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

Effects of oxygen partial pressure (PO2 ) control on the electrical properties and microstructural development of (Ba1-xHox)0.997TiO3 were studied. An oxidation condition (PO2 ~ 1.0 atm) was maintained during the heating process, and then the specimen was sintered in a reducing atmosphere (PO2 < 10–9 atm) at 1350 C, followed by the annealing process at 1000 C and PO2 = 1 atm. The switching temperature (TS) from the oxidation atmosphere to the reducing condition was changed from 1100 to 1350 C. A significant decrease in the room-temperature resisitivity (q25) was observed as TS was increased. The temperature coefficient of resistance (TCR) was independent of the change in TS, and closed pores decreased with increasing TS.