Vitreous alkali tungstates

The glass-forming tendencies of alkali tungstates were studied in terms of crit. cooling rates in the compn. range M2WO4-WO3, where M is alkali. The ir spectra indicate that cryst. monotungstates are built up of WO4 tetrahedra; the tendency to form WO6 octahedra increases with increasing WO3 content. The vitreous system formation was attributed to the formation of chains of WO4 tetrahedra and by disproportionation reactions between the chains. The compns. corresponding to the lowest crit. cooling rate for each alkali tungstate system were Li2O(WO3)1.82, Na2O(WO3)1.63, K2O(WO3)1.78, Rb2O(WO3)1.91, Cs2O(WO3)1.82. The glass-forming tendency increased in the series Cs+ <Rb+ <K+ <Na+. Li+ did not fall naturally in the series after Na+, possibly due to the ordering effect exerted by Li+ on melts, caused by its low coordination no. with O ions. [on SciFinder (R)]