High-temperature thermistors based on yttria and calcium zirconate

Abstract

Two oxide systems, yttria and calcium zirconate, have been systematically studied for their potential use as thermistor materials above 1000°C. Both oxides have a sensitivity (temperature coefficient of resistance) of about 1.5% °C −1 or higher. Doping yttria with zirconia results in a slight decrease in sensitivity, but enables the system 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, limited to atmospheres without methane and/or possibly other hydrocarbon gases. The results of feasibility tests of a.c.-powered thermistors based on yttria and calcium zirconate suggest that an excitation circuitry can be used for designing a thermistor display device.