Abstract
The effects of Fe-substitution on partially Yb filled skutterudites YbyFexCo4-xSb12 are presented from the viewpoint of crystal structure and thermoelectric, magnetic, and transport properties. A series of polycrystalline n-type YbyFexCo4-xSb12 (0.21 ≤ y ≤ 0.47, 0 ≤ x ≤ 0.76) samples were prepared using a high-pressure and high-temperature method. X-ray diffraction data suggest that all the compounds are high-purity skutterudites. For the YbyFexCo4-xSb12 with Yb content higher than 0.29 and Fe content lower than 1, the lattice constant shows a saturated behavior despite the change in the Yb/Fe content. Rietveld refinement based on the synchrotron radiation X-ray data implies that the rectangular Sb4 ring is transformed into square with increasing Yb content and/or Fe substitution content. The Yb valence gradually decreases as the Fe content increases from magnetic susceptibility analysis. According to the specific heat analysis, higher Yb filling benefits the lower Debye temperature while the Fe substitution leads to an increased Debye temperature. The Einstein temperature decreased with increasing Yb filling fraction, but Fe substitution for the Co site does not change the Einstein temperature further. Fe-substitution causes the reduction of total thermal conductivity κ, which mainly originates from the decrease of electron thermal conductivity contribution. The resistivity, Seebeck coefficient, thermal conductivity, and figure of merit (ZT) were effectively tuned due to the optimization of the carrier concentration. At the same carrier concentration, the hall mobility was decreased by Fe substitution. The proper Fe substitution content (0.2 in Yb0.25Fe0.2Co3.8Sb12) can result in a relatively high effective mass.
Highlights
Following Slack’s ideal thermoelectric (TE) materialPhonon Glass and Electron Crystal concept, CoSb3 based skutterudites, which have an open structure (cage-like cubic unit cell (Im3) with two icosahedron oversized voids at the2a positions (12-coordinated)) and crystal-like electric transport properties,1–3 have been intensely pursued as one of the most promising TE materials
We studied the influence of both Yb filling and Fe substitution on the crystal structure and physical properties of YbyFexCo4-xSb12 and compared the crystal structure, TE properties, and magnetic properties of YbyCo4Sb12 and
X-ray diffraction (XRD) and EPMA results indicate that the synthesized compounds were high purity skutterudites
Summary
Phonon Glass and Electron Crystal concept, CoSb3 based skutterudites, which have an open structure CoSb3 skutterudites can dramatically reduce their relatively high phonon mobility (thermal conductivity) while keep their excellent electric mobility. The high-pressure synthesis technique can improve the filling fraction limit (FFL) of Yb in CoSb3 and provide a wider tuning of jL.. To further optimize the TE performance, the excess electrons in Yb0.29Co4Sb12 can be compensated by introducing a hole donor element in the. We studied the influence of both Yb filling and Fe substitution on the crystal structure and physical properties of YbyFexCo4-xSb12 and compared the crystal structure, TE properties, and magnetic properties of YbyCo4Sb12 and. The physical properties were studied by measuring the dc magnetic susceptibility, specific heat, magnetroresistivity (MR), electric resistivity, Seebeck coefficient, Hall effect, and thermal conductivity
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