Fabrication of High Curie-Point Lead-Free PTCR Materials Using Gd-Doped BaTiO₃-(Bi_1/2K_1/2)TiO₃ System

Abstract

Fabrication of high Curie point (Tc) PTCR materials using BaTiO₃ (BT)-(Bi_1/2K_1/2)TiO₃ (BKT) ceramics was investigated. Fine powders of BT, which was synthesized by hydrothermal process, were used as starting materials. BT powders, Bi₂O₃, KHCO₃, TiO₂ and Gd(NO₃)₃ (water solution) were mixed with (C₂H₅O)₄Si by wet milling for 24 h. After drying, the powders were pressed into disks, which were diameter of 20 mm and thickness of 2 mm. These disks were sintered at 1130 – 1280 °C for 2 h in air. The samples containing 5 – 7 mol% BKT have the room temperature resistivity lower than 600 Ωcm, PTCR jump higher than 2.4 order of magnitude, and Tc higher than 175 °C. Especially, the sample containing 6 mol% BKT has the room temperature resistivity of 270 Ωcm, PTCR jump of 2.4 order of magnitude, and Tc of 185 °C and it was the excellent high Tc lead-free PTCR materials which was fabricated by firing in air.