Significantly enhanced breakdown strength and energy density in sandwich-it structured NBT/PVDF composites with strong interface barrier effect

The sandwich-structured composites comprised of two outer layers of NBT dispersed in a PVDF matrix to provide high dielectric constant (epsilon') and a middle layer of pure PVDF to offer high breakdown strength (E-b) are prepared by a solution casting layer-by-layer process. Experimental results indicate that the E-b and energy density (U) of sandwich-structured composites are improved significantly via tailoring the contents of NBT fillers. The sandwich-structured composites with optimized filler content result in enhanced E-b of 410kV/mm with a high saturate electric displacement of 14.49 mu C/cm(2), and thus an impressive U of 12.5J/cm(3) is obtained. Moreover, compared with single-layer composites, sandwich-structured composites exhibit the higher E-b and U. It can be explained that sandwich-structured composites prevent the formation of conductive paths due to strong interface barrier effect of between the outer layer and middle layer. In addition, the breakdown behavior of single-layer and sandwich-structured composites are understood by employing the impedance spectroscopy technique