Ion sublattice

The conducting ion sublattice in FICs is generally considered molten . The molten sublattice model for fast ion conduction was first proposed by Strock (1936) on the basis of structural and thermodynamic data for Agl. In most FICs, the entropy of the phase transition to the FIC state is larger than the entropy of melting. For example, in Agl the entropy of the transition at 420 K from the -form to the a-form (FIC state) is 14.7 J deg mol , whereas the entropy of melting at 861 K is only 11 J deg mol . ... 

The existence of Schottky or Frenkel defects, or both, within an ionic solid provides a mechanism for significant electrical conductance through ion migration from site to empty site (leaving, of course, a fresh empty site behind).4 Solid /3-AgI provides a classic example of a nonmetallic solid with substantial electrical conductivity at elevated temperatures at 147 °C, it undergoes a transition to a-Agl in which the silver ion sublattice is disordered and consequently allows for relatively free movement of Ag+ and... 

Figure 5.1 Frenkel and Schottky defects. In the Frenkel case (left), a member of the lightly shaded ion sublattice is found in the wrong kind of interstice. In the Schottky defect (right), an ion and a counter-ion (here presumed to have equal but opposite charges) are completely missing. Unshaded circles represent the vacant sites.

Conversely, the presence of some metal ions of lower oxidation state in the metal ion sublattice requires vacant anion sites to balance the charge. In some cases, the charge imbalance is caused by ions of some other element or, rarely, by multiple valence of the anions. In any event, the empirical formula of a recognizable solid transition metal compound may be variable over a certain range, with nonintegral atomic proportions. Such non-stoichiometric compounds may be regarded as providing extreme examples of impurity defects. 

We can formulate the kinetic equations for (A, BJO oxide solutions. If it is assumed that the oxygen component (or rather the oxygen ion sublattice) is immobile (which, in the case of metal alloy oxidation, would forbid any internal reaction) and, furthermore, that AGa0 > AGB0, then the oxidation product is essentially AB204 as indicated in Figure 9-3. Let us, for the moment, disregard 1) the influence... 

From Eqn. (9.16), we see that the metal A is precipitated within the rigid, dense-packed oxygen ion sublattice of the oxide matrix. The local volume at the reaction front is thus increased by the molar volume per mole of vacancies. Large strains and stresses are the immediate result. In contrast, if (A,B)304 is internally reduced to yield (A, B)0, the oxygen ion sublattice remains essentially undistorted, except for... 

The ZnS zinc blende structure is cubic. The unit cell may be described as a face-centered sulfide ion sublattice with zinc ions in the centers of alternating minicubes made by partitioning the main cube into eight equal parts. 

Recent studies of the saturated phases indicate that the ions in neighbouring channels are shifted over c/2 with respect to each other and that this body-centred ion sublattice floats freely along the c direction with respect to the polymer lattice. Anisotropic temperature factors with a very, large component in the c direction have been determined for cesium by Ma et al. [76,106]. They calculate intensities based on a P4j2,2 unit cell... 

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