Inelastic neutron scattering measurements on several Tl filled skutterudites (Tl0.5Co3.5Fe0.5Sb12 , Tl0.8Co3FeSb12 , and Tl0.8Co4Sb11Sn ) all show a sharp peak in the vibrational density of states at 57±2 K , which is absent in the unfilled skutterudite CoSb3 . Heat capacity measurements on Tl0.8Co4Sb11Sn as compared to CoSb3 are consistent with the presence of a localized vibrational mode associated with the “rattling” thallium atoms in this filled skutterudite compound. Both results are well described by a localized Einstein mode model with an Einstein temperature ΘE of 53±1 K . These data provide perhaps the clearest example of local mode behavior in a concentrated metallic system.
Physical Review Letters