Study On Barium Strontium Titanate And Potassium Sodium Niobate Based Lead-free Piezoceramics

Lead based piezoelectrics, represented by Pb(Zr,Ti)O3(PZT), are widely used for piezoelectric actuators, sensors and transducers due to their high-performance piezoelectric properties. However, with respect to legislation, lead is considered to be toxic and has been expelled from many commercial applications. Therefore, it is of crucial importance to find some lead-free counterparts of high environment compatibility and good piezoelectric properties. Recently, perovskite type lead-free ceramics, mainly based on K0.5Na0.5NbO3(KNN) and Ba0.8Sr0.2TiO3(BST), have been proposed as promising candidates to replace PZT piezoceramics in some special application fields. In this dissertation, following works are carried out:(1) Lead-free piezoceramics of (1-x)K0.5Na0.5NbO3-xBi0.8La0.2FeO3[(1-x)KNN-xBLF,0.005<x<0.04] were synthesized and investigated systemically. Structures of the ceramics were characterized by x-ray diffraction and transmission electron microscopy. X-ray diffraction patterns indicated the existence of an orthorhombic-tetragonal morphotropic phase boundary (MPB) near x=0.01. Highest electric performances were observed near the MPB, the maximum remnant polarization, piezoelectric coefficient, and coupling factor were measured to be22.5μC/cm2,144pC/N, and0.34, respectively. The effects of BLF on structures and electric properties were discussed.(2) Lead-free ceramics of (1-x)Ba0.8Sr0.2TiO3-xBiAlO3[(1-x)BST-xBA,(0<x<0.12)] had been synthesized and the structures and properties had been investigated systemically. X-ray diffraction patterns indicated that the solid solution limit was close to x=0.04, and a morphotropic phase boundary (MPB) separating tetragonal and pseudocubic phases existed near x=0.02. The ferroelectricity weakened monotonously with increasing x, accompanied by weakened butterfly shaped bipolar strain-electric field curves. The temperature dependent properties of the composition with x=0.02had been typically investigated, showing that with increasing temperature, the ferroelectricity tended to be weakened. Pure electrostrictive effect had been found in the compositions with x=0.02and0.03close to room temperature temperature. Based on the results, the effects of BA on structures and electric properties were discussed.