Close-packed Anion Research Articles

Preparation and structure of anhydrous zinc chloride

The product is monophasic and has a crystal structure different from that of another author's phases, though still based on tetrahedral zinc coordination in a close-packed anion lattice. It does undergo phase transformations in ambient atmosphere. Syntheses of two sample products are described. Powders and crystals of either sample showed a characteristic x-ray diffraction pattern which did not change with time. Single crystal diffraction data enabled all reflections to be indexed on the basis of an orthorhombic unit cell. Contents of the cell, calculated density, and probable space group are also tabulated.

A New Notation System of Close-packed and lts Related Structures

A new simple notation describing close-packed structures was given. The layer sequence of close-packed anions was represented by the symbols of polytypism, and the arrangement of cations in the tetrahedral and octahedral voids was indicated briefly by the fractions of the voids occupied. A rhenium trioxide and a cristobalite.q, tructures were expressed in terms ofdefect of anions fromclose-packing.The arrangement of cesium chloride was also represented by a stackingof ionic layers.The structures of about a hundred inorganic compounds were described (Table 2N7), and the correlation of these structures was discussed.

On the relation between molybdenum trioxide and rhenium trioxide type crystal structures

The structural relatiion between MoO3-type and ReO3-type is clarified by considering layers of anions parallel to (13{\bar 1})MoO3 and (111)ReO3. MoO3 is then seen to be approximately cubic close-packed anions while ReO3 is cubic close-packed anions but with one-quarter of the anion sites unoccupied. The two structures may then be interconverted by a rotation operation resembling that which links ReO3- and PdF3-type structures. Photographs of ball models are used to illustrate the relations. No compounds are known which exhibit direct transition from ReO3-type to either MoO3- or PdF3-type. This is probably because of the large change in volume per anion. The interface between ReO3 and the close packed structures may be described as a dilation fault.

The rhenium-oxygen system at high pressure: Structure and characterization of a new rhenium oxide

The rhenium-oxygen system has been studied under 65 kbar pressure. In addition to the known ReO 2, ReO 3, and Re 2O 7 phases, a new, nonstoichiometric phase has been found. This phase can be represented as Re 1+ x O 3 where values of x from 0.14 to 0.21 have been observed. The structure of this new phase has been determined for x = 0.16. The space group is P6 322, and the hexagonal cell dimensions are a = 4.8350 ± 0.0006 Å and c = 4.5350 ± 0.001 Å. The structure is based on hexagonally close-packed oxygens with rheniums in certain of the octahedral sites. Crystals of this new rhenium oxide show metallic conductivity. The relation of the Re 1+ x O 3 structure to other structures with hexagonal close-packed anions is discussed.

Classification, representation and prediction of crystal structures of ionic compounds

The aim of this paper is to show that with the aid of a qualitative model of ionic bonding, including polarizability, many crystal structures, mainly of halides and chalcogenides, can be explained or even predicted. Polarization of O 2− and F − ions may be neglected unless these ions have very small, or small and highly charged cation neighbours. The polarizability of a few large cations is assumed also to play a rôle. The cation polyhedron may have a shape different from that expected for the ionic model as a result of nonionic bonding types; the theoretical shapes can be used empirically in the structure prediction. Section I deals with the background of this ionic picture. Section II deals with the sharing of corners and/or edges and/or faces of cation polyhedra. Pictures of various types of sharing polyhedra are given, with octahedra as an example. An explanation is offered for Wadsley's rule of maximal edge-sharing in his shear-structures, which seemed to violate Pauling's third rule. In Section III a classification of crystal structures is given in plots of cation coordination versus stoichiometry, expressed as the ratio nr. anions/nr. cations, for simple compounds and complex anions. The average cation coordination is plotted against stoichiometry if one is interested in the changes of structure under high pressure. Section IV deals with the description of crystal structures by space-filling polyhedra, which are an aid towards finding relationships between structures and towards predicting new ones. Simple structures with close-packed anions or cations are explained by the ionic model using these SFP in Section V. In Section VI some structure predictions (e.g., of Sc 2S 3, Li 2CuO 2, SrCuO 2, Sr 2CuO 3, and SrCu 2O 2) are discussed, and some results of recent structure determinations carried out in the author's laboratory (of the above-mentioned SrCuO-compounds, β-BaPdO 2, MgAl 2S 4, FeAl 2S 4 and MgGa 2S 4) are given.

Magnetic properties, conductivity and ionic ordering in Fe 1- xCu xCr 2S 4

Magnetic properties, conductivity and ionic ordering in Fe 1- xCu xCr 2S 4