POSSIBLE UNIVERSALITIES IN THE AC FREQUENCY-RESPONSE OF DISPERSED, DISORDERED MATERIALS

The plausibility of recent suggestions that the electrical conductivit y of crystalline and glassy disordered materials may often arise from two separate physical processes, each involving dispersed response, is examined by means of a detailed, complex-non-linear-least-squares ana lysis of small-signal frequency-response data on CaTiO3:30%Al3+ over a temperature range from 51 to 626 K. Earlier preliminary analysis on a few of the available 16 data sets, which showed that they could indee d be described by a combination of conductive-system dispersion and di electric-system dispersion, is confirmed and extended. Complex non-lin ear least squares analysis provides a high-resolution method of isolat ing, identifying, and examining these separate response contributions. It was found that the conductive-system part of the full response cou ld be well represented over a wide temperature range by a power-law mo del with an exponent close to 0.5, presence of diffusion. A new analys is procedure showed that the relaxation time and de conductivity exhib ited the same thermally activated temperature response with no pre-exp onential T dependence. The dielectric system dispersion was well descr ibed by a thermally activated exponential-distribution-of-activation-e nergies model, whose effective power-law exponent exhibited [1-(T/T-0) ] temperature dependence from 51 to 296 K. Thus, when the present anal ysis methods were applied to these data, the constant-loss 'second uni versality', found earlier for this and other materials, one which invo lves a power-law exponent of unity, did not appear in the 64 to 224 K region where it was previously identified for the present material.