High-Temperature Transport Properties of the Zintl Phases Yb11 GaSb9 and Yb11 InSbg9

Two rare-earth Zintl phases, Yb11GaSb9 and Yb11InSb9, were synthesized in high-temperature self-fluxes of molten Ga and In, respectively. Structures were characterized by both single-crystal X-ray diffraction and powder X-ray diffraction and are consistent with the published orthorhombic structure, with the space group Iba2. High-temperature differential scanning calorimetry (DSC) and thermal gravimetry (TG) measurements reveal thermal stability to 1300 K. Seebeck coefficient and resistivity measurements to 1000 K are consistent with the hypothesis that Yb11GaSb9 and Yb11InSb9 are small band gap semiconductors or semimetals. Low doping levels lead to bipolar conduction at high temperature, preventing a detailed analysis of the transport properties. Thermal diffusivity measurements yield particularly low lattice thermal conductivity values, less than 0.6 W/m K for both compounds. The low lattice thermal conductivity suggests that Yb11MSb9 (M = Ga, In) has the potential for high thermoelectric efficiency at high temperature if charge-carrier doping can be controlled.