Preparation And Electrical Properties Of （1-x）Pb(Mg_1/3Nb_2/3)O₃-xPbTiO₃ Relaxor-based Ferroelectric Ceramics By Reaction-Sintering Method

Relaxor-based ferroelectric ceramics （1-x）Pb(Mg_1/3Nb_2/3)O₃-xPbTiO₃ （PMN-PT） exhibit excellent collective electrical properties and optical performance, which make them acquire broad applications in multi-layer ceramic capacitors, high-performance piezoelectric actuators and transducers, and optical devices.In this thesis relaxor-based ferroelectric ceramics （1-x）Pb(Mg_1/3Nb_2/3)O₃-xPbTiO₃ （PMN-PT） were prepared by the reaction-sintering method. The influences of sintering temperature and the content of PbTiO₃ （PT） on the phase structure, microstructure morphology, dielectric properties, ferroelectric properties and piezoelectric properties were studied systematically. X-ray diffraction （XRD） measurement confirms that phase-pure perovskite PMN-PT ceramics of all the composition can be prepared by the reaction-sintering method at certain sintering temperature range. Based on the integral analysis of microstructure, relative density and electrical properties of the sintered ceramics, the appropriate sintering temperatures for PMN-PT is determined as being 1240-1260℃. The content of PT exerts successive influences on the sintering capability, phase structure and electrical properties of the PMN-PT ceramics. With the increase of the PT content, the crystal structure of the PMN-PT ceramics changes from rhombohedral phase, across the coexistence of rhombohedral phase and tetragonal phase, and to tetragonal phase gradually, accompanied by the change from typical relaxor ferroelectrics to normal ferroelectrics. The morphotropic phase boundary of the PMN-PT system locates at x=0.3-0.34, where the ceramics with the MPB composition exhibit enhanced microstructure and excellent electrical properties, particularly superior piezoelectric properties. The 0.66PMN-0.34PT ceramics sintered at 1240℃exhibit the maximum value of d33, which is 715pC/N. The 0.7PMN-0.3PT ceramics sintered at 1260℃exhibit the maximum value ofεmax （1kHz）, which is 39351. The 0.8PMN-0.2PT ceramics sintered at 1270℃exhibit the maximum value of Pr, which is 39.07μC/cm².The sintering temperature of the PMN-PT ceramics prepared by the reaction-sintering method is relatively high, which leads to high production cost, rather serious evaporation of lead during sintering and deterioration of electrical properties. Therefore, the influences of sintering aids on the PMN-PT ceramics prepared by the reaction-method were studied in this thesis. The phase structure, microstructure morphology, and electrical properties of the WO3-, Sb2O3-, SrCO₃-, Li₂CO₃-, and CuO-doped 0.8PMN-0.2PT ceramics were studied in detail. All the WO3-, Sb2O3- and SrCO₃-doped 0.8PMN-0.2PT ceramics sintered at 1090-1150℃contain pyrochlore phase, and the sintered ceramics exhibit low relative density and poor electrical properties. For the Li₂CO₃- and CuO-doped 0.8PMN-0.2PT, pure perovskite structure ceramics can be obtained at relatively low sintering temperatures. The Li₂CO₃- and CuO-doped 0.8PMN-0.2PT ceramics sintered at 1090-1120℃exhibit high densification and excellent electrical properties indicating that such sintering aids are effectively in decreasing sintering temperature of the PMN-PT ceramics prepared by the reaction-sintering method. 3mol% CuO-doped 0.8PMN-0.2PT ceramics sintered at 1090℃exhibit the largest relative density and excellent integral electrical properties, where the relative density is 92.51%, and the values ofεmax （1kHz）, Pr and d33 are 23612, 22.54μC/cm² and 302pC/N, respectively. Therefore, CuO doping can decrease the appropriate sintering temperature of the PMN-PT ceramics prepared by the reaction-sintering method to 1090℃, proving that CuO is an efficient sintering additive.