In situ high pressure neutron diffraction and Raman spectroscopy of 20BaO-80TeO₂ glass

The short-range structure of 20BaO-80TeO₂ glass was studied in situ by high pressure neutron diffraction and high pressure Raman spectroscopy. Neutron diffraction measurements were performed at the PEARL instrument of the ISIS spallation neutron source up to a maximum pressure of 9.0 ± 0.5 GPa. The diffraction data was analysed via reverse Monte Carlo simulations and the changes in the glass short-range structural properties, Ba-O, Te-O and O-O bond lengths and speciation were studied as a function of pressure. Te-O co-ordination increases from 3.51 ± 0.05 to 3.73 ± 0.05, Ba-O coordination from 6.24 ± 0.19 to 6.99 ± 0.34 and O-O coordination from 6.00 ± 0.05 to 6.69 ± 0.06 with an increase in pressure from ambient to 9.0 GPa. In situ high pressure Raman studies found that the ratio of intensities of the two bands at 668 cm^-1 and 724 cm^-1 increases from 0.99 to 1.18 on applying pressure up to 19.28 ± 0.01 GPa, and that these changes are due to the conversion of TeO₃ into TeO₄ structural units in the tellurite network. It is found that pressure causes densification of the tellurite network by the enhancement of co-ordination of cations, and an increase in distribution of Te-O and Ba-O bond lengths. The original glass structure is restored upon the release of pressure.