Dual-chip Electrical Properties And Temperature Stability Of Piezoelectric Ceramics Pzt-pzn-of Pnn

In the recent years, the applications of piezoelectric ceramics have been extended from traditional sonar and ultrasound sections to almost every technological area, such as chip-type piezoelectric bimorphs. The use of piezoelectric bimorph micro-cantilevers (BMC) has become a fundamental technology in the field of micro-electromechanical systems (MEMS). For piezoelectric bimorphs to generate opposite strains in the thickness direction; piezoelectric bimorphs are configured to operate either in series or in parallel electrically. Under an applied electric field, a stress discontinuity is generated at the interface between two piezoelectric active layers, which produces bending moments and structural deformation. The ceramics suitable for the application of bimorphs should generate large displacement. It need the materials have high piezoelectric constant (d₃₃), high electromechanical coupling factor (k_p), low mechanical quality factor (Q_m),and the higher temperature stabilities of frequencies and electromechanical coupling factors, etc.In order to improve the electricial properties and the temperature stabilities of the PZT-PZN-PNN system, the effects of PZT and PNN contents, different Zr/Ti ratios, and the addition of the fifth component PMW on the phase structure, microstructure, electrical properties and their temperature stability of PZT-PZN-PNN based ceramics are investigated in this work.Firstly, PZT-PZN-PNN ternary system piezoelectric ceramics with the different PZT contents are successfully prepared by the conventional mixed-oxide method. The results reveale that the phase structure of all samples is pure perovskite phase. The dielectric studies indicate that the ceramics become more relaxor with decreasing PZT content to 0.81. The temperature coefficient of the relative dielectric content△ε_r/ε_r25℃ increases almost linearly with increasing the temperature when the temperature changes from -20 to 120℃.△ε_r/ε_r25℃ decreases gradually with the increasing of the PZT contents. In a word, the optimized piezoelectric properties are obtained when the PZT contents is 0.83: d₃₃=477 pC/N, k_p=0.71, Q_m=98, tanδ=0.0070 andε_r=2228.In addition, for PZT-PZN-PNN ternary systems when the PZT content is 0.83, the ceramics with different PNN contents are prepared by the conventional mixed-oxide method. The results reveales that the phase structure of all samples is pure perovskite phase. The dielectric studies indicate that that the ceramics become more relaxor with with increasing the PNN contents. The optimized piezoelectric properties are obtained when the PNN contents is 0.36: d₃₃=527pC/N, k_p =0.78, Q_m=122, tanδ=0.0060,ε_r =2465, andâ–³f_r/f_r25℃= 1.50% at 120℃.Besides, there are some reports which show materials whose composition far from the MPB in the tetragonal region has negative TCF. The changing of composition from T to R regions lead to the variation of the TCF from negative to positive. During the process, there is a composition (M) with the minimum TCF and the better electricial properties exisits. In order to find this composition, effect on Zr/Ti ratios on the electricial properties and temperature stabilities of PZT-PZN-PNN are investigated. The optimized system are obtained, which is as follows:0.83Pb(Zr_0.496Ti_0.504)O₃-0.17 {0.64Pb(Zn_1/3Nb_2/3)O₃-0.36Pb(Ni_1/3Nb_2/3)O₃}+0.3wt%CeO₂ +0.1wt%MnO₂. The values of d₃₃, k_p, Q_m tanδandε_r are 552 pC/N, 0.77, 70,0.0150,2659 and andâ–³f_r/f_{r25 888} = 1.03% at 120℃, respectively.Finally, in order to further improving the temperature stabilities and the electrical properties for the practical bimorphs applications, PMW is added to the system and another optimized composition is as follows:0.83Pb(Zr_0.480Ti_0.520)O₃-0.17(0.64Pb(Zn_1/3Nb_2/3)O₃-0.36Pb(Ni_1/3Nb_2/3)O₃)+ 1.60mol% Pb(Mg_1/2W_1/2)O₃ +0.3wt%CeO₂+0.1wt%MnO₂. This composition shows the optimized piezoelectric and dielectric properties, the values of d₃₃, k_p, Q_m tanδandε_r are 565 pC/N, 0.78, 89, 0.0066, 2523 and andâ–³f_r/f_r25℃=-0.32% at 120℃, respectively, which makes the ceramics with this composition to be very promising for the application of bimorphs.