Development of PTCR Characteristic in Vacuum-Sintered BaTiO₃-Based Ceramics by Addition of Partially Oxidized Ti Powder

Abstract

The compact of the mixture composed of (Ba, Sr)TiO₃ ceramics powder and partially oxidized Ti powder (5.0mass% O) which was named TiO₂(Ti) powder was found to show PTCR characteristic, when the compact was sintered in vacuum at 1623 K for 3.6 ks, and then heated in air at 853 K for 0.3 ks. Some properties of the sintered compacts were investigated.
The results obtained were as follows; (1)Obvious PTCR characteristic developed at TiO₂(Ti) contents of 5-7vol%. (2)The transformation from tetragonal structure (ferroelectric phase) to cubic structure (paraelectric phase) of (Ba, Sr)TiO₃ phase in the sintered and then annealed compact was suggested to occur only near the grain boundary and surface of the (Ba, Sr)TiO₃ grains. (3)The dielectric constant ratio of ε _{?? .540K}/ε _{?? t} was 1/8, which was below the value (1/3) of (Ba, Sr)TiO₃ air-sintered compact without TiO₂(Ti), (4)The oxygen content of (Ba, Sr)TiO₃ phase fairly decreased with increasing TiO₂(Ti) content. (5)The densification and grain growth of the compact with 5-7vol% TiO₂(Ti) hardly occured by the sintering. (6)The mechanism for the development of PTCR characteristic by the addition of TiO₂(Ti) was discussed, based on Heywang-Jonker's model.