DEFECT STRUCTURE AND SOLUBILITY RANGE OF GALLIUM-DOPED COBALT OXIDE

The electrical conductivity sigma of polycrystalline cobalt oxide dope d with gallium oxide, Co(1-x)G(2x/3)O, was measured as a function of t emperature (800-1400 degrees C), oxygen activity (10(-4)-0.21) and com position x (0-0.125). The phase boundary of the solid solution as a fu nction of temperature and oxygen activity was ascertained by a well-de fined change of the slope in the sigma-T-Arrhenius plot. As a function of Ga2O3-content, the electrical conductivity runs through more or le ss distinct minima at all temperatures and oxygen activities. To expla in these dependencies, a defect model was developed, which contains di fferent defect associates and a 4:1-cluster. It emerges from a model i n which associated holes contribute to the total conductivity as well as free holes. Due to this fact different mobilities result for the re spective holes.