Structural properties of Cr2O3-Fe2O3-P2O5 glasses, Part I

The structural properties of xCr(2)O(3)-(40-x)Fe2O3-60P(2)O(5), 0 <= x <= 10 (mol%) glasses have been investigated by Raman and Mossbauer spectroscopies, X-ray diffraction (XRD) and differential scanning calorimetry (DSC). The Raman spectra show that the addition of up to 5.3 mol% Cr2O3 does not produce any changes in the glass structure, which consists predominantly of pyrophosphate, Q(1), units. This is in accordance with O/P approximate to 3.5 for these glasses. The increase in glass density and T-g that occurs with increasing Cr2O3 suggests the strengthening of glass network. The Mossbauer spectra indicate that the Fe2+/Fe-tot ratio increases from 0.13 to 0.28 with increasing Cr2O3 content up to 5.3 mol%, which can be related to an increase in the melting temperature from 1423 to 1473 K. After annealing, the 20Cr(2)O(3)-30Fe(2)O(3)-60P(2)O(5) (mol%) sample was partially crystallized and contained crystalline beta-CrPO4 and Fe-3(P2O7)(2). The SEM and AFM micrographs of the partially crystallized sample revealed randomly distributed crystals embedded in a homogeneous glass matrix. EDS analysis indicated that the glass matrix was rich in Fe2O3 (39.6 mol%) and P2O5 (54.9 mol%), but contained only 5.5 mol% of Cr2O3. These results suggest that the maximum solubility of chromium in these iron phosphate melts is 5.5 mol% Cr2O3. (C) 2007 Elsevier B.V. All rights reserved.