Substantial thermal conductivity reduction in mischmetal skutterudites Mm_xCo₄Sb₁₂ prepared under high-pressure conditions, due to uneven distribution of the rare-earth elements

Abstract

Low-cost n-type Mischmetal-filled CoSb3 skutterudites with elemental filling-fraction separation, prepared at high pressure, exhibit markedly low lattice thermal conductivity.

Phase Formation Behavior and Thermoelectric Transport Properties of P-Type YbxFe3CoSb12 Prepared by Melt Spinning and Spark Plasma Sintering

“…1 3 2reflections are clearly observed in Yb 0.9 Fe 3 CoSb 12 . These results suggest that a composite of two different skuttrudites was generated by MS and SPS due to uneven distribution of cations, and the formation of two different filled skutterudites has been reported previously [14][15][16][17][18]. The calculated lattice constants of the majority skutterudite (9.0820(1) Å for Yb 0.85 Fe 3 CoSb 12 and 9.0881(7) Å for Yb 0.9 Fe 3 CoSb 12 ) are smaller than those of the minority skutterudite (9.1659 5 (μHall) at 300 K by using a Hall measurement system (HMS-3000, Ecopia, Chandler Heights, AZ, USA) with a van der Pauw configuration.…”

“…Distinct left shoulders (red arrows in Figure 1b) can be seen in all XRD peaks of Yb0.85Fe3CoSb12, and separated smaller XRD peaks (blue arrows in Figure 1b) of the (0 3 1) and (1 3 2) reflections are clearly observed in Yb0.9Fe3CoSb12. These results suggest that a composite of two different skuttrudites was generated by MS and SPS due to uneven distribution of cations, and the formation of two different filled skutterudites has been reported previously [14][15][16][17][18]. The calculated lattice constants of the majority skutterudite (9.0820(1) Å for Yb0.85Fe3CoSb12 and 9.0881(7) Å for Yb0.9Fe3CoSb12) are smaller than those of the minority skutterudite (9.1659(5) Å for Yb0.85Fe3CoSb12 and 9.2037(9) Å for Yb0.9Fe3CoSb12), indicating that the compositions of the composite are YbxFe3−yCo1+ySb12 (Co-rich skutterudite) and YbzFe3+yCo1−ySb12 (Fe-rich skutterudite), related with the size difference between Fe 2+ (CN = 6, 0.61 Å) and Co 3+ (CN = 6, 0.55 Å) [22].…”

“…In PbTe-based TE alloys, this approach has been widely used with decomposition during the cooling process and resulted in the formation of nanocomposites with uniformly distributed nanoinclusions [12,13]. Recently, several studies for the preparation of bulk-type materials with multiple phases have been reported in La-, Ce-, and Yb-filled skutterudites mainly due to the uneven distribution of cations [14][15][16][17][18].…”

Unveiling the Correlation between the Crystalline Structure of M‐Filled CoSb3 (M = Y, K, Sr) Skutterudites and Their Thermoelectric Transport Properties

“…In our previous work, we have described the phase-segregation in filler-rich and filler-poor phases for some skutterudite compounds prepared under high pressure, which has been a key element to account for the thermoelectric improvement of these materials. [45][46][47][48] This segregation is manifested in the SXRD patterns as a splitting of the diffraction peaks at high scattering angles, in such a way that the patterns could be analyzed as a mixture of two skutterudite phases with very close unit-cell parameters and different filling factors, as M-rich and M-poor phases. This phenomenology can only be detected thanks to the high angular resolution of this technique.…”

“…These are compared with our previously reported data on M x Co 4 Sb 12 (M = La, Ce, Yb), yielding a thorough description of the structural modifications that take place upon filling without doping at Co or Sb site. [45][46][47][48] Synchrotron data permit us to perform a more exhaustive and detailed analysis of the slightest structural changes suffered by the skutterudite structure with much better resolution than that reported until now. This set of information is related to the chemical changes that have been described in relation to band convergence and increased DOS in the conduction band [42][43][44] and the thermoelectric transport properties of the differently single-filled compounds.…”