Improved thermoelectric performance in Yb14Mn1-xZnxSb11 by the reduction of spin-disorder scattering

Rare-earth transition metal compounds Yb14Mn1-xZnxSb11, isostructural with Ca14AlSb11, have been prepared using a metal flux growth technique for thermoelectric property measurements (with x = 0.0, 0.2, 0.3, 0.4, 0.7, 0.9, and 1.0). Single-crystal X-ray diffraction and electron microprobe analysis data indicate the successful synthesis of a solid-solution for the Yb14Mn1-xZnxSb11 structure type for 0 < x < 0.4. Hot-pressed polycrystalline samples showed that the product from the flux reaction was a pure phase from x = 0 through x = 0.4 with the presence of a minor secondary phase for compositions x > 0.4. High-temperature (298 K-1275 K) measurements of the Seebeck coefficient, resistivity, and thermal conductivity were performed on hot-pressed, polycrystalline samples. As the concentration of Zn increases in Yb14Mn1-xZnxSb11, the Seebeck coefficient remains unchanged for 0 <= x <= 0.7 indicating that the free carrier concentration has remained unchanged. However, as the nonmagnetic Zn2+ ions replace the magnetic Mn2+ ions, the spin disorder scattering is reduced, lowering the resistivity. Replacing the magnetic Mn2+ with non magnetic Zn2+ provides an independent means to lower resistivity without deleterious effects to the Seebeck values or thermal conduction. Alloying the Mn site with Zn reduces the lattice thermal conductivity at low temperatures but has negligible impact at high temperatures. The reduction of spin disorder scattering leads to an similar to 10% improvement over Yb14MnSb11, revealing a maximum thermoelectric figure of merit (zT) of similar to 1.1 at 1275 K for Yb14Mn0.6Zn0.4Sb11.