Mechanism of ac and dc conduction in chalcogenide glasses

We have investigated the dc and ac conductivities of Se75Te20Sn5 glass from 80 to 290 K in the frequency range 40 to 10(6) Hz. The behavior of the ac conductivity with temperature, T, is similar to that observed in many chalcogenide glasses. In this frequency range the ac conductivity sigma(omega) is proportional to omega (s) . The frequency exponent shows a T dependence. The experimental data have been analyzed using the modified bi-polaron correlated barrier hopping model, which assumes that the relaxation time should contain a Meyer-Neldel rule term. It is observed that this model is consistent with temperature dependent dc conductivity, sigma (dc), ac conductivity, sigma (ac), and s, for activation energies above 0.1 eV. At high frequency, that is, low activation energy, the behavior changes. We suggest that in this regime, the carriers may tunnel rather than hopping. We also present a correlation between the residual ac prefactor sigma (00)(omega) and the Meyer-Neldel temperature (T (MN)), similar to that previously reported for dc conductivity. This similarity points strongly to the dc and ac conduction mechanisms being the same. .