Fabrication and High\nDielectric Properties of Sandwich-Structured\nBa<sub>0.6</sub>Sr<sub>0.4</sub>TiO<sub>3</sub>/Polyvinylidene Fluoride\nLayered Composites with Multiscale Parallel Interfaces

Ba<sub>0.6</sub>Sr<sub>0.4</sub>TiO<sub>3</sub>/polyvinylidene\nfluoride (BST/PVDF) dielectric functional composites have been widely\nused in flexible wearable devices, capacitors, and energy storage\ndevices. In addition to the ceramic phase type, polymer matrix type,\ncomposition, and interfacial connectivity of BST/PVDF composite materials,\ntheir morphology also significantly influences their electrical characteristics.\nTherefore, herein, sandwich-structured BST/PVDF layered composites\nwere designed and prepared via tape-casting processing using different\ntypes of BST fillers [i.e., formless zero-dimensional (0D)-BST, rod-like\none-dimensional (1D)-BST, and plate-like two-dimensional (2D)-BST].\nThe microstructures and electrical characteristics of sandwich-structured\nBST/PVDF composites were studied in relation to the BST morphology.\nThe effects of the internal mechanisms of different interfacial models\non the breakdown strength of BST/PVDF composites were discussed. According\nto our findings, unlike the 0D-BST and 1D-BST powders, 2D-BST powders\nform multiscale parallel interfaces in sandwich-structured composites\ndue to their unique lamella-like morphology, which enhances the breakdown\nstrength of sandwich-structured composites. Sandwich-structured BST/PVDF\ncomposites containing 2D-BST powders exhibit good electrical characteristics\nwith an energy storage density of 19.71 J/cm<sup>3</sup>, an energy\nstorage efficiency of 85.3%, a dielectric constant of 30.4 (1 kHz),\na dielectric loss of 0.036 (1 kHz), and a dielectric tunability of\n93.2%. This study provides a method for preparing functional composites\nwith high dielectric tunability and high energy storage characteristics.