Systematic prediction of new ferroelectrics in space groups P3₁ and P3₂

A total of 16 new structures reported in the ICSD under space groups P3₁ and P3₂, of which six have two or more isostructural entries, satisfy the structural criteria for ferroelectricity. Three new members of the ferroelectric stillwellite family satisfy the structural criteria, ten structures are dubious or incorrect, one is probably pyroelectric, but is unlikely to become ferroelectric, and three others are either incompletely solved or incompletely refined.

Structure–property correlation over five phases and four transitions in Pb₅Al₃F₁₉

Calorimetric and dielectric properties are correlated with structure in each of the five phases formed by Pb₅Al₃F₁₉. Maximum atomic displacements range from 1.21 (6) Å at the lowest- to 0.7 (4) Å at the highest-temperature phase transition. The introduction of 3d electrons into the lattice disturbs the equilibria that stabilize the three intermediate phases.

Features of the electron density in magnesium diboride: reconstruction from X-ray diffraction data and comparison with TB-LMTO and FPLO calculations

Features of the atomic interactions in MgB₂ are considered using the multipole-model electron density reconstructed from a room-temperature single-crystal X-ray diffraction experiment. These features are compared with theoretical calculations performed by tight-binding linear muffin-tin orbital (TB-LMTO) and full-potential non-orthogonal local orbital (FPLO) methods.

Structures of Na_0.74WO₃

The structures of the four phases of the tungsten bronze Na_xWO₃ have been determined using the high-resolution powder diffractometer (HRPD), ISIS, Rutherford Appleton Laboratory, England. At low temperatures the octahedra are tilted; in Glazer's notation the structures follow the sequence a⁺a⁺a⁺, a⁺a⁺a⁰, a⁰a⁰c⁺, a⁰a⁰a⁰ with increasing temperature. This is the first time the structure of a phase with two plus tilts has been reported.

Phase transitions in KTP isostructures: correlation between structure and T_c in germanium-doped RbTiOPO₄

Crystals of germanium-doped RbTiOPO₄ have been characterized by X-ray diffraction and dielectric measurements. A direct correlation between the room-temperature split positions of the rubidium cations and the phase-transition temperature (T_c) has been discovered. General trends regarding the relationship between the room-temperature structures of KTP-like compounds and their T_c values are discussed.

Sodium percarbonate between 293 and 100 K

The structure of sodium percarbonate, Na₂CO₃·1.5H₂O₂, has been determined at temperatures between 293 and 100 K. As the temperature drops, hydrogen peroxide becomes ordered, and a phase change takes place at 240 K when the room-temperature space group, Cmca, is replaced by Pbca.

Synthesis and structure of M_0.5Bi₃P₂O₁₀ (M = Ca, Sr, Ba, Pb) series

Single-crystal X-ray diffraction on a series of M_0.5Bi₃P₂O₁₀ compounds with M = Ca, Sr, Ba, Pb shows that they are isostructural with Bi_6.67P₄O₂₀. Infinite Bi₂O₂ chains are interconnected via polyhedra with sandwiched phosphate tetrahedra.

Structural investigation of the Na–Fe–Mo–O system

The crystal structures of the orthomolybdates NaFe₄(MoO₄)₅, α- and β-NaFe₂(MoO₄)₃ and Na₃Fe₂(MoO₄)₃ are described and compared with each other and other related structures.

Temperature-resolved study of the structural behaviour of nickel octa­hexyl phthalocyanine up to the liquid crystal transition

Temperature-resolved structural `snap-shots' of the title compound have been determined, showing molecular mobility details in the pathway to the liquid crystal discotic mesophase. DSC measurements corroborate the fact that an intermediate transition to a less well ordered crystalline form takes place at 326 K.

The phases of [(CH₃)₄N](ClO₄) at low temperature

The low-temperature phase of [(CH)N](ClO) is solved. A phase transition is produced by the electrostatic interactions of the ClO ions, thus giving orientational domains with varying population.

A database survey of molecular and crystallographic symmetry

CSDSymmetry, a database that brings together information concerning molecular and crystallographic symmetry, has been used to probe relationships between the symmetry of occupied Wyckoff positions and the molecules they accommodate.

X-ray studies on crystalline complexes involving amino acids and peptides. XLI. Commonalities in aggregation and conformation revealed by the crystal structures of the pimelic acid complexes of L-arginine and DL-lysine

A comparison of the structures presented here with similar structures shows how the effects of change in composition and sometimes chirality can be accommodated with minor adjustments in essentially the same aggregation pattern and molecular conformation.

Investigation of diffraction line broadening due to compositional fluctuations in L-alanine-doped triglycine sulfate

Strain broadening of the powder diffraction peaks from L-alanine doping in triglycerine sulfate (LATGS) is analyzed using Williamson–Hall methods for peak-profile analysis. The results show that L-alanine doping in TGS leads to anisotropic strain broadening of the powder peaks.

A neutron diffraction study of xylitol: derivation of mean square internal vibrations for H atoms from a rigid-body description

A neutron diffraction study of xylitol is presented and estimates of the internal mean-square displacements of the H atoms obtained by subtraction of a rigid-body model from the total H-atom mean-square displacements are given. The result is compared with similar analyses of 12 other neutron diffraction studies found in the literature.

Supramolecular aggregation in 4,4′-bipyridin-1,1′-ium dichloride, 4,4′-bipyridin-1,1′-ium dinitrate and 4,4′-bipyridin-1-ium bromide

Analyses of short contacts in 4,4′-bipyridin-1,1′-ium dichloride, 4,4′-bipyridin-1,1′-ium dinitrate and 4,4′-bipyridin-1-ium bromide monohydrate show that supramolecular aggregation in these complexes is dominated by discrete bipyridinium cations and anions. These ions form chains stabilized by various interactions in a three-dimensional framework.

Monitoring structural transformations in crystals. 5. A topotactic [2 + 2]-photodimerization reaction

The behaviour of the substrate and the product molecules during a topotactic photodimerization reaction was monitored by X-ray diffraction.

Can we predict lattice energy from mol­ecular structure?

Multilinear-regression analyses between the mol­ecular structures of 226 organic compounds and their enthalpies of sublimation are analysed. A predictive model of enthalpy of sublimation is tested on a 35-compound validation data set.