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

The structural properties of xCr2O3–(40 − x)Fe2O3–60P2O5, 0 ⩽ x ⩽ 10 (mol%) glasses have been investigated by Raman and Mössbauer 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, Q1, units. This is in accordance with O/P ≈ 3.5 for these glasses. The increase in glass density and Tg that occurs with increasing Cr2O3 suggests the strengthening of glass network. The Mössbauer spectra indicate that the Fe2+/Fetot 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 10Cr2O3–30Fe2O3–60P2O5 (mol%) sample was partially crystallized and contained crystalline β-CrPO4 and Fe3(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.