Abook reviews274276X-ray Diffraction for Materials Research: From Fundamentals to Applications. By Myeongkyu Lee. CRC Press, 2016. Hardback, pp. 302. Price GBP 99. ISBN 9781771882989.
http://scripts.iucr.org/cgi-bin/paper?xo0055
Copyright (c) 2017 International Union of Crystallographyurn:issn:2053-2733Fertey, P.2017-03-13doi:10.1107/S2053273317000602International Union of CrystallographyENbook reviewX-ray diffractionmaterials characterizationtext/htmlX-ray Diffraction for Materials Research: From Fundamentals to Applications. By Myeongkyu Lee. CRC Press, 2016. Hardback, pp. 302. Price GBP 99. ISBN 9781771882989.text3732017-03-13Copyright (c) 2017 International Union of CrystallographyActa Crystallographica Section Abook reviews277278Symmetry and Physical Properties of Crystals. By Cécile Malgrange, Christian Ricolleau and Michel Schlenker. Springer, 2014. Pp. xxv + 522. Price EUR 94.94, GBP 81.00, USD 119.99. ISBN 978-94-017-8992-9.
http://scripts.iucr.org/cgi-bin/paper?xo0074
Copyright (c) 2017 International Union of Crystallographyurn:issn:2053-2733Grimmer, H.2017-04-20doi:10.1107/S2053273317002832International Union of CrystallographyENbook reviewcrystal symmetrycrystal physicstext/htmlSymmetry and Physical Properties of Crystals. By Cécile Malgrange, Christian Ricolleau and Michel Schlenker. Springer, 2014. Pp. xxv + 522. Price EUR 94.94, GBP 81.00, USD 119.99. ISBN 978-94-017-8992-9.text3732017-04-20Copyright (c) 2017 International Union of CrystallographyActa Crystallographica Section Abook reviews279280