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

Abstract

Skutterudite‐type pnictides based on CoSb3 are promising semiconductor materials for thermoelectric applications. An exhaustive structural characterization by synchrotron X‐ray powder diffraction of different M‐filled CoSb3 (M = Y, K, Sr, La, Ce, Yb) skutterudites, with a panoply of M atoms with very different chemical nature, allows to better understand the effects of filling from a crystallo‐chemical point of view. These analyses focus on the correlation of chemical and structural features with the enhanced thermoelectric properties displayed by certain families of filled‐CoSb3 skutterudites. These are mainly determined by Sb positional parameters, yielding Oftedal plots that depend on the filling fraction, ionic state, and atomic radius of the filler. Together with the distortion of [Sb4] rings and [CoSb6] octahedra present in the skutterudite structure, these results are linked to the band‐convergence concept and its influence on the thermoelectric transport properties. Here, the structural changes observed in the different chemical compositions are relevant to understand the improved thermoelectric performance of single partially filled n‐type skutterudites.

Strongly reduced lattice thermal conductivity in Sn-doped rare-earth (M) filled skutterudites MxCo4Sb12−ySny, promoted by Sb–Sn disordering and phase segregation

“…The bigger B E for the Ce-and Yb-lled compounds indicates the effect of band convergence for both compositions, with the almost temperature independent at line for Yb-the result that we are looking for, since band converge has been proven useful to enhance the thermoelectric performance in skutterudites. 8,28,39 This band convergence is also the reason why the electronic quality factor increases somewhat with temperature, until the bipolar conduction kicks in. The temperature dependent thermal conductivity is plotted in Fig.…”

“…Remarkably, the lling fraction is increased by Sn-doping for Ce-, La-and Yb-lled skutterudites. Thus, the compounds display a lower structural distortion (more perfect (Sb, Sn) 4 squares) than their undoped counterparts, which is benecial for the thermoelectric performance because of the associated band convergence 28,39 and enhanced resonant scattering of phonons. 40…”

Metastable Materials Accessed under Moderate Pressure Conditions (P ≤ 3.5 GPa) in a Piston-Cylinder Press

“…The filling fraction fluctuation reduces the lattice thermal conductivity, via strain-field scattering of high-energy phonons. This strategy of favouring the uneven filling factor under HP conditions has been extended to other elements, such as K, Sr, Y and more [ 90 ].…”

SnSe:Kx intermetallic thermoelectric polycrystals prepared by arc-melting

“…Nevertheless, some of the more successful types of thermoelectrics are based on tellurides [17], such as bismuth telluride (Bi 2 Te 3 ) [4-7, [18][19][20][21][22], lead telluride (PbTe) [23][24][25] and germanium telluride (GeTe) [26][27][28][29][30][31]. Skutterudites are another attractive family of thermoelectrics, as they are high mobility semiconductors that chemically and structurally offer many ways of doping and property tuning [1, 32,33]. They can be prepared by various methods in addition to conventional metallurgy, including high-pressure synthesis [34][35][36], melt spinning [37,38], microwave synthesis [39], etc.…”

“…The advantage of using KH as starting material to introduce K has to do with its easy handling, avoiding issues with ambient oxidation, with the expectation that H 2 is released and lost during synthesis. A similar method, using KH, was employed recently to produce K-filled CoSb 3 skutterudite under high pressure [32]. The synthesis may also help avoiding the formation of tin oxide, which has been shown to be responsible for an undesired increase of effective thermal conductivity [83][84][85].…”