RAMAN STUDIES OF AG2O-CENTER-DOT-WO3-CENTER-DOT-TEO2 TERNARY GLASSES

A Raman study was carried out on rAg(2)O . (1 - x)[yWO(3) . (1-y)TeO2] (x = 0.3, 0.4) ternary glasses with respect to composition and temper ature. The crystallization process and structural units making up the ternary glasses were analyzed in detail. Ag2O addition was found to pr omote the formation of TeO3 tetragonal pyramid and WO4 units in the gl asses at the expense of TeO4 tetragonal bipyramid and WO6 units. The a ddition of Ag2O also lengthens the Te-O bond, whereas WO3 increases th e vibrational wavenumber of the TeO3 units. The crystallization of the glasses is a two-step ordering process of the TeO4 units and complete ordering is hindered by the more rigid WO, units. However, the onset of crystallization does not follow a simple pattern with the content o f WO3. The proportion of the TeO4 units is always small at the onset o f crystallization and increases close to the completion of crystalliza tion, regardless of whether the crystal is formed from the melt by coo ling or from the glass state by heating. (C) 1998 John Wiley & Sons, L td.