Theoretical calculations of elastic properties and phonon dispersion of Se-Ge glass with various concentrations of Ge

The acoustic Gruneisen constants gamma(g)(L) and gamma(g)(T) have been calculated through Schofield's (Sch) equations and Bhatia-Singh's (BS) parameters for different concentrations of Ge in Se. The calculated results are in good agreement with experiment. The BS parameters have been used to calculate the phonon frequencies. The third order elastic constants (TOECs) have been calculated using Shiren's non-linear parameter, Thurston's equations and Rao-Venkatesh equation for this glass. The calculated TOECs have been: used to compute the pressure derivative of bulk modulus and is found to be in excellent agreement with experiment. The Smith-DeLaunay-Nath equation has been used to derive the absorption band position. From Smith DeLaunay-Nath's equation a new equation is derived to evaluate the which is found to be slightly higher than gamma(g)(HT). The slight difference between calculated gamma(g)(el) and gamma(g)(HT) may be due to the non-excitation of some vibrational frequencies at which the measurements have been made. The phonon frequency heights both in the case of longitudinal omega(L)(k) and transverse omega(T)(k) peaks, the TOECs, the absorption band position shows a sharp change and clearly demonstrate the formation of a new Species attributed to be GeSe4 at about 25 at.% of Ge. Experimentally the elastic moduli also show the same trend. No changes could be observed in the case of acoustic Gruneisen constants and pressure variation of bulk modulus.