Structure and piezoelectric properties of Bi0.5Na0.5TiO3–Bi0.5K0.5TiO3–BiFeO3 lead-free piezoelectric ceramics

Lead-free piezoelectric ceramics (1 − x − y)Bi0.5Na0.5TiO3–xBi0.5K0.5TiO3–y BiFeO3(abbreviated as (1 − x − y)BNT–xBKT–yBF, with x = 0.12–0.24, y = 0–0.07) were studied, and effects of amount of Bi0.5K0.5TiO3 and BiFeO3 on structure and electrical properties were examined. An obvious change in crystalline structure and microstructure with the increase of KBT and BF concentrations was observed. The morphotropic phase boundary (MPB) between rhombohedral and tetragonal locates in the range of 0.18 < x < 0.21 and 0 < y < 0.05 in (0.97 − x)BNT–xBKT–0.03BF and (0.82 − y)BNT–0.18BKT–yBF systems, respectively. The piezoelectric constant d33 and the electromechanical coupling factor kp of the ceramics attain maximum values of 170 pC N−1 and 0.366 at x = 0.18 and y = 0.03. The mechanisms of intrinsic and extrinsic contributions to piezoelectric properties for the ceramics were discussed.