Effect of vacuum dehydroxylation on the UV transparency and structure of metaphosphate glasses

UV cutoff of calcium metaphosphate glass shifts towards shorter wavelengths in the initial stage dehydroxylation in vacuum. IR reflection spectral study reveals that it is due to the combined effects of polymerization of the phosphate glass network and formation of small metaphosphate rings caused by the decrease in OH content. This is supported by the decrease of Q(2) sites (decrease in optical basicity) in the P-31 MAS NMR spectra. On further dehydroxylation, the shifting of UV cutoff towards longer wavelengths is attributed to the increase of Q(1) and Q(2) sites (increase in optical basicity) associated with the formation of nonbridging oxygens (NBOs). It is caused by the preferential loss of P2O5 and simultaneous decrease of OH groups during exhaustive dehydroxylation for a prolonged period of melting in vacuum. (C) 2001 Elsevier Science B.V. All rights reserved.