Lattice oxygens

Daw et al. [632] made a microscopic and crystallographic study of talc dehydroxylation. Nucleation, to yield enstatite, occurs inhomogeneously within the particles, perhaps at dislocations. Later, this product is topo-tactically orientated with respect to the reactant lattice, though with extensive faulting on the (010) plane owing to misfit, in addition to the attempt to preserve the oxygen lattice. In an isothermal study (1100— 1160 K) of the same reaction, Ward [633] found first-order obedience and the value of E determined (422 kJ mole-1) is close to that estimated for... 

The interaction of tin oxide and water also leads to a decrease of the sensor resistance, for which several reaction mechanisms were proposed. The first mechanism involves tin and oxygen lattice atoms reacting with water [1] ... 

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). 

Consider the available fluorine sites to be the lattice positions of a cubic, close-packed, two-dimensional lattice. These are the oxygen positions of a cubic, close-packed, oxygen lattice in the (111) type planes. Aluminum ions are situated below this two-dimensional anion layer. Suppose a fraction f of all the sites is randomly occupied by fluorine atoms the remaining sites are occupied by O with zero magnetic moment. 

In the compounds so far discussed, the oxygen lattice is intact, and two kinds of ions occupy the positions of one kind, leaving a certain number of positions unoccupied. The opposite type, with gaps in the oxygen positions, has been observed as well. A good example is... 

The width of non-stoichiometry remarkably depends on temperature. These compounds show non-stoichioraetry in both the cation-rich and cation-poor sides. At the stoichiometric composition, more than 15 per cent of the metal and oxygen lattice sites are vacant. 

It is instructive to write the compositions of the /l- and /T-aluminas with the oxygen lattice content the same in both cases, that is Na3Al33051 and... 

Introduction of extrinsic dopants (for instance metals with oxidation number three on substitutional metal lattice sites or halogens with oxidation number minus one on oxygen lattice sites in MO oxides)... 

An enormous range of properties is found in oxides. The most successful and most widely used substrate for GaN to date is sapphire, AI2O3. Except for wurtzite materials, few of the unit cells in these materials match with GaN, but it is usually useful to think of these systems as having a close-packed nitrogen lattice in GaN matching to a near close-packed oxygen lattice in the oxide. 

The spinel structure and spinel related structures are found in a large number of oxides. The (111) face is usually the lowest surface energy face, so it is typically easy to prepare. The oxygen lattice is face-centred cubic, which presents a similar stacking layer along [1 1 1] as found in the wurtzite structure along [0 0 0 1],... 

Stable phases in the rare earth oxide systems are tabulated and discussed. New data on the structure of sesquioxides quenched from the melt are reported. The structural interrelations between the A, B, and C type sesquioxides and the fiuorite dioxides are pointed out. The sequences of several intermediate oxides in the CeO, PrO., and TbO, systems are observed to be related to the fluorite structure and the C form sesquioxide with respect to the metal atom positions. A hypothetical homologous series of the general formula Mn02n i, related to the fluorite structure and the A form sesquioxide with a more or less fixed oxygen lattice, is suggested. 

A simple analysis would predict that the conductivity should be a maximum when half the oxygen lattice sites are vacant however, this is not the case. In Figure 14, the effect of various rare earth dopants on the properties of CeCh show that the ionic conductivity is highly dependent on the ionic radius of the dopant. Moreover, the conductivity increases and then decreases across the rare earth dopant series from Yb to Ta, peaking at Gd (Figure 14). A similar observation has been made for Zr, with the peak occurring at Sc. It is clear that the conductivity drops with relatively modest additions of the rare earth ion, when the vacancy concentration is only a few percent. 

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