Properties of Multilayer NTC Perovskite Thermistors Prepared by Tape Casting, Lamination and Cofiring

Abstract

The paper reports on processing and characterization of multilayer NTC (negative temperature coefficient) perovskite thermistors. Three materials La0.8Sr0.2Ti0.4Fe0.6O3, CaTi.0.8Co0.2O3 and CaTi0.9Y0.1O3 with the stable perovskite structure were synthesized by solid state reactions and used for preparation of slurries for tape casting. Green sheets with screen printed internal Pt electrodes were stacked, laminated isostatically and cofired at 1250-1350°C. SEM observations revealed dense, fine-grained microstructure of ceramic layers, lack of delaminations and cracks and a good cooperation between ceramic and Pt electrode layers. Resistance-temperature characteristics of the fabricated multilayer thermistors were measured in the temperature range 20-820°C. The temperature coefficients of resistance were high, ranging from-9.7 to-1%/°C. Two developed compositions CaTi.0.8Co0.2O3 and CaTi0.9Y0.1O3 were found to be suitable for use at a higher temperature range of 150-500°C. The endurance tests showed small resistance changes (below 1%) after long term ageing at 300-400°C.