Low-temperature sintering of BaTiO3 positive temperature coefficient of resistivity (PTCR) ceramics

Abstract

Donor–acceptor-codoped and Ti-excess barium titanate ceramics BaTi1.007−x−yNbxMnyO3 with positive temperature coefficient of resistivity (PTCR) behavior were prepared via the mixed oxide route. Resistivity versus temperature characteristics of samples sintered in air at 1350 °C were investigated as a function of dopant concentrations. A low room-temperature resistivity ρRT = 80 Ωcm and large resistivity change ρmax/ρmin of four orders of magnitude at the Curie temperature was observed for x = 0.002 and y = 0.0003. To reduce the sintering temperature and enable low-temperature sintering of PTCR ceramics, several additives inducing liquid-phase sintering were tested. We report on the effect of BaB2O4 and LiF–SrCO3 additives on the sintering behavior, microstructure, and ρ(T) characteristics. It is shown by dilatometry that the sintering temperature is drastically reduced. PTCR ceramics with resistivity change ρmax/ρmin of two orders magnitude were obtained with addition of 3 wt% BaB2O4 and sintering at 950 °C, or with a combined addition of 3 wt% BaB2O4 and 0.25 wt% LiF–SrCO3 and sintering at 900 °C.