Fabrication of High Curie-Point PTCR Materials Using Gd-Doped BaTiO₃-(Bi_1/2Na_1/2)TiO₃ System

Abstract

Fabrication of high Curie-point (Tc) PTCR materials using BaTiO₃ (BT) -(Bi_1/2Na_1/2)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 (ρ_RT) 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 ρ_RT of 1500 Ω・cm and PTCR jump of 4.6 orders of magnitude with Tc about 180℃.