Electrical properties of polycrystalline ZnO: Cu obtained from freeze-dried ZnO plus copper(II) acetate powders

Highly homogeneous mixtures of powders containing ZnO and monohydrated copper(II) acetate, (CH3COO)(2)Cu.H2O, AcCuH2O were obtained by freeze drying. Thermal analysis and high-temperature X-ray diffraction showed that pure freeze-dried AcCuH2O powder decomposed to CuO, in air, at temperatures above 325degreesC. Due to the polymeric nature of AcCuH2O, the powder mixtures were compacted without pressing additives. Pellets with ZnO+xmol % Cu (x=0.05, 0.5, and 5.0) compositions were sintered in air from 750 to 1150degreesC for 1 h. After sintering, the density, shrinkage and mass loss increased as the concentration of AcCuH2O increased. A microstructural analysis of samples sintered at 950degreesC for 1 h revealed Cu-doped ZnO grains with Cu-clusters of x=5.0 mol % Cu; the J-E curves showed that both the breakdown electric field, E-br, and the nonlinearity coefficient, alpha, increased as x increased from 0.05 to 0.5. Complex acceptor defects involving Cu-Zn(+) in the grain boundary are believed to have compensated for the n-type conductivity of the ZnO grains, giving rise to high E-br values. (C) 2002 Kluwer Academic Publishers.