The filled skutterudite CeOs4Sb12 and its nonmagnetic analogue LaOs4Sb12 have been synthesized in single-crystal form using the molten-metal-flux growth technique with Sb flux. Electrical resistivity measurements on CeOs4Sb12 indicate that it is a Kondo insulator with an energy gap of ΔE/kB~10 K. Lattice parameter and magnetic susceptibility measurements suggest that the Ce ions are trivalent in CeOs4Sb12. Specific heat and magnetization measurements reveal an enhanced value of the electronic specific heat coefficient γ~92 mJ mol-1 K-2 and Pauli susceptibility, reminiscent of a moderately heavy-fermion material.

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