High-temperature electrical and thermal transport properties of fully filled skutterudites RFe4Sb12 (R = Ca, Sr, Ba, La, Ce, Pr, Nd, Eu, and Yb)

Abstract

Fully filled skutterudites RFe 4 Sb 12 (R ¼ Ca, Sr, Ba, La, Ce, Pr, Nd, Eu, and Yb) have been prepared and the high-temperature electrical and thermal transport properties are investigated systematically. Lattice constants of RFe 4 Sb 12 increase almost linearly with increasing the ionic radii of the fillers, while the lattice expansion in filled structure is weakly influenced by the filler valence charge states. Using simple charge counting, the hole concentration in RFe 4 Sb 12 with divalent fillers (R ¼ Ca, Sr, Ba, Eu, and Yb) is much higher than that in RFe 4 Sb 12 with trivalent fillers (R ¼ La, Ce, Pr, and Nd), resulting in relatively high electrical conductivity and low Seebeck coefficient. It is also found that RFe 4 Sb 12 filled skutterudites having similar filler valence charge states exhibit comparable electrical conductivity and Seebeck coefficient, and the behavior of the temperature dependence, thereby leading to comparable power factor values in the temperature range from 300 to 800 K. All RFe 4 Sb 12 samples possess low lattice thermal conductivity. The correlation between the lattice thermal resistivity W L and ionic radii of the fillers is discussed and a good relationship of W L $ (r cage Àr ion ) 3 is observed in lanthanide metal filled skutterudites. CeFe 4 Sb 12 , PrFe 4 Sb 12, and NdFe 4 Sb 12 show the highest thermoelectric figure of merit around 0.87 at 750 K among all the filled skutterudites studied in this work.

Enhanced thermoelectric performance in p-type Ca0.5Ce0.5Fe4−xNixSb12 skutterudites by adjusting the carrier concentration

“…Truly, n-type skutterudites, possessing large effective masses and thus high power factors, have extensively obtained high ZTs exceeding 1.4 in double or triple filling system owing to the drastic decrease in lattice contribution to thermal transport [6][7][8][9][10][11][12]. P-type skutterudites based mainly on FeSb 3 [13][14][15][16][17] and being essential to module fabrications, however, exhibit relatively low ZTs for their low values of Seebeck coefficients. Therefore it is of great importance to improve the thermoelectric performances of p-type skutterudites which is tricky and needs to touch upon some fundamental physical issues.…”

“…Besides substitution at cation site, filling in the nanocages by rare earth, alkali or alkaline earth metal element is actually becoming popular to form a so-called filled skutterudites [6][7][8][9][10][11][12][13][14][15][16][17]22,23]. The main benefit of filling atoms is the introduction of excessive scattering to heat transport phonons originated from the "rattling" effect in the local structures.…”

Phonon engineering through crystal chemistry

“…Experimentally, materials in which guest atoms are strong rattlers are found to exhibit extremely low k L . 68,70 While it is widely accepted that rattling atoms result in strongly localized modes within the acoustic frequency range, the mechanism by which rattler modes reduce k L is under debate. Historically, the reduction in k L has been attributed to resonant scattering by the guest atom.…”

Thermoelectric Performance Enhancement of CeFe4Sb12 p-Type Skutterudite by Disorder on the Sb4 Rings Induced by Te Doping and Nanopores

“…However, RFe 4 Sb 12 itself is not a very good thermoelectric material, having a relatively low Seebeck coefficient and very high hole concentration. 14,15 To improve its thermoelectric properties, researchers either substitute at the Fe site with some electron donors, for example, Co/Ni, [8][9][10]12,[15][16][17][18][19] find new filling atoms, 9,12,20 10,11,21 All of these works focused on the intrinsic void and cation site. Besides the intrinsic void, the key characteristic of the skutterudite structure is the nearly square fourmembered rings of pnicogen atoms.…”