Crystal lattice and phase transitions in Na₄TiP₂O₉ (NTP) and Na_4.5FeP₂O₈(O,F) (NFP) superionic conductors as a function of high pressures and temperatures

The lattice dynamics of Na₄TiP₂O₉ (NTP) and Na_4.5FeP₂O₈(O,F) (NFP) crystals, which are superionic conductors with Na⁺-ion conductivity, were studied under high pressures. Lattice constants as functions of hydrostatic pressure were measured on a four-circle diffractometer using a high-pressure cell with diamond anvils.

Cation distribution and crystal chemistry of Y₃Al_5−xGa_xO₁₂ (0 ≤ x ≤ 5) garnet solid solutions

Investigation of the cation distributions in Y₃Al_5−xGa_xO₁₂ (0 ≤ x ≤ 5) garnet solid solutions using single-crystal X-ray diffraction shows that Ga³⁺, which is larger than Al³⁺, preferentially occupies the tetrahedral site rather than the octahedral site, contrary to the effect of cation size. This peculiar cation distribution is most probably caused by both the strong covalency of the Ga—O bond and the need to decrease the neighbouring cation–cation repulsive force.

Electron density distribution and Madelung potential in α-spodumene, LiAl(SiO₃)₂, from two-wavelength high-resolution X-ray diffraction data

The experimental electron density features derived from both high-resolution Mo Kα and Ag Kα X-ray diffraction data are compared for the natural mineral α-spodumene, LiAl(SiO₃)₂. The kappa-refinement atomic net charges have been used to calculate the Madelung potential. An estimate of the chemical formula electrostatic energy is given.

Single-crystal neutron diffraction study of β-Cs₃(HSO₄)₂[H_2−x(S_xP_1−x)O₄] (x ≃ 0.5) at 15 K

The structure of β-Cs₃(HSO₄)₂[H_2−x(S_xP_1−x)O₄] has been studied by neutron diffraction methods and can be adequately described by two different models for the disorder on H and S/P atom sites. The disorder is responsible for the relatively high proton conductivity at room temperature.

Arrangement of C atoms in the SiC–C solid solution

On the basis of microstructure characteristics (strain and crystallite size) and lattice parameters investigated by X-ray powder diffraction methods, a structural model for the SiC–C solid solution is proposed. The behaviour of the structure under high-pressure and high-temperature sintering and annealing in a vacuum is described.

Structures of Bi₁₄WO₂₄ and Bi₁₄MoO₂₄ from neutron powder diffraction data

The (isomorphous) structures of Bi₁₄WO₂₄ and Bi₁₄MoO₂₄ have been solved and refined using neutron powder diffraction data in the space group I4/m. The structure adheres closely to a fluorite-type δ-Bi₂O₃-related parent structure. The metal atoms are compositionally ordered. Substantial displacive disorder is evident around the W site, which appears to be coordinated by a highly disordered O-atom tetrahedron.

The crystal structure of Ca₇Zr₇Ta₆O₃₆ refined using synchrotron-radiation data

The crystal structure of Ca₇Zr₇Ta₆O₃₆ is solved and refined in space group Fddd using single-crystal X-ray diffraction data.

Synchrotron X-ray analysis of the electron density in HoFe₂

The deformation electron density (Δρ) for the HoFe₂ Laves compound obtained from synchrotron X-ray diffraction data shows excess electron density midway along the Ho–Ho, Ho–Fe and Fe–Fe contacts which challenges the conventional understanding of electron interactions in magnetic materials.

Determination of the site of incorporation of cobalt in CoZnPO-CZP by multiple-wavelength anomalous-dispersion crystallography

A five-wavelength MAD experiment conducted at ELETTRA Sincrotone, and subsequent crystallographic analysis, shows that substitution of cobalt in CoZnPO-CZP occurs primarily at one of the two sites, with an occupancy of 24–30%. Site-specific occupancies of as low as 12–15% should, in general, be discernible by this method.

Structural investigation of the negative-thermal-expansion material ZrW₂O₈

The structure of the negative-thermal-expansion material ZrW₂O₈ has been determined by parametric Rietveld refinement of high-resolution neutron powder diffraction data collected at 260 temperatures between 2 and 520 K. Despite data collection times of just 5 min at each temperature, it is shown that full anisotropic refinement of the structure is possible.

Disparate atomic displacements in skutterudite-type LaFe₃CoSb₁₂, a model for thermoelectric behavior

Mean-square atomic displacements in LaFe₃CoSb₁₂ show that the La atom exhibits an anomalously large displacement. The large-amplitude rattling of the La atom is linked to the dramatic decrease of the lattice thermal conductivity and this structure–property relationship offers a new paradigm for the exploration of thermoelectric materials.

The crystal structure of the B-site ordered complex perovskite Sr(Yb_0.5Nb_0.5)O₃

The room-temperature crystal structure of Sr(Yb_0.5Nb_0.5)O₃ is monoclinic and can be derived from a triclinic distortion of the prototype cubic cell. The ordering of the different species of B-site cation, Yb³⁺ and Nb⁵⁺, inherently causes a volume difference between the YbO₆ and NbO₆ octahedra. The triclinic distortion of the prototype cell is caused by a⁻a⁻c⁺ octahedral tilting of the two octahedra with differing volumes. This volume difference is shown to inevitably inhibit the rigid rotation of the octahedra.

Structure analysis of new homologous compounds Ga₂O₃(ZnO)_m (m = integer) by high-resolution analytical transmission electron microscopy

The crystal structure of Ga₂O₃(ZnO)_m studied by high-resolution analytical transmission electron microscopy is reported.

Accurate charge densities in days — use of synchrotrons, image plates and very low temperatures

Accurate very low temperature synchrotron-radiation data can now be measured within days, making electron-density studies of compounds beyond the first transition series more frequently within reach.

Thermal vibrations in potassium 3-benzoyl-2-thiophene­carboxylate

Thermal vibration analysis indicates that an experimentally determined distance between atomic centroids can be significantly different from the mean interatomic distance that is of chemical interest. This is especially true for distances involved in weak interactions.

Four-component intergrowth structures of the metal-ion cage complexes fac-(1,5,9,13,20-penta­methyl-3,7,11,15,18,22-hexa­azabi­cyclo[7.7.7]tri­cosane)M^II diperchlorate hydrate, [M(C₂₂H₄₈N₆)](ClO₄)₂.xH₂O, M = Ni, Zn

These isomorphic crystal structures are described as intergrowths of four substructures, each a different modulation of an idealized parent structure of space group C2/c. Two substructures correspond to alternative orientations of a C1¯ structure for which x = 0, and two substructures correspond to alternative origins of a P2₁/n structure for which x = 1. The MN₆ coordination geometry is essentially octahedral, in contrast to the trigonal-prismatic geometry observed for the Cd^II and Hg^II complexes of the same ligand.

Crystal structures of [18]aneN₆H₂K[Co(CN)₆].4H₂O, [16]aneN₄H₂K[Co(CN)₆] and [12]aneN₄H₃[Co(CN)₆].2H₂O. Insight into the electrostatic and hydrogen-bonding interaction in self-assembling supercomplexes

The crystal structures of the three supercomplexes [18]aneN₆H₂K[Co(CN)₆].4H₂O, [16]aneN₄H₂K[Co(CN)₆] and [12]aneN₄H₃[Co(CN)₆].2H₂O, and the second-sphere interactions in the binding of the [Co(CN)₆]³⁻ complex ions with the protonated polyammonium macrocycles are reported.

Polynuclear chloromercurate(II) systems in their chloropyridinium salts

The chloromercurate(II) salts of monochloropyridines display a variety of anion stoichiometries and structures. The 2-chloropyridinium salt has the anion stoichiometry [HgCl₃]⁻, but the anions are infinite chains composed of [HgCl₃]⁻, HgCl₂ and Cl⁻ moieties linked by longer Hg⋯Cl contacts. Chains of interconnected [HgCl₄]²⁻ and HgCl₂ entities in the 3- and 4-chloropyridinium salts yield the rare [Hg₃Cl₁₀]⁴⁻ stoichiometry. Second forms of the 3- and 4-chloropyridinium salts contain distorted [Hg₂Cl₆]²⁻ moieties linked into chains and symmetrical discrete [Hg₂Cl₆]²⁻anions, respectively.

The geometry and structural properties of the 4,8,12-trioxa-4,8,12,12c-tetra­hydrodibenzo[cd,­mn]pyrene system in the cationic state. Structures of a planar organic cation with various monovalent and divalent anions

The planarity of the 4,8,12-trioxa-4,8,12,12c-tetrahydrodibenzo[cd,mn]pyrenylium cations in several salts and their structural chemistry are described.

Molecular aggregation in crystalline 1:1 complexes of hydrophobic D- and L-amino acids. I. The L-isoleucine series

The crystal structures of seven complexes of L-isoleucine with various D-amino acids with hydrophobic side chains are reported. Similarities and differences in the molecular packing and in the conformation of the partner molecule are discussed.

Chiral recognition between host and guest: a bi­naphthyl-18-crown-6 host with D-phenylglycinium methyl ester perchlorate guest. A difficult structure solved with CRUNCH

The crystal structure of a highly discriminating chiral host, in its complex with a chiral cationic guest, shows the influence of C—H⋯O and C—H⋯π interactions on the unanticipated orientation of the guest in the host cavity. These interactions are very similar, but not identical, in the two independent complexes in the asymmetric unit.

3(5),4-Di­methyl- and 3,4,5-tri­methylpyrazole at 200 K. X-ray crystallography and quantum-chemical analysis

The crystal and molecular structure of 3(5),4-dimethylpyrazole and 3,4,5-trimethylpyrazole have been determined at 200 K. Ab initio calculations at HF and B3LYP/6-31G** levels have been undertaken in order to estimate the influence of the methyl substituent on the pyrazole.

Phase-transition-induced twinning in the 1:1 adduct of hexa­methylene­tetramine and azelaic acid

Phase III of the 1:1 adduct of hexamethylenetetramine and azelaic acid presents phase-transition-generated TLQS twinning, with a superposition of a carboxylic acid and a carboxylate form of azelaic acid. Four possible single-domain states are predicted by group theory; only one type of domain wall is observed and is explained in terms of intermolecular interactions.