Properties of non-stoichiometric PTCR ceramics

BaO- and TiO₂-rich BaTiO₃ (BT) ceramics were studied to disclose the relations among nonstoichiometry, phase formation, microstructure evolution and the positive temperature coefficient of resistance (PTCR) property. Both La³⁺ and Sb ³⁺ make BT ceramics semiconducting by way of A-site substitution. The available range of doping amount to obtain minimum resistivity increased with increasing TiO₂ excess up to 7 mol.%. The second phase for TiO₂ -rich compositions was Ba ₆Ti₁₇O₄₀ which promoted grain growth and increased conductivity. The elimination of the grain boundary in the grain growth controls the PTCR jump. Better crystalline BT grains were provided by increasing the sintering temperature and TiO₂ excess. For BaO-rich compositions, the second phase Ba₂TiO ₄ was formed and retarded grain growth. High resistivity (>10⁸ Ω-cm) was usually found. A nonstoichiometric composition with a slight TiO₂-rich content results in a better PTCR property