Electrical conductivity and electrical stability of Bi/Mg modified NiO ceramics for NTC thermistors

Thermistors with negative temperature coefficient (NTC) of resistivity are important components for temperature sensors and actuators. High material constant (B value) of NTC thermistor, i.e. high-temperature sensitivity, is one of key focuses. Herein, Bi/Mg modified NiO based ceramics for NTC thermistors were prepared by conventional solid-state reaction method. Introduction of Bi2O3 significantly enhances the sintering ability of ceramics and reduces the sintering temperature from 1380 to 1250°C. Mg-doping (i.e. preparation of Ni1-xMgxO ceramics, where x=0, 0.02, 0.05, 0.07 and 0.1) has significant effect on room temperature resistivity (ρ25). Phase composition, microstructure, electrical property and electrical stability were investigated. All prepared ceramics have the phase with rock-salt structure and show typical NTC characteristics with B values higher than 5300K. The electrical stability with an optimized resistance-change rate of 1.02%after being aged at 150°C for 500 h is achieved. The electrical properties of the ceramics were analysed by combining X-ray photoelectron spectra with complex impedance spectra.