Ac and dc conductivities in V2O5-P2O5 glasses containing alkaline ions

We investigated the ac and dc conductivity in 50V(2)O(5)-(50 x)P(2)O(5-x)A(2)O (A = Li, Na, K) glasses as a function of temperature. The measurements were carried out in the frequency range from 10(-4) to 10(7) Hz. For all compositions, the dc conductivity decreased with the increasing alkali ion content. The decrease in conductivity was more pronounced for larger alkali ions. The ac conductivity exhibited a universal dynamic response: sigma(ac) = A omega(s(T)). For glasses containing less than 10 mol% of alkaline ions, the exponent s(T) temperature dependence was typical as that for electronic conducting glasses and decreased from a value near to unity at a low temperature (153 K) to 0.5 at 423 K. A small variation only (from 0.99 to 0.95) of s(T) was observed in the mixed electronic-ionic regime. This behavior is known as nearly constant loss (NCL). We found that the NCL behavior could be observed in a very wide range of temperature and frequency in mixed electronic-ionic conducting glasses. (C) 2010 Elsevier B.V. All rights reserved.