The phonon densities of states of trigonal,vitreous and red amorphous selenium

For trigonal, vitreous and red amorphous Se the phonon densities of states F(hω) have been determined by inelastic neutron scattering from powder samples. For trigonal Se F(hω) is compared with the phonon dispersion measured by Teuchert1] and a frequency spectrum derived from a model calculation by Etchepare et al.2]. This calculation helps interpreting the changes in characteristic vibrational modes when going from the ordered to the disordered phase of Se. It is shown that at present, however, the models for trigonal Se are not good enough to calculate a reliable F(hω). The ω-dependence of F(hω) at low frequencies nicely confirms the predictions of a model which was developed for high polymeric chains by Genensky et al.3]. For all three modifications the lattice specific heat c_v(T) was deduced from the phonon spectra. The data obtained for the different modifications are compared among each other and also with the measured data of Grosse et al.4] (c_v(T) for red amorphous Se has not been measured before). From our data as well as from the c_p-data of Grosse the Debye temperatures as a function of temperature have been calculated. For vitreous Se between 10 and 160 K the agreement is excellent, for trigonal Se there are certain deviations which are discussed.