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, UNi4B, UPt2In and UCu3+xCa2-x. The value of S at 300 K ranges from 16 to 70 muV/K. The rather large S is attributed to the strong scattering of conduction electrons by the 3f 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. (C) 2000 Elsevier Science B.V. All rights reserved.