LiTaO_3掺杂对K_(0.5)Na_(0.5)NbO_3基无铅压电陶瓷性能的影响

Effects of LiTaO_3 addition on electric properties of K_(0.5)Na_(0.5)NbO_3 ceramics

采用传统陶瓷工艺制备了LiTaO3掺杂的K2.5Na0.5NbO3基无铅压电陶瓷（记为KNN＋xLT，x=0～8%（摩尔分数）），并研究了陶瓷的晶相、显微结构和压电、铁电等性能。研究结果表明，KNN＋xLT陶瓷的正交相-四方相准同型相界（MPB）位于4％〈x〈6％处。随着LiTaO3含量的增加，陶瓷的正交→四方结构相变温度（RT）向低温方向移动，而四方→立方结构相变温度（t）向高温方向移动。陶瓷的压电常数d33和机电耦合系数kp随LiTaO3含量的增加均先增大后减小，而剩余极化强度P1则随之逐渐减小，矫顽场Ec逐渐增大。当x=6%时，陶瓷具有较好的压电和铁电性能：d33=190pC／N，kp=40．0％，Pr=22．0μC／cm^2，Ex=1.78kV／mm，Tc=440℃。该体系陶瓷具有较高的压电常数和比较大的平面机电耦合系数，是一种应用前景良好的压电铁电材料。

The LiTaO3 modified K0.5 Na0.5 NbO3 （abbreviated to KNN ＋xLT, x = 0-8mol % ） lead-free piezoelectric ceramics have been synthesized by the conventional ceramic fabrication technique. The effects of LiTaO3 addition on the crystalline phase, microstructure, piezoelectric and ferroelectric properties of the ceramics were investigated. The results show that the morphotropic phase boundary（MPB） between orthorhombic and tetragonal phases in KNN＋xLT ceramics appears to be at 4 % 〈x〈6 %. With increasing the LiTaO3 amount, the phase transition temperature（TO-T） of orthorhombic to tetragonal decreases while the Curie temperature Tc increases in the dielectric constant-temperature curves. In addition,the remanent polarization decreases and the coercive filed increases with increasing the amount of LiTaO3. At x=6% ,the optimal electric properties were obtained：piezoelectric constant d33 = 190pC/N, planar electromechanical coupling factor kp =40.0 %, remanent polarization Pr = 22.0μC/cm^2 ,coercive filed Ec = 1.78kV/mm, and the curie temperature Tc = 440℃ respectively. The results show that the ceramics are good candidates for lead-free piezo-and ferroelectric materials because of their larger piezoelectric and planer electromechanical coupling coefficients.