Low-energy modes and medium-range correlated motions in Pd79Ge21 alloy glass

It is well known that there are excess modes over the sound wave in low energy region below about 10 meV in glass materials, which do not exist in corresponding crystalline materials. We examined the low energy modes in a Pd79Ge21 alloys glass by means of inelastic neutron scattering. Measurements were performed on the crystal analyzer type time-of-flight spectrometer LAM-40 with PG(002) and Ge(311) analyzer mirror, which is installed at KENS. The dynamic structure factor S(Q,ω) was obtained over the wide momentum range from 0.5 to 5.2A-1. The measured S(Q,ω)'s have almost same momentum (Q) dependence at each energy (ℎω) in the energy range from 2.0 to 8.0 meV. In the energy region below 3 meV, we found a small shoulder peak at Q = 1.7A-1 in the momentum dependence of S(Q,ω). It corresponds to a prepeak in S(Q). Therefore it is concluded that the low energy modes in Pd79Ge21 alloy glass is mainly contributed from medium-range correlated motions in the cluster consisting of a few chemical short-range structure units of Pd6Ge trigonal prism. (author)