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14 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Fabrication of stable electrode/diffusion barrier layers for thermoelectric filled skutterudite devices

Disclosed are methods for the manufacture of n-type and p-type filled skutterudite thermoelectric legs of an electrical contact. A first material of CoSi2 and a dopant are ball-milled to form a first powder which is thermo-mechanically processed with a second powder of n-type skutterudite to form a n-type skutterudite layer disposed between a first layer and a third layer of the doped-CoSi2. In addition, a plurality of components such as iron, and nickel, and at least one of cobalt or chromium are ball-milled form a first powder that is thermo-mechanically processed with a p-type skutterudite layer to form a p-type skutterudite layer “second layer” disposed between a first and a third layer of the first powder. The specific contact resistance between the first layer and the skutterudite layer for both the n-type and the p-type skutterudites subsequent to hot-pressing is less than about 10.0 μΩ·cm2.

Jie, Qing↗
DOE OSTI2026

Hierarchical microstructure of Yb-filled skutterudites through ultrasonically atomized spherical powders for enhanced thermoelectric performance

Hierarchical microstructures are widely explored as a strategy to reduce lattice thermal conductivity in thermoelectric materials while preserving favorable electronic transport. Here we demonstrate that ultrasonic atomization of precursor powders provides an intrinsic pathway to generate such architectures in n-type Yb0.3Co4Sb12 skutterudites. Materials were synthesized by both conventional sealed-ampoule and ultrasonic atomization routes, each yielding essentially single-phase skutterudite after densification. However, the atomized spherical powders undergo a distinct reaction-driven microstructural evolution during thermal treatment prior to densification. Electron microscopy reveals that the skutterudite phase within the particles induces swelling, cracking, and fragmentation of the droplets before consolidation. Multimodal structural and microstructural characterizations show that densification of these fragmented powders produces a hierarchical microstructure consisting of submicron grains, micrometer-scale faceted crystallites, and powder-derived domains separated by oxide-decorated boundaries. Comprehensive thermoelectric transport measurements evidence that this multiscale architecture lowers the lattice thermal conductivity while maintaining favorable electronic transport, leading to an average ~10% enhancement in the thermoelectric figure of merit. Complementary 121Sb Mössbauer spectroscopy further indicates lattice softening in the atomized material. These results demonstrate that ultrasonic atomization provides an effective route to engineer hierarchical microstructures in skutterudite thermoelectrics and offers a promising strategy for tailoring thermal transport in energy-conversion materials.

Bouteiller, Hugo [ORNL] (ORCID:0009000421322962)↗
DOE OSTI2021

Anharmonicity in partially filled skutterudites Yb x Co 4 Sb 12

Here, we report an experimental investigation of Yb filler ion dynamics in partially filled skutterudite samples Yb x Co 4 Sb 12 ( x = 0.26 and x = 0.4). From extended x-ray absorption fine structure (EXAFS) measurements at the Yb L 2 -edge, the mean-square displacements of the Yb fillers were extracted over a wide temperature range from 10 to 500 K. We found that the low-temperature dynamics of Yb fillers are described well using a harmonic oscillator approximation with Einstein temperatures of 70 ± 5 K for both samples. This finding is consistent with the observed low-energy phonon mode at 5.3(5) meV in the inelastic x-ray scattering (IXS) data. However, the temperature dependence deviates from the harmonic approximation at high temperatures due to significant cubic anharmonicity, which was revealed in the EXAFS cumulant analysis. Our study also demonstrates that complementary information on filler dynamics in skutterudites can be acquired using EXAFS and IXS.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Boosting Thermoelectric Performance in Nanocrystalline Ternary Skutterudite Thin Films through Metallic CoTe 2 Integration

Metal–semiconductor nanocomposites have emerged as a viable strategy for concurrently tailoring both thermal and electronic transport properties of established thermoelectric materials, ultimately achieving synergistic performance. In this investigation, a series of nanocomposite thin films were synthesized, embedding metallic cobalt telluride (CoTe 2 ) nanophase within the nanocrystalline ternary skutterudite (Co(Ge 1.22 Sb 0.22 )Te 1.58 or CGST) matrix. Our approach harnessed composition fluctuation-induced phase separation and in situ growth during thermal annealing to seamlessly integrate the metallic phase. The distinctive band structures of both materials have developed an ohmic-type contact characteristic at the interface, which raised carrier density considerably yet negligibly affected the mobility counterpart, leading to a substantial improvement in electrical conductivity. The intricate balance in transport properties is further influenced by the metallic CoTe 2 phase’s role in diminishing lattice thermal conductivity. The presence of the metallic phase instigates enhanced phonon scattering at the interface boundaries. Consequently, a 2-fold enhancement in the thermoelectric figure of merit (zT ~ 1.30) is attained with CGST-7 wt. % CoTe 2 nanocomposite film at 655 K compared to that of pristine CGST.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Hybridization-driven strong anharmonicity in Yb-filled skutterudites

A high-pressure study of the structural and thermal transport properties is carried out on one of the most efficient filled skutterudites, $\mathrm{Yb_{0.3}Co_4Sb_{12}}$, to understand the relatively low thermal conductivity behavior in this family. By combining x-ray diffraction and Raman scattering measurements, we detect a phase transition at around 12.4 GPa. The mode Grüneisen parameters of the observed phonon modes are obtained from the determined bulk modulus and the phonon frequency shifts with pressure. The strong anharmonicity in this material is demonstrated by the obtained large average Grüneisen parameter. We also find the depressed group velocity within the low-frequency range, the flat guest mode avoided crossing with the acoustic-phonon mode, and the significant contribution of optical phonons. The hybridization of the guest atom and host lattice and the related enhanced anharmonicity are suggested to account for the low lattice thermal conductivity in the studied system. So, these findings provide new insight into how phonon-phonon interactions lower lattice thermal conductivity in this important thermoelectric family.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Robust superconductivity and the suppression of charge-density wave in the quasi-skutterudites Ca 3 ( Ir 1 – x Rh x ) 4 Sn 13 single crystals at ambient pressure

Single crystals of the quasi-skutterudite compounds Ca 3 (Ir 1-x Rh x ) 4 Sn 13 (3–4–13) were synthesized by flux growth and characterized by x-ray diffraction, energy dispersive x-ray spectroscopy, magnetization, resistivity, and radio frequency magnetic susceptibility techniques. The coexistence and competition between the charge density wave (CDW) and superconductivity was studied by varying the Rh/Ir ratio. The superconducting transition temperature, T c , varies from 7 K in pure Ir (x = 0) to 8.3 K in pure Rh (x = 1). Temperature-dependent electrical resistivity reveals monotonic suppression of the CDW transition temperature, T CDW (x). The CDW starts in pure Ir, x = 0, at T CDW ≈ 40 K and extrapolates roughly linearly to zero at x c ≈ 0.53–0.58 under the superconducting dome. Magnetization and transport measurements show a significant influence of CDW on superconducting and normal states. Meissner expulsion is substantially reduced in the CDW region, indicating competition between the CDW and superconductivity. The low-temperature resistivity is higher in the CDW part of the phase diagram, consistent with the reduced density of states due to CDW gapping. Its temperature dependence just above T c shows signs of non-Fermi liquid behavior in a cone-like composition pattern. We conclude that the Ca 3 (Ir 1-x Rh x ) 4 Sn 13 alloy is a good candidate for a composition-driven quantum critical point at ambient pressure.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2022

Calorimetric study of skutterudite (CoAs2.92) and heazlewoodite (Ni3S2)

Abstract Nickel and cobalt arsenides, sulfarsenides, and sulfides occur in many hydrothermal ore deposits, but their thermodynamic properties are not well known, in some cases not known at all. In this work, we determined a full set of thermodynamic properties for heazlewoodite and skutterudite. Both phases were synthesized in evacuated silica tubes at elevated temperatures, and electron microprobe analyses gave their compositions as Ni3S2 and CoAs2.92, respectively. Enthalpies of formation were measured by high-temperature oxide-melt solution calorimetry. The reference phases were pure elements, thus eliminating any systematic errors related to such phases. The enthalpies of formation at T = 298.15 K and P = 105 Pa are –216.0 ± 8.4(2σ) and –88.2 ± 6.1 kJ·mol−1 for Ni3S2 and CoAs2.92, respectively. Entropies were calculated from low-temperature heat capacity (CP) data from relaxation (PPMS) calorimetry and are 133.8 ± 1.6 and 106.4 ± 1.3 J·mol–1·K–1, respectively. The calculated Gibbs free energies of formation are –210.0 ± 8.4 and –79.9 ± 6.2 kJ·mol−1 for Ni3S2 and CoAs2.92, respectively. The PPMS CP data, together with a set of differential scanning calorimetry measurements, were used to derive CP polynomials up to 700 K with the Kieffer model based on previously published frequencies of acoustic and optic modes. Equilibrium constants for selected reactions with an aqueous phase were calculated up to 700 K. Geochemical modeling in these systems, however, should await until more reliable data for other phases from the system Co-Ni-As-S are available.

Geochemistry & Geophysics↗
DOE OSTI2026

An International Round-Robin Study on Thermoelectric Module Testing and Development of Standard Power Generation Modules

An international round-robin study on thermoelectric power generation modules was conducted with nine participating laboratories. Two types of commercially available bismuth telluride modules, 30 mm × 30 mm and 40 mm × 40 mm, were used. A test protocol was followed with five temperature set points from 50°C to 150°C. Graphite sheets were used as thermal interface materials with test pressure at 100 psi (0.69 MPa). The results showed large lab-to-lab variations and the key source of uncertainty for module efficiency was identified as the heat flux measurement. In the meantime, significant uncertainty was also found in maximum electrical power (P max ) measurements. As a result of the round-robin, a “standard module” with 4 × 4 legs on a 20 mm × 20 mm platform was suggested. A skutterudite module and a half-Heusler module were produced with identical geometry and 4 mm × 4 mm × 8 mm legs. All transport properties to calculate the figure-of-merit, zT, were measured from ambient temperature to 500°C. Module performance was measured by two laboratories. Two finite-element-analysis (FEA)-based models were developed independently to simulate and predict the module performance. In conclusion, the standard modules eliminated significant test uncertainties and are aimed at assisting device design and achieving more accurate performance predictions.

Round-robin↗
DOE OSTI2022

Harnessing interpretable and unsupervised machine learning to address big data from modern X-ray diffraction

The information content of crystalline materials becomes astronomical when collective electronic behavior and their fluctuations are taken into account. In the past decade, improvements in source brightness and detector technology at modern X-ray facilities have allowed a dramatically increased fraction of this information to be captured. Now, the primary challenge is to understand and discover scientific principles from big datasets when a comprehensive analysis is beyond human reach. We report the development of an unsupervised machine learning approach, X-ray diffraction (XRD) temperature clustering (X-TEC), that can automatically extract charge density wave order parameters and detect intraunit cell ordering and its fluctuations from a series of high-volume X-ray diffraction measurements taken at multiple temperatures. We benchmark X-TEC with diffraction data on a quasi-skutterudite family of materials, (Ca x Sr 1–x ) 3 Rh 4 Sn 13 , where a quantum critical point is observed as a function of Ca concentration. We apply X-TEC to XRD data on the pyrochlore metal, Cd 2 Re 2 O 7 , to investigate its two much-debated structural phase transitions and uncover the Goldstone mode accompanying them. We demonstrate how unprecedented atomic-scale knowledge can be gained when human researchers connect the X-TEC results to physical principles. Specifically, we extract from the X-TEC–revealed selection rules that the Cd and Re displacements are approximately equal in amplitude but out of phase. This discovery reveals a previously unknown involvement of 5d 2 Re, supporting the idea of an electronic origin to the structural order. Our approach can radically transform XRD experiments by allowing in operando data analysis and enabling researchers to refine experiments by discovering interesting regions of phase space on the fly.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Pressure-induced shift of effective Ce valence, Fermi energy and phase boundaries in CeOs 4 Sb 12

Abstract CeOs 4 Sb 12 , a member of the skutterudite family, has an unusual semimetallic low-temperature L -phase that inhabits a wedge-like area of the field H —temperature T phase diagram. We have conducted measurements of electrical transport and megahertz conductivity on CeOs 4 Sb 12 single crystals under pressures of up to 3 GPa and in high magnetic fields of up to 41 T to investigate the influence of pressure on the different H – T phase boundaries. While the high-temperature valence transition between the metallic H -phase and the L -phase is shifted to higher T by pressures of the order of 1 GPa, we observed only a marginal suppression of the S -phase that is found below 1 K for pressures of up to 1.91 GPa. High-field quantum oscillations have been observed for pressures up to 3.0 GPa and the Fermi surface of the high-field side of the H -phase is found to show a surprising decrease in size with increasing pressure, implying a change in electronic structure rather than a mere contraction of lattice parameters. We evaluate the field-dependence of the effective masses for different pressures and also reflect on the sample dependence of some of the properties of CeOs 4 Sb 12 which appears to be limited to the low-field region.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2020

Enhancing superconductivity of Y 5 Rh 6 Sn 18 by atomic disorder

Here, we investigate the effect of enhancement of superconducting transition temperature $T_c$ by nonmagnetic atom disorder in the filled skutterudite-related tetragonal Y 5 Rh 6 Sn 18 compound doped with Ca. We documented experimentally that Y 5 Rh 6 Sn 18 and its Ca-doped alloys are electronically inhomogeneous at the nanoscale, when Ca content is smaller than ~1.5 in the Y 5– x Ca x Rh 6 Sn 18 system, while for $\textit{x}$ ≥ 1.5 much stronger chemical phase inhomogeneity is observed with an about 20% volume fraction of the second 3:4:13 cubic phase, which we interpret as a fluctuation of stoichiometry within the bulk sample. Then the enhancement of $T_c$ vs $\textit{x}$ could be modeled by a mechanism proposed in recent theoretical reports for increasing the mean-field transition temperature $T_c$ in the presence of nonmagnetic disorder. The increase in disorder with doping increases the sample inhomogeneity and causes a systematic increase in $T_c$, while for two-phase $\textit{x}$ ≥ 1.5 samples the critical temperature $T^{\star}_c ≈ 2 × T_c$ rapidly increases. Based on band structure calculations performed under pressure, we demonstrate how the change in density of states would affect $T_c$ of Y 5 Rh 6 Sn 18 . We obtained the Grüneisen parameter $γ_G$ larger for the inhomogeneous phase with respect to $γ_G$ of the bulk $T_c$ phase and attribute the enhancement of $T_c$ to larger stiffening of the high-temperature $T^{\star}_c$ phase.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2020

Materials Data on NiS2 by Materials Project

NiS2 is Skutterudite-like structured and crystallizes in the triclinic P1 space group. The structure is three-dimensional. there are two inequivalent Ni4+ sites. In the first Ni4+ site, Ni4+ is bonded to six S2- atoms to form NiS6 octahedra that share corners with eight equivalent NiS6 octahedra, corners with six SNi3S tetrahedra, and edges with two equivalent NiS6 octahedra. The corner-sharing octahedra tilt angles range from 62–63°. There are a spread of Ni–S bond distances ranging from 2.23–2.78 Å. In the second Ni4+ site, Ni4+ is bonded to six S2- atoms to form NiS6 octahedra that share corners with eight equivalent NiS6 octahedra, corners with six SNi3S tetrahedra, and edges with two equivalent NiS6 octahedra. The corner-sharing octahedra tilt angles range from 62–63°. There are a spread of Ni–S bond distances ranging from 2.23–2.78 Å. There are four inequivalent S2- sites. In the first S2- site, S2- is bonded to three Ni4+ and one S2- atom to form distorted SNi3S tetrahedra that share corners with three NiS6 octahedra, corners with thirteen SNi3S tetrahedra, and an edgeedge with one SNi3S tetrahedra. The corner-sharing octahedra tilt angles range from 66–77°. The S–S bond length is 2.10 Å. In the second S2- site, S2- is bonded to three Ni4+ and one S2- atom to form distorted SNi3S tetrahedra that share corners with three NiS6 octahedra, corners with thirteen SNi3S tetrahedra, and an edgeedge with one SNi3S tetrahedra. The corner-sharing octahedra tilt angles range from 66–76°. The S–S bond length is 2.10 Å. In the third S2- site, S2- is bonded to three Ni4+ and one S2- atom to form distorted SNi3S tetrahedra that share corners with three NiS6 octahedra, corners with thirteen SNi3S tetrahedra, and an edgeedge with one SNi3S tetrahedra. The corner-sharing octahedra tilt angles range from 66–76°. In the fourth S2- site, S2- is bonded to three Ni4+ and one S2- atom to form distorted SNi3S tetrahedra that share corners with three NiS6 octahedra, corners with thirteen SNi3S tetrahedra, and an edgeedge with one SNi3S tetrahedra. The corner-sharing octahedra tilt angles range from 66–77°.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Tl(CoSb3)16 by Materials Project

Tl(CoSb3)16 is Skutterudite-derived structured and crystallizes in the monoclinic C2/m space group. The structure is three-dimensional. there are five inequivalent Co2+ sites. In the first Co2+ site, Co2+ is bonded to six Sb+0.69- atoms to form CoSb6 octahedra that share corners with six CoSb6 octahedra and a faceface with one TlSb12 cuboctahedra. The corner-sharing octahedra tilt angles range from 52–53°. There are a spread of Co–Sb bond distances ranging from 2.53–2.55 Å. In the second Co2+ site, Co2+ is bonded to six Sb+0.69- atoms to form corner-sharing CoSb6 octahedra. The corner-sharing octahedral tilt angles are 52°. There are one shorter (2.53 Å) and five longer (2.54 Å) Co–Sb bond lengths. In the third Co2+ site, Co2+ is bonded to six Sb+0.69- atoms to form corner-sharing CoSb6 octahedra. The corner-sharing octahedra tilt angles range from 51–53°. There are two shorter (2.53 Å) and four longer (2.54 Å) Co–Sb bond lengths. In the fourth Co2+ site, Co2+ is bonded to six Sb+0.69- atoms to form corner-sharing CoSb6 octahedra. The corner-sharing octahedral tilt angles are 52°. All Co–Sb bond lengths are 2.54 Å. In the fifth Co2+ site, Co2+ is bonded to six Sb+0.69- atoms to form CoSb6 octahedra that share corners with six CoSb6 octahedra and faces with two equivalent TlSb12 cuboctahedra. The corner-sharing octahedra tilt angles range from 52–53°. There are two shorter (2.54 Å) and four longer (2.55 Å) Co–Sb bond lengths. Tl1+ is bonded to twelve Sb+0.69- atoms to form TlSb12 cuboctahedra that share faces with eight CoSb6 octahedra. There are four shorter (3.40 Å) and eight longer (3.41 Å) Tl–Sb bond lengths. There are sixteen inequivalent Sb+0.69- sites. In the first Sb+0.69- site, Sb+0.69- is bonded in a 2-coordinate geometry to two Co2+ atoms. In the second Sb+0.69- site, Sb+0.69- is bonded in a 2-coordinate geometry to two Co2+ atoms. In the third Sb+0.69- site, Sb+0.69- is bonded in a 2-coordinate geometry to two Co2+ atoms. In the fourth Sb+0.69- site, Sb+0.69- is bonded in a 2-coordinate geometry to two Co2+ and one Tl1+ atom. In the fifth Sb+0.69- site, Sb+0.69- is bonded in a 2-coordinate geometry to two Co2+ and one Tl1+ atom. In the sixth Sb+0.69- site, Sb+0.69- is bonded in a 2-coordinate geometry to two Co2+ atoms. In the seventh Sb+0.69- site, Sb+0.69- is bonded in a 2-coordinate geometry to two Co2+ atoms. In the eighth Sb+0.69- site, Sb+0.69- is bonded in a 2-coordinate geometry to two Co2+ atoms. In the ninth Sb+0.69- site, Sb+0.69- is bonded in a 2-coordinate geometry to two equivalent Co2+ atoms. In the tenth Sb+0.69- site, Sb+0.69- is bonded in a 2-coordinate geometry to two equivalent Co2+ atoms. In the eleventh Sb+0.69- site, Sb+0.69- is bonded in a 2-coordinate geometry to two equivalent Co2+ atoms. In the twelfth Sb+0.69- site, Sb+0.69- is bonded in a 2-coordinate geometry to two equivalent Co2+ and one Tl1+ atom. In the thirteenth Sb+0.69- site, Sb+0.69- is bonded in a 2-coordinate geometry to two equivalent Co2+ atoms. In the fourteenth Sb+0.69- site, Sb+0.69- is bonded in a 2-coordinate geometry to two equivalent Co2+ atoms. In the fifteenth Sb+0.69- site, Sb+0.69- is bonded in a 2-coordinate geometry to two equivalent Co2+ atoms. In the sixteenth Sb+0.69- site, Sb+0.69- is bonded in a 2-coordinate geometry to two equivalent Co2+ and one Tl1+ atom.

36 MATERIALS SCIENCE↗