Conductivity anomalies in tungstate-phosphate glasses: evidence for an ion-polaron interaction?

Conductivity anomalies are observed in mixed ion-polaron conducting glasses in the system Li 2O: WO 3: P 2O 5. Deep minima in conductivity (reminiscent of the mixed alkali effect) occur when small amounts of Li 2O are introduced into WO 3 − y : P 2 O 5 glasses. By contrast, glasses melted in air are always deep blue in colour, except when large amounts of Li 2O are incorporated. It is suggested that negatively charged polarons (effectively the d-electron located on a W 5 + centre) interact strongly with mobile cations to form uncharged diffusing entities. This may be a general phenomenon in mixed ionic electronic conductors where mobilities of ions and electrons are comparable in magnitude.