2018 年 67 巻 4 号 p. 474-478
Fabrication of high Curie-point (Tc) PTCR materials using BaTiO3 (BT) -(Bi1/2Na1/2)TiO3 (BNT) ceramics was investigated. Fine powders of BaTiO3, which was synthesized by thermal process, were used as starting materials. BaTiO3 powders, Bi2O3, Na2CO3, TiO2 and Gd(NO3)3 (water solution) were mixed with (C2H5O)4Si by wet milling for 24h. After drying, the powders were pressed into disks, which were a diameter at 20mm and thickness of 2mm. These disks were sintered in air at 1340℃ for 2h. Gd-doped 95 mol% BT-5 mol% BNT samples with 1.2 mol% of excess of Na2CO3 have low room-temperature resistivity (ρRT) in the range of Gd concentration from 0.08 to 0.1 mol%. Tc of the samples increased from 170℃ to 180℃ with an increase in the amount of BNT (5 to 8 mol%). As a result, 0.1 mol% Gd and 1.6 mol% of excess Na2CO3 doped 92 mol% BT-8 mol% BNT sample has ρRT of 1500 Ω・cm and PTCR jump of 4.6 orders of magnitude with Tc about 180℃.