Electrical Conductivity of RuO₂–Borosilicate Glasses: Effect of the Synthesis Route

Abstract

Although glass–RuO2 composites are well known for their particular electrical properties, the reasons for their very low percolation thresholds are still subject to debate. In this paper, a detailed study of the influence of various experimental parameters (temperature, RuO2 content, stirring, etc.) on the electrical conductivity and, in particular, on the percolation threshold in borosilicate glass–RuO2 composites is presented. This percolation threshold is shown to increase by a factor of two (from 0.6 to 1.2 vol%) when stirring is applied during synthesis and by more than a factor of three (>2.1 vol%) when a sol–gel route is used. Besides, the study of various synthesis temperatures reveals that the electronic part of the electrical conductivity is highly correlated to Ru solubility in the glass matrix. It can be concluded from these various experiments that both the presence of dissolved ruthenium in the glass matrix and the possibility of RuO2 particles to rearrange in the melt in order to form kind of a network are necessary for a low percolation threshold.

Electrical Conductivity of Mullite Ceramics

“…). The spike, the length of which increases with temperature is due to the electrode polarization effects, and, is characteristic of ionic conductors …”

Glasses and Glass-Ceramics for Nuclear Waste Immobilization

“…4). They represent only a weak fraction in the glass (<1 vol%), but their presence in the melt increases its viscosity and affects its electrical conductivity (Pflieger R., Malki M., Guari Y., Larionova J. and Grandjean A. 2009), and during cooling they may act as nucleation sites for heterogeneous crystallization (Pacaud F., Fillet C. and Jacquet-Francillon N. 1991, Orlhac X., Fillet C. and Phalippou J.…”

Behaviour of ruthenium dioxide particles in borosilicate glasses and melts

“…This is why such composites have been widely used in electronic applications such as thick film resistors (see for example [8] and [2]). The electrical conductivity of the glass melt is also a key parameter in the process of nuclear waste vitrification, the waste-glass frit mixture being heated by Joule effect, and the electrical conductivity of RuO 2 -glass frit composites has been studied in our laboratories both in the solid and molten states [1,9], showing a percolation threshold below 1 vol.%, so far below the RuO 2 amount necessary for a geometrical percolation (i.e., necessary for randomly distributed spheres to touch), which is 16 vol.% [10] but in good agreement with the results obtained on lead glasses by Kusy [11] in the 4.2-300 K temperature range (v c = 2-4 vol.%). This very low percolation threshold might be partially explained by a connected network formed by the RuO 2 particles but since the particles are always separated by a glass film, 'relays' for the electrons are necessary, such as nanoparticles of Ru or RuO 2 , or dissolved ruthenium atoms/ions.…”