Abstract
CoSb3-based skutterudite is a promising mid-temperature thermoelectric material. However, the high lattice thermal conductivity limits its further application. Filling is one of the most effective methods to reduce the lattice thermal conductivity. In this study, we investigate the Ce filling limit and its influence on thermoelectric properties of p-type Fe3CoSb12-based skutterudites grown by a temperature gradient zone melting (TGZM) method. Crystal structure and composition characterization suggests that a maximum filling fraction of Ce reaches 0.73 in a composition of Ce0.73Fe2.73Co1.18Sb12 prepared by the TGZM method. The Ce filling reduces the carrier concentration to 1.03 × 1020 cm−3 in the Ce1.25Fe3CoSb12, leading to an increased Seebeck coefficient. Density functional theory (DFT) calculation indicates that the Ce-filling introduces an impurity level near the Fermi level. Moreover, the rattling effect of the Ce fillers strengthens the short-wavelength phonon scattering and reduces the lattice thermal conductivity to 0.91 W m−1 K−1. These effects induce a maximum Seebeck coefficient of 168 μV K−1 and a lowest κ of 1.52 W m−1 K−1 at 693 K in the Ce1.25Fe3CoSb12, leading to a peak zT value of 0.65, which is 9 times higher than that of the unfilled Fe3CoSb12.
Highlights
With the consumption of traditional fossil fuels and the aggravation of environment pollution, exploring new and effective energy utilization techniques has experienced increasing significance [1,2,3]
The n of thermoelectric materials can be optimized by valence electron counts engineering [13,14], modulation doping [15], and band gap engineering [16]
The as-cast ingots were cut into cylinder samples with a diameter of 12.8 mm, and the oxide layer on the surface was cleaned before being put into a high-purity alumina tube with an inner diameter of 13 mm to execute the temperature gradient zone melting (TGZM) process, which was described in detail in previous reports [54,55]
Summary
With the consumption of traditional fossil fuels and the aggravation of environment pollution, exploring new and effective energy utilization techniques has experienced increasing significance [1,2,3]. The thermoelectric performance is fundamentally characterized by the material dimensionless figure-of-merit (zT), defined as zT = S2 σT/κ, where S, σ, κ and T are the Seebeck coefficient, electrical conductivity, thermal conductivity (comprised of electronic contribution κ e and lattice contribution κ l ) and temperature in Kelvin, respectively [7,8,9]. S, σ, and κ e are related to each other as a function of other fundamental parameters, such as carrier concentration (n) [10,11,12]. These fundamental parameters need to be optimized. Other than the interrelated parameters, reducing κ l can achieve a low κ and high zT [17]. The reduced κ l can be achieved by introducing additional structure defects, such as point defects [18], dense grain boundaries [19], and nanoprecipitates [20,21] for strengthening phonon scattering
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