High Tc lead-free BaTi O3 - (Bi12 Na12) Ti O3 positive temperature coefficient of resistivity ceramics with electrically heterogeneous structure

A distinct positive temperature coefficient of resistivity effect has been observed in BaTi O3 - (Bi12 Na12) Ti O3 (BT-BNT) ceramics sintered in a N2 flow with low O2 concentration. With the addition of BNT, the samples exhibit resistivity jumps of ∼ 103 - 105 starting at ∼190-210 °C. X-ray diffraction results indicate that the BNT phase and BT phase formed a solid solution during sintering. An electrically heterogeneous structure, consisting of the grain interiors, outer grain shells, and grain boundaries, is revealed by the complex impedance analyses. The observed dc resistivity jump is attributed to the rapid resistivity rise in both grain boundaries and grain shells.