ICT2014 Abstracts

Yb-doped n-type skutterudites have been widely studied in the past decade due to their good thermoelectric properties, yet there has been debate about the solubility limit of Yb in skutterudite phase. In this paper, a series of isothermal sections of the ternary phase diagram of Yb-Co-Sb system were studied, and different phase regions near CoSb₃ were identified. The three-phase region on the Co-rich side of Yb-doped skutterudites (CoSb₃, CoSb₂ and YbSb₂) results in a fixed skutterudite composition Yb_xCo₄Sb₁₂ with maximum Yb content at a certain temperature (for example x = 0.44 ± 0.01 at 700C), whereas the three-phase region (CoSb₃, YbSb₂ and liquid) on the Sb-rich side leads to a fixed composition Yb_xCo₄Sb₁₂ with relatively lower Yb content at a given temperature (x = 0.26 ± 0.02 at 700C). As temperature increases, the Yb content in both fixed compositions increases as well. This gives guideline for synthesizing samples with the optimum carrier concentration and thus optimized thermoelectric properties in a flexible composition range. The phase regions near CoSb₃ and the temperature dependence of Yb solubility in skutterudite phase also explain the debate about Yb solubility.