Ac relaxation mechanism in some cuprate glasses

Abstract

Electrical conductivity and dielectric properties of some unconventional lead cuprate glasses have been reported in the temperature range of 80-550 K and in the frequency range 10² -10⁶ Hz. The experimental data have been analyzed in the light of different theoretical models. It has been observed that at low temperatures, the ac conductivity is much higher than the dc conductivity and the hopping of electrons between localized states near the Fermi level is the dominant loss mechanism. At higher temperatures, the ac conductivity approaches the dc conductivity and the dipolar relaxation model with a distribution of relaxation times can give the best description of the experimental data. Dipolar relaxation occurs due to the hopping of charge carriers within a range of energies near the mobility edge. The conductivity relaxation model provides satisfactory values of low- and high-frequency dielectric constants and dc conductivity. On the other hand, the random-free-energy-barrier model is not consistent with the dielectric data. The unconventional glass network former PbO gives rise to large values of the low- and high-frequency dielectric constants and a narrower distribution of relaxation times than the conventional network formers.