Electric-field-induced strain contributions in morphotropic phase boundary composition of (Bi_1/2Na_1/2)TiO₃-BaTiO₃ during poling

The microscopic contributions to the electric-field-induced macroscopic strain in a morphotropic 0.93(Bi_1/2Na_1/2TiO₃)−0.07(BaTiO₃) with a mixed rhombohedral and tetragonal structure have been quantified using full pattern Rietveld refinement of in situ high-energy x-ray diffraction data. The analysis methodology allows a quantification of all strain mechanisms for each phase in a morphotropic composition and is applicable to use in a wide variety of piezoelectric compositions. It is shown that during the poling of this material 24%, 44%, and 32% of the total macroscopic strain is generated from lattice strain, domain switching, and phase transformation strains, respectively. The results also suggest that the tetragonal phase contributes the most to extrinsic domain switching strain, whereas the lattice strain primarily stems from the rhombohedral phase. The analysis also suggests that almost 32% of the total strain is lost or is a one-time effect due to the irreversible nature of the electric-field-induced phase transformation in the current composition. This information is relevant to on-going compositional development strategies to harness the electric-field-induced phase transformation strain of (Bi_1/2Na_1/2)TiO₃-based lead-free piezoelectric materials for actuator applications