Local Chemical Clustering Enabled Ultrahigh Capacitive Energy Storage in Pb-Free Relaxors

Chemical Framework to Design Linear-like Relaxors toward Capacitive Energy Storage

“…Moreover, the energy storage properties well outperform other lead-free bulk ceramics, such as BT-based, BNT-based, NN-based, and AN-based RFEs (Figure S6). ,,,, For BT-D2, a high W rec of 12.1 J cm –3 with a high η of 91.1% under an E B of 74 kV mm –1 is obtained (Figure h). The W rec achieved in BT-D2 represents the highest reported value in BT-based ceramic systems (Figure i and Table S4).…”

“…The energy storage capacity of a dielectric material is determined by its polarization traits and breakdown strength ( E B ). Lead-free relaxor-ferroelectric (RFE) solid solutions exhibit desirable merits of large polarization ( P m ) and small hysteresis ( H ), making them the preferred option for high-performance dielectric capacitors. − Owing to the high chemical flexibility of perovskites that allow for various atomic combinations at both A- and B-sites, substantial lead-free RFEs have been explored to optimize energy-storage performance. − ,− Examples include BaTiO 3 (BT)-based, ,, Bi 0.5 K 0.5 TiO 3 (BKT)-based, − SrTiO 3 (ST)-based, , Bi 0.5 Na 0.5 TiO 3 (BNT)-based, ,,− (K,Na)­NbO 3 (KNN)-based, , NaNbO 3 (NN)-based, , and AgNbO 3 (AN)-based ,, relaxors, and their corresponding W rec in bulk ceramics has been significantly improved, with values typically ranging from 4 to 8 J cm –3 .…”

“…It is widely believed that the relaxor feature in perovskite solid solutions is derived from unique polar structure resulting from local compositional heterogeneity. , Therefore, the most common approach to regulating polar structure and enhancing energy storage performance of RFEs is through chemical composition design, which typically involves multiple substitution and mixing of different perovskites. − Several chemical composition design strategies have been explored, such as transforming the ferroelectric (FE) state with high polarization to the RFE state by incorporating a linear dielectric component, ,, introducing highly polarizable ions into paraelectric/weak-FE components to enhance local polarization, ,, merging different perovskites to form polymorphic polar nanoregions, ,, and increasing configurationally entropy to promote polar disorder . In addition, various mesoscopic structural modification methods have been adopted to improve the E B . ,,, Despite the considerable endeavors and advancements in the chemical compositional design of RFE-based energy storage dielectrics, the influence of inherent ion characteristics on the polar inhomogeneity is still not well articulated.…”

“…Accordingly, A-site Bi and Ag ions and B-site Ti, Nb, Fe, Ta, and Zn ions have large D values and are assigned as ferroelectrically active ions. These ferroelectrically active ions are often preferred in order to achieve a large P m . ,,, On the other hand, these nonferroelectric A -site ions are divided into framework ions with a large ionic radius and rattling ions with a small ionic radius. The framework ions include Ba and K, while rattling ions contain Na, Ca, La, Sm, etc.…”

“…As illustrated in Figure d, high concentrations of large framework ions afford a host framework that has oversized AO 12 cages . The ferroelectrically active ions can induce large local polarization due to their strong covalent bonding ,, and will facilitate local polar reorientation under an electric field. ,, Importantly, the small rattling ions can undergo significant local polar extension under a high electric field thanks to the ample space for ionic displacements provided by the oversized AO 12 cages. Indeed, if a rattling ion replaces a framework ion within the oversized AO 12 cages, there is about 0.6 Å displacement space due to their considerable size differences.…”