BST-P(VDF-CTFE) nanocomposite films with high dielectric constant, low dielectric loss, and high energy-storage density

Free-standing, flexible, and transparent ceramic-polymer nanocomposite films with a uniform thickness of about 5 μm were fabricated using a simple spin-coating process, in which the polymer solution with a high concentration was used. Ba_0.5Sr_0.5TiO₃ (BST) nanoparticles and P(VDF-CTFE) 91/9 mol.% (VC₉₁) copolymer were used as ceramic filler and polymer matrix, respectively. Microstructures, dielectric properties, and energy-storage performances of the BST-VC₉₁ nanocomposite films have been investigated. With increasing volume fraction of BST, the dielectric constant increases, while the dielectric loss decreases. A dielectric constant of about 38.4 at 100 Hz associated with a dielectric loss of only about 0.02 was obtained in the nanocomposite film with 40 vol% of BST. It is experimentally found that the temperature dependences and the frequency dispersions of dielectric properties were strongly influenced by the volume fraction of BST, especially at high temperatures. Good temperature stability and small frequency dispersion of dielectric constant can be obtained in the BST-VC₉₁ nanocomposite films with 40 vol% and 50 vol% of BST, which are also associated with a low dielectric loss. It is concluded that the motion of the polymer chains is the micro-origin of the relaxation process observed at high temperatures. With increasing volume fraction of BST, the dielectric breakdown strength decreases, while the maximal polarization and remnant polarization increase. The maximal charge-energy density and discharge-energy density of about 21.7 J/cm³ and 7.5 J/cm³ are obtained in the BST-VC₉₁ nanocomposite film with 30 vol% BST under 2500 kV/cm, which are more than 2 times larger than those observed in pure VC₉₁ film under the same electric field.