Mixed ionic and electronic conductivity of RuO2–glass composites from molten state to glassy state

This paper presents an experimental study of the electrical conduction mechanisms in RuO2–glass composites from molten to glassy states. The purpose of this experimental work is to investigate the electrical properties of molten borosilicates containing a dispersion of micrometric RuO2 particles by changing the morphology of the particles (grains or needles) and the nature of the matrix (good or poor ionic conducting matrix). Laboratory-scale composites were made by mixing and melting oxide powders. The temperature dependence of the conductance was measured by complex impedance spectroscopy, using a 4-electrode cell, from 1200 °C to 200 °C. The electrical conductivity of RuO2–glass composites revealed that even with low RuO2 content, electronic and ionic transport occurred over a wide temperature range. The RuO2 particle dispersion significantly enhances the total electrical conductivity up to 1200 °C. Percolation theory was used to model the electronic contribution to the conductivity. Electronic transport in the molten state can be described by the tunneling barrier model, previously suggested in the literature for solid composites. The ruthenium impurity concentration within the tunnel barriers depends on the RuO2 solubility. It is presumed to control the molten state electrical conductivity variations.