Cubic compounds

Of the 5521 compounds crystallizing in the mentioned 128 structure types, 46% belong to a single-environment group (structures in which all atoms have the same type of environment), 37% have two environment types, 9% three and the rest four or more environments (=98% of the cubic compounds crystallize in structure types with 1, 2, 3 or 4 AET). 

The layered oxides LiNiOj and LiCoOj also have the 3R form AbC(a)BcA(b)CaB. In this structure, the oxygen lattice considered alone has cubic close packing ACBACB (or equivalently ABCABC). As a result, these compounds are closely related to cubic compounds. To visualise the structure of LiNiOj or LiCoOj, for example, start from cubic NiO or CoO (AbCaBcAbCaB), and replace every second layer of Ni or Co by Li. In the case of Ni this replacement may be incomplete, and the Li layers may contain residual Ni (Dahn, von Sacken and Michal, 1990b). 

Spinels are cubic compounds, but the structure can be described as layers of close-packed oxygen. The sites available both for the transition metals and guests are octahedral and tetrahedral, as in Fig. 7.1(a). Unlike the layered compounds in Fig. 7.5, however, where every second metal layer is empty, the metal atoms of the host occupy octahedral or tetrahedral sites in every layer. 

Fig. 24. Spectra of three compounds with rock salt structure and one nearly cubic compound (TiO), showing variations of extended fine structures, general similarity of spectra, and special low energy absorption of the metallic TiC.

There are a large number of scientifically and industrially important zinc prodncts and compounds for which it would be valuable to have a characterization method, such as NMR, complementary to powder X-ray diffraction. The observation of Zn NMR in cubic compounds, e.g. ZnS (sphaelerite), ZnSe and ZnTe ° was reported from Mossbauer and NQR ° measurements, which yield a variety of coupling constants at 4.2 K, viz. 13 8.4/MHz , 12 45.2/MHz and 13 620.8/MHz - °. 

In simple cubic compounds like NiO, MnO and CoO the metal ions lie on a face-centred cubic. As pointed out by Ziman (1952), for this structure and for spherical orbitals, antiferromagnetism with a finite Neel temperature must be due to interaction between next-nearest neighbours, because in any antiferromagnetic structure each moment will have as many parallel as antiparallel neighbours. In NiO and CoO the orbitals are not spherical, but in MnO the 3d5 ion is spherical In this compound the Neel temperature is therefore anomalously low, and there remains abnormally strong short-range order above the Neel temperature (Battles 1971). 

Seyboldt (1960) first discovered an extremely boron-rich rare earth cubic compound with only 1-2 atomic percent of rare earth. Early notations of this compound have varied from RB ioo to RB 7o to RB so (an early review of the Y-B... 

Experimental results obtained for the cubic compounds Am02(CaFo... 

X-ray powder pattern was diflFerent and corresponded to tetragonal K3UO2F5 (J5). The third preparation resulted in a mixture of the two compounds, K3UO2F5 and the cubic compound. This was the first time in which a mixture of two compounds was produced. 

As yet the cubic compound has not been identified. Table X gives the infrared spectra of the cubic compound, K3UO2F5, K3NPO2F5, and UF4. The bands at 480 cm. and 370 cm. are attributed to the metal-fluorine bond, and the bands at 850 cm. and 740 cm. result from the metal-oxygen bond. Thus, these data indicate a similarity in structure between the unknown cubic compound and the K3UO2F5. 

The non-stoichiometric, interstitial cubic compounds TiB, TiBg, TiC and TiN are very stable, strongly exothermic, and refractory. TiC is widely used in association with WC for tipping high-speed tools. 

The nature of the CFI in compounds of samarium, such as SmAl2 (151,152), SmPt2 (153,154), SmAl3 (155), SmSn3 (153,156-158) and SmX (X = P, As, Sb, Bi) (159,160), have been examined in detail and reviewed critically in recent years (2,3). In general, it has been observed that the spin-orbit interaction term plays a significant role, and in cubic compounds the effects of both fourth and... 

Non-variational calculations of the excited acceptor states in cubic compound semiconductors using the finite element method and Arnoldi algorithm have also been performed, with application to some II—VI and III—V compounds [51,52]. The nS3/2 states (n = 1 to 8) have been calculated in the spherical approximation for //, varying between 0 and 0.95 in steps of 0.05 while the nP3/2 (r3), nP5/2 (r3) and nP5/2 7) states (n = 2 to 5) have been calculated including the cubic term 6 (6 = 0.05 and 0.15) for the same domain of variation of /. The case of the single and double acceptors in GaAs has been specifically studied by Fiorentini [18]. A discussion of the results of these calculations will be presented in relation to the experimental data. 

The spin susceptibility derived from the x and K values at Tc is enhanced by a factor of 5.4 as compared with that estimated from the band calculation due to ferromagnetic spin fluctuation,107,108 and the related cubic compound... 

The cubic compound UInAu2 with Heusler structure was studied by Besnus et al. (1987). The lattice parameter a = 696.9 pm indicates a U-U spacing of 493 pm. ThInAu2, like the compounds of the REInAu2 series with light rare earths (Besnus et al. 1986), undergoes a structural transformation from cubic to tetragonal symmetry below 190 K (a = 707.0 pm at 300 K). 

A set of 18 dielectric ion polarizabilities, ap, derived from cubic compounds by Roberts, assuming = 2.387 A ... 

In 1%7 cubic compounds M, 4Cu3 4li03 [M" Cd, Ca] were described, the X-ray powder diagrams of ndiich could ea y be indexed if a perovddte stmcture was as-sumed ). The ligand-field spectra were not in accord with a d cation in the 12-oo-ordinated A site of this lattice type, however ) (Fig. 1). We hence decided to perform an X-ray and neutron diffraction structure analysis with a powder sample of the Ca compound and found a unit cell ch is sdiematically shown in Fig. 

Region III is rich in cubic compounds and practically all of them are formed with p elements. Cerium monopictinides and monochalcogenides have the NaCl structure and CeXj (with X = In, Tl, Pb) the AuCus structure, all of them face-centered cubic (fee) type. CeBg has the CaBg structure, which is simple cubic and is closely related to the CsCl structure, whereby the Bg octahedra occupy the Cl positions. 

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