Structure, microstructure and electrical properties of (1 − x − y)Bi0.5Na0.5TiO3-xBi0.5K0.5TiO3-yBi0.5Li0.5TiO3 lead-free piezoelectric ceramics

The ternary system (1 − x − y)Bi0.5Na0.5TiO3-xBi0.5K0.5TiO3-yBi0.5Li0.5TiO3 (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 Tm (the temperature at which dielectric constant ɛr reaches the maximum) increase. With the addition of Bi0.5K0.5TiO3, the remanent polarization Pr increased but the coercive field Ec decreased. With the addition of Bi0.5Li0.5TiO3, Pr increased obviously and Ec increased slightly. Due to the stronger ferroelectricity by modifying Bi0.5K0.5TiO3 and Bi0.5Li0.5TiO3, the piezoelectric properties were enhanced at x = 0.22 and y = 0.10, which were as follows: Pr = 31.92 μC/cm2, Ec = 32.40 kV/cm, ɛr = 1118, tan δ = 0.041, d33 = 203 pC/N and Kp = 0.31. The results show that the BNKLT-x/y ceramics are promising candidates for the lead-free materials.