NTC characteristics of bismuth based ceramic at high temperature

NTC characteristics of a ceramic based on Bi₂O₃ doped with TiO₂, Ta₂O₅ and WO₃ have been studied over a temperature range of 100 to 700°C. The material was pressed into pellets and sintered in air from 700 to 1000°C at 100°C intervals for 14 h. The microstructure was studied using SEM and evidence of a sintered body with grain sizes approximately 7–10 μm was observed in the material fired at 1000°C. XRD analysis indicated the emergence of a monophase material when sintered at 1000°C, which clearly verified along with the SEM studies, the completion of the sintering process. Electrical characterisation of the material was done by measuring the resistance and the capacitance over a temperature range of 100 to 700°C, in air. The material showed good NTC characteristics over the whole range of temperature with thermistor constants B=4840 K and ΔE=386 meV. The capacitance changed significantly over the temperature range (∼10⁻¹¹ F at 100°C to ∼10⁻⁶ F at 700°C).