Acoustic and optical properties of $(Li2O)0.2−x(Na2O)x(TeO2)0.8$ glasses

We study the ultrasonic properties of five different samples of $Na2O-Li2O-TeO2$ glass system within the temperature range 140–420 K (for longitudinal polarization) and 140–300 K (for transverse polarization). The variation of ultrasonic velocity of all samples shows negative gradient with temperature and has been explained by the existing theories. No well defined broad peak has been observed in the temperature variation of attenuation and a mixed alkali type peak starts growing at temperature ≈350 K. Composition dependence of elastic properties and density shows maximum or minimum at a critical concentration of $Na2O.$ Optical transmission and reflection spectra were recorded in the UV-visible region at room temperature. The physical quantities such as optical energy gap, refractive index and optical dielectric constant were evaluated from the spectra. The theoretical fitting of the optical absorption indicates that the present glass system behaves as indirect gap semiconductor.