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

Lead free positive temperature coefficient of resistivity (PTCR) thermistors with switching temperature T-S of 155 degrees C were synthesized from 0.95BaTiO(3)-0.05(Bi1/2K1/2)TiO3 solid solution for high temperature applications, utilizing the conventional ceramic fabrication technique, which involved sintering ceramics in N-2 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. (C)2013 The Ceramic Society of Japan. All rights reserved.