Electrical behavior of RuO2-glass composites: The effect of RuO2 particle size on the percolation threshold

Abstract

Even small amounts of the fission byproduct ruthenium can increase the overall electrical conductivity of nuclear glasses by several orders of magnitude. In this context, the main goal of the present work is to evaluate the dependence of RuO2 particle size on the electrical behavior and percolation threshold of RuO2-glass composites. For this purpose, a set of sodium borosilicate glasses with different RuO2 content or distinct particle size is synthesized and characterized by X-ray diffraction and scanning electron microscopy. The electrical properties of these composites are assessed by impedance spectroscopy in a temperature range below the glass transition. The obtained results expose a transition in the electrical behavior of the RuO2-glass composites in the vicinity of the percolation threshold. The composites are mostly ionic conductors for low RuO2 content, but they become predominantly electronic conductors for RuO2 contents beyond the percolation threshold. The dependence of their electrical conductivity on temperature is also revealing. The composites showing ion-conducting behavior exhibit a strong and crescent dependence of the conductivity on temperature, while the electron-conducting composites show a metal-like conductivity. Even more noteworthy, the dependence of the electrical behavior on the RuO2 particle size unveils an extremely low percolation threshold (~1% vol.) and consequently higher conductivity for the glass composites synthesized with the nanometric RuO2 powder. These results bring new insights into the discussion of why these composites present such a low percolation threshold and suggest that the particle size of precursor powders play a crucial role in their final electrical properties.