Iron speciation and coordination in lithium borate glasses

Abstract

This study explores the impact of Li2O content and Fe2O3 addition on the physical, optical, and structural properties of lithium borate glasses. Optical absorption spectra and XANES pre-edge features confirm the absence of significant Fe2+, indicating that iron is predominantly present as Fe3+. The optical absorption spectra exhibit characteristic features of Fe3+ ions, including a blue shift of the absorption edge as Li2O content increases, which is attributed to the conversion of BO3 to BO4 units. X-ray absorption spectroscopy reveals that Fe3+ ions are present in tetrahedral coordination, with the coordination number increasing at low Li2O concentrations. Raman spectroscopy further confirms that iron alters the connectivity of the borate network by disrupting superstructural borate units and forming links with boron atoms, particularly when Fe3+ occupies tetrahedral sites.