Structure of sodium phosphate glasses containing Al2O3 and/or Fe2O3. Part I

The relationship between the composition and structure for three series of glasses: Na2O-Al2O3-P2O5 (NAP); Na2O-Al2O3-Fe2O3-P2O5 (NAFP), and Na2O-Fe2O 3-P2O5 (NFP) has been studied. The structural changes in the NAP, NAFP and NFP glasses have been investigated by Raman and by Raman difference spectro scopy (RDS). The Raman spectra show that the addition of Al2O3 content to s odium phosphate glasses has a different effect on the phosphate network tha n the addition of Fe2O3. With increasing Fe2O3 content up to 20 mol% the st ructure changes from the chain-Eke metaphosphate to the pyrophosphate struc ture. The iron ions play an important role in forming P-O-Fe bonds that str engthen the cross-bonding of shorter pyrophosphate chains. On the other han d, with increasing Al2O3 content up to 20 mol%, the sodium metaphosphate is replaced by aluminium metaphosphate where Al(OP)(6) units cross-link phosp hate chains. The addition of Fe2O3 to Al2O3 in phosphate glasses containing both Al2O3 and Fe2O3 (NAFP series), enhances the formation of pyrophosphat e units because iron ions have stronger effect on the depolymerization. of metaphosphate chains if compared to the aluminium ions. (C) 2001 Elsevier S cience B.V. All rights reserved.