Electrostrictive Effect In BaTiO₃ Based Ternary Ceramics And Bi_0.5Na_0.5TiO₃ Based Ternary Ceramics

With the expanding applications of piezoelectric/electrostrictive ceramics, the requirements of materials become much stricter. Although the performance of lead-based materials is very remarkable, the main ingredient of lead-materials is harmful to environment and human healthy, because it is volatile and toxic. At present, the production and sales of electronic components containing lead have been limited in some developed countries. Therefore, it is urgent to look for lead-free piezoelectric /electrostrictive materials with excellent performance. Much work has been done in the last decade on the development of lead-free piezoceramics, which is considered as the replacement for lead-zirconate-titanate (PZT) as the main material for electromechanical devices such as actuators, sensors, and transducers. In specific but narrow application ranges the new materials appear adequate, but are not yet well suitable to replace PZT on a broader basis. So research of lead-free piezoelectric/ electrostrictive materials with excellent performance will be a research hotspot in the related fields for a long time.Bi0.5Na0.5TiO3 based, BaTiO3 based and K0.5Na0.5NbO3 based lead-free piezoelectric ceramics are three kinds of materials that are the most widely used, respectively. We can improve the performance of these materials by a variety of methods such as ionic substitution, doping and multicomponent combination. In this dissertation, electrostriction of BaTiO3 based ternary ceramics has been investigated. Meanwhile, Bi(Zn0.5Ti0.5)03 has been introduced to the BNT-KNN system, electrostriction of Bi0.5Na0.5TiO3 based ternary ceramics also has been investigated.The main results are summarized as follows:1. BaTiO3-rich (0.94-x) BaTiO3-0.06Ko.5Nao.5NbO3-xBi0.5Nao.5Ti03 (x=0.05, 0.10,0.15,0.20,0.25,0.30,0.35) ternary ceramics were prepared by conventional solid solution methods. X-ray diffraction (XRD) pattern demonstrated that the samples have typical perovskite structures. SEM results revealed that BNT doping could increase grain size and compactness. The results of the piezoelectric and ferroelectric tests showed that the higher BNT content leads to larger maximum polarization and strain when x> 0.20. S-P2 profiles indicate the electrostrictive behaviors of all ceramics. The electrostrictive coefficient of the composition with x= 0.20 can reach 0.034 m4C-2. Relative dielectric constant (εr) and loss tangent (tanδ) show distinct ralaxor characteristic of all ceramics. Addition of BNT also results in the increasement of Tm.2. Bi0.5Nao.5Ti03-rich (0.9625-x)Bi0.5Nao.5Ti03-0.0375BiZno.5Tio.503-xK0.5Na0.5NbO3 (x=0,0.05,0.10,0.15,0.20,0.25) ternary ceramics were prepared by conventional solid solution methods. X-ray diffraction (XRD) patterns indicate typical perovskite structures of all ceramics. SEM results reveale that the ceramics is comprised of cubic-like grains and KNN doping could lead to smaller grain size. The results of electrical properties tests show that the addition of KNN could lead to depolarization of the system more easly. The S-P2 curves for the composition with x=0.20 and 0.25 are linear while other composition are deviated from liner relation. It indicates that ceramics start to show electrostrictive characteristics when KNN content reached a certain value. The electrostrictive coefficient with x=0.25 was calculated to be 0.032 m4C-2. Relative dielectric constant (εr)and loss tangent (tan8) show distinct ralaxor characteristic of all ceramics, and lower Tm, lower Td, better temperature stability with more KNN addition.