Elastic and structural studies of Te0₂-Nb₂0₅-ZnO and TeO₂-Nb₂O₅-ZnO-Er₂O₃ tellurite glass systems / Nur Baizura Mohamed

Ternary (90-x)TeO2-10Nb2O5-(;c)ZnO, x - 0 - 15 mol% and 75TeO2-(10-^)Nb2O5- 15ZnO-(y)Er203, y = 0.0 - 2.5 mol% glass systems have been prepared by meltquenching method. Elastic properties together with structural properties of the glasses were investigated by measuring sound velocity using the pulse-echo-overlap technique and Fourier Transform Infrared (FTIR), respectively. For (90-x)TeO2- 10Nb2O5-(x)ZnO glass, ultrasonic velocities, related elastic moduli and Debye temperature were observed to drop at x = 5mol% but increased back at x > 5 mol%. The former is suggested to be due to increase in non-bridging oxygen (NBO) ions as a direct effect of TeC>2 reduction while the latter occur is suggested due to increase in bridging oxygen (BO) ions which improved the glass network rigidity. For 75TeC>2- (10-j)Nb2O5-15ZnO-(y)Er2O3 glass, shear velocity, shear modulus, Young's modulus and Debye temperature were observed to initially decrease at y = 0.5 mol% but remained constant between .v = 1.0 mol% to y = 2.0 mol%, before increasing back with Er203 addition aty = 2.5 mol%. The initial decrease of shear velocity and related elastic moduli are suggested to be due to increase in NBO ions. This was followed by competition between BO and NBO ions in the glass network between y = 0.5 to 2.0 mol%, where BO seems to be more dominant compared to NBO when Nb205 content reached 2.5 mol% replacement with Er203. FTIR analysis on infrared (IR) absorption peak of Nb06 octahedral, Te03 trigonal pyramid (tp), Te04 trigonal bipyramid (tbp) and Zn04 tetrahedral indicates variation of BO and NBO in the glass network and this supports the explanation for the elastic properties given for both glasses. The combined results of ultrasonic velocity and IR absorption spectra revealed that each structural compound, Te02, Nb205, ZnO and Er203 play significant roles in formation of both BO and NBO and modifications of the glass network structure.