Study On The Design And Mechanism Of The New System Of High Curie Temperature Piezoelectric Ceramics

Recent years, the rapidly expanding demand for piezoelectric actuators and sensors working under harsh environment, especially in the aerospace and automotive industries, has motivated a great deal of research interest for high temperature piezoelectric ceramics which has Curie temperature of much higher than 400℃. In this paper, on the basis of common high Curie temperature piezoelectric ceramic system, we originally proposed two new high Curie temperature piezoelectric ceramic PbTiNb2O8 and PbZrNb2O8. Secondly, studies LiYW2O8 doped PbTiO3 piezoelectric ceramics was studied. The relationship between the bond valence of O ions and the Curie temperature Tc, and the influence of the tetragonality on the dielectric properties and piezoelectric properties were investigated. Finally the double perovskite modified PbTiO3 piezoelectric ceramics were investigated. In order to obtain high Curie temperature piezoelectric ceramics, double perovskite modified PbTiO3 piezoelectric ceramics was fabricated, with the analysis in their phase transition, piezoelectric properties, and high temperature depolarization performance.The PbTiNb2O8 and PbZrNb2O8 ceramic samples were prepared via traditional solid phase reaction. With the sintering temperature of 1120℃ and 970℃, PbTiNb2O8 ceramics and PbZrNb2O8 ceramics have the highest Tc of 700.1 ℃ and 559.6℃, respectively. Crystal structure Space group of PbTiNb2O8 and PbZrNb2O8 ceramic were Amm2 and C222. The depolarization temperature of PbTiNb2O8 and PbZrNb2O8 ceramic were 560℃ and 480 ℃, respectively. The main electrical performance of PbTiNb2O8 and PbZrNb2O8 ceramics were:d33= 16pC/N, kp=0.11, Qm=102 and d33=20 pC/N, kp=0.16, Qm=42, respectively. Moreover PbTiNb2O8 and PbZrNb2O8 ceramics have rather low dielectric loss with～10-4.The PbTiO3-xwt% LiYW2O8 (x=0.05,0.15,0.25,0.35) piezoelectric ceramic were prepared by the two-step sintering method.To explore the structure origin of high Curie temperature Tc bond valence of oxygen ions was studied. The results showed that the higher the bond valence, the highter Curie temperature Tc. The Tetragonality is higher, the value of d33 and ε are also higher, and the value of Np is lower. The PbTiO3-0.15wt% LiYW2O8 ceramic has the highest Curie temperature (508℃).The double perovskite modified PbTiO3 piezoelectric ceramics was prepared by the two-step sintering method. The crystal structure of modified PbTiO3 had changed greatly with the addition of double perovskite. With the increase of ionic radius difference between impurity and PbTiO3, the crystal structure of modified PbTiO3 changed from Tetragonal (P4mm) to Orthorhombic (Pmm2), and became more ordered. Studies shown that the maximum point of the dielectric loss curves was related to the depolarization of piezoelectric ceramics, and the minimum point were related to the phase transition temperature below or at the Curie temperature. All modified PbTiO3 ceramics exhibit higher depolarization temperature, The depolarization temperature of PT-BFM. PT-BNM, PT-YNM and PT-SNM was 470℃,480℃,495℃,505℃, respectively.