Structure and oxygen mobility in mayenite (Ca₁₂Al₁₄O₃₃): a high-temperature neutron powder diffraction study

The crystal structure of mayenite is described as an aluminate framework filled with disordered calcium and `extra' oxygen. The high oxygen ionic conductivity at high temperatures proceeds via an exchange of the latter with framework oxygen.

Inversion of 4f-states in CeB₆ thermally excited at 430 K

The thermally excited electron-density distribution of CeB₆ measured at 430 K exhibited a significant electron population in Ce 5d-Γ₈ orbitals, which caused an inversion of 4f Γ₈–Γ₇ energy levels, in turn resulting in a greater electron population in 4f-Γ₇.

Revision of pyrrhotite structures within a common superspace model

The structure of the pyrrhotite compound family has been reinvestigated in the framework of the superspace formalism. A common model with a unique superspace symmetry is also confirmed by first-principles calculations.

Hexagonal ferrites: a unified model of the (TS)_nT series in superspace

A large number of hexagonal ferrites can be derived from the Y ferrite Ba₂M₂Fe₁₂O₂₂ by introducing stacking faults. Structures with different compositions and lattice periodicity reaching hundreds of Ås are currently known. A single model based on the superspace approach is proposed which is able to fully describe the diversity of these structures.

X-ray powder diffraction structural characterization of Pb_1 − xBa_xZr_0.65Ti_0.35O₃ ceramic

The structure of Pb_1 − xBa_xZr_0.65Ti_0.35O₃ ceramic materials with 0.00 ≤ x ≤ 0.40 was studied by synchrotron X-ray powder diffraction. The series shows a phase transition from rhombohedral to cubic at 543 and 463 K for x = 0.10 and 0.20, respectively, whereas the samples with x = 0.30 and 0.40 show a cubic structure from 10 to 450 K.

Structure of RbFeO₂, refined from a reticular pseudomerohedrally twinned crystal with six domains

A multiply twinned crystal of RbFeO₂ has been studied by single-crystal X-ray diffraction.

Structure determination of structurally complex Ag₃₆Li₆₄ gamma-brass

The crystal structure of the Ag₃₆Li₆₄ gamma-brass was determined by Rietveld analysis of the synchrotron X-ray powder diffraction data. The bonding nature of the gamma-brass structure was clarified by analyzing the bond-length distribution.

Synthesis, characterization and phase transitions in the inorganic–organic layered perovskite-type hybrids [(C_nH_2n + 1NH₃)₂PbI₄], n = 4, 5 and 6

The thermochromic, reversible, first-order phase transitions in [(C_nH_2n + 1NH₃)₂PbI₄], n = 4, 5 and 6, were structurally characterized via single-crystal X-ray diffraction. The transitions are found to be associated with a concerted movement of both organic and inorganic components.

Asymmetric hydrogen bonds in a centrosymmetric environment. III. Quantum mechanical calculations of the potential-energy surfaces for the very short hydrogen bonds in potassium hydrogen di­chloromaleate

According to earlier crystal structure determinations of potassium hydrogen dichloromaleate the H atoms are non-centered in the hydrogen bonds, although the environment is centrosymmetric. The experimental results have now been verified by quantum mechanical calculations of the potential-energy surfaces.

Experimental charge density of L-alanyl-L-prolyl-L-alanine hydrate: classical multipole and invariom approach, analysis of intra- and intermolecular topological properties

Topological and atomic properties of the tripeptide L-Ala-L-Pro-L-Ala hydrate were obtained from a full multipole refinement, an invariom transfer and from a theoretical calculation. They were quantitatively compared with each other and with results from the literature. The hydrogen-bond topology was critically examined via a comparison with promolecular densities.

Knowledge-based model of hydrogen-bonding propensity in organic crystals

A new method is presented to predict which donors and acceptors form hydrogen bonds in a crystal structure, based on the statistical analysis of hydrogen bonds in the Cambridge Structural Database. The approach has potential application in identifying both likely and unusual hydrogen bonding, which can help to rationalize stable and metastable crystalline forms, of relevance to the drug development process in the pharmaceutical industry.

Structures of tetra­bromo­thiophene and tetra­bromo­selenophene: the influence of the heteroatom on the heterophene packing

The different phases and crystal structures of C₄Br₄S and C₄Br₄Se are explained on the basis of the close-packing of the Br atoms.

Three-dimensional hydrogen-bonded frameworks in organic crystals: a topological study

Hydrogen-bonded frameworks in organic crystals have been classified into topological types of three-periodic nets. The relations between net topological types, space-group symmetry of crystals, site symmetry and point-group symmetry of molecules are discussed, and a set of rules for the crystal design of molecular frameworks is proposed.

Order–disorder transition in monoclinic sulfur: a precise structural study by high-resolution neutron powder diffraction. Corrigendum

A corrigendum to the paper by David et al. (2006), Acta Cryst. B62, 953–959.