Electrical conductivity enhanced dielectric and piezoelectric properties of ferroelectric 0-3 composites

We have investigated the effects of electrical conductivity of the constituents on the dielectric and piezoelectric properties of ferroelectric 0-3 composites. The time-dependent internal electric fields are first derived, which can be induced by an applied ac field in dielectric measurement or stress in piezoelectric measurement. Our previously developed model [C. K. Wong, Y. M. Poon, and F. G. Shin, J. Appl. Phys. 90, 4690 (2001)] has been extended to include the additional contribution from the electrical conductivities and the frequency of measurement, which can be significant for ceramic/polymer composites possessing high conductivity in the matrix phase. The model provides an explanation to the surprisingly high piezoelectric d33 values reported by, e.g., Chen et al. [Sens. Actuators, A 65, 194 (1998)]. Explicit expressions for the transient and steady-state responses are given and the effective permittivity, d33, d31, and dh coefficients have been derived.