Abstract
Abstract ZnO powders prepared from the thermal decomposition of Zn-oxalate, Zn-carbonate and Zn-nitrate have been characterised in relation to the formation of sintered ceramics exhibiting nonlinear resistivity. The particle characteristics such as size, shape, lattice strain, the point defect contents and the nonstoichiometry with respect to δ Zn value in Zn 1+ δ O are found to depend upon the mechanism of reactions of ZnO formation and the effect of back reaction from the evolved gases. The most important characteristic of ZnO powder that considerably influences the nonlinear property of the ceramics is δ Zn . Optimum current-voltage characteristics for the sintered products are obtained when δ Zn in the starting material is in the range 8·5–12 ppma. Because of nonstoichiometry, the native donor states are built in the powder particles. The depletion layers formed at the pre-sintering stage are retained during sintering, as a result of the high valent transition metal ions preferentially present at the grain boundary regions. The energy barriers are stabilised around the grain boundaries by this process.
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