Tuning the dielectric, ferroelectric, and energy storage properties of Ca-substituted Na0.5Bi0.5TiO3 perovskites synthesized via the molten salt method

Abstract

In recent years, dielectric capacitors based on ferroelectric compounds have attracted great interest as energy storage materials. Solid solutions based on Na_0.5Bi_0.5TiO₃ (NBT-based) exhibit relatively high polarization and are considered promising dielectric energy storage materials. We have prepared (Na_0.5Bi_0.5)_1-xCa_xTiO₃ ceramics (x = 0, 0.125, and 0.25) by the molten salt method and investigated their structures, dielectric properties, and energy storage properties. The structural refinement using the Rietveld method reveals overall structural distortions in all samples, including A-site shifting, TiO₆ octahedral distortion, and Ti–O–Ti tilting, which result in a non-centrosymmetric structure responsible for the observed ferroelectric properties. With the increase in Ca²⁺ content, the grain size and maximum dielectric constant gradually decrease. Furthermore, the peak of the maximum dielectric constant (T_m) shifts to lower temperatures, indicating the enhancement of polarization dynamics. As a result, optimum properties are identified in (Na_0.5Bi_0.5)_0.75Ca_0.25TiO₃ (x = 0.25) with a recoverable energy density of 9.938 mJ/cm³ and an outstanding energy efficiency of 80.8 % at a low electric field of 25 kV/cm. A ferroelectric polarization measurement at 150–190 °C for samples with x = 0.25 showed an increase in the values of P_m, W_rec, and ƞ is stable at high temperatures. This indicates that the energy storage material has good thermal stability at high temperatures.