ac conductivity in Bi4Sr3Ca3CuyOx (y=0–5) and Bi4Sr3Ca3−zLizCu4Ox (z=0.1–1.0) semiconducting oxide glasses

Semiconducting oxides such as Bi4Sr3Ca3CuyOx (y=0–5) and Bi4Sr3Ca3−zLizCu4Ox (z=0.1, 0.5, and 1.0), many of which become superconductors in their glass-ceramic phases, have been studied over the wide temperature (77–450 K) and frequency (100–104 Hz) ranges. The universal power-law behavior [exponent s≤1 in σ(ω)=σ0+Aωs] is found to be valid for most of these glasses. Little deviation from this limiting behavior is also observed for some glass compositions in the low-temperature and high-frequency regions. The correlated barrier hopping model based on the pair approximation is found to be more appropriate for explaining the frequency and temperature-dependent ac conductivity data. The random walk type of model, on the other hand, is found to be valid for a limited range of temperature.