Structure, thermal analysis and optical properties of lithium tungsten-titanophosphate glasses

A melt-quenching method is used to prepare homogeneous glasses inside the 20Li2O-(50-x)Li2WO4-xTiO2-30P2O5 (x = 0, 5, 8, 10 and 15 mol%) system. The amorphous and glassy states of the glasses are evidenced by the X-ray diffraction and differential scanning calorimetry (DSC) analysis, respectively. The glasses were found to be colorless. The determined parameters for the glasses such as density, molar volume and glass transition temperature (Tg) depend strongly on the chemical composition of the glasses. The density and Tg are found to decrease and increase with TiO2 content, respectively. Infrared (IR) spectroscopy is used to characterize their structural approach. This technique has allowed the identification of different phosphate structural units mainly pyrophosphate and metaphosphate in their structure. From the absorption edge studies, the values of the optical band gap, Eg, and Urbach energy, ΔE, were evaluated. The optical band gap is found to depend on the glass composition and it decreases as the content of the TiO2 increases.