Contribution of atom vibrations to the latent heat of germanium

There is general agreement that atomic vibrations dominate the entropy of solid and liquid phases of materials. The changes of vibrational and configurational entropies upon melting are expected to be responsible for the latent heat, L = TΔS, but the relative importance of each is largely unknown today. Here, we report the vibrational spectra of germanium from 300-1373K measured with ARCS, a high flux direct geometry neutron spectrometer. Inelastic neutron spectra at temperatures below, near, and above the melting temperature of germanium (T_m = 1211K) allowed for direct assessment of the role of vibrational thermodynamics during melting. A large collapse of the higher frequency modes in the solid to lower frequencies was observed upon melting. Analysis of the vibrational spectra across the melting transition showed that at most 60% of the entropy of melting originates from the lower frequencies of atomic motion in the liquid phase. The remainder is probably from the larger configurational entropy of the liquid. Classical and ab-initio calculations are being performed to assess the change in phonon frequencies with temperature, and across the melting transition.