MANUFACTURE OF GRAIN BOUNDARY BARRIER TYPE HIGH ELECTROSTATIC CAPACITANCE CERAMIC VARISTOR

摘要

PURPOSE:To obtain varistors of high insulation and high electrostatic capacitance and to dispense with the steps of applying and diffusing CuO, Bi2O3, etc., after semiconduction by mixing a powder of perovskite oxide consisting mainly of SrTiO3 with specified amounts of sintering promoter, semiconduction promoter, high oxygen-permeable solid electrolyte, and grain boundary depletion layer former, by sintering a mixture at a specified temperature in a reducing atmosphere, and by heat-treating a mixture at a specified temperature in an oxidizing atmosphere. CONSTITUTION:Strontium titanate is mixed with the following: 0.1-5.0wt% of sinter promoter TiO2-Al2O3-SiO2 that forms a liquid phase at high temperature; 0.05-2.0wt% of semiconductor promoter Nb2O5 dissolved into a perovskite phase; 0.1-10.0wt% of high oxygen-permeable solid electrolyte ZrO2 serving as grain growth controller; and 0.2-7.0wt% of composite SrO.1/3 MnO.1/3Ta2O5 as grain boundary depletion layer former serving as grain growth controller. After a mixture is calcined and pulverized in dry system, it is dried, granulated, molded, sintered in a reducing atmosphere at 1250-1500 deg.C, and pulverized again in dry system. The next step is to mold the powder into paste by use of resin and organic solvent to prepare a sheet 1: some of sheets 1 are stacked to form internal electrodes 2, which are in turn sintered in a reducing atmosphere at 1250-1500 deg.C and heat-treated in an atmosphere at 800-1150 deg.C to regulate electrodes 3.