Thermal and Optical Properties of New Tellurite Glasses

Abstract

New optical tellurite glasses have been synthesized in the form 80TeO2-5TiO2-(15-x)WO3-xAnOm where AnOm is Nb2O5, Nd2O3 and Er2O3 and x = 0.01, 0.1, 1, 3, 5 and 7 mol%. Densities of the prepared glasses were measured at 20ºC and molar volumes were calculated.

Thermal properties such as glass transition temperature Tg and specific heat capacities in the glassy state Cpg and supercooled liquid state Cpl were determined by using differential scanning calorimetry (DSC) techniques. Thermal stability S and Hurby’s parameter H of the glasses have been estimated. Good thermal stabilities have been achieved for most of the prepared samples. Values of the ratios Cpl/Cpg have been found to range from (1.46 to 1.90), suggesting that these glass forming melts can be classified as fragile liquids. Fragility were found to vary with modifier content, it increases with increasing Er2O3 and decreases with (Nb2O5 and Nd2O3) contents. Quantitative analysis of Tg accompanied with structural correlations was carried out using the calculated number of bonds per unit volume, average stretching force constant and crosslink density that present in the glass network.

Optical properties in the range of ultraviolet, visible and infrared spectrum were studied. In the visible range, linear refractive indices of the prepared samples were measured by using traveling microscope techniques at wavelengths: 486.13 nm, 587.56 nm, 589 nm, and 656.27 nm. They were found to range from (1.945 to 2.22) and showed remarkable composition dependence. The modified glasses exhibit high refractive index nλ and low Abbe number. The linear refractive indices were found to increase as the modifiers concentrations of transition metals Nb5+ and the rare earth cations (Nd3+ and Er3+) increases. In contrast Abbe number was found to decrease as the modifiers concentration increases. Electronic polarizability and molar refractivity of these glasses have been estimated.

In the ultraviolet range, optical absorption spectra were recorded for the present glass systems in the range of 200-900 nm. The optical energy gaps Eopt and Urbach energies have been calculated from the optical absorption edge. Variation of Eopt with WO3 content was observed and found to be from (2.42-3.59 eV). The energy levels of WO3 being introduced between (Eopt) of TeO2 resulting in lowering Eopt with increasing WO3 content. Compositional dependence of ultraviolet cut-off was observed and found to range from (418-445 nm). Finally, in the IR range, infrared absorption spectra were measured in the range of (4000-200) cm-1 for pure TeO2 and the modified glasses. Structural variation of pure TeO2 was evident from the disappearance of the absorption band at 774 cm-1 and the slight shift of the absorption edge towards low wavenumber regions.