Structural, optical, dielectric and thermal properties of molybdenum tellurite and borotellurite glasses

Molybdenum tellurite and borotellurite glasses were prepared and structure-property correlations were carried out by density, X-ray diffraction, dielectric measurements, differential scanning calorimetry, UV–visible, infrared, Raman and B11 Magic Angle Spinning Nuclear Magnetic Resonance studies. The short-range structure of molybdenum tellurite glasses consists of TeO4, TeO3 and MoO6 structural units. Increase in MoO3 concentration from 20 to 50mol% decreases the TeO coordination from 3.48 to 3.26 and lowers the glass transition temperature (Tg) due to increase in the concentration of weaker MoO bonds at the expense of stronger TeO bonds. Refractive index of molybdenum tellurite glasses increases while the dielectric constant decreases with increase in MoO3 concentration. The addition of B2O3 in the tellurite network enhances Tg and suppresses the tendency towards crystallization. The effects of B2O3 are similar to that of MoO3 and it produces structural transformations: TeO4→TeO3 and BO4→BO3. The addition of B2O3 does not significantly modify the optical properties but the dielectric constant decreases by a small amount. Glass sample of 20MoO3-80TeO2 was annealed at 280°C for ~500h and changes in its density and thermal properties were studied; it was found that the annealing increases the glass density slightly, but it causes a drastic enhancement of Tg by 10°C, due to the structural rearrangements in the intermediate range order without effecting TeO and MoO speciation.