Thermoelectric properties of Se and Zn/Cd/Sn double substituted Co₄Sb₁₂ skutterudite compounds

Abstract

Double-doped skutterudite CoSb compounds are reported as a good n-type thermoelectric system which operate in the mid-temperature range. Instead of filling the skutterudite phase to minimize the thermal conductivity, it is proposed to induce disorder in the pnicogen rings by the substitution of Zn/Cd/Sn and Se. Structural analyses of the prepared compounds were carried out by Rietveld refinement process. The compounds show overall reduction in thermal conductivity, particularly the lattice part. Since vibration modes of heat-carrying phonons predominantly fall within the frequency range of the pnicogen rings, double substitutions on those pnicogen rings are particularly helpful in distracting the thermal transport. As larger mass difference and strain fluctuations can more efficiently scatter the heat-carrying phonons through short mean free path, it drastically restrains the thermal transport of the compounds, and this effect has been successfully demonstrated using the Debye-Callaway-Klemens model. Smooth electrical transport behavior is observed in all the samples and the power factor values are quite comparable to reported values. Phonon scattering mechanism and local distortion in the structure of the compounds is also evaluated by Raman analysis. Collectively, a high peak ZT of ∼0.7 and ∼0.65 at 673 K is obtained for CoSbSeZn and CoSbSeSn compounds which shows more than 50% enhancement relative to the pristine CoSb system.

Structural Properties and Thermoelectric Performance of the Double-Filled Skutterudite (Sm,Gd)y(FexNi1-x)4Sb12

“…An even more effective approach aimed at the depression of λph consists of the introduction of a structural disorder through the substitution of Co by Fe/Co [36,37,38,39], Co/Ni [40,41] Fe/Ni [29,34,38,42,43] or Fe/Co/Ni [30,31], the substitution of Sb by Sb/Sn or Sb/Ge [36], or multiple filling of the cavity by DD (didymium) [36,38,41], Mm (mischmetal) [31,41], Ce/Yb [30], Ce/Nd [44], Ce/Yb/In [45] or by a mixture of alkaline-earths [46] with the possible addition of lanthanide elements [41,42] and elements of the IIIB group [47]. Multiple filling, in particular, was thoroughly studied [48], since it ensures a broadening of the range of phonon frequencies which can be perturbed by the rattling movement of doping ions. For this reason, when designing a multiple doping, a significant difference in the mass of the different fillers is generally recommended.…”

Enhancement in Thermoelectric Performance in Ti-doped Yb0.4Co4Sb12 Skutterudites via Carrier Optimization and Phonon Anharmonicity

“…Figure b presents the comparison plot of zT with those of recently reported single- and double-doped Co 4 Sb 12 -based materials, where the composition Yb 0.4 ­Co 3.96 ­Ti 0.04 ­Sb 12 exhibits the maximum zT of ∼0.85 at 623 K, which is considerably larger than that of the previously reported compositions, such as Ta 0.6 ­Co 4 ­Sb 12 , Cl 0.5 ­Co 4 ­Sb 12 , Dy 0.7 ­Co 2.5 ­Fe 1.5 ­Sb 12 , Ce 0.75 ­Fe 3 ­Co­Sb 12 , and Co 4 ­Sb 12 ­Se 0.1 ­Zn 0.04 . Moreover, a further improvement in zT can be made possible via a proper choice of doping elements with the selected filler atoms, resulting in an efficient TE material for midtemperature applications.…”

“…(a) Temperature dependence of figure of merit of Yb z Co 4−x Ti x Sb 12 (where z = 0, x = 0 or z = 0.4, x = 0, 0.04, and 0.08) with previously reported values of Ta 0.6 Co 4 Sb 12 45 and Ce 0.75 Fe 3 CoSb 12 . 66 (b) Comparative results of zT with previous reports of Ta 0.6 Co 4 Sb 12 , 45 Cl 0.6 Co 4 Sb 12 , 53 Dy 0.7 Co 2.5 Fe 1.5 Sb 12 , 65 Ce 0.75 Fe 3 CoSb 12 , 66 and Co 4 Sb 12 Se 0.1 Zn 0.04 67.…”

“…66 and Co 4 Sb 12 Se 0.1 Zn 0.04 . 67 Moreover, a further improvement in zT can be made possible via a proper choice of doping elements with the selected filler atoms, resulting in an efficient TE material for midtemperature applications. The room temperature TE parameters of all the compositions, such as carrier mobility (μ), total thermal conductivity (κ total ) Seebeck coefficient (S), electrical resistivity (ρ), and carrier concentration (n e ) have been listed in Table 1.…”

Roadmap on thermoelectricity

“…The most remarkable hallmark of filled skutterudites resides in the possibility to partly fill the cage in the 2a crystallographic position, allowing to significantly lower k ph thanks to the rattling movement of the guest ion(s). Many attempts have been done to use various fillers with the aim to perturb the transmission of different phonon frequencies [94,95]. The most effective way seems to be multifilling: filling RE y Fe x Ni 1−x Sb 12 by (Gd,Sm) instead of only Sm, for example, lowers thermal conductivity by ∼1 Wm −1 K −1 at 700 K for x = 0.8 [95].…”