PTCR Properties of BaTiO3 Ceramics Fabricated by Combination of Sintering in Reducing Atmosphere and Post Oxidation Treatment
Nobuyuki TAKEUCHI, Shinya HAYASHI and Hisayoshi KOBAYASHI
Abstract: Room temperature (R.T.) resistivity and the positive temperature coefficient of resistivity (PTCR) of Gd-Mn codoped BaTiO3 from powders obtained by hydrothermal synthesis were investigated. Mixtures of Gd(NO3)3, Mn(NO3)2, and BaTiO3 powders (average particle size ; 0.5ƒÊm) obtained by hydrothermal synthesis were dried and pressed into pellets with a diameter of 2 cm. Then, the pellets fired at 1380 Ž for 2 h in 0.1%H2-Ar atmosphere and oxidized at the temperature range of 1000 to 1300 Ž for 1h during cooling period. Fired sample which had low R.T. resistivity and remarkable PTCR characteristics was obtained for 0.2 mol%Gd-0.075 mol%Mn codoped BaTiO3 which fired at 1380 Ž in 0.1%H2-Ar, oxidized for 1h at 1300 Ž and cooled to R.T. in air . PTCR jump of the sample cooled in air was 300 times higher than that of the sample cooled in 0.1%H2-Ar. This result indicated that absorbed oxygen which was introduced into grain boundary by oxidation at 1300 Ž, was not desorbed during cooling in air from 1300 to 1200 Ž. Key Words:Barium titanate, Reducing atmosphere, PTCR, Hydrothermal synthesis