Phase transition sequence in Pb-free 0.96(K0.5Na0.5)0.95Li0.05Nb0.93 Sb0.07O3−0.04BaZrO3 ceramic with large piezoelectric response

The piezoceramic 0.96(K0.5Na0.5)0.95Li0.05Nb0.93Sb0.07O3−0.04BaZrO3 (KNLNS0.07-BZ), which shows large piezoelectric response (d33 ≈ 425 pC/N), has been considered as one of the promising Pb-free substitutions for Pb(Zr,Ti)O3. In this paper, we investigate the phase transition sequence for KNLNS0.07-BZ by employing the dielectric measurement, mechanical spectroscopy, as well as Raman spectroscopy. Two ferroelectric-ferroelectric transitions have been detected by inspecting anomalies in the spectra, indicating the existence of three ferroelectric phases. Moreover, in-situ X-ray diffraction study has been further performed on KNLNS0.07-BZ to identify the crystal structure for each phase. The result reveals that the phase sequence for KNLNS0.07-BZ evolves from tetragonal (T) to rhombohedral (R) via an intermediate orthorhombic (O) phase. And the piezoelectric-optimal region for KNLNS0.07-BZ locates on a T-O boundary rather than the previously reported T-R boundary. Strong piezoelectricity may stem from the easier polarization rotation on the T-O boundary with reduced polarization anisotropy.