Effect of nanocrystallization on the electrical conduction of silver lithium phosphate glasses containing iron and vanadium

xLi(2)O center dot(20-x)Ag2O center dot 20Fe(2)O(3)center dot 60P(2)O(5) glasses (x = 0, 5, 10, 15 and 20 mol%) and 5Ag(2)O center dot 15Li(2)O center dot 5V(2)O(5)center dot 15Fe(2)O(3)center dot 60P(2)O(5) glass were prepared by melt-quenching of the reagent mixture at 1000 degrees C. Glass transition temperature (T-g) and crystallization temperature (T-c) of these samples were determined by differential thermal analysis (DTA). It proved that T-g increased with Li2O content. XRD of as-quenched glasses confirmed their amorphous nature. XRD of samples heat treated for one hour at temperature near their Tc, indicated nanocrystals precipitated in the glassy matrix with an average particle size of 35 nm. Mossbauer results revealed that the relative fraction of Fe2+ was decreased with an increasing Li2O content. The isomer shift values of Fe3+ lie in a range of 0.38-0.45 mm s(-1), while those for Fe2+ were 1.10-1.31 mm s(-1). Heat-treated sample of 5Ag(2)O center dot 15Li(2)O center dot 5V(2)O(5)center dot 15Fe(2)O(3)center dot 60P(2)O(5) glass exhibit an enhancement of the electrical conductivity by three orders of magnitude due to the 3d-electron (polaron) hopping from V4+ to V5+ in the "vanadate glass" units.