Mixed former effect in sodium phospho tellurate glasses

Abstract Glasses in the binary system xNa 2 P 2 O 6 -( l − x ) Na 2 Te 2 O 5 have been synthesised for 0≤ x ≤1. For all compositions, the glasses are transparent and appear homogeneous. Nevertheless for compositions near x = 0.4 glasses seem to be heterogeneous on SEM observations. Glass transition temperatures for all the compositions are between 220 and 310 °C. Conductivity data have been obtained using impedance techniques in the 100–250 °C temperature range. The σT product obeys an Arrhenius relationship with a composition-independent pre-exponential term A . The value of log A ≈ 4.8 is in agreement with an indirect interstitial mechanism model for sodium cation migration. Isothermal conductivity curves with x show a maximum in the ionic conductivity. This mixed network former effect may be justified by assuming an endothermic mixture between sodium phosphate and sodium tellurate.