Structure of copper tellurite and borotellurite glasses by neutron diffraction, Raman, 11B MAS-NMR and FTIR spectroscopy

The structure of copper tellurite and borotellurite glasses is studied by x-ray and neutron diffraction, reverse Monte Carlo (RMC) simulations, FTIR, Raman and B-11 MAS-NMR spectroscopy. Copper tellurite sample with 15 mol% CuO forms precipitates of tetragonal TeO2 within the glass matrix on melt quenching. The glass forming ability of the xCuO-(100-x)TeO2 system enhances with increase in CuO concentration from 15 to 20 mol% and also with the addition of B2O3. RMC simulations on the neutron diffraction data found that the Cu-O and Te-O bond lengths are approximately at equal distances in the range: 1.96 to 1.98 +/- 0.02 angstrom, while the nearest O-O distance is at 2.71 +/- 0.02 angstrom. Neutron and Raman results on the Te-O speciation are in agreement and confirmed that the Te-O coordination decreases with an increase in CuO and B2O3 molar concentrations in the tellurite and borotellurite glasses, respectively. RMC studies found that Cu2+ has tetrahedral coordination with oxygen, as predicted by Jahn-Teller distortion and that Cu-O and Te-O structural units have very similar size and geometry. The copper tellurite glass-ceramic sample with 15 mol% CuO was heat treated and it formed crystalline precipitates of TeO2 and CuTe2O5 upon devitrification; the average Te-O coordination was significantly smaller in the glass as compared to that in the crystalline sample.