Investigations of domain switching and lattice strains in (Na,K)NbO3-based lead-free ceramics across orthorhombic-tetragonal phase boundary

Various strain contributions of (Na0.52K0.48 − x)(Nb0.92 − xSb0.08)O3− xLiTaO3 ceramics in the proximity of orthorhombic (O) and tetragonal (T) polymorphic phase boundary (PPB) were quantitatively resolved by means of synchrotron x-ray diffraction together with macroscopic strain measurements. Compared with O-rich compositions with a governing mechanism of intrinsic lattice strains, T-rich compositions exhibited a dominant strain mechanism from reversible domain switching. Quantitative analysis of diffraction data suggested that extrinsic strain contributions should depend on not only the lattice distortion δ, but also the poling texture Δf, phase content (for PPB compositions) and domain types. Smaller lattice distortion and higher poling texture tended to enhance the number of irreversible domain switching in O-rich compositions, thus leading to larger fraction of intrinsic lattice strain contribution. The calculated results demonstrated that the product of two parameters Δf and δ would give a reliable estimation of domain-switching strains for T-phase compositions but an overestimation for O-phase compositions.