Thermoelectric Properties of Microstructurally Modified CoSb3 Skutterudite by Hf-Addition (original) (raw)
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HPHT synthesis and thermoelectric properties of CoSb3 and Fe0.6Co3.4Sb12 skutterudites
Journal of Alloys and Compounds, 2009
P-type skutterudite compounds CoSb 3 and Fe 0.6 Co 3.4 Sb 12 with bcc crystal structure were prepared by high pressure and high temperature method. The electrical resistivities, Seebeck coefficients and thermal conductivities of the samples were measured in the temperature range of 300-680 K. The temperaturedependent thermoelectric transport properties, including electrical resistivity, Seebeck coefficient and thermal conductivity were investigated in detail. The results indicate that with temperature increasing the electrical resistivity increases, the Seebeck coefficient first increases and then decreases after about 580 K. The thermal conductivity decreases with increasing temperature. Compared with those of the same samples prepared at ambient pressure, the electrical transport properties of the samples prepared by HPHT method are improved greatly. The room temperature power factor of Fe 0.6 Co 3.4 Sb 12 is nearly four times higher than that of the same sample prepared at ambient pressure. The dimensionless thermoelectric figure of merit, ZT, reaches the maximal values of 0.17 and 0.09 for CoSb 3 and Fe 0.6 Co 3.4 Sb 12 respectively at 550 K.
ACS Applied Energy Materials, 2019
Filled skutterudites constitute an important class of efficient and stable thermoelectric materials for power generation; however, their commercialization has been hampered due to the usage of expensive rare-earth elements as "fillers" and the nonavailability of the efficient and compatible p-type counterpart. In view of this, we report a state-of-the-art thermoelectric figure of merit (ZT) in rareearth-free p-type unfilled CoSb 3 skutterudite co-doped with Fe and Se, synthesized using a facile process of arc-melting and spark plasma sintering, which is both fast and scalable. The doping of Fe and Se have been chosen in accordance with the first-principles-based density functional theory (DFT) calculations which suggested that Fe leads to p-type conduction in CoSb 3 , while Se strengthens the thermoelectric properties. The experimental results also suggest that the optimized partial substitutional doping of Fe at the Co-site and Se at the Sb-site in CoSb 3 leads to a favorable tuning of the electrical and thermal transport properties, which resulted in a high ZT ∼ 0.7 at 870 K in an optimized skutterudite composition of Fe 0.25 Co 0.75 Sb 2.965 Se 0.035 , which is the highest value reported thus far for unfilled CoSb 3-based p-type skutterudites. The resulting ZT of Fe 0.25 Co 0.75 Sb 2.965 Se 0.035 is higher by 2 orders of magnitude than that for its pristine counterpart. In addition, the theoretically estimated transport properties of pristine and doped CoSb 3 , calculated employing the density functional theory (DFT) and Boltzmann transport equations, were found to be in good qualitative agreement with those measured experimentally.
Improved thermoelectric performance of (Fe,Co)Sb3-type skutterudites from first-principles
Journal of Applied Physics, 2016
Skutterudite materials have been considered as promising thermoelectric candidates due to intrinsically good electrical conductivity and tailorable thermal conductivity. Options for improving thermal-to-electrical conversion efficiency include identifying novel materials, adding filler atoms, and substitutional dopants. Incorporating filler or substitutional dopant atoms in the skutterudite compounds can enhance phonon scattering, resulting in reduction of thermal conductivity, as well as improving electrical conductivity. The structures, electronic properties, and thermal properties of double-filled Ca 0.5 Ce 0.5 Fe 4 Sb 12 and Co 4 Sb 12À2x Te x Ge x compounds (x ¼ 0, 0.5, 1, 2, 3, and 6) have been studied using density functional theory-based calculations. Both Ca/Ce filler atoms in FeSb 3 and Te/Ge substitution in CoSb 3 cause a decrease in lattice constant for the compounds. As Te/Ge substitution concentration increases, lattice constant decreases and structural distortion of pnictogen rings in the compounds occurs. This indicates a break in cubic symmetry of the structure. The presence of fillers and substitutions cause an increase in electrical conductivity and a gradual decrease in electronic band gap. A transition from direct to indirect band-gap semiconducting behavior is found at x ¼ 3. Phonon density of states for both compounds indicate phonon band broadening by the incorporation of fillers and substitutional atoms. Both systems are also assumed to have acoustic-modedominated lattice thermal conductivity. For the Co 4 Sb 12À2x Te x Ge x compounds, x ¼ 3 has the lowest phonon dispersion gradient and lattice thermal conductivity, agreeing well with experimental measurements. Our results exhibit the improvement of thermoelectric properties of skutterudite compounds through fillers and substitutional doping. V
ACS Omega
We report a systematic investigation of the microstructure and thermoelectric properties of refractory element-filled nanostructured Co 4 Sb 12 skutterudites. The refractory tantalum (Ta) metal-filled Co 4 Sb 12 samples (Ta x Co 4 Sb 12 (x = 0, 0.4, 0.6, and 0.8)) are synthesized using a solid-state synthesis route. All the samples are composed of a single skutterudite phase. Meanwhile, nanometer-sized equiaxed grains are present in the Ta 0.2 Co 4 Sb 12 and Ta 0.4 Co 4 Sb 12 samples, and bimodal distributions of equiaxed grains and elongated grains are observed in Ta 0.6 Co 4 Sb 12 and Ta 0.8 Co 4 Sb 12 samples. The dominant carrier type changes from electrons (n-type) to holes (p-type) with an increase in Ta concentration in the samples. The power factor of the Ta 0.6 Co 4 Sb 12 sample is increased to 2.12 mW/mK 2 at 623 K due to the 10-fold reduction in electrical resistivity. The lowest lattice thermal conductivity observed for Ta 0.6 Co 4 Sb 12 indicates the rattling action of Ta atoms and grain boundary scattering. Rietveld refinement of XRD data and the analysis of lattice thermal conductivity data using the Debye model confirm that Ta occupies at the voids as well as the Co site. The figure of merit (ZT) of ∼0.4 is obtained in the Ta 0.6 Co 4 Sb 12 sample, which is comparable to single metalfilled p-type skutterudites reported to date. The thermoelectric properties of the refractory Ta metal-filled skutterudites might be useful to achieve both n-type and p-type thermoelectric legs using a single filler atom and could be one of replacements of the rare earth-filled skutterudites with improved thermoelectric properties.
Thermoelectric properties of hot-pressed skutterudite CoSb[sub 3]
Journal of Applied Physics, 2007
In the present work, skutterudite CoSb 3 were fabricated by hot pressing at different sintering temperatures under vacuum and argon. For the prepared compacts, the phase, the microstructure, and the temperature dependent thermoelectric properties were characterized. The correlation of the materials factors: density, grain size, Sb content, with the thermoelectric variables: Seebeck coefficient, electrical conductivity, thermal conductivity, and dimensionless figure of merit ͑ZT͒, is presented. The achieved ZT values are also compared with those reported in the literature. The investigated samples show larger electrical conductivity due to existence of metallic Sb and smaller thermal conductivity because of fine-grained structure. A maximal ZT of 0.11 was achieved for the samples sintered at 853 K under vacuum and at 773 K under argon. A moderate improvement on ZT for pure CoSb 3 is shown in the present work.
Journal of Electronic Materials, 2011
Void-filling in the CoSb3 skutterudite lattice with different kinds of heavy elements has proven to be an effective mechanism to enhance thermoelectric performance due primarily to a reduction in lattice thermal conductivity. Specifically, our findings on the series Inx Yby Co4Sb12 [0 ≤ (x, y) ≤ 0.2] have further motivated an attempt to form triple-filled skutterudites Ce0.1Inx Yby Co4Sb12 with In and Yb concentrations [0 ≤ (x, y) ≤ 0.2] and with the Ce concentration held constant (Ce0.1). All of these samples have been prepared via a simplified melting–annealing–sintering procedure and were first characterized by means of x-ray powder diffraction and scanning electron microscopy, followed by measurements of the Hall coefficient, electrical and thermal conductivities, and Seebeck coefficient. Our aim is to further elucidate the roles of the three elements (Ce, In, and Yb) in these materials. Compared with the addition of just In or Yb, we found that simultaneous addition of both In and Yb reduced the lattice thermal conductivity without significantly degrading the power factor. Further addition of the third element (Ce), along with In and Yb, also produced a similar result. However, we noticed that some of the In and Yb were also observed in the form of secondary phases (InSb and Yb2O3), not entering entirely as filler atoms. As a result of our investigation, several compositions achieved increased sustainability and enhanced thermoelectric performance, with maximum ZT values of about 1.3 to 1.4 obtained at around 800 K.
Renewable Energy
A thermoelectric material with sufficient performance at high temperatures is a key factor for thermoelectric generation from solar-thermal energy (I. R. radiation). In this study, we analyzed CoSb3 skutterudite compounds as a thermoelectric material at high temperatures and synthesized filled skutterudites with two types of filler atoms: 1) Yb- and La-fillers with a different electronegativity (X) from the Sb atoms and 2) the In-filler with nearly the same electronegativity (X) as the Sb atoms. All the samples were sintered with the spark plasma sintering method, and their thermoelectric properties were investigated. From the results, the Yb atoms were the most effective in decreasing the thermal conductivity of this system due to their very different electronegativity (X) value from the Sb atoms and lower melting temperature than that of the La-filler. In addition, In-filled compositions had high power factor values while the In-free composition had the lowest power factor value d...
Thermoelectric properties of p-type filled skutterudites SxCo4Sb12
Nucleation and Atmospheric Aerosols, 2020
The electronegativity difference between the filler and the host atom of skutterudites determines the bonding type, which effects the thermoelectric properties. The electropositive elements with low electronegativity compared to Sb atom can form n-type filled skutterudites. In this study, the electronegative element sulphur has filled into voids. A series of S x Co 4 Sb 12 (x= 0.05 to 0.4) compounds were synthesized by the solid-state method. CoSbS secondary phase was observed for x > 0.05. Filling fraction of sulphur into the void (̴ 0.04) was calculated using electron probe microanalyzer which agrees with Rietveld refinement of the X-ray diffraction pattern. The transport properties were measured from 350 K to 723 K. The positive Seebeck coefficient (S) confirms p-type semiconducting nature. S and the electrical resistivity (ρ) decreased with increasing x due to increased carrier concentration (n). All the samples except x=0.05 possess almost same S and ρ due to saturation of filling fraction. The enhanced phonon scattering in S x Co 4 Sb 12 resulted in low thermal conductivity (κ). The highest zT of 0.18 at 623 K was achieved for S 0.15 Co 4 Sb 12 .