Composition induced structure evolution and large strain response in ternary Bi0.5Na0.5TiO3-Bi0.5K0.5TiO3-SrTiO3 solid solution

A ternary perovskite lead-free solid solution Bi0.5Na0.5TiO3-Bi0.5K0.5TiO3-SrTiO3 was designed and fabricated using a conventional fabrication process. The temperature and composition dependence of the ferroelectric, dielectric, piezoelectric, and electromechanical properties were systematically investigated, and a schematic phase diagram was established. The introduction of the SrTiO3 was found to induce a structure evolution from the ferroelectric rhombohedra to ergodic relaxor pseudocubic phases. At a critical composition with SrTiO3 of 0.15, large strain level of ∼0.25% was obtained under a moderate field of 4.4 kV/mm at 0.1 Hz and the normalized strain reached up to 585 pm/V. Through the combination of the X-ray diffraction results with the piezoresponse force microscopy analysis, the composition induced structure evolution process and intrinsic mechanism responsible for the large strain response were discussed. The large strain level also makes the system quite promising for application to “on-off” actuators.