Thermal expansion of silico-phosphate glasses with small additions of Fe2O3: EPR and dilatometric studies

Abstract

Electron paramagnetic resonance (EPR) and dilatometric measurements in phosphosilicate glass have been made in order to elucidate an anomalous trend of the linear thermal expansion coefficientβ when Fe2O3 was added to the composition. The g≃2 and geff≃4.27 EPR lines were attributed, respectively, to undistorted and octahedrally coordinated Fe3+ ions, and to Fe3+ ions in low symmetry (rhombic) sites. The Fe3+ ion distribution in the network at different temperatures has been explained by a model of chemical insertion and it has been proved that the Fe3+ ions have two kinds of role as network modifiers. A relationship has also been found betweenβ and the amounts of Fe2O3 added in the range 0 to 12 wt %.