LIMITING BEHAVIOR OF AC CONDUCTIVITY IN IONICALLY CONDUCTING CRYSTALS AND GLASSES - A NEW UNIVERSALITY

The ac conductivity sigma(omega) of three ionically conducting crystalline materials (NaCl:Zn2+, KTaO3:Co2+, 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 sigma(omega) - sigma-0 + A-omega-s] 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.