Electric field induced intermediate phase and polarization rotation path in alkaline niobate based piezoceramics close to the rhombohedral and tetragonal phase boundary

High resolution synchrotron x-ray and dielectric measurements on unpoled and poled (Na,K)(Nb,Sb)O3-LiTaO3-xBaZrO3 lead-free ceramics close to the rhombohedral-tetragonal (R-T) phase boundary have suggested an additional lattice distortion induced by poling field. This intermediate phase (IP) is consistent with the orthorhombic (O) symmetry but lower symmetries cannot be discarded. As a result, a modified polarization rotation path along R-IP-T in poled ceramics would be responsible for their high piezoelectric activity owing to the effect of the IP bridging the R and T phases. Simultaneously, the electric field induced phase transition would probably contribute to the observed large piezoelectric strains.