Significantly reduced hysteresis in (Fe1/2Nb1/2)4+-modified 0.75Na1/2Bi1/2TiO3-0.25SrTiO3 lead-free piezoceramics with large strain

Aiming to get the NBT-based lead-free ceramic with high strain and low strain hysteresis for practical actuator applications, a solid solution of complex-ion (Fe_1/2Nb_1/2)⁴⁺doped 0.75Na_1/2Bi_1/2TiO₃-0.25SrTiO₃ ((Na_1/2Bi_1/2)_0.75Sr_0.25Ti_1-x(Fe_1/2Nb_1/2)_xO₃, abbreviated as NBST-100xFN) was designed and prepared, and its phase structure, micromorphology, ferroelectric, strain, dielectric and piezoelectric performances were systematically investigated. It was found that the incorporation of (Fe_1/2Nb_1/2)⁴⁺ causes a structure transition from the ferroelectric/relaxor (FE/RE) mixed phases to relaxor (RE) phase, increasing to a promising strain performance at x = 0.04 featured by not only a moderate strain value of 0.26%, corresponding normalized strain d₃₃* of 371 pm/V, but also a very small strain hysteresis of 22%. In addition, the NBST-4FN ceramic sample also exhibits an unexceptionable frequency-dependence of unipolar strain. This study provides a new understanding and design idea for the practical actuator application of high strain NBT-based lead-free ceramics with ultra-low hysteresis.