Dielectric properties of sandwich-structured BaTiO₃/polyimide hybrid films

In this paper, sandwich structured polyimide hybrid films were prepared by layered coating, in which middle layer is different volume fraction BT/PI monolayer film and both the bottom and the top layers are pure PI. Compared with monolayer hybrid films, sandwich structured hybrid films exert much lower dielectric loss and conductivity, which owe to pure PI layers as insulation layers effective block off conductive paths of middle layer. Besides, the SEM images show hybrid film has obvious layering and without defects. This sandwich structure can redistribute electric field between three layers to optimize breakdown performance, which correspond to data processed by Weibull breakdown distribution. When the intermediary volume fraction is 3 vol%, the breakdown strength of sandwich structured hybrid films is 344.26 kV/mm, which is 1.26 times enhancement than pure PI film. In addition, based on the improvement of the breakdown strength, the energy storage density of hybrid films is improved significantly. When the electric field is 344.26 kV/mm, its energy storage density reached 1.94 J/cm³, which is 1.72 times enhancement of pure PI film.