Thermoelectric properties of single-crystal CeRhSn with valence fluctuations

The thermoelectric power S, electrical resistivity rho and thermal conductivity K have been measured for single crystals of CeRhSn and LaRhSn with the hexagonal ZrNiAl-type structure. For CeRhSn, a broad maximum of 60 muV/K appears in S(T) along both the a- and c-axes at 160 K, being typical of a valence-fluctuating Ce compound. The rho(a)(T) exhibits a high maximum of 350 muOmegacm at 70 K, whereas rho(c)(T) decreases monotonically on cooling from 300 to 1.3 K. Although the measured K(T) for CeRhSn is smaller than that for LaRhSn, the phonon contribution K-ph for the former is approximately twofold that for the latter. The relation K-ph(LaRhSn) < K-ph(CeRhSn) < K-ph(LaRhIn) suggests that the phonon scattering induced by atomic disorder is most significant in LaRhSn. The thermoelectric figure of merit Z for CeRhSn has the maxima of 3 x 10(-4) K-1 at 160 K and 7 x 10(-4) K-1 at 130 K along the a- and c-axes, respectively.