HIGH-TEMPERATURE THERMISTORS BASED ON YTTRIA AND CALCIUM ZIRCONATE

Two oxide systems, yttria and calcium zirconate, have been systematica lly studied for their potential use as thermistor materials above 1000 degrees C, Both oxides have a sensitivity (temperature coefficient of resistance) of about 1.5%degrees C-1 or higher. Doping yttria with zi rconia results in a slight decrease in sensitivity, but enables the sy stem to be used in a humid environment without protective coating. The electrical response of calcium zirconate is found to be sensitive to methane, but is practically unaffected by humidity and carbon monoxide . The use of a calcium zirconate-based thermistor is, therefore, limit ed to atmospheres without methane and/or possibly other hydrocarbon ga ses. The results of feasibility tests of a.c.-powered thermistors base d on yttria and calcium zirconate suggest that an excitation circuitry can be used for designing a thermistor display device.