Abstract
Cobalt, nickel and zinc germanate were prepared by solid state reactions between the relevant oxides in air. Ceramics with monophase structures could be obtained by adopting the optimum temperature and time. The as-fired ceramics exhibited insulating properties; however, by an additional heat treatment under reducing conditions, variable electrical conductivity could be induced in the ceramic bodies. Temperature/resistivity characteristics of these materials showed typical semiconducting behaviour. X-ray studies showed that despite the changes in electrical behaviour, and apparent changes in colour after annealing, the structures remained unaltered. Microstructural studies using scanning electron microscopy also showed that there were no substantial changes due to the reductive annealing processes.
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