Materials with low thermal conductivity are essential to providing thermal insulation to many technological systems, such as electronics, thermoelectrics and aerospace devices. Here, we report ultra-low thermal conductivity of two oxide materials. Sr 2 FeCoO 6−δ has a perovskite-type structure with oxygen vacancies. It shows a thermal conductivity of 0.5 W m −1 K −1 , which is lower than those reported for perovskite oxides. The incorporation of calcium to form Ca 2 FeCoO 6−δ , leads to a structural change and the formation of different coordination geometries around the transition metals. This structural transformation results in a remarkable enhancement of the thermal insulation properties, showing the ultra-low thermal conductivity of 0.05 W m −1 K −1 , which is one of the lowest values found among solid materials to date. A comparison to previously reported perovskite oxides, which show significantly inferior thermal insulation compared to our materials, points to the effect of oxygen-vacancies and their ordering on thermal conductivity.
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Comparative Thermal Insulation Nature of Ca 2 FeMnO 6−δ and Sr 2 FeMnO 6−δ
In this study, we investigate the utility of Ca2FeMnO6-
- NSF-PAR ID:
- 10491329
- Publisher / Repository:
- The Electrochemical Society
- Date Published:
- Journal Name:
- ECS Advances
- Volume:
- 3
- Issue:
- 1
- ISSN:
- 2754-2734
- Format(s):
- Medium: X Size: Article No. 014001
- Size(s):
- ["Article No. 014001"]
- Sponsoring Org:
- National Science Foundation
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Abstract Ultrafast time‐domain thermoreflectance (TDTR) is utilized to extract the through‐plane thermal conductivity (
Λ LSCO) of epitaxial La0.5Sr0.5CoO3−δ (LSCO) of varying thickness (<20 nm) on LaAlO3and SrTiO3substrates. These LSCO films possess ordered oxygen vacancies as the primary means of lattice mismatch accommodation with the substrate, which induces compressive/tensile strain and thus controls the orientation of the oxygen vacancy ordering (OVO). TDTR results demonstrate that the room‐temperatureΛ LSCOof LSCO on both substrates (1.7 W m−1K−1) are nearly a factor of four lower than that of bulk single‐crystal LSCO (6.2 W m−1K−1). Remarkably, this approaches the lower limit of amorphous oxides (e.g., 1.3 W m−1K−1for glass), with no dependence on the OVO orientation. Through theoretical simulations, origins of the glass‐like thermal conductivity of LSCO are revealed as a combined effect resulting from oxygen vacancies (the dominant factor), Sr substitution, size effects, and the weak electron/phonon coupling within the LSCO film. The absence of OVO dependence in the measuredΛ LSCOis rationalized by two main effects: (1) the nearly isotropic phononic thermal conductivity resulting from the imperfect OVO planes when δ is small; (2) the missing electronic contribution toΛ LSCOalong the through‐plane direction for these ultrathin LSCO films on insulating substrates. -
Electron doping in perovskites is an effective approach to design and tailor the structure and property of materials. In A 2 BB′O 6−δ -type double perovskites, B-site cation order can be tunable by A-site modification, potentially leading to significant effect on the oxygen nonstoichiometry of the compounds. La 3+ -doped Sr 2 FeMoO 6−δ (Sr 2−x La x FeMoO 6−δ , SLFM with 0 ≤ x ≤ 1) double perovskites have been designed and characterized systematically in this study as anode materials for solid oxide fuel cells. Rietveld refinement of powder X-ray diffraction reveals a crystalline symmetry transition of SLFM from tetragonal to orthorhombic with the increase of La content, driven by the extra electron onto the antibonding orbitals of e g and t 2g of Fe/Mo cations. An increase in Fe/Mo anti-site defect accompanies this phase transition. Solid oxide fuel cells incorporating the Sr 1.8 La 0.2 FeMoO 6−δ (SLFM2) anode demonstrate impressive power outputs and stable performance under direct CH 4 operation because of its altered electronic structure, desired oxygen vacancy concentration and enhanced reducibility. Density functional theory plus U correction calculations provide an insight into how La doping affects the Fe/Mo anti-site defects and consequently the oxygen transport dynamics.more » « less
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Abstract Inspired by significant local distortions found near vacancies in a neutron pair distribution function analysis study (G. King et al.,
Inorg. Chem. 2012, 51, 13060) of Sr2 MSbO5.5 (M = Ca and Sr), this computational study finds minimum‐energy structures with these and related distortions using density functional theory (DFT) with the Perdew‐Burke‐Ernzerhof (PBE) functional as implemented in the Vienna Ab Initio Simulations Package (VASP) (G. Kresse and J. Furthmüller,Phys. Rev. B , 1996, 54, 11169; G. Kresse and J. Hafner,Phys. Rev. B , 1993, 47, 558; G. Kresse and J. Furthmüller,Comput. Mater. Sci. , 1996, 6, 15). All structures were optimized using the conjugate gradient method. The global minima found for both systems featured trigonal bipyramid SbO5 structures and edge sharing with M‐centered polyhedra. However, while calcium ions occupied full and partial octahedra, the larger strontium ions were more commonly found in full and partial pentagonal bipyramids. Molecular dynamics with velocity rescaling at1200 K revealed movements of the oxygen vacancy via polyhedral rotations. This work highlights the need to consider both square pyramid to trigonal bipyramid rearrangements around small ions and rotational polyhedral movements in simulating oxygen vacancy conduction in oxygen‐deficient double perovskites. -
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Abstract Solid-state control of the thermal conductivity of materials is of exceptional interest for novel devices such as thermal diodes and switches. Here, we demonstrate the ability to
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