Rock-Salt-Type

The influence of Zn-deposition on Cu(lll) surfaces on methanol synthesis by hydrogenation of CO2 shows that Zn creates sites stabilizing the formate intermediate and thus promotes the hydrogenation process [2.44]. Further publications deal with methane oxidation by various layered rock-salt-type oxides [2.45], poisoning of vana-dia in VOx/Ti02 by K2O, leading to lower reduction capability of the vanadia, because of the formation of [2.46], and interaction of SO2 with Cu, CU2O, and CuO to show the temperature-dependence of SO2 absorption or sulfide formation [2.47]. 

Bismuth(V) oxide and bismuthates are even less well established though a recent important development has been the synthesis and structural characterization of LisBiOs, prepared by heating an intimate mixture of Li20 and Q -Bi203 at 650° for 24 h in dry O2. The structure is of the defect rock-salt type with an ordering of... 

The heavier metal tantalum is distinctly less inclined than niobium to form oxides in lower oxidation states. The rutile phase TaOz is known but has not been studied, and a cubic rock-salt-type phase TaO with a narrow homogeneity range has also been reported but not yet fully characterized. TazOs has two well-established polymorphs which have a reversible transition temperature at 1355°C but the detailed structure of these phases is too complex to be discussed here. 

In order to construct an MeX-type compound (X Me = 1) using only octahedral elements, the octahedrons must be linked via their faces i.e. by sharing of three angles. This arrangement of the octahedral polyhedrons yields a rock-salt type structure (NaCl type structure). 

Fig. 43 shows fragments of X-ray powder diffraction patterns of compounds with rock-salt-type structures. 

In all cases, broad diffuse reflections are observed in the high interface distance range of X-ray powder diffraction patterns. The presence of such diffuse reflection is related to a high-order distortion in the crystal structure. The intensity of the diffuse reflections drops, the closer the valencies of the cations contained in the compound are. Such compounds characterizing by similar type of crystal structure also have approximately the same type of IR absorption spectra [261]. Compounds with rock-salt-type structures with disordered ion distributions display a practically continuous absorption in the range of 900-400 cm 1 (see Fig. 44, curves 1 - 4). However, the transition into a tetragonal phase or cubic modification, characterized by the entry of the ions into certain positions in the compound, generates discrete bands in the IR absorption spectra (see Fig. 44, curves 5 - 8). 

Fig. 44. IR absorption spectra of Li3Ta04 (1), Li4Ta04F (2), LiJJbOfr (3), Li3Ti03F (4)- rock-salt-type structures with disordered ionic arrangement and high-temperature modifications of Li3Ta04 (5), Li4Ta04F (6), Li3Nb04 (7), LiMO.F (8).

The magnetic stractures of the cubic fluoroperovskites AMeFs (Me + = Mn, Fe, Co, Ni) also belong to the G-type 273). Connected with the magnetic ordering below the Ne l-points, small distortions occur which have been studied in the case of potassium compounds by Okazaki and Suemune 237) and by Beckman and Knox 26, 27). A theoretical interpretation of such distortions, which were observed in antiferromagnetic oxides of the rock-salt type also, is given by Kanamori 179, 180). 

Kapustinskii s formula and, 1 177-179 Templeton s calculations and, 1 179-181 nuclear recoil and, 1 272-278 in water, 39 401 35, see also Alkali, halide crystals Rock-salt-type alkali halide crystals... 

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... 

The great ability of the perovskite structure AMOs and of the rock salt type structure AO to adapt to each other, forming intergrowths (AMOs)m(AO)n, as shown, for instance in titanates (Sr-Ti03)mSr0 (n=l) (1). 

The general formulation of these oxides, (ACuOg.x)m(AO)n, reflects for each of them the number m of copper layers which form each perovskite slab, and the number n of AO layers which form each rock salt-type slab (the AO layers which lie at the boundary of the perovskite slabs and rock salt type slabs can only be counted as for 1/2). Thus all these oxides (2-34) can be represented by the symbol [m,n] in which m,n will be integral numbers. In most of these oxides one observes for one compound only one m and n value, corresponding to single intergrowths. 

Lone pair cations exhibit external pairs of electrons which do not participate in the bonds but can influence dramatically the geometry of the structures (52). This is the case of cations like Bi(III), Pb(II) or T1(I) whose 6s2 lone pairs have been shown to present an important stereochemical activity. Such cations which can be found in the rock salt type layers are capable of influencing the oxygen framework and may consequently affect the superconducting properties of the layered cuprates. 

TABLE 1.6 Compounds that have the NaCl (rock-salt) type of crystal structure... 

IV. The Dissolution Process of Rock-Salt-Type Alkali Halide Crystals... 

Variables 2 and Zj are charges of ions i and j Ay is the Pauling factor defined as Ay = (1 + zjnx + z-Jn i, where nK and nj represent the numbers of electrons in the outermost shell of ions i and j, respectively Cy = (3/2) aiajEiEj/(Ei + Ej) and dy = (9/4e2)Cy(a, 1/Ar1 + atjE/Nj), where a denotes the polarizability of ions, N is the number of the total electrons of an ion, and E is the first ionization potential, evaluated from the Equation Ef = Nle2h2I Tr2mai for ion i, where h and m are the Planck constant and the mass of the ion, respectively. Values of p, b, and cr are estimated from isothermal compressibilities and thermal expansion coefficients of 17 rock-salt-type crystals of alkali halides by Fumi and Tosi (15). 

Since ion-ion-pair potentials have been thoroughly investigated for rock-salt-type crystals by Tosi and Fumi (15) and those for other type salts have not been as well studied, the MD simulations have been carried out for alkali fluoride and chloride crystals of the rock-salt type NaF, KF, CsF, LiCl, NaCl, and KC1. Due to the limitation of computer times, the simulations have been carried out for only 12 to 20 ps depending on the systems. The experimental conditions for the simulations are summarized in Table II. 

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