Limiting behavior of ac conductivity in ionically conducting crystals and glasses: A new universality

The ac conductivity {σ}({ω}) of three ionically conducting crystalline materials (NaClZn²⁺, KTaO₃:Co³⁺,H⁺, and CeO₂:Gd³⁺) and two glasses have been studied over an unusually wide temperature range. In all cases, limiting power-law behavior [exponent s=1 in {σ}({ω})=σ₀+Aωˢ] is observed at relatively low temperatures. It is concluded that this limiting behavior is a universal phenomenon. Available theoretical explanations have been examined and found to be unsatisfactory.