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 stu dy reveals that it is due to the combined effects of polymerization of the phosphate glass network and formation of small metaphosphate rings caused b y the decrease in OH content. This is supported by the decrease of Q(2) sit es (decrease in optical basicity) in the P-31 MAS NMR spectra. On further d ehydroxylation, the shifting of UV cutoff towards longer wavelengths is att ributed to the increase of Q(1) and Q(2) sites (increase in optical basicit y) associated with the formation of nonbridging oxygens (NBOs). It is cause d by the preferential loss of P2O5 and simultaneous decrease of OH groups d uring exhaustive dehydroxylation for a prolonged period of melting in vacuu m. (C) 2001 Elsevier Science B.V. All rights reserved.