Defect Structure in the Alkali-Gallate Fast Ion Conductors.
Abstract
The defect structure of the alkali gallate fast ion conductors has been examined. It has been shown that for crystals prepared from K(,2)O-Ga(,2)O(,3) starting materials, the defect responsible for nonstoichiometry is a complex Frenkel defect, which introduces both interstitial oxygen and interstitial potassium into the crystals. For crystals prepared from Na(,2)O-Ga(,2)O(,3) starting materials, two complementary defect processes occur. The first is the Frenkel defect observed in K (beta) gallate. The second is the substitutional replacement of Ga('3+) by Na('+) in tetrahedral sites. This second process is unique among the alumina isomorphs. It has also been shown that "self -doping" by Na('+) is responsible for the stabilization of Na (beta)" gallate. The physical origin of nonstoichiometry has been discussed in terms of Pauling's electrostatic valence principle. Models for short range correlations in the crystals have also been presented. These include models for correlations between carriers and charge compensation defects, for correlations between carriers and carriers, and for lattice relaxations in the vicinity of point defects. These models have been qualitatively related to the conduction process. The mixed ion effect has also been analyzed. It has been shown that the anomalous drop in conductivity is accompanied by the partitioning of mixed ion carriers into different sites. The increased activation energy for conduction is qualitatively associated with an increase in the activation energy required to break up defect clusters plus an increase in the activation energy required for lattice migration.
- Publication:
-
Ph.D. Thesis
- Pub Date:
- 1981
- Bibcode:
- 1981PhDT........18A
- Keywords:
-
- Physics: Condensed Matter;
- Crystal Defects;
- Electric Conductors;
- Gallium Compounds;
- Potassium Compounds;
- Sodium Compounds;
- Activation Energy;
- Interstitials;
- Ionic Crystals;
- Lattice Vibrations;
- Metal Oxide Semiconductors;
- Solid-State Physics