Oxygen loss, semiconductivity, and positive temperature coefficient of resistance behavior in undoped cation-stoichiometric BaTiO3 ceramics -: art. no. 094102

Stoichiometric BaTiO3 ceramics fabricated from sol-gel-derived powders and sintered at temperatures <= 1100 degrees C are highly insulating and electrically homogeneous. At higher sintering temperatures, samples gradually lose oxygen and the conductivity increases as a consequence. The latter phenomena are very sensitive to the furnace atmosphere and are partially reversible during cooling when partial reoxidation can occur. This results in ceramics that are often electrically heterogeneous with insulating surfaces or grain boundaries but semiconducting grain cores. In samples that were heated at 1450 degrees C in N-2 and quenched, a positive temperature coefficient of resistance (PTCR) effect was observed, associated with an additional impedance arising from space-charge effects. These results demonstrate that, depending on sample processing, insulating cation-stoichiometric BaTiO3 can instead be semiconducting and under certain circumstances, exhibit a PTCR effect, without the need for donor dopant additives.