Bulk and conductive mode investigations of Pb free PTCR ceramics with high switch temperature

Abstract

Lead free positive temperature coefficient of resistivity (PTCR) thermistors with switching temperature T_S of 155°C were synthesized from 0.95BaTiO₃–0.05(Bi_1/2K_1/2)TiO₃ solid solution for high temperature applications, utilizing the conventional ceramic fabrication technique, which involved sintering ceramics in N₂ flow followed by air annealing. Addition of sintering aid AST (Al₂O₃:SiO₂:TiO₂ with 4:9:3 molar ratio) and Mn improved the bulk PTCR response. Impedance spectroscopy analysis confirmed the bulk T_S and revealed a third ferroelectric resistance-capacitance (RC) element along with a semiconducting grain and PTCR active ferroelectric grain boundary. The investigation of local electrical activity adopting hot-stage conductive mode microscopy revealed the existence of type-I grain boundary-electron beam induced current (GB-EBIC) contrast pertinent to the presence of negatively charged interfaces neighbored with compensating positive space-charge layers typical of double Schottky barrier within the Pb free PTCR system.