Electrical Conductivity and Structural Properties of Cesium Iron Phosphate Glasses: A Potential Host for Vitrifying Nuclear Waste

Abstract

The thermally stimulated current (TSC) and dc conductivity for iron phosphate glasses containing up to 28 mol% Cs₂O have been measured in a temperature range from 120 to 400 K. The dc conductivity and activation energy were constant and independent of Cs₂O content. With increasing cesium concentration in cesium iron phosphate glasses the slowly moving cesium ions are more tightly bound to the non-bridging oxygen ions and make no measurable contribution to dc conductivity. The dc conduction in these glasses is totally electronic, controlled by electron hopping between iron ions. The ionic conduction is immeasurably small because of the low mobility of the cesium ions. This agreement is reinforced by the excellent chemical durability of the glasses, where the dissolution rate at 90^oC changes little with increasing Cs₂O content. Raman spectroscopy indicated that the structure of these glasses was composed of predominantly pyrophosphate (P₂O₇) groups, but the metaphosphate chains (PO₃) also existed.