Vibrational and Electronic Contributions to the Specific Heat of Pd₅₆₁Phen₃₆O₂₀₀

Abstract

Specific heat measurements have been performed on the metal cluster compound Pd₅₆₁Phen₃₆O₂₀₀, which consists of Pd₅₆₁ clusters surrounded by ligand shells. Above 1 K the specific heat can be successfully described by a contribution due to vibrations of the cluster as a whole, modeled via the Debye scheme, and a contribution due to vibrations within the cluster. The intra-cluster vibration frequencies are calculated in an elastic continuum approach. By solving the Navier equation, using stress free boundary conditions, eigenvalue equations for the spheroidal and toroidal oscillations are obtained. The results compare well with those of molecular dynamics calculations and experiment. The most salient feature of the specific heat below 1 K is a linear contribution C = γT, which is interpreted as an electronic contribution. The observed value of γ is about one third of the value of bulk Palladium.