Study Of PLZT Piezoelectric Ceramics

Lead lanthanum zirconnate titanate (denoted as PLZT) ferroelectric ceramics exhibits excellent ferroelectric, pyroelectric and piezoelectric properties. It constitutes a broad category of compositions ranging from those best suited for piezoelectric applications to those specifically designed for pyroelectric devices. In this paper, Pb_0.93La_0.07(Zr_0.6Ti_0.4)_0.9825O₃ (denoted as PLZT7/60/40) piezoelectric ceramics were prepared by conventional mixed-oxide method(CMO) and the processing parameters such as calcining temperature, sintering temperature, PbO content and oxidation treatment were firstly investigated. At the basis of the above result, effects of La content and dopants of CeO₂ and Nb₂O₅ on phase structure, microstructure, dielectric and piezoelectric properties of the system were studied in detail. Comparing with the CMO method, PLZT7/60/40 piezoelectric ceramic samples were also fabricated by hot-pressing technique.The study on the processing parameters indicated that the formation of PLZT solid solution was promoted by increasing calcining temperature. And with increasing the sintering temperature, the bulk density, dielectric and piezoelectric properties of the ceramic increased at first and then decreased. In order to get better piezoelectric properties, effects of rich lead and oxidation treatment on the electrical properties were studied. The results showed that both density and electrical properties of the ceramic were enhanced by adding appropriate excess lead. And at an excess of 1.0wt% PbO, the electrical properties parameters wereε_r=3190, tgδ=1.79%, d₃₃=623pC/N, K_p=0.58, Q_m=68. The properties of the ceramic didn't change after two hours oxidation treatment under 850℃.The study of the effects of La content on phase structure, microstructure and electrical properties of the system indicated that the system transformed from the rhombohedral phase to tetragonal phase with increasing La content. It also showed that d₃₃ and K_p first increased and then decreased and Q_m showed the opposite trend with the increase of La content. When the La content was 7mol%(denoted as PLZT7/60/40), better piezoelectric properties of the system were obtained. Based on the system PLZT7/60/40, two dopants of CeO₂ and Nb₂O₅ were added to the system respectively. The results indicated thatε_r,d₃₃ and K_p obviously increased after adding CeO₂. Besides,ε_r,d₃₃ and K_p firstly increased and then decreased and Q_m showed the opposite trend with increasing CeO₂ content . The dopant of Nb₂O₅ had the same effects as CeO₂, but with the increase of Nb₂O₅ content,ε_r,d₃₃ and K_p still increased. When the doping content of Nb₂O₅ was 0.6wt%, the property parameters wereε_r=5753, tgδ=2.27%, d₃₃=789pC/N, K_p=0.63, Q_m=37.The results of the hot-pressed ceramics showed that hot-pressed technique can reduce the sintering temperature and increase the density of the ceramic. High density ceramics (99% of the theoretical value) were obtained by hot-pressing at 1025℃and 60Mpa. Besides,ε_r, K_p and d₃₃ obviously increased comparing to the traditional ceramic formation technique.