P-31 MAS AND B-11 NMR-STUDY OF SODIUM RICH BOROPHOSPHATE GLASSES

P-31 MAS and B-11 NMR have been used to investigate the structure of g lass samples with the chemical composition (1-x)NaPO3-xNa2B4O7. The P- 31 resonance spectra present several Gaussian lines which are due to d ifferent environments around the PO4 units. In addition to the phospha te units occurring for R greater-than-or-equal-to 1 in the R Na2O-P2O5 system (i.e. middle: MP, end: EP and monomeric: MO units), typical ph osphate units included in borophosphate groups have been identified in MAS spectra. From B-11 spectra, the boron atom fraction in four fold coordination has been determined. Addition of Na2B4O7 progressively pr oduces a shortening of the phosphate chains. The borate groups, mainly under the BO4/2- form compensated by phosphate units, are used as bra nching units between chains, with a probable tendency to form random p hosphate groups, resulting in the formation of borophosphate groups of the form: BOPO22- OP and BOPO2- OP (MB1) then BOPO2- OB and BOPO2- OP (MB2), as x increases up to 0.2. In the borate rich concentration ran ge (0.20 < x less-than-or-equal-to 1), borate groups including boron a toms in three and four fold coordination such as those found in pure v itreous Na2B4O7, would be considered. The phosphate units bridging the borate groups (MB2) are located out of the borate network and progres sively disappear, giving up their places to BOPO32- (EB) and MO units as x increases.