Ordered Rock Salt Structures

For o-Li ,Mn02, 50% of the Mn ions need to change position in order to form spinel. The characteristics of the orthorhombic, a-NaFe02-type layered, and spinel structures as well as many other ordered rock-salt structures have been covered in detail by Thackeray. ... 

The possibility that Mn generally favors tetrahedral coordination as its valence approaches +2 (i.e., d ) is unlikely given that MnO has a rock-salt structure not zinc blende or some other structure with Mntet. Instead, the driving force for Mn movement out of the octahedral sites of 7-Lii/2Mn02 into neighboring Li layer tetrahedral sites appears to be due to the unique cationic ordering and associated cationic interactions that are present in 7-Lii/2Mn02. 

Such vibrational structure in the spectra of the Bi3+ ion has also been observed in a few other host lattices, viz. CaO and SrO (rock salt) [8,9], NaLn02 (Ln = Sc, Y, Gd, Lu, ordered rock salt) [10], CaS [11], YA13B4012 [12], Ca3(P04)2 [13], and CaS04 [14]. A structural requirement for the occurrence of this vibrational structure seems to be that the Bi3 + ion occupies a relatively small six-coordinated site, with CaS04 as an exception (eight coordination). Due to a low site symmetry and/or the simultaneous occurrence of... 

Titanium Monoxide. Titanium monoxide [12137-20-1 /, TiO, has a rock-salt structure but can exist with both oxygen and titanium vacancies. For stoichiometric TiO, the lattice parameter is 417 pm, but varies from ca 418 pm at 46 atom % to 4162 pm at 54 atom % oxygen. Apparently, stoichiometric TiO has ca 15% of the Ti and O sites vacant. At high temperatures (>900° C), these vacancies are randomly distributed at low temperatures, they become ordered. Titanium monoxide may be made by heating a stoichiometric mixture of titanium metal and titanium dioxide powders at 1600°C... 

All of the insulator rock salt structures of Table VIII exhibit face-centered ordering of the second kind, which means that the 180° cation-anion-cation interactions arc stronger than the 90° interactions. Comparison of the calculated and observed N6el temperatures for the oxides was given in Table XIII. That 7V for a-MnS is greater than that for MnO follows qualitatively from the fact that the S2 ion has a greater tendency for covalent bonding than 02 . 

The increase of the sensitivity towards surface reactions along the band series III > II > I (when observed) accounts well for the involvement in such absorptions of surface ions with coordination number decreasing in the same order III < II < I. As indicated above, AEOs have the rock salt structure, with both cations and anions octahedrally six-coordinated in the bulk. Their surface morphology results from the intersection of nano 001 planes, which leads to the exposure of five-(5C), four- (4C) and three- (3C) coordinated ions of facelets, edges and comers respectively. A general consensus has been reached that such sites are responsible for the optical transitions resulting in bands I, II and III, respectively. On this basis, the trend in the intensities of such bands for each AEO (Eigure 2.5) can also... 

Vibrational spectroscopies give rise to interesting information on the microscopic structure of soUd-solution mixed oxides. For example, the state of vanadium in soUd solution in Ti02 anatase catalysts [59], the partial ordering of cations in comndum-type Fe-Cr oxides [60], the real presence of Ti" in the silicalite framework of TSl catalysts [58] and the solubility of AT ions in the NiO rock-salt structure [61] have been objects of IR spectroscopic studies. 

Silver iodide is the only silver halide with an adamantine structure, the two elements having covalent radii in the ratio 1.34 1.33. Both AgCl (1.34 0.99) and AgBr (1.34 1.14) have a rock-salt structure and an ionic character. Gold (I) fluoride is unknown, and the chloride, bromide, iodide decrease in stability in that order, the formation of Aul being endothermic (d H, 5.52 kcal). With the exception of Aul, all are converted by water to the trihalide and metal, the chloride the most readily, possibly because the most soluble. 

At high pressures (34CiPa), UN transforms from cubic rock salt structure [256]) to hexagonal symmetry. At 10 MPa, IJN, is known to form with the fluorite structure Ut = 5.31 A) [257]. UjN, has the bixbyite structure [257]. UN is paramagnetic with a susceptibility maximum at 53 K. The higher nitrides are nonstoichiometric and have antiferromagnetic ordering temperatures from 94 K to 8 K (UN,.55 to UN,., ) [258],... 

So-called ternary or mixed oxide systems based on the rock salt structure are well established. Thus LiFe02 exists both in a disordered form in which Li and Fe are randomly distributed on the metal sites, and as an ordered variant with tetragonal symmetry. Rhombohedral distortions are found for LiNi02, LiV02, and NaFe02 in which the cations are ordered on different sublattices. The HCP counterpart of the sodium chloride structure, the so-called Nickel Arsenide stucture (5ee Chalcogenides Solid-state Chewistr, is found only for the heavier members of the Oxygen family. 

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