A study of the vibrational spectrum of amorphous and crystalline SeTe samples by inelastic neutron scattering

Abstract

The vibrational density of states of both crystalline (trigonal) and amorphous samples of Se96.85Te3.15, Se93.6Te6.4, Se86.6Te13.4, Se79Te21 and of crystalline Se have been determined by inelastic neutron scattering. In each case the spectrum was found to be divided into three bands which for the amorphous specimens are at 5.6, 14 and 30.5 meV and for the crystalline specimens are at 6.5, 14 and 28.5 meV. At the lowest energies the amorphous samples, in common with other amorphous materials, show an omega 2-dependence which then increases over a short range to a higher power of the energy. The crystalline specimens have an omega 1.5-dependence at low energies. The temperature dependence of the specific heat of crystalline Se calculated from these data is in good agreement with that quoted in the literature. S(Q) for the amorphous samples was also measured and this shows that the first- and second-neighbour distances are similar to those for crystalline Se. This study suggests that crystalline SeTe resembles a chain polymer of helical chains with weak inter-chain bonding. In the amorphous samples the structure is similar but with inter-chain entanglements.