The effect of Fe on the structure and electrical conductivity of sodium borosilicate glasses.

We report the synthesis and characterization of iron-bearing sodium borosilicate glasses with an Fe2O3 content lower than 10 mol%. Using Mössbauer spectroscopy we demonstrate that Fe ions most probably have a tetrahedral oxygen environment for an iron oxide content higher than 5 mol%. Additionally, the Mössbauer results along with the X-ray diffraction studies indicate the formation of magnetite nanoclusters. The electrical conductivity of iron-containing sodium borosilicate glasses is studied over a wide temperature range. The impact of iron content on the dielectric permittivity and electrical properties is discussed. Finally, ionic conduction is identified in the high temperature region and its physical origin is explained. A similar activation energy of the dc conductivity and the activation energy of the electrical relaxation suggest that both the relaxation and conduction processes can be ascribed to the same type of entities.