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ISSN: 2053-2733

January 2005 issue

Highlighted illustration

Cover illustration: An experimentally derived plot of the Fermi hole mobility function (FHMF) for urea. The FHMF can be interpreted as a potential energy surface for electron transfer. This plot was obtained from a Hartree-Fock wavefunction constrained to fit measured X-ray diffraction structure factors, using the Tonto program. See Jayatilaka & Grimwood [Acta Cryst. (2004), A60, 111-119].

phase transitions


Acta Cryst. (2005). A61, 1-2
doi: 10.1107/S0108767304033434

Acta Cryst. (2005). A61, 3-18
doi: 10.1107/S0108767304020318
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The uses of Landau-type theories to describe structural, microstructural and mesostructural features of materials undergoing phase transitions are reviewed.

Acta Cryst. (2005). A61, 19-27
doi: 10.1107/S010876730402598X
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Molecular dynamics (MD) has evolved into a reliable technique for simulating incommensurate modulated phases. The application of a compensating external pressure tensor to organic materials allows a better fit to the experimental measurements. An overview of the MD method and its applications is presented here.

Acta Cryst. (2005). A61, 28-38
doi: 10.1107/S0108767304019269
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Typical experimental observations of structural phase transitions from and to the quasicrystalline state as well as their microscopic interpretation are reviewed.

Acta Cryst. (2005). A61, 39-50
doi: 10.1107/S0108767304026625
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Recent experiments on the magnetic properties of A–Mg–R (A = Zn and Mg; R = rare-earth elements) icosahedral quasicrystals are reviewed. Emphasis is placed on the origin of their spin-glass-like behavior; discussion is made based on existing data sets ranging from bulk magnetization to neutron diffraction.

Acta Cryst. (2005). A61, 51-61
doi: 10.1107/S0108767304025437
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An overview is presented of inorganic compounds with low-dimensional electronic structures, and of X-ray diffraction as a tool to study the properties of charge-density waves (CDWs).

Acta Cryst. (2005). A61, 62-76
doi: 10.1107/S0108767304025802
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This review describes how the unique orientational properties of the C60 fullerene molecule influence the structure and phase transitions of the C60 monomer and polymer.

Acta Cryst. (2005). A61, 77-92
doi: 10.1107/S0108767304023013
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Oxidation/reduction reactions in three-dimensional or layered manganites and cuprates are accompanied by the formation of domain structures. The microstructure of several representatives was studied by means of electron diffraction and high-resolution electron microscopy.

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The application to perovskite crystallography of group-theoretical methods, as implemented in the computer program ISOTROPY, is reviewed. The results have been used, in combination with high-resolution X-ray or neutron powder diffraction in fine temperature steps, to study structural phase transitions in perovskites.

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Recent X-ray diffraction studies of liquid crystals are reviewed. The topics are twist grain-boundary phases, antiferroelectric phases studied using resonant diffraction and smectic phases within gel structures.

obituaries


research papers


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The article presents a comprehensive theoretical description of the anomalous scattering method along with simulated numerical examples. The method is based on physical properties of parametric X-radiation.

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An approximate analytical expression for the three-beam diffraction profile in a crystal plate subjected to elastic strain is derived.

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A direct method for transforming angle-dependent diffraction data into depth-dependent data by the use of regularization techniques is presented, including method validation and application to experimental data.

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A drastic improvement of the original charge-flipping algorithm is presented. The phase space is explored more efficiently by a special treatment of weak reflections in the iteration process. Paradoxically, it is better not to use observed moduli of weak reflections: in the search for a solution, they create only unwanted constraints.

international union of crystallography


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