Physical properties and valence state of cerium in the filled skutterudite CePt4Ge12

Electronic, magnetic, and transport properties of the filled platinum-germanium skutterudite CePt4Ge12 are investigated. High resolution x-ray absorption spectroscopy measurements at the cerium LIII edge demonstrate that Ce in this compound has a temperature-independent valence close to three. However, magnetic susceptibility, thermopower, Hall effect, and electronic specific heat reveal a broad maximum at Tmax = 65-80 K, suggesting the presence of valence fluctuations. The Sommerfeld coefficient γ = 105 mJ mol-1 K-2, deduced from specific heat, indicates moderately enhanced band masses for CePt4Ge12. We discuss these findings and conclude that CePt4Ge12 represents a system at the border between intermediate valence (IV) and Kondo lattice behavior. In addition, the lattice specific heat and the thermal conductivity are discussed with respect to the vibrational dynamics of Ce in the [Pt4Ge12] framework. (paper)