UCLA

Yb₁₄MnSb₁₁ is a promising thermoelectric material for high temperature applications with values of the non-dimensional figure of merit ZT peaking at 1.4 above 1200 K. Yb₁₄MnSb₁₁ exhibits low lattice thermal conductivity values and a p-type semimetallic behavior. This compound is a member of a large family of Zintl phases with a "14-1-11" A₁₄MPn₁₁ stoichiometry (Pn = As, Sb, Bi; A = Ca, La, Sr, Yb, Eu; M = Mn, Al, Cd, Ga, In, Nb, Zn). There is significant interest in investigating how substitutions on any of the atomic sites impact the band gap, lattice thermal conductivity and charge carrier concentration and mobility.

High energy ball milling is shown here to be a convenient method of synthesis to prepare Yb₁₄MnSb₁₁ and solid solution systems derived from this compound by substitution of elements. Here compositions in the Yb₁₄Mn_1-xAl_xSb_11-yBi_y, Yb₁₄MnSb_11-yAs_y, Yb_14-xCa_xMnSb₁₁, Yb_14-xLa_xMnSb₁₁ and Yb_14-xNa_xAlSb₁₁ systems are considered. Characterization of the synthesized compositions was done by X-ray diffraction, electron microprobe. High temperature measurements of the electrical and thermal transport properties were carried out up to 1275 K. The experimental results on solid solution samples are compared to that of pure Yb₁₄MnSb₁₁ samples prepared by the same synthesis technique. A single parabolic band degenerate Fermi statistical model was used to estimate various properties such as effective mass. Calculated lattice thermal conductivity in solid solutions was also compared to various models. Though some increase in ZT was calculated below 900K, none of the derivatives studied were calculated to have a averge ZT significantly higher than Yb₁₄MnSb₁₁.