The Composition and Temperature‐Dependent Structure Evolution and Large Strain Response in (1− x )( Bi _0.5 Na _0.5 ) TiO ₃ − x Ba ( Al _0.5 Ta _0.5 ) O ₃ Ceramics

Abstract

The (1− x ) ( Bi 0.5 Na 0.5 ) TiO 3 − x Ba ( Al 0.5 Ta 0.5 ) O 3 ((1− x ) BNT ‐ x BAT ) lead‐free piezoceramics was fabricated using a conventional solid‐state reaction method. The temperature and composition‐dependent strain behavior, dielectric, ferroelectric (FE), piezoelectric, and pyroelectric properties have been systematically investigated to develop lead‐free piezoelectric materials with large strain response for actuator application. As the BAT content increased, the FE order is disrupted resulting in a degradation of the remanent polarization, coercive field, and the depolarization temperature ( T d ). A large strain of 0.36% with normalized strain d 33 * = 448pm/V was obtained for the optimum composition x = 0.045 at room temperature. The bipolar and unipolar strains for the compositions x = 0.035 and x = 0.04 reach almost identical maximum values when the temperature is in the vicinity of their respective depolarization temperature ( T d ). The Raman‐spectra analysis, macroscopic properties, thermal depolarization results, and temperature‐dependent relationships of both polarization and strain demonstrated that the origin of the large strain response for this investigated system is attributed to a field‐induced relaxor to FE phase transformation.