| Owing to flexibility, low acoustic impedance, biocompatibility and easy processing, 0-3 type piezoelectric composite can be widely used in the field of hydrophone, ultrasonic sensors and so on. At present, the piezoelectric property of 0-3type piezoelectric composite is far less than piezoceramics, because ceramic phase uniformly distributed in the organic polymer materials, which resulted in low polarization. Therefore, it is an effective approach to improve 0-3 piezoelectric composite piezoelectric properties by enhancing its polarizability. This work mainly improved electrical and mechanical performance of 0-3 type piezoelectric ceramic/polymer composite by adjusting the ratio of different elements of the ceramic and the proportion of ceramic in composite materials based on previous work. Firstly,the lead lanthanum zironate titanate(PLZT) was synthesized by conventional solid reaction process based on the best performance of Zr/Ti. Then 0-3 PLZT/PVDF piezoelectric composite was prepared by tape casting, meanwhile regulated the percentage of ceramic phase to improve the electrical performance. The main results are shown below:(1) In the second chapter, lead-based perovskite structure of different Zr/Ti ratio(Pb0.96La0.04)(Zrx Ti0.975-x Al0.025)0.99O3(PLZT, x=0.535, 0.538, 0.540, 0.543, 0.545,0.548) piezoelectric ceramics have been prepared by a conventional solid reaction process. In a series of PLZT, we adjusted different Zr/Ti near the same phase boundary(MPB). With the increasing of Zr/Ti, the phases of PLZT ceramics shift from rhombohedral phase to tetragonal phase, meanwhile grain size of PLZT ceramic phase, the relative dielectric constant εr and dielectric loss tanδ constantly increasing.When Zr/Ti>0.543/0.432, Curie temperature increased rapidly. d33 and Kp increased to the maximum(465 p C/N and 0.76) at Zr/Ti =0.543/0.432 and then decreased, whileεr and tanδ kept increasing.(2) The third chapter is based on Zr/Ti of the best integrated piezoelectric properties and mechanical properties in the second chapter, and we still adopted the solid reaction process to prepare(Pb1–x Lax)(Zr0.543Ti0.432Al0.025)1–x/4O3(PLZT, x=0.01,0.02, 0.03, 0.04, 0.05, 0.06) piezoelectric ceramic by adjusting La content in PLZT. With the increasing of La content, the phases of PLZT ceramics shift from rhombohedral phase to tetragonal phase, morphotropic phase boundary(MPB) shift to tetragonal phase, the crystal cell parameters increase gradually. Curie temperature decreased to the minimum(170 ℃ at x=0.02) and then increased rapidly. εr increased at first then decreased, tanδ kept decreasing. After studying the impact of different sintering temperature on electrical properties of PLZT piezoelectric ceramics, it proved that appropriate elevated temperature was beneficial to the growth of the grain and material density or other comprehensive performance.But too high sintering temperature made Pb O volatilization, which caused material defects and the decline of comprehensive performance. Finally we determined experiment scheme of the best comprehensive properties of PLZT piezoelectric ceramics. Experiment formula:(Pb0.98La0.02)(Zr0.543Ti0.432Al0.025)0.995O3,sintering temperature: 1310 ℃/2 h, electrical properties: εr=1850, d33=495, Kp=0.767,tanδ=0.017.(3) In the fourth chapter, tape casting was adopted to recombine PLZT piezoelectric ceramics powder and organic polymer PVDF, after hot-pressure treatment, high density composite material with no obvious bubbles in compounds.In this chapter we studied the impact of different ceramic phase ratio to the performance of 0-3 type piezoelectric composite material. With the increase of ceramic phase, the piezoelectric and dielectric properties increased, but too high ceramic phase will lead the pores, defects, cracks in the interface of the composite material, which was unfavorable to the polarization and final comprehensive performance of electric composite material. |
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