Rocksalt, crystal structure

Figure 10.1 Schematic layers of Ti and C atoms in the rocksalt crystal structure of TiC.

Perhaps the most simple crystals in this class are the alkaline earth oxides. They are II-VI compounds and have rocksalt crystal structures. Data for their hardnesses versus their bond moduli (optical band gaps per molecular volumes) are displayed in Figure 11.4. 

Rocket propulsion oxidizers, 18 384-385 Rocks, weathering of, radiation and, 3 299 Rocksalt, crystal structure of, 2 6, 29 Rock-salt-type alkali halide crystals, dissolution process, 39 411 19 alkali chlorides, 39 413, 416 alkali fluorides, 39 413-415... 

Few oxide superconductors were known prior to 1985 and we shall now return to these so that we can discuss these materials in reference to their crystal structure classes. There are only three broad structural categories in which most of the oxide superconductors occur. The important structural types include sodium chloride (rocksalt, or Bl-type), perovskite (E2X), and spinel (Hlx). 

STRUCTURE. CdS Can exist in three different crystal structures hexagonal (wurtzite), cubic (zincblende)— both tetrahedrally coordinated and cubic (rock-salt), which is sixfold coordinated. Except in a few cases, the rocksalt modification of CdS has been observed only at very high pressures CD films of this phase have never been reported. The other two phases have been reported to occur in CD films under various conditions. The wurtzite phase is thermodynamically slightly more stable, and invariably forms if the zincblende phase is heated above 300-400°C. The low-temperature CD method therefore can allow the formation of the zincblende phase, and this phase is commonly obtained in CD CdS films. Very often, a mixture of wurtzite and zincblende phases has been reported in the literature. There are many variables that affect the crystal structure, including the nature of the complex, the substrate, and sometimes even stirring. 

The rocksalt crystal structure belongs to the cubic system with space group 0 (Pm3m). It consists of two face-centered cubic (fee) sublattices, which are occupied by one atom species each. The two sublattices are shifted along one half of the diagonal of the primitive unit cell against each other. The rocksalt lattice is sixfold coordinated. 

Both A - and Ei-modes are Raman and IR active. The two nonpolar E2-modes E and E are Raman active only. The Bi-modes are IR and Raman inactive (silent modes). Phonon dispersion curves of wurtzite-structure and rocksalt-structure ZnO throughout the Brillouin Zone were reported in [106-108]. For crystals with wurtzite crystal structure, pure longitudinal or... 

The T-point optical phonons of a crystal with rocksalt structure belong to the irreducible representation... 

Knapp et al. (144) show that for oxides containing 3d elements in spinel, perovskite, rocksalt, or zircon-type structures, the K-edge XANES spectra are quite independent of 3d electron occupation but instead nicely correlate with the crystal structure type. Various studies of Ti K edges of titanium oxides and other titanium compounds have been reported (40,158,172,177, 297). 

A good example of these principles is the rocksalt structure we will consider MgO to be specific. In the bulk crystal structure, both cations and anions have six nearest-neighbor ligands in an octahedral configuration this is the ideal... 

The silver halides, with the exception of one crystal modification of Agl, have cubic crystal structures. Crystal structure data, relevant lattice properties and low temperature dielectric constants, are collected in Table 3. AgF, AgCl, and AgBr all have the NaCl rocksalt structure in which there are four silver halide pairs per nonprimitive unit cell with cation-anion nearest neighbor distances equal to one-half a lattice constant. 

Figure 2-6. The B1 or NaCl (rocksalt) crystal structure. (From Klein and Hurlbut [411].)...

The crystal structure of magnesium oxide is illustrated in Figure 37. This is one of the simplest structures and is very similar to that of rocksalt, NaCl. Each Mg atom is surrounded by six O atoms, and to preserve electrical neutrality, each O atom is surrounded in turn by six Mg atoms. The entire lattice can be considered as built up from cubes, with O and Mg atoms at alternate corners this is the only known crystalline form of MgO and is sometimes called periclase. 

The earliest nonmetallic superconductors were NbO and NbN. Both materials have a rocksalt crystal structure. What was significant about the discovery of superconductivity in these materials (they are of no practical use) is that they linked the phenomenon to ceramics and cubic crystal structures. 

In Table 2.5 we give general information about all the cubic structures under consideration prototype name, Pearson and strukturbericht designations, space group and Wyckoff positions occupations, and possible equivalent description of the structure. All these structures contain one formula unit in the primitive unit cell Z=l). For the structures cF with a face-centered cubic lattice the number of atoms is given for the cubic unit cell consisting of four primitive unit cells (this is traditional for crystal-structure databases). In computer calculations only the atoms inside the primitive unit cell have to be included two atoms for diamond, rocksalt, zincblende and cesium... 

Table 3.1 Crystal structure (space group), melting point crystal density g and color of some transition-metal carbides and nitrides, rs = rocksalt.

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