Effect of particle size and volume fraction of BaTiO3 powders on the functional properties of BaTiO3/poly(ε-caprolactone) composites

Abstract

A systematic study concerning the effect of particle size and volume fraction of BaTiO3 filler on the functional properties of composite materials with poly-(ε-caprolactone) polymer matrix obtained by solvent casting method was performed. Two series of xBT-(1-x)PCL composites prepared by using BaTiO3 powders with two different particles size (60 nm and 400 nm) in different amounts (x = 2; 5; 10 and 20 vol %) were investigated. The X-ray diffraction analysis indicated a particle size dependence of phase symmetry for BT filler powders (cubic phase for ultrafine particles and tetragonal phase for larger particles size) and the formation of pure composites consisting of orthorhombic PCL and cubic or tetragonal BT with no chemical reactions between them. The micrographs of the composites revealed the formation of homogeneous composites with two distinct phases, a good dispersion of ferroelectric phase into the polymer matrix and a low content of air pores. Dielectric investigations at room temperature showed the increases of permittivity with increasing the particle volume fraction of ferroelectric filler as result of the “sum property” of the effective permittivity in composites. For a given concentration, the permittivity of composites increases with particle size, as result of a size effect of BT powder. The composites with low BT addition presents stable dielectric properties at bending cycles. The polarization-field dependences also show a BT-induced size dependence, i.e. at a given value of field, polarization is higher for the composites with coarser BT particles. The composition x = 0.05 with coarse particles can be considered as an optimum among these series for the stored energy density.