Glasses in the SbPO4–WO3 system

Glasses in the binary system (100 − x)SbPO₄–xWO₃ (20 ⩽ x ⩽ 60, x in mol%) have been prepared and characterized. Differential thermal analysis (DTA) shows that the glass transition temperature, T_g, increases from 412 °C, for samples containing 20 mol% of WO₃, to 481 °C observed for glass containing 60 mol%. Sample containing 40 mol% in WO₃ were observed to be the most stable against devitrification. The structural organization of the glasses has been studied by using Fourier transform infra-red (FTIR), Raman, ³¹P Magic angle spinning (MAS) and spin echo nuclear magnetic resonance (NMR) spectroscopies. Results suggest two distinct networks comprising the glass structure, one with high SbPO₄ content and the other characteristic of the highest WO₃ content samples. The glasses present photochromic properties. Colour changes are observed for samples after exposure to ultraviolet or visible laser light. XANES, at L₁ absorption edge of tungsten, suggests partial reduction from W⁶⁺ to W⁵⁺ species during the laser irradiation. The photochromic effects and the colour changes, promoted by laser excitation, are reversible and easily removed by heat for during 1 h at 150 °C. Subsequent ‘write/erase’ cycles can be done without degradation of the glasses.