Thermoelectric material development. Final report (original) (raw)
Related papers
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.
High figure of merit in Eu-filled CoSb3-based skutterudites
Applied Physics Letters, 2002
The relatively high mobility of these compounds, as compared to that of La-and Ce-filled skutterudites, may play a role in the large thermoelectric figure of merit ͑ZTϾ1 at 700 K͒ of Eu 0.42 Co 4 Sb 11.37 Ge 0.50 . We discuss the significant potential of these compounds for thermoelectric applications.
Phase compatibility and thermoelectric properties of compounds in the Sr–Ca–Co–O system
Journal of Applied Physics, 2010
Two low-dimensional cobaltite series in the Sr-Ca-CoO system have been investigated for their solid solution limit, structure, and compatibility phase relationships ͑850°C in air͒. Thermoelectric properties have been measured for selected members of these solid solutions. In ͑Ca, Sr͒ 3 Co 4 O 9 , which has a misfit layered structure, Sr was found to substitute in the Ca site to a limit of ͑Ca 0.8 Sr 0.2 ͒ 3 Co 4 O 9. Compounds in the homologous series, A n+2 Co n CoЈO 3n+3 ͓where A = Sr, Ca, ͑Ca,Sr͒, or ͑Sr,Ca͔͒, consist of one-dimensional parallel Co 2 O 6 6− chains that are built from successive alternating face-sharing CoO 6 trigonal prisms and "n" units of CoO 6 octahedra along the hexagonal c-axis. In the Ca n+2 Co n CoЈO 3n+3 series, only the n = 1 phase ͑Ca 3 Co 2 O 6 ͒ could be prepared under the present synthesis conditions. Sr substitutes in the Ca site of Ca 3 Co 2 O 6 to a limit of ͑Ca 0.9 Sr 0.1 ͒ 3 Co 2 O 6. In the Sr n+2 Co n CoЈO 3n+3 series, Ca substitutes in the Sr site of the n = 2, 3, and 4 members to a limit of ͑Sr 0.7 Ca 0.3 ͒ 4 Co 3 O 9 , ͑Sr 0.67 Ca 0.33 ͒ 5 Co 4 O 12 , and ͑Sr 0.725 Ca 0.275 ͒ 6 Co 5 O 15 , respectively. While the members of the Ca n+2 Co n CoЈO 3n+3 and Sr n+2 Co n CoЈO 3n+3 series have reasonably high Seebeck coefficients and relatively low thermal conductivity, the electrical conductivity needs to be increased in order to achieve high ZT values.
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
Chemistry of Materials, 2001
15 Se 15 (V) were prepared by the molten flux method as silver rodlike air-stable crystals. They all crystallize in the monoclinic space group P2 1 /m with a ) 17.4481(8) Å, b ) 4.1964(2) Å, c ) 21.695(1) Å, ) 98.850(1)°f or I, a ) 17.454(5) Å, b ) 4.201(1) Å, c ) 21.760(6) Å, ) 98.550(5)°for II, a ) 17.3160(7) Å, b ) 4.1406(2) Å, c ) 21.6401(8) Å, ) 99.139(1)°for III, a ) 17.1204(6) Å, b ) 4.1568(2) Å, c ) 21.6362(8) Å, ) 98.706(1)°for IV, and a ) 17.167(4) Å, b ) 4.1494(9) Å, c ) 21.684-(5) Å, ) 98.664(3)°for V (Z ) 2 for all compounds). The general formula A 1+x M 4-2x M′ 7+x Se 15 (A ) K, Rb; M ) Pb, Sn; M′ ) Bi, Sb) is derived from a large degree of variability in composition that is expressed in terms of mixed occupancy among A + , M 2+ , and M′ 3+ atoms.
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.
Finding new thermoelectric compounds using crystallographic data: atomic displacement parameters
Eighteenth International Conference on Thermoelectrics. Proceedings, ICT'99 (Cat. No.99TH8407)
A new structure-property relationship is discussed which links atomic displacement parameters (ADPs) and the lattice thermal conductivity of clathrate-like compounds. For many clathrate-iike compounds, in which one of the atom types is weakly bound and "rattles" within its atomic cage, room temperature ADP information can be used to estimate the room temperature lattice thermal conductivity, the vibration frequency of the "rattler", and the temperature dependence of the heat capacity. Neutron data and X-ray crystallography data, reported in the Iitcraturc, are used 10 apply this analysis m several promising classes of Lhcrmoclcctric materials.