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

Abstract 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 B 11 Magic Angle Spinning Nuclear Magnetic Resonance studies. The short-range structure of molybdenum tellurite glasses consists of TeO 4 , TeO 3 and MoO 6 structural units. Increase in MoO 3 concentration from 20 to 50 mol% decreases the Te O coordination from 3.48 to 3.26 and lowers the glass transition temperature (T g ) due to increase in the concentration of weaker Mo O bonds at the expense of stronger Te O bonds. Refractive index of molybdenum tellurite glasses increases while the dielectric constant decreases with increase in MoO 3 concentration. The addition of B 2 O 3 in the tellurite network enhances T g and suppresses the tendency towards crystallization. The effects of B 2 O 3 are similar to that of MoO 3 and it produces structural transformations: TeO 4  → TeO 3 and BO 4  → BO 3 . The addition of B 2 O 3 does not significantly modify the optical properties but the dielectric constant decreases by a small amount. Glass sample of 20MoO 3 -80TeO 2 was annealed at 280 °C for ~ 500 h 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 T g by 10 °C, due to the structural rearrangements in the intermediate range order without effecting Te O and Mo O speciation.