EFFECT OF SOAKING TIME ON THE TEMPERATURE-COEFFICIENT OF RESISTIVITY OF SEMICONDUCTING BARIUM-TITANATE PTCR CERAMICS

The influence of soaking time at 1200 degrees C on the temperature coe fficient of resistivity (TCR) of semiconducting barium titanate cerami cs has been investigated. It is found that soaking duration has influe nce on the room-temperature resistivity, the maximum resistivity, the temperature (T-max) at which the maximum resistivity appears, and TCR of the positive temperature coefficient of resistivity (PTCR) ceramics . The increased room-temperature resistivity with the increase of soak ing time is contributed mainly by the increase of grain boundary resis tivity examined by the complex-plane impedance method. The obtained su rface acceptor density (N-s) by capacitance-voltage measurement is fou nd to increase with the soaking duration. The higher N-s contributes t o higher built-in potential and results in lower T-max and higher maxi mum resistivity. Therefore, the increased surface acceptor density fro m increasing the soaking time at 1200 degrees C increases the temperat ure coefficient of resistivity of PTCR ceramics.