DIELECTRIC-PROPERTIES OF EPOXY-BARIUM TITANATE-CARBON BLACK COMPOSITES

Frequency-domain dielectric measurements on epoxy-barium titanate-carb on black composites from 100 Hz to 1 MHz and from room temperature to + 200 degrees C are reported. The results are presented mainly in the form of plots of the real and imaginary parts of the relative permitti vity versus temperature for different frequencies and of the resistivi ty versus frequency for different temperatures. The basic composite co nsisted of 56 vol% barium titanate and 44 vol% epoxy. To this basic co mposite small amounts of carbon black were added to increase the elect rical conductivity of the epoxy matrix, thus reducing the relaxation t ime and increasing the high frequency permittivity. When the carbon bl ack concentration was near the percolation threshold, high permittivit ies were obtained even at high frequencies since the relaxation time w as reduced to less than a microsecond. A further increase in the carbo n black concentration lead to short-circuiting the charge build-up on the barium titanate/epoxy interfaces and loss of the high permittivity . The experimental results are interpreted in terms of the theory of d ielectric loss in heterogeneous materials.