Modification in the crystallinity, optical and dielectric behavior of PVA polymer with CaTiO₃ and graphite nanoflakes

Calcium titanate powder CaTiO₃ was subjected to heat treatment and utilized to fabricate hybrid nanocomposite films of polyvinyl alcohol (PVA)/graphite nanoflakes by solution casting technique. The effects of various content of graphite (0, 4, and 8 wt%) on the crystal microstructure, optical parameters, and dielectric behavior of the PVA containing 4wt% of CaTiO₃ were investigated. The X-ray diffraction analysis showed a heat treatment of CaTiO₃ increased the crystal size and lattice strain. The addition of graphite into the PVA containing heat-treated CaTiO₃ weakened the intensity of the main diffraction peaks in PVA films, indicating the drop of crystallinity. The optical absorption spectrum revealed a greater value of optical absorption and index of refraction for the PVA blend containing thermal-treated CaTiO₃ than untreated CaTiO₃. The incorporation of thermal-treated calcium titanate with graphite dropped the optical energy gap of PVA from 6.4 to 5.2 eV. That was followed by a subsequent increment in the value of Urbach energy in the prepared composite films. Dielectric characterizations showed the addition of heat-treated calcium titanate with graphite improved the low-frequency dielectric constant of the polymer and enhanced the ac conductivity by up to seven orders of magnitude. The increase of ac conductivity was found to be consistent with the rise in the value of loss tangent in the nanocomposite.