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 11B 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 Å, while the nearest O–O distance is at 2·71±0·02 Å. 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.