Network dynamics of chalcogenide glasses. II. Silicon diselenide

The scattering function S(Q,E) of vitreous ${\mathrm{SiSe}}_2$ at 50 K was measured with inelastic neutron scattering over a wide range of variables (0.5${̊}^{\mathrm{-}1}$, -20<E<80 meV), with use of a chopper spectrometer at the Intense Pulsed Neutron Source. The data are analyzed in terms of the effective one-phonon density of states G(E), the Q dependence of S(Q,E) at different values of energy transfer E, and the elastic structure factor $S_{\mathrm{el}(\mathrm{Q}}$). The data are discussed in terms of the normal modes of vibration of a Si(${\mathrm{Se}}_{1/2}$ ${)}_4$ molecule. Certain features in the data can be generally identified with such modes on the basis of the behavior of the dynamic structure factor S(Q,E) at fixed E. Other features imply more complex structural entities, including edge-linked tetrahedral chains characteristic of crystalline ${\mathrm{SiSe}}_2$ and an admixture of corner-sharing units, not found in the crystal.