Ionic conductivity in glasses and melts (up to 1950 K):: Application to the CaO-SiO2 system

The electrical properties of the CaO-SiO2 system have been investigated in a wide temperature range (up to 1950 K) using a specific device developed in this laboratory. Conductivity data were obtained in the liquid, undercooled-liquid, and glassy states for two different compositions. In the solid state, the conductivity is determined by the jump of the Ca2+ cations along the non-bridging oxygens. This mechanism is thermally activated with a high activation energy value. A second regime was observed in the molten state where the conductivity follows the phenomenological Vogel-Tammann-Fulcher (VTF) law. In this regime, the conductivity is enhanced because the softening and the deformation of the network facilitate the migration of the alkaline-earth cations.