Mössbauer spectroscopic study of γ-ray irradiated potassium borate glasses

Potassium borate glasses denoted by the formula xK₂O · (100 ? x)B₂O₃ · 7Fe₂O₃ were irradiated with ⁶⁰Co-γ-rays at room temperature. Mössbauer parameters for the irradiated glasses containing alkali equal to or higher than 20 mole% showed that the s-electron density at the iron nucleus increased without any change of the steric configuration of oxygen atoms around the iron nucleus. The increase of s-electron density was ascribed to electron transfer from the nonbridging oxygen to the iron nucleus. The presence of the nonbridging oxygen was also confirmed by the irradiation effect of the borate glass (x = 30) prepared using the enriched isotope of ⁵⁷Fe₂O₃. Mössbauer parameters for the irradiated glass suggest that the newly observed Fe²⁺ ions are in tetrahedral symmetry.