Unusual synchronous behavior of polarization and relaxation in Aurivillius superlattice

Bismuth layer-structure ferroelectric (BLSF) materials have potential for energy storage applications because of their high-temperature stability and excellent resistance to electric breakdown; however, they suffer from an asynchronous behavior of polarization and relaxation upon an impurity element. Herein, using systematic computational and experimental investigations, we report that, in sharp contrast to typical perovskite and bismuth layer-structure ferroelectric structures, the high-content La in Bi${}_3$TiNbO${}_9$ can produce greatly enhanced dielectric relaxation and out-of-plane polarization simultaneously. The underlying mechanism is the manipulation of La-O bonds within sequence-disordered Bi${}_2$O${}_2$ layered counterpart rather than the quasiperovskite counterpart in the $Fmmm$ phase dominant superlattice, which is essentially contrariwise in the $A{2}_{1}am$ phase dominant sample prepared in most previous experiments. Furthermore, we demonstrate that atomic defect engineering, specifically line dislocation resulting from the replacement of Bi with La${}^{3+}$ ions in Bi${}_3$TiNbO${}_9$, can provide an additional out-of-plane polarization. As a result, a high recoverable energy density $W_{\mathrm{rec}}$ of 8.7 J/cm${}^3$ and efficiency $\eta$ of 80.5%, together with excellent thermal stability and an ultra-fast discharge rate, are achieved in Bi${}_2$LaTiNbO${}_9$ superlattice. The present results yield a significant advance in the research field of dielectric energy storage of BLSF-based ceramics, suggesting a new paradigm that may stimulate the development of high-temperature, high-performance energy storage capacitors.