High temperature thermoelectric properties of Yb_14-xCa_xMnSb₁₁ made by reaction of the elements

The properties of the isovalent substitution of Ca²⁺ for Yb²⁺ will be presented for the Yb_14-xCa_xMnSb₁₁ solid solution made by a direct reaction of elements (x = 0, 1, 2, 3, 4) with excess Mn (2×). Composition and phase purity was analyzed via powder X-ray diffraction. Electron microprobe analysis showed the presence of Mn inclusions. High temperature thermoelectric property measurements were performed including Seebeck, resistivity, and thermal conductivity (300-1300 K). While all the samples had impurities present, the Seebeck coefficients were enhanced, electrical resistivity was higher and showed a peak at approximately 800 K which may be attributed to Mn inclusions. The total thermal conductivity was lowered compared with Yb₁₄MnSb₁₁, as expected for replacing the heavier Yb²⁺ with the lighter Ca²⁺ cation. The maximum zT for the Yb_14-xCa_xMnSb₁₁ system was observed for x = 2, reaching the value of 1 at 1200 K.