Defect chemistry of donor-doped BaTiO with BaO-excess for reduction resistant PTCR thermistor applications - redox-behaviour.

The electrical conductivity of donor-doped BaTiO thermistor ceramics with excessive BaO revealing a reduction-persistent PTCR effect has been carefully examined depending on materials' composition and oxygen partial pressure at moderate temperatures between 973 and 1273 K. This thermal regime represents the range which is relevant for the realization of insulating grain boundaries in these electrically inhomogeneous ceramic materials through reoxidation. Based on the experimental results strong evidence for a general correlation between the PTCR characteristics, DC-conductivity and the herewith associated defect chemistry significant to thermistor applications is presented for the system (Ba, La)TiO, where m designates the BaO-excess (m≥ 1).