Composition‐induced structural transitions and enhanced strain response in nonstoichiometric NBT‐based ceramics

Abstract

AbstractIn this work, the nonstoichiometric 0.99Bi0.505(Na0.8K0.2)0.5‐xTiO3‐0.01SrTiO3 (BNKST(0.5‐x)) ceramics with x=0‐0.03 were synthesized by conventional solid‐state reaction method. The composition‐induced structural transitions were investigated by Raman spectra, dielectric analyses, and electrical measurements. It is found that the relaxor phase can be induced through the modulation of the (Na, K) content. The (Na, K) deficiency in BNKST(0.5‐x) ceramics favors a more disordered local structure and can result in the loss of long‐range ferroelectricity. The x=0.015 critical composition possesses relatively high positive strain Spos of 0.42% and large signal piezoelectric constant d33* of 479 pm V−1 at 6 kV mm−1, along with the good temperature (25‐120°C) and frequency (1‐20 Hz) stability. The recoverable large strain responses in nonstoichiometric ceramics can be attributed to the reversible relaxor‐ferroelectric phase transition, which is closely related to the complex defects (, , and ) and the local random fields. This work may be helpful for the exploration of high‐performance NBT‐based lead‐free materials by means of A‐site compositional modification.