Effect of A-site substitutions on energy storage properties of BaTiO₃-BiScO₃ weakly coupled relaxor ferroelectrics

Weakly coupled relaxors based on compositions (1-x) BaTiO₃-xBiMeO₃, where Me is a metal ion, have attracted attention as potential candidates for high-temperature high-energy density capacitors. However, the necessary Bi content is typically high with x = 0.3-0.4. In order to reduce problems associated with compatibility for base metal electrodes and due to additional problems due to Bi volatility, it is desirable to lower the Bi content in the overall composition for these materials. Here, we have explored a possible way to reduce BiMeO₃ content through additional A-site substitutions viz. Ca and Sn. The relaxor nature and energy storage properties of Sn-modified (Ba,Ca)(Ti)O₃-BiScO₃ ceramics were determined from their dielectric and ferroelectric behaviors. The material showed attractive properties in terms of a frequency-independent (200 Hz-1 MHz) dielectric response from room temperature to 200°C, extremely low loss and high-energy storage efficiency. The structural phenomena underlying the functional properties of Sn-modified (Ba,Ca)TiO₃-BiScO₃ are characterized from temperature-dependent X-ray diffraction and pair distribution function analysis. In broader terms, the study illustrates the potential for tailoring relaxor behavior in Pb-free ferroelectrics by combining phenomena, such as quantum fluctuations and lone pair stereochemical effect associated with different solid-solution substitutions.