Dielectric and Piezoelectric Properties of Bi0.5K0.5TiO3-BaNb2O6 Lead-Free Piezoelectric Ceramics

Abstract

Lead-free piezoelectric ceramics (1 − x)Bi0.5K0.5TiO3-xBaNb2O6 [(1 − x)KBT-xBN] with x ranging from 0 to 0.03 have been synthesized by a conventional solid-state reaction method. The effects of BaNb2O6 addition on the crystal structure, microstructure, and dielectric and piezoelectric properties of the Bi0.5K0.5TiO3 ceramic were investigated. In the studied composition range, the x-ray diffraction patterns revealed that single perovskite phase formed in specimens with x < 0.03 and a trace secondary phase could be detected for x = 0.03. A morphotropic phase boundary separating rhombohedral and tetragonal phases was identified in the range of x = 0.01 to 0.02, where the optimum dielectric and piezoelectric properties were achieved with values of dielectric constant e = 2960, piezoelectric constant d33 = 96 pC/N, electromechanical coupling factor kp = 17.8%, and mechanical quality factor Qm = 150. Dielectric study revealed that all samples showed diffuse phase-transition characteristics. Furthermore, polarization–electric field (P–E) hysteresis loops were of slim-loop type with small remanent polarization values for all compositions. The related physical mechanisms for the enhancement of dielectric and piezoelectric properties are discussed. The results demonstrate a tremendous potential of the studied system for use as lead-free piezoelectric ceramics.