Heavy fermion behaviour of the cerium-filled skutterudites CeFe4Sb12 and Ce0.9Fe3CoSb12

The low temperature properties of polycrystalline samples of the filled skutterudites CeFe4Sb12, Ce0.9Fe3CoSb12 and La0.9Fe3CoSb12, as well as the unfilled skutterudites Fe0.05C0.95Sb3 and CoSb3, have been investigated by means of electrical resistivity, specific heat and magnetic susceptibility measurements. The resistivity of CeFe4Sb12 exhibits a rather abrupt drop-off with decreasing temperature near 100 K; this drop-off temperature increases with increasing applied hydrostatic pressure, which is reminiscent of the onset of coherence in so-called Kondo lattice materials. The compounds CeFe4Sb12 and Ce0.9Fe3CoSb12 exhibit values of the electronic specific heat coefficient and Pauli susceptibility at low temperature which are enhanced over those of the lanthanum-filled and unfilled skutterudites. These quantities yield a Wilson ratio of order unity, which indicates that they both correspond to the properties of itinerant electrons. These transport, magnetic and thermodynamic properties suggest a moderately heavy fermion ground state in CeFe4Sb12 and Ce0.9Fe3CoSb12.