Preparation And Characterization Of PST-based Relaxor Ferroelectric Ceramics

In this thesis, relaxor ferroelectric ceramics (1-x)Pb(Sc1/2Ta1/2)O3-xPbTiO3 (PSTT) and xPb(Sc1/2Ta1/2)O3-yPbTiO3-zPbZrO3(PSTZT) with B-site ions was prepared by one-step sintering method. The properites of PSTT and PSTZT ceramics were analyzed, researched and compared deeply by XRD, SEM, etc., including crystalline, micostructure, dielectric, piezoelectric, pyroelectric and ferroelectric properties. In this paper, our work includes:1,PSTT ceramics with pure perovskite phase were obtained by one-step sintering method and sintered at 1250℃. The content of perovskite phase of PSTT ceamics was affected by PT content. At the same sintering temperature and time, the higher the PT content was, the purer the perovskite phase of PSTT ceramics was. Appropriate excess PbO is helpful to obtain the pure perovskite phase of PSTT ceramics.2,Reletive dielectric constant of PSTT ceramics prepared by one-step sintering method could achieved 2500~3000 at room temperature and 1kHz, and its dielectric loss at room temperature was lower, about 0.01 to 0.03. The highest peak dielectric constant was nearly to 20000. The crystalline and piezoelectric properties of PSTT(x) indicate that the MPB are close nearly to PSTT(45), because there was d33 of about more 450 pC/N and kp of about 0.58 at x=0.45. The pyroelectric coefficient of PSTT(45) was about 3.4×10-8C/cm2·K.3,Two different processing (isostantic processing and ordinary processing) were also used to prepare PSTT ceramics in this dissertation. The properties of PSTT ceramics prepared by using the isostantic processing were superior to those of PSTT ceramics prepared by using ordinary processing. It had been found that the best piezoelectric constant d33=546pC/N and elecromechanical coupling facor kp=0.62 of PSTT ceramics prepared by isostantic processing, however, the best d33 =446pC/N and kp=0.5798 of PSTT ceramics prepared by using ordinary processing.4,PSTZT ceramics with high content of perovskite phase were prepared by one-step-sintering-mothed. It was found that the MPB of the PSTZT50 system lies in the range of PZ=0.75~0.78. The best properties of the PSTZT50 ceramics were that d33=324 pC/N and kp=0.52 at PZ=0.78. But in PSTZT54 system, no apparent d33 peaks could be observed when PZ content changed and d33 value fluctuated without abrupt jump at about 60pC/N.5,Pinched hysteresis loops were founded in PSTZT ceramics when x =0.83～0.93. This is due to the pinned domain walls of the dipolar defects, and the Sc3+ and Ta5+ ions maybe substituted for the Ti4+ and Zr4+ ions in B site of PZT system. The results show the normal domain rotation is impeded by the slow response of defect dipoles, which leads to unsaturated loop, but the impurities pinning could be removed through rising temperature and decrease the freqency.