Analysis of impedance and admittance data for solids and liquids

Some problems of analyzing small-signal impedance data on solids or liquids are discussed. A method of using ordinary nonlinear least squares fitting procedures with minor modification to fit at the same time real and imaginary functions of the same set of unknown parameters to complex data is described in detail. This method of complex least squares fitting, which has several advantages over p~'evious approaches, is i l lustrated by fitting equivalent circuit impedances to some polycrystal l ine p-alumina impedance data and to synthetic impedance and admittance data calculated from a theo-retical model of the response of homogeneous material with completely blocking electrodes. When different physical processes yield response in over-lapping frequency regions so that the different processes lead to some melding of effects in an impedance plane representation, interpretat ion of equivalent circuit parameters becomes difficult even when the degree of fit of the model to the data is excellent. In particular, low frequency extrapolat ion i the im