Phase evolution and associated electrical properties of Al-doped KNN–Bi0.5Na0.5ZrO3 lead-free piezoelectric ceramics

Samples of Al-doped (1– x )K 0.5 Na 0.5 Nb 0.965 Sb 0.035 O 3 – x (Bi 0.82 Al 0.18 ) 0.5 Na 0.5 ZrO 3 [((1– x )KNNS– x BANZ)] ( x = 0.02, 0.03, 0.04, and 0.05) have been prepared by a conventional solid-state method. The results of XRD analysis suggest that the ceramics underwent a typical phase transition from orthorhombic (O) to tetragonal (T) as x was increased. According to the Raman shifts of key vibrational modes, lattice deformation and associated phase transition have been qualitatively deduced. Moreover, the ceramic with x = 0.05 exhibits enhanced piezoelectric properties compared with K 0.5 Na 0.5 NbO 3 due to an O-T phase boundary ( d 33 ≈ 258 pC/N and k p ≈ 0.40). More importantly, the mechanism through which small ions function in a KNN lattice, as well as the phase transition, is addressed herein. • The bending vibration of NbO 6 octahedra contributes to formation of a T phase at room temperature. • The many more polarization states in an O-T phase coexistence regime make a greater contribution to property enhancement than domain motion. • A large strain of about 0.13% (@30 kV/cm) was obtained for x = 0.05.