Large thermoelectric power in several metallic compounds of cerium and uranium

The thermoelectric power S was measured from 1.5 to 500 K for CePdSb, CeRhSn, CeIrSn, UNi 4B, UPt 2In and UCu 3+ x Ga 2− x . The value of S at 300 K ranges from 16 to 70 μV/K. The rather large S is attributed to the strong scattering of conduction electrons by the 4f or 5f electrons in the vicinity of the Fermi level. A Lorentzian 4f-band model, which was previously proposed for valence fluctuating compounds, reproduces the temperature dependence of S for CeRhSn and CeIrSn. However, it can not reproduce the upward curvature of S( T) at low temperatures for the U compounds. We propose here a two-5f-bands model, which consists of a narrow (5–20 meV) and a wide (37–82 meV) Lorentzian density of states. The good fitting to the data of S( T) for the above U compounds suggests the presence of two energy scales.