Kondo insulating behaviour in the filled skutterudite compound CeOs₄Sb₁₂

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/k_B~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.