Size-dependences of the dielectric and ferroelectric properties of BaTiO₃/polyvinylidene fluoride nanocomposites

Composites containing pure, uniform, and well-dispersed ferroelectric barium titanate (BaTiO₃) nanocrystallites with various particle sizes as active phase and polyvinylidene fluoride (PVDF) polymer as matrix are fabricated using a two-step mixing and hot-pressing technique. The dependences of the dielectric and ferroelectric properties of the as-prepared composites on the nanoparticle sizes are investigated systematically. The polarization- electric field hysteresis loops are displayed, indicating the ferroelectricity for the BaTiO₃/PVDF nanocomposites. The remanent polarization is found to increase as the size of BaTiO₃ particles increases from 25 to 500 nm. The dielectric constant of the composites exhibits a complex variation as a function of the BaTiO₃ nanoparticle sizes: it reaches a maximum value in the composites with BaTiO₃ nanoparticle sizes of 80-100 nm and decreases again when the particle size is further reduced under 50 nm.