The modulation on morphotropic phases in high-entropy perovskite thin films with enhanced energy storage properties

The (1-x)(0.96Bi_0.5Na_0.5TiO₃-0.04BaTiO₃)-x(Bi_0.2Na_0.2K_0.2La_0.2Sr_0.2)TiO₃ ((1-x)(BNT–4BT)-xBNKLST, x = 0, 0.3, 0.5 and 1) high-entropy perovskite thin films are prepared by sol–gel and spin coating synthesis routes. The mixture of the pseudo-cubic phase of BNKLST and the rhombohedral phase of BNT–4BT results in the morphotropic phase structures of the high-entropy perovskite, e.g., the ratio of rhombohedral to pseudo-cubic phases is about 7:3 for the thin film with x = 0.5. The piezoelectric property of thin films is enhanced due to the reduced energy barrier as caused by the coexisting polar micro- and nano-domains. More importantly, the additions of BNKLST into BNT–4BT could not only reduce the dielectric loss, but also improve the electric breakdown fields of thin films. Although the maximal polarization is slightly reduced due to the change of TiO₆ octahedral tilting with an enhanced structural symmetry, the remanent polarization could maintain at a small value, which leads to the enhanced recoverable energy storage density and efficiency. The thin film with x = 0.5 exhibits an excellent energy storage density of 16.92 J/cm³ with an efficiency of 59.4% at 1500 kV/cm, which is promising for energy storage applications. This work demonstrates that the modulation of the morphotropic phase structure of the high-entropy perovskite thin films is effective in improving their energy storage properties.