Physical phenomena of the cage compounds RE₃Pd₂₀Si₆ (RE = Yb, Lu)

Features of atomic rattling motion (anharmonic thermal vibrations), a phenomenon that relates to a new route for devising materials for thermoelectric applications of complex metal alloys, have been detected in certain members of the RE₃Pd₂₀X₆ (RE = rare-earth element, X = Si or Ge) series of compounds relating to details of their particular crystal structure. In this work, thermal properties of Yb₃Pd₂₀Si₆ and Lu₃Pd₂₀Si₆ are reported as a first account of their position with respect to atomic rattling in an attempt to demystify the conditions that favour this dynamic materials property.