Notes for Authors

Structure of Na₃NdSi₆O₁₅.2H₂O – a Layered Silicate with Paths for Possible Fast-Ion Conduction

The structure of Na₃NdSi₆O₁₅.2H₂O, a compound previously and erroneously reported as NaNdSi₆O₁₃(OH)₂.nH₂O, is described. Channels likely to serve as pathways for easy ion transport are identified.

Room-Temperatrue Structure and Geometrical Analysis of the Cubic–Tetragonal Phase Transition in Dodecasil 3C-THF

From the structure refinement of dodecasil 3C, it follows that the deformation from the ideal cubic to the tetragonal structure is mainly related to (i) a local tilt system and (ii) tetragonal tetrahedral distortion.

Pressure-Induced Fm-3m R-3 Phase Transition in NaSbF₆

The pressure-induced phase transition and the subsequent structural changes in NaSbF₆ are described by means of a sphere-packing deformation which is superimposed by cation–cation repulsions.

Octahedral Tilting in Perovskites. I. Geometrical Considerations

The 23 Glazer tilt systems which describe octahedral tilting distortions in perovskites are examined. Unavoidable distortions of the octahedra and cation ordering are considered.

Octahedral Tilting in Perovskites. II. Structure Stabilizing Forces

The 23 Glazer tilt systems which describe octahedral tilting distortions in perovskites are examined. The forces which stabilize each tilt system are explored.

Ag₂Ti₂P₂S₁₁: A New Layered Thiophosphate. Synthesis, Structure Determination and Temperature Dependence of the Silver Distribution

The structure of a new quaternary phosphosulfide, Ag₂Ti₂P₂S₁₁, is determined from single crystal X-ray diffraction data. The structure is analysed and the temperature dependence of the silver atomic displacement parameters is studied by means of a Gram–Charlier anharmonic development of the atomic displacement factor. It is shown that the Ag distribution is primarily static in nature.

Refinement of Ammonium Perrhenate Structure Using a Pseudo-Spin Model for the Ammonium Ion Orientation

The structure of ND₄ReO₄, assuming two ammonium ion orientations with variable occupancy, has been determined by Rietveld refinement using previously published powder neutron diffraction data. The resulting ammonium ion orientations and occupancies are in good agreement with pseudo-spin theory.

Transferability of Empirical Force Fields in Silicates: Lattice-Dynamical Evaluation of Atomic Displacement Parameters and Thermodynamic Properties for the Al₂OSiO₄ Polymorphs

Atomic displacement parameters, Raman and IR spectra have been calculated by lattice dynamics for aluminium silicates Al₂OSiO₄ (andalusite and kyanite).

`Inverted Twinning' in Intergrowth Tungsten Bronzes

A new type of twinning is described, revealed by high-resolution electron microscopy. Across the twin boundary the two intergrown structure elements are interchanged and the structure is thus `inverted' and in general the two `twin' parts represent different members of the intergrowth family.

Distortion Characteristics Across the Structural Phase Transition in (Cu_1−xZn_x)WO₄

Microscopic distortion patterns associated with a structural phase transition in (Cu_1-xZn_x)WO₄ have been measured using Rietveld analysis of neutron powder diffraction data. It is clearly demonstrated that the transition driving force is the Jahn–Teller effect on the Cu²⁺ cations.

Importance of True Satellite Reflections in the Analysis of Modulated, Composite Crystal Structures. I. A New Refinement of [M₂Cu₂O₃]_7+δ[CuO₂]₁₀, M = Bi_0.06Sr_0.46Ca_0.48

The composite, incommensurately modulated structure of [M₂Cu₂O₃]_7+δ[CuO₂]₁₀, M = Bi_0.06Sr_0.46Ca_0.48 and δ = 0.03 has been refined against 603 main reflections, 428 first-order and 64 second-order satellite reflections. Special problems relating to synchrotron radiation experiments are discussed. It is shown that the inclusion of true satellite reflections in the refinement is necessary to avoid large correlations between thermal displacement parameters and modulation displacement parameters, and thus to obtain a physically reasonable model.

Importance of True Satellite Reflections in the Analysis of Modulated, Composite Crystal Structures. II. The Structure of [M'₂Cu₂O₃]₇[CuO₂]₁₀, M' = Bi_0.04Sr_0.96

The four-dimensional, composite, incommensurately modulated structure of [(Bi_0.04Sr_0.96)₂Cu₂O₃]₇[CuO₂]₁₀ has been determined. Refinements have been based on 549 main reflections, 442 first-order and 183 second-order satellite reflections. The structure is compared with a previously published model and those of the BiSrCaCu oxide superconductors and the structural chemistry is discussed.

A Re-investigation of the Crystal Structure of the Perovskite PbZrO₃ by X-ray and Neutron Diffraction

Powder neutron diffraction and low-temperature single-crystal X-ray diffraction are used to re-investigate the room-temperature phase of PbZrO₃. Evidence is given to show that the oxygen substructure is ordered and forms regular ZrO₆ octahedra.

4f-Electron Density Distribution in Crystals of CeB₆ at 165 K and its Analysis Based on the Crystal Field Theory

The electron density distibution in CeB₆ crystals was measured at 165 K by X-ray diffraction using the relativistic scattering factors for Ce, avoiding the multipole diffraction effect and selecting ω and χ angles of the four-circle diffractometer, at which the temperature of the sample was stable. The analysis based on crystal field theory confirmed that the large peaks on the deformation density map around the Ce atom approximate the Ce 4f-electrons on the t_1u-orbitals.

Ab Initio Structure Determination of Two Polymorphs of Cyclo­pentadienylrubidium in a Single Powder Pattern

The different FWHM distributions of the Bragg reflections are used to dissect the powder pattern of cyclopentadienylrubidium (RbCp) into the contributions of two polymorphs. Both phases, which could be solved ab initio from a single powder pattern, are found to be composed of polymeric zigzag chains.

Isothermal Compressibility and Pressure Dependence of the Crystal Structures of the Superconducting Charge-Transfer Salt κ-(BEDT-TTF)₂Cu(NCS)₂ [BEDT-TTF = Bis(ethylenedi­thio)tetra­thia­fulvalene]

This paper reports the isothermal compressibility and the pressure dependence of the crystal structures of the superconducting charge-transfer salt κ-(BEDT-TTF)₂Cu(NCS)₂.

Conformational Isomerism of the Host as a Factor in Molecular Recognition in Host–Guest Inclusion Complexes: Example of Tris(5-acetyl-3-thienyl)methane

Tris(5-acetyl-3-thienyl)methane is a rare example of a host molecule which has many potential conformers. Analysis of the substantial but still incomplete database of published crystal structures suggests that each group of isomorphous crystals contains only one sort of conformer, but a variety of guests. A mechanism is proposed by which the inclusion complexes are formed.

Single-Crystal Neutron Diffraction Analysis of Anion–Cation Interactions in Perdeutero­acetylcholine Bromide at 100 K

Pulsed neutron diffraction is used to investigate cation–anion hydrogen-bond interactions in a single crystal of perdeuteroacetylcholine bromide. The pyramidal configuration of C—O⋯Br⁻ contacts is in good agreement with ab initio molecular orbital predictions.

Experimental and Theoretical Studies of Charge Density Distribution in E-Tetra­ethyl-1,4-di­ammoniumbut-2-ene.2PF₆

Charge density studies of E-tetraethyl-1,4-diammoniumbut-2-ene.2PF₆ show that the electrostatic potential is positive at all points on the surface of the cation, which is used as an antifungal agent.

Neutron powder diffraction study of α-Ti(HPO₄)₂.H₂O and α-Hf(HPO₄)₂.H₂O; H-atom positions. Erratum

Correction to Acta Cryst. (1996). B52, 896-898.