Scaling Features of Conductivity Spectra Reveal Complexities in Ionic, Polaronic Andmixed Ionic-Polaronic Conduction in Phosphate Glasses
28 Pages Posted: 26 Mar 2019 First Look: Accepted
The scaling behaviour of six series of mixed ion-polaron glasses with the composition xWO3/MoO3-(30-0.5x)Li2O/Na2O/Ag2O-(30-0.5x)ZnO-40P2O5, 0≤x≤60 mol%, has been studied using Summerfield and Sidebottom scaling procedures that are model free. The validity of the Sidebottom scaling procedure for each individual glass confirms that all glasses obey time-temperature superposition principle implying that the conduction mechanism does not change with temperature. On the other hand, Summerfield scaling is not found valid for all glasses. First, this deviation is observed in all glasses containing Li2O up to 20 mol% of MoO3/WO3. We relate this result to a non-typical interaction of Li+ ion with the compact zinc phosphate network resulting either in change of its hopping distance or in available conduction pathways for it as a function of temperature. Second, non-Summerfield scaling was also observed for glasses containing Li2O/Na2O/Ag2O with about 30 to 40 mol% of WO3. Thus, the origin of this deviation lies in the significant amounts of both types of charge carriers - ions and polarons, and their differently thermally activated mobilities. Finally, based on a comparison of master-curves of all glasses with varying fractions of Li2O/Na2O/Ag2O and MoO3/WO3 we identify varied effects of the transition metal oxide on the transport of mobile ions as also the presence of mixed ion-polaron conduction.
Keywords: electrical conductivity, polaron, ionic diffusion, impedance spectroscopy, phosphate glasses, structure-property relationship
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