Cubic structure cations

For cubic structures with more than one interionic distance—as, for instance, spinels (multiple oxides of type AB2O4 with A and B cations in tetrahedral and octahedral coordination with oxygen, respectively)—it is stiU possible to use equation 1.109, but the partial derivatives must be operated on the cell edge, which is, in turn, a function of the various interionic distances (OttoneUo, 1986). 

Monoxides of 3d transition metals, TiO to NiO, possess the rocksalt structure and exhibit properties shown in Table 6.3. While TiO and VO exhibit properties characteristic of itinerant (or nearly itinerant) d electrons, MnO, FeO, CoO and NiO show localized electron properties. The properties can be understood in terms of the possible cation-cation and cation-anion-cation interactions in the rocksalt structure (Fig. 6.12(a)). Direct cation-cation interaction can occur through the overlap of cationic t2g orbitals across the face diagonal of the cubic structure. When this interaction is strong R < and b > b, cationic t2g orbitals are transformed into a cation sublattice t%g band if this band is partly occupied, the material would be... 

D. Reinen, C. Friebel Local and Cooperative Jahn-Teller Interactions in Model Structures. Spectroscopic and Structural Evidence . Hellner The Frameworks (Bauver-bande) of the Cubic Structure Types /.S/iam/r Polyhalogen Cations... 

Scandium complexes with chloride ion in aqueous solution, and there is ion-exchange evidence for anionic species, presumably ScClJ aq, in concentrated hydrochloric acid,119 while values of K = 90 and K2 - 37 for the first two association constants have been reported.1211 Solid salts of the anions ScClt-, St Cll- and ScCl2- have been isolated with alkali metal cations.121,122 It seems likely that both the first two species are octahedral and bridged-octahedral respectively, in line with Cs2NaScCl6 which has an X-ray powder pattern in accord with a face-centred cubic structure.123... 

These revolutionary ideas lead to further neutron measurements of the structure of zeolite A, which have confirmed the correctness of the traditional 4 0 ordering scheme.58 59 Neutron diffraction traces for several samples of a dehydrated Na zeolite A with Si to A1 ratios of 1.03, 1.09 and 1.12 failed to show any rhombohedral distortions similar to those reported in ref. 57, and in each case the data was consistent with a cubic structure.58 Neutron diffraction experiments on a T1 exchanged sample of the same Na zeolite that had shown the rhombohedral distortion in ref. 57 showed that the crystals now had cubic symmetry59 60 and therefore the distortion that had been measured for the Na zeolite A must be very sensitive to the identity of the exchangeable cations. Profile refinement of this neutron data56 57 also showed a pronounced bimodal distribution of the bond lengths as would be predicted by the 4 0 model. In conclusion it appears that the chemical shifts observed in the n.m.r. experiments can be influenced by factors such as local strain, as well as by the local environment of each Si atom. 

Metallic compositions are primarily encountered for stoichiometries A3C60. These salts are superconducting and they adopt, in general, either fee or primitive cubic structures, in which the three cations occupy the available octahedral and tetrahedral interstitial sites. Charge transfer is essentially complete and the... 

An additional interesting property of cubic oxides is their ability to form solid solutions (25) that maintain the original cubic structure. In these solids the cation sites can be shared between the two competitive cations over a wide range of compositions. This is the case for the NiO-MgO system, for which the Mg Nii O solid solution can be prepared with 0 < x < 1 because of the very similar ionic radii of the cations jr(Mg2+) = 0.72 A and r(Ni2+) = 0.69 A], Another relevant case is CoO-MgO. 

In host matrices with cubic structure (e.g., AO = MgO, CaO, NiO, or SrO), the coordination number of the guest cation is 6 when substituting, for example, for bulk Mg2+ ions but M5C, M4C, and M3c dopant cations are obtained when the substitution occurs with surface Mg2+ or Ca2+ ions located on terraces, steps, or corners (1, 25, 331). As has been mentioned, at low x values M cations are isolated in the matrix, but increasing x leads to pairs, triplets, etc. (25, 332). 

In Figure 2.18a, the comer-sharing octahedra that form the skeleton of the ideal close-packed perovskite cubic structure is shown, in which the center of the cube is occupied by the A cation. Alternatively, this structure can be viewed with the B cation placed in the center the cube (see Figure 2.18b) [8],... 

The fast, ion conduction properties of a-Agl is a result of the large anionic radius of I- and the low cationic radius of Ag+, immersed in a cubic structure containing 42 vacant sites between octahedral and tetrahedral sites. Because of this fact, Ag+ has a high mobility in this cubic structure [22],... 

Fig. 57. The cubic structure of Co9S8 coordination polyhedra around the cations circles cations...

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