Low-temperature sintering of BaTiO3-based semiconducting ceramics using sodium vapor

Abstract

Semiconducting BaTiO3-based ceramics for positive temperature coefficient (PTC) thermistors have conventionally been sintered at ∼1400°C in a reducing atmosphere. In the present study, sintered BaTiO3-based semiconductor ceramics were obtained by exposing green compacts of BaTiO3 powder to Na vapor in an Ar atmosphere. The Na vapor functioned as both a reducing agent and a sintering accelerator. Densification and grain growth of BaTiO3 proceeded during heating at 800°C or higher. PTC thermistor properties with 1.9 orders of magnitude were observed at temperatures near the Curie temperature of BaTiO3 (120°C). Contamination of sodium in the BaTiO3-based ceramics was rather small (∼ 0.2 wt%) and tiny areas containing Na were found in some of the fracture surfaces of ceramics.