Comparative study of dielectric properties of the PVDF composites filled with spherical and rod-like BaTiO₃ derived by molten salt synthesis method

In the molten salt environment, the BaTiO₃ spherical nanoparticles (BTNPs) and BaTiO₃ nanorods (BTNRs) have been synthesized, respectively, in which spherical TiO₂ and rod-like BaTi₂O₅ are precursors. The dissolution–precipitation is the main dominated mechanism in the formation of BTNPs, while the dissolution–diffusion is the main mechanism responsible for the formation of BTNRs. The latter is also called as topochemical mechanism, which is associated with the assembly of [TiO₆] octahedron units in the transformation from BaTi₂O₅ to BaTiO₃. By using these two kinds of BT as fillers, polyvinylidene fluoride (PVDF)-based composites, BTNPs/PVDF and BTNRs/PVDF, have been constructed and their dielectric properties have been investigated. It was found that there were three main factors related to filler morphology affecting the dielectric properties of the composites, i.e., intrinsic polarization of filler, the interface polarization and electric field distribution between the filler and the matrix. Though the spontaneous polarization of 600-nm-sized BTNPs is larger, the interfacial area of BTNRs/PVDF composite is larger than that of BTNPs (600 nm)/PVDF composite, which is advantageous to enhance the interface polarization. Moreover, the analysis through Potential-Across model revealed that BTNRs/PVDF composite has stronger electric field intensity distribution across BTNRs filler in comparison with BTNPs/PVDF, which plays the key role in improving the dielectric properties of composites. This work not only presents the BTNRs/PVDF composite with good dielectric performance, the related design and the theory analysis also facilitate the development of more new high dielectric composites based on morphology control of ferroelectric filler.