Microstructure and dielectric properties of sub-micron hollow sphere (Ba_0.6Sr_0.4)TiO₃/PVDF composites

Hollow sphere (Ba_0.6Sr_0.4)TiO₃ (HS-BST) powders with sub-micron size and different shell thickness were synthesised through template-assisted method. HS-BST/poly(vinylidene fluoride) (PVDF) composites were prepared using tape casting method. The effects of particle size and shell thickness of HS-BST on the microstructure, dielectric tunability, and energy storage properties of HS-BST/PVDF composites were investigated. Results showed that all HS-BST particles were uniformly dispersed in PVDF matrix without agglomeration. With decreasing the size of HS-BST particles, the dielectric constant and loss of HS-BST/PVDF composites decreased, while the breakdown strength initially decreased and then increased. In addition, the theoretical model of the dielectric tunability of inorganic/organic system related to the shape factor (n) of inorganic particles was used to simulate and n value of 0-dimensional spherical particles was estimated. For HS-BST/PVDF composite, the n in the model was 2–2.5, corresponding to HS-BST particles with a diameter ranging from 0.44 to 2.57 μm, and a shell thickness ranging from 40 to 500 nm.