Microstructure and electrical properties of (1 - x)[0.82Bi_0.5Na_0.5TiO₃-0.18Bi_0.5K_0.5TiO₃]-xBiFeO₃ lead-free piezoelectric ceramics

(1 - x)[0.82Bi_0.5Na_0.5TiO₃-0.18Bi_0.5K_0.5TiO₃]-xBiFeO₃ lead-free piezoelectric ceramics (abbreviated as BNKT-BFx with x varying from 0 to 0.10 mol) were prepared by solid-state reaction process. Variation of the microstructure and piezoelectric properties of BNKT-BFx ceramics with BF content was investigated. The results indicated that the piezoelectric constant d₃₃, the planar electromechanical coupling factor k_p and mechanical quality factor Q_m varied with the BF amount. X-ray diffraction (XRD) analysis showed that the incorporated BF diffused into BNKT lattice to form a solid solution. Scanning electron microscope (SEM) also indicated that BF in high amount affected the microstructure. The morphotropic phase boundary (MPB) with rhombohedral and tetragonal coexistence for the ceramics lies in the range of x = 0-0.06 in (1 - x)BNKT-xBF system. The optimum values of d₃₃ and k_p are 122 pC/N and 0.317 at x = 0.04.