Lead free PTCR ceramics and its electrical properties

摘要

Lead free positive temperature coefficient of resistivity (PTCR) ceramics based on BaTiO_3-(Bi_(1/2)Na_(1/2))TiO_3 (BT-BNT) solid solution were prepared by a conventional solid state reaction method using high purity reagents. Temperature dependence of the electrical resistivity was measured and a typical PTCR effect was confirmed in the solid solutions up to 30mol percent addition of BNT. Especially 8.8mol percent BNT added sample indicated superior PTCR properties by optimizing the preparation conditions. Thermal electrical properties and crystal structure were investigated in order to elucidate the origin of the PTCR effect in this system. The DSC spectra of this system indicated the transition to cubic from tetragonal crystal structure and the transition temperature increased with BNT addition up to about 175 deg C. Also the boundary layer on the grains was observed by Scanning Spreading Resistance Microscope (SSRM) technique. And then the broad signal of electron emission concerning the interface states was observed using Isothermal Capacitance Transient Spectroscopy (ICTS) technique. In our study, it was found that the PTCR ceramics in BT-BNT system has extremely similar properties to the conventional lead contained one.