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

The low temperature properties of polycrystalline samples of the filled skutterudites CeFe4Sb12 ,C e 0 : 9 Fe3CoSb12 and La0:9Fe3CoSb12, as well as the unfilled skutterudites Fe0:05Co0:95Sb3 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.