Effects of oxygen partial pressure control on the microstructure and PTCR properties of Ho doped BaTiO₃

Abstract

Effects of oxygen partial pressure ( ${\hbox{P}}_{{\hbox{O}}_{\hbox{2}} }$) control on the electrical properties and microstructural development of (Ba_1-xHo_x)_0.997TiO₃ were studied. An oxidation condition (${\hbox{P}}_{{\hbox{O}}_{\hbox{2}} }$ ∼ 1.0 atm) was maintained during the heating process, and then the specimen was sintered in a reducing atmosphere (${\hbox{P}}_{{\hbox{O}}_{\hbox{2}} }$ < 10⁻⁹ atm) at 1350 °C, followed by the annealing process at 1000 °C and ${\hbox{P}}_{{\hbox{O}}_{\hbox{2}} }$ = 1 atm. The switching temperature (T_S) from the oxidation atmosphere to the reducing condition was changed from 1100 to 1350 °C. A significant decrease in the room-temperature resisitivity (ρ₂₅) was observed as T_S was increased. The temperature coefficient of resistance (TCR) was independent of the change in T_S, and closed pores decreased with increasing T_S.