Study On BMT-PT Based Piezoelectric Ceramic

(1-x)Bi(Mg_1/20Ti_1/2O₃–xPbTiO3 piezoelectric ceramics were prepared by conventional solid solution method. The properties nearby the Morphotropic phase boundary (MPB), the effects of Mg/Ti ratio, the choosing of polarization condition and the effects of MnO₂ doping were discussed by phase analyzing using X-ray diffraction (XRD), Microstructure observation using the scanning electronic microscope (SEM) and dielectric, piezoelectric properties analyzing.The effects of PT content on the system were studied. The MPB lay in a broad composition region. The c/a ratio increased with the enhancement of PT content, as a result, the rhombohedral phase transforms into tetragonal phase gradually. The dielectric peak moved to right, which indicates the increase of Curie temperature. When sinter temperature was 1025℃, the optimum properties of d33=196pC/N,K_p=29.5%,ε^T₃3/ε0=1006,tanδ=4.3%,Tc=480℃were obtained with x=0.4.The effects of Mg/Ti ratio and sintering temperature on the properties of the system were studied on the basis of 0.6Bi(MgyTiz)O3–0.4PbTiO3. When sinter temperature was 1075℃, the optimum properties of d33=190pC/N,K_p=30.2%,ε^T₃3/ε0=934,tanδ=3.9% were obtained. The optimum electric field was 4.5kV/mm. In addition, the effect of temperature on piezoelectric properties was also investigated. The piezoelectric properties can be kept until 250℃without any decrease and there was only a little decrease between 250℃～350℃, decreased from 192pC/N to 164pC/N, which indicates that this system has a potential applications.The effects of MnO₂ doping on 0.6Bi (Mg_1/20Ti_1/2O₃–0.4PbTiO3 system were studied by mixing dopant and other raw materials altogether. When MnO₂ addition was lower than 1mol%, Mn2+ ion dissolved into the perovskite structure, which lead to the transformation of tetragonal phase, formation of internal bias filed which can stable spontaneous polarization and increase of Curie temperature; when MnO₂ addition was higher, excess Mn2+ ions accumulated at the grain boundaries. When sinter temperature was 1050℃, MnO₂ addition was 1mol%, the optimum properties of d33=112pC/N,K_p=22.5%,ε^T₃3/ε0=734,tanδ=1.96%,Tc=511℃were obtained. KEY WORDS:piezoelectric ceramics, high Curie temperature, Morphotropic phase boundary, MnO₂ doped.