Impedance and dielectric spectroscopy analysis of high TC lead-free BaTiO3-(Bi1/2Na1/2)TiO3 positive temperature coefficient resistivity ceramics

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 PTCR effect takes place. Finally, the room-temperature resistivity of the BBNT8 is studied by measuring the permittivity-frequency characteristics.