We present low-temperature heat and charge transport as well as caloric properties of a ThAsSe single crystal. An extra -AT(1/2) term in the electrical resistivity, independent of magnetic fields as high as 14 T, provides evidence for an unusual scattering of conduction electrons. Additionally, both the thermal conductivity and the specific heat show a glass-type temperature dependence which signifies the presence of tunneling states. These observations apparently point to an experimental realization of a two-channel Kondo effect derived from structural two-level systems.

The current paper gives an overview of the newly obtained thermal expansion coefficients of skutterudites as well as those so far available in literature. Thermal expansion was determined for CoSb 3 , Pt 4 Sn 4.4 Sb 7.6 , for As-and Ge-based skutterudites as well as for various high-ZT skutterudites ͑microand nanostructured͒ with didymium ͑DD͒ and mischmetal ͑Mm͒ as filler atoms in frameworks of ͑Fe 1−x Co x ͒ 4 Sb 12 and ͑Fe 1−x Ni x ͒ 4 Sb 12 , and for double and triple-filled skutterudites such as Ca 0.07 Ba 0.23 Co 3.95 Ni 0.05 Sb 12 and Sr 0.025 Ba 0.075 Yb 0.1 Co 4 Sb 12 . For low temperatures, a capacitance dilatometer was used ͑4-300 K͒, whereas for temperatures 300Ͻ T Ͻ 750 K, a dynamic mechanical analyzer was employed. For a set of Ge-, P-, and Sb-based skutterudites, lattice parameters of single crystals, measured at three different temperatures, were used to derive the thermal expansion coefficient. The semiclassical model of Mukherjee ͓Phys. Rev. Lett. 76, 1876 ͑1996͔͒ has been successfully used to quantitatively describe the thermal expansion coefficient in terms of Einstein and Debye temperatures, which compare well with the corresponding results from specific heat, electrical resistivity, or temperature dependent x-ray measurements.

Magnetization, specific heat, and electrical resistivity measurements were made on single crystals of the filled skutterudite compound PrOs4As12. Specific heat measurements indicate an electronic specific heat coefficient γ ∼ 50−200 mJ/mol K 2 at temperatures 10 K ≤ T ≤ 18 K, and ∼ 1 J/mol K 2 for T ≤ 1.6 K. Magnetization, specific heat, and electrical resistivity measurements reveal the presence of two, or possibly three, ordered phases at temperatures below ∼ 2.3 K and in fields below ∼ 3 T. The low temperature phase displays antiferromagnetic characteristics, while the nature of the ordering in the other phase(s) has yet to be determined.

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