Structure, microstructure and electrical properties of (1-x-y)Bi_(0.5)Na_(0.5)TiO_3-xBi_(0.5)K_(0.5)TiO_3-yBi_(0.5)Li_(0.5)TiO_3 lead-free piezoelectric ceramics

摘要

The ternary system (1 - x - y)Bi_(0.5)Na_(0.5)TiO_3 -xBi_(0.5)K_(0.5)TiO_3 -yBi_(0.5)Li_(0.5)TiO_3 (abbreviated to BNKLT-x/y) was synthesized by conventional oxide-mixed method. The phase structure, microstructure, and dielectric, ferroelectric and piezoelectric properties of the ceramics were investigated. The X-ray diffraction patterns showed that pure perovskite phase with rhombohedral structure can be obtained in all the ceramics. The grain size varied with x and y. The temperature dependence of dielectric constant and dielectric loss revealed there were two phase transitions which were from ferroelectric (tetragonal) to anti-ferroelectric (rhombohedral) and anti-ferroelectric to paraelectric (cubic). Either increasing x or y content can make T_m (the temperature at which dielectric constant epsilon_r reaches the maximum) increase. With the addition of Bi_(0.5)K_(0.5)TiO_3, the remanent polarization P_r increased but the coercive field E_c decreased. With the addition of Bi_(0.5)Li_(0.5)TiO_3, P_r increased obviously and E_c increased slightly. Due to the stronger ferroelectricity by modifying Bi_(0.5)K_(0.5)TiO_3 and Bi_(0.5)Li_(0.5)TiO_3, the piezoelectric properties were enhanced at x = 0.22 and y = 0.10, which were as follows: P_r = 31.92 mu C/cm~2, E_c = 32.40 kV/cm, epsilon_r = 1118, tan delta = 0.041, d_(33) = 203 pC/N and K_p = 0.31. The results show that the BNKLT-x/y ceramics are promising candidates for the lead-free materials.