Low-temperature thermoelectric properties of Yb₁₄MSb₁₁(M = Mn, Zn)

Abstract

We have synthesized Yb14MnSb11 and Yb14ZnSb11 to study the thermoelectric properties at low temperature (4<T<300 K). The materials were characterized by means of susceptibility (χ), resistivity (ρ), thermopower (S) and thermal conductivity (κ) measurements. The κ(T) is dominated by phonon heat transport, and the Jahn–Teller effect in the MnSb4 tetrahedra does not make a significant contribution to the reduction of the thermal conductivity at intermediate temperatures and above. A sharp minimum in κ(T) for M = Mn occurs in the ferromagnetic transition at TC = 54 K. The thermopower for Yb14MnSb11 is positive and increases upon heating, while that for Yb14ZnSb11 exhibits a negative peak at 60 K, before increasing and becoming positive. These different behaviors support the assertion that the Yb ions are in a divalent state in the former and in a valence fluctuating state in the latter.