Structural study of thin films prepared from tungstate glass matrix by Raman and X-ray absorption spectroscopy

Thin films were prepared using glass precursors obtained in the ternary system NaPO 3 BaF 2 WO 3 and the binary system NaPO 3 WO 3 with high concentrations of WO 3 (above 40% molar). Vitreous samples have been used as a target to prepare thin films. Such films were deposited using the electron beam evaporation method onto soda-lime glass substrates. Several structural characterizations were performed by Raman spectroscopy and X-ray Absorption Near Edge Spectroscopy (XANES) at the tungsten L I and L III absorption edges. XANES investigations showed that tungsten atoms are only sixfold coordinated (octahedral WO 6 ) and that these films are free of tungstate tetrahedral units (WO 4 ). In addition, Raman spectroscopy allowed identifying a break in the linear phosphate chains as the amount of WO 3 increases and the formation of P O W bonds in the films network indicating the intermediary behavior of WO 6 octahedra in the film network. Based on XANES data, we suggested a new attribution of several Raman absorption bands which allowed identifying the presence of W O − and W O terminal bonds and a progressive apparition of W O W bridging bonds for the most WO 3 concentrated samples (above 40% molar) attributed to the formation of WO 6 clusters.