高温无铅BaTiO_3-(Bi_(1/2)Na_(1/2))TiO_3正温度系数电阻陶瓷阻抗和介电谱分析

Impedance and dielectric spectroscopy analysis of high TC lead-free BaTiO_3-(Bi_(1/2)Na_(1/2))TiO_3 positive temperature coefficient resistivity ceramics

采用固相反应法制备了Y2O3施主掺杂的92 mol%BaTiO3-8 mol%(Bi1/2Na1/2)TiO3(BBNT8)高温无铅正温度系数电阻(positive temperature coe?cient resistivity,PTCR)陶瓷.利用透射电镜观察材料的显微结构,发现陶瓷的显微结构主要包括晶粒和晶界两部分,观察不到明显的壳层结构.进一步利用交流阻抗谱研究了陶瓷的宏观电学性能,发现陶瓷的总电阻是晶粒和晶界两部分的贡献,而晶粒电阻很小,在居里温度以上变化不大,材料的PTCR效应主要是晶界部分的贡献.当温度高于居里温度时,随着温度的升高,晶界介电常数逐渐减小,导致势垒增加,晶界电阻增大,从而产生正温度系数效应.最后,通过测试材料的介电频谱特性,研究计算了陶瓷的室温电阻率.

92 mol%BaTiO3-8 mol% （Bi1/2Na1/2）TiO3 （BBNT8） lead-free positive temperature coefficient resistivity （PTCR） ceramics doped with Y2O3 are prepared by the solid state reaction method. The microstructure of the sample is observed by transmission electron microscope. Results show that the microstructure of the sample mainly consists of grain and grain boundary, and no obvious shell structure is found. The electrical properties of the sample are further analyzed using the impedance spectroscopy. It is found that the total resistance of BBNT8 is composed of the resistances of grain and grain boundary. The resistance of grain is low and slightly changes with temperature when the temperature is above the Curie temperature. The PTCR effect of the material is mainly dominated by the grain boundary resistance. As the temperature increases up to above the Curie temperature, the grain boundary permittivity decreases, leading to the increase of the potential barrier height and the resistivity of the grain boundary. As a result, the distinct PTCReffect takes place. Finally, the room-temperature resistivity of the BBNT8 is studied by measuring the permittivity-frequency characteristics.