Structural study of glasses in the binary system NaPO3–MoO3 by X-ray absorption spectroscopy at the Mo K and L3 edges

Glasses were prepared in the binary system (100 − x)NaPO3–xMoO3 with x varying from 0 to 50 mol%. An increase in the MoO3 concentration promotes a strong absorption in the visible and near infrared attributed to Mo reduction during glass synthesis. X-ray absorption measurements were performed at the Mo K and L3 edges to investigate both the coordination number and oxidation state of Mo in these glasses. The evolution of the pre-peak observed at the K edge suggests that Mo atoms are six-fold coordinated in these glasses. This hypothesis was confirmed by data obtained at the Mo–L3-absorption edge. Since the final electronic states at the L3-absorption edge are mostly orbitals of d-character which are splitted by the ligand field, the amplitude of the d-orbital splitting could be estimated and the related coordination number of Mo obtained. Finally, the oxidation state of Mo could be related with a change of the white line intensity at the Mo–L3 edge. These results confirm that the optical absorption in the visible is due to Mo reduction and that transparent samples prepared by slow cooling contain less reduced Mo species.