Tunneling of large polarons in semiconducting zinc vanadate glasses

The ac electrical properties of several compositions of the semiconducting zinc vanadate glasses have been studied in the frequency range 10 Hz-2 MHz and in the temperature range 93-423 K. It has been observed that the ac conductivity shows power law dependence. The experimental data for the conductivity have been analyzed in the framework of several theoretical models based on quantum mechanical tunneling and classical hopping over barriers in order to determine the conduction mechanism. It has been observed that the model based on the tunneling of large polarons, out of the several models discussed, could explain adequately the temperature and frequency dependence of the ac conductivity and its power law exponent. The parameters obtained from the fits of this model with the experimental results are reasonable.