Exploring high-entropy perovskites for high energy storage capacity

Abstract

Ferroelectric materials are of great interest due to their numerous technological applications such as capacitors, sensors and actuators. One of the most widely used materials, due to their great properties, are ceramics type PbZrxTi1-xO3 (PZT) -with perovskite structure-, nevertheless, their high toxicity caused by the presence of lead has prompted the development of new ferroelectric materials such as high entropy perovskites. High entropy perovskites contain five or more different cations in their composition that distorts the structure lattice, reducing the symmetry and obtaining interesting electrical properties. One of the promising lead-free ferroelectrics is Bi0.5Na0.5TiO3 (BNT), however, it presents drawbacks such as a high coercive field and a low electrical breakdown strength, preventing complete polarization. For this reason, over the past few years, high entropy perovskites based on BNT have attracted much attention and are expected to reveal exceptional electrical properties. In this research project, (Ba0.2Na0.2Bi0.2Ca0.2Sr0.2)TiO3 (BNBCST) and (Ba0.2Li0.2Bi0.2Ca0.2Sr0.2)TiO3 (BLBCST) compositions obtained by solid-state reaction were studied. Furthermore, in the case of BNBCST, the synthesis conditions were optimized, resulting the optimal conditions calcination at 1000 ºC for 10 h and sintering at 1200 ºC for 4 h by the conventional method. In addition, the novel microwave-assisted synthesis was studied, making it possible to reduce the synthesis time to 50 min, minimizing the loss of volatile elements. The subsequent characterization with X-Ray Diffraction and Energy Dispersive X-ray Spectroscopy confirmed the presence of a single phase in the BNBCST composition and a secondary minority phase in the case of BLBCST. By means of Impedance Spectroscopy and hysteresis cycles, the electrical behavior of both compositions was evaluated. In both cases it was observed a relaxor-type phase transition. The sodium composition synthetized by the microwave proves to be the best candidate for energy storage.