Improved thermoelectric performance in Yb₁₄Mn _1-xZn_xSb₁₁ by the reduction of spin-disorder scattering

Rare-earth transition metal compounds Yb₁₄Mn _1-xZn_x,Sb₁₁, isostructural with Ca ₁₄AlSb₁₁, 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 Yb₁₄Mn_1-xZn_xSb₁₁ 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 Yb ₁₄Mn_1-xZn_xSb₁₁, 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 ̃10% improvement over Yb₁₄MnSb₁₁, revealing a maximum thermoelectric figure of merit (zT) of ̃1.1 at 1275 K for Yb₁₄Mn_0.6Zn _0.4Sb₁₁.