Polarization Stability and Its Influence on Electrocaloric Effects of High Entropy Perovskite Oxide Films

Abstract

In principle, the configurational entropy inherent in High Entropy Oxides (HEOs) could facilitate large electrocaloric effects (ECE) by promoting polar entropy. In this study, it is demonstrated that the time stability of the remanent polarization can be tuned via B-site disorder in High Entropy Perovskite Oxides (HEPO) films. Eight HEPO powders were synthesized; the propensity for perovskite phase formation was consistent with the Goldschmidt tolerance factor. While entropic contributions stabilize HEPO, they do not fully predict the stabilization. Relative dielectric permittivities between 2000 to 600 can be achieved for the B-site disordered HEPO films with loss tangents below 6% at room temperature. All films showed similar polarization-electric field loops with maximum polarization up to 48 $\mu \mathrm{C}$$\mu \mathrm{C}$ cm⁻² and a remanent polarization $\ge$$\ge$ 20 $\mu \mathrm{C}$$\mu \mathrm{C}$ cm⁻² measured at room temperature with applied electric field of 1100 kV cm⁻¹ at a frequency of 10 kHz. The temperature of the dielectric maximum (T_max) increased from 105°C to 225°C with increasing average ion size on the B-site. Polarization stability of the HEPO films was investigated using Positive-Up-Negative-Down (PUND) measurements. It was found that in some HEPO films, 24% of the remanent polarization decayed within 2 s. By employing the time stability of the remanent polarization, enhanced electrocaloric effects of HEPO film was predicted to be 14.9 K and 11.5 J Kg⁻¹ K⁻¹ at an applied field of 1120 kV cm⁻¹, for electrocaloric temperature change and entropy change, respectively.