コアシェル構造ナノ粒子を用いた無鉛ＰＴＣ素子の開発

抄録

BaTiO₃-（Bi_1/2Na_1/2）TiO₃ （BT-BNT） positive temperature coefficient of resistivity （PTC） ceramics were successfully prepared by a wet-chemistry route. With 2 mol％ BNT addition, the obtained BT-BNT ceramics had semiconductivity and exhibited a PTC behavior at about 155℃ . The onset temperature of the PTC effect increased to 165℃ for the 4 mol％ BNT added samples. Room-temperature resistivity rRT increased with the content of BNT added and the ceramics changed from a semiconductor to an insulator, which was consistent with the variation of the microstructure. The temperature of resistivity anomaly in BT-BNT ceramics also increased with increasing BNT content. A small amount of manganese （Mn） dopant was found to improve the PTCR effect in the BT-BNT system. The possible mechanism underlying the PTCR effect in BTBNT ceramics was proposed. We also observed PTC effect on the 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℃. 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.