Preparation And Temperature Sensitivity Of(K_0.5Bi_0.5)TiO₃-and LaCrO₃-based Ceramics

The temperature-sensitive ceramic components have been widely applied in temperature compensation, temperature detection, temperature the control and suppressing the surge current. For high-temperature relaxation problem of Mn-Ni-Co and other transition metal oxides, and environmental pollution of lead-contained PTC materials,(K0.5Bi0.5)(Ti1-2xMoxMx)O3(M=Cu, x=0.01,0.02,0.06,0.065; M=Zn, x=0.02,0.04,0.06,0.08) and (La1-xSrx)(Cr1-xFex)O3(x=0,0.01,0.03,0.05,0.07) were prepared in order to study and explore the related temperature-sensitive characteristics. The powers were prepared by Steric Entrapment Synthesis (SES) mothed, and the ceramics were sintered by a conventional sintering process. The phases and microstructures of the prepared materials were investigated by X-ray diffraction and scanning electron microscope, the R-T characteristic of ceramics was measured and the conductivities were investigated by AC impedance measurement. The work is summaried as the following:1) The (K0.5Bi0.5)(Ti1-2xMoxMx)O3ceramics have a tetragonal perovskite-type structure. Compared with the curie temperature of K0.5Bi0.5TiO3, which is380℃, the (K0.5Bi0.5)(Ti1-2xMoxMx)O3ceramics have much lower curie temperatures. For example, the curie temperature of K0.5Bi0.5s(Ti0.88Cu0.o6Mo0.06)O3is155℃. It can indicate that Cu/Mo or Zn/Mo co-replaced Ti-crystalline site in the K0.5Bi0.5TiO3ceramic can significantly reduce the curie temperature.The (K0.5Bi0.5)(Ti1-2xMoxMx)O3ceramics show good property with positive temperature coefficient (PTC) characteristic. Through AC impedance measurement at different temperatures, the PTC characteristics related to both the grain effect and the grain boundary effect. Besides, changing the process of sistering and extending properly the sistering time can reduce the room temperature resistivity and improve the ratio of RMax/R25.Sistering at lower temperature for longer keeping time can improve the homogeneity of electrical resistivity of the prepared ceramics. 2) The R-T characteristic of (La1-xSrx)(Cr1-xFex)O3ceramics show good properties of negative temperature coefficient (NTC). The conduction activation energy changes at130℃, at which phase transition may take place as analyzed by DSC. The cramic sintering properties can be improved by adding some oxides. The resistance of ceramics can be reduced by being sintered at lower temperatures. The influence of glass phase content on R-T characteristic, sintering property and density of LaCrO3ceramics were also investigates.