Process control during diamond coating of tools: F.Deuerler et al. (Fachhochschule Gelsenkirchen, Bocholt, Germany.) Int. J. Refractory Metals Hard Mater., vol 16, no 3, 1998, 191–199

Abstract

The present study focuses on the effect of indium doping on the microstructure and electrical properties of Y-doped ZnO varistor ceramics. At a given concentration of the rare-earth element yttrium, the leakage currents of sintered varistors first decreased markedly with increased indium doping, before increasing at higher doping levels. The nonlinear coefficient showed the opposite trend. A fraction of the doped In3+ ions dissolved into the grains and caused the grain resistance to decrease, leading to a low level residual voltage. The In3+ ions present at the grain boundaries increased the barrier height, and further inhibited increases in the leakage current. When doped with 0.025 mol% indium and 0.9 mol% yttrium, the sintered varistors showed optimal electrical properties with a leakage current of 4.15 μA/cm2, nonlinear coefficient of 51.84, residual voltage ratio of 1.61, and voltage gradient of 615.59 V/mm.