High-temperature ac electrical behaviour of polycrystalline calcium zirconate

The a.c. electrical response of undoped polycrystalline calcium zirconate was evaluated at elevated temperatures (900 less than or equal to T less than or equal to 1400 degrees C) in air as a function of frequency in the range 5 Hz to 13 MHz. A systematic analysis of the a.c. electrical data revealed semicircular relaxation(s) in the impedance, admittance and modulus planes. An equivalent circuit model, representing grain and grain-boundary regions, is proposed. This circuit can be transformed to another representation which incorporates a possible trapping effect across the grain boundaries. The equivalence of these two representations is demonstrated by examining the correspondence between the two sets of circuit elements without resorting to empirical distributed-element models.