ICT2014 Abstracts

Yb₁₄MnSb₁₁ is a high efficiency p-type thermoelectric material in the high temperature region (zT ~ 0.8 at 1200K). While it has excellent stability and thermal properties, this p-type compound has a high carrier concentration (1.3*10²¹cm^-3). The addition of a rare earth (RE) metal should provide an additional electron to the compound, thereby reducing the carrier concentration. In principle, this has been shown for RE = La where the zT is improved to greater than 1 for the compound Yb_13.4La_0.6MnSb₁₁. Other RE cations should also optimize carrier concentration and at the same time change the volume of the structure, leading to effects in both electrical resistivity and Seebeck coefficient. Additionally, cation alloying should have the effect of reducing the low thermal conductivity further. Therefore, we have partially substituted Yb with Pr and Sm and characterized these phases by powder X-Ray diffraction. Phase pure powder samples of Yb_14-xRE_xMnSb₁₁ (RE = Pr and Sm, x = 0.2, 0.4, 0.6, 0.7, 0.8, 0.9 and 1) were synthesized by annealing at 1375 K for one week. The substitution limit for Pr and Sm in Yb₁₄MnSb₁₁ was determined to be 0.7 and 0.9 according to powder X-ray diffraction pattern. Bulk powder was pressed into dense pellets with larger than 97% density by using Spark Plasma Sintering (SPS). The pellets were further studied by electron microprobe and powder X-ray diffraction. Compared with Yb₁₄MnSb₁₁, the Seebeck coefficient of Yb_14-xPr_xMnSb₁₁ (x= 0.2, 0.4, 0.6, 0.8) increases by 25% with increasing electrical resistivity. Considering thermal conductivity which showed a subtle drop, zT value of Yb_13.8Pr_0.2MnSb₁₁ reached 1.2 at 1275 K, showing a small enhancement compared to Yb_13.4La_0.6MnSb₁₁.