- Award ID(s):
- 1700030
- NSF-PAR ID:
- 10062589
- Date Published:
- Journal Name:
- RSC Advances
- Volume:
- 8
- Issue:
- 1
- ISSN:
- 2046-2069
- Page Range / eLocation ID:
- 28 to 37
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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The structure of a series of lanthanide iron cobalt perovskite oxides, R (Fe 0.5 Co 0.5 )O 3 ( R = Pr, Nd, Sm, Eu, and Gd), have been investigated. The space group of these compounds was confirmed to be orthorhombic Pnma (No. 62), Z = 4. From Pr to Gd, the lattice parameter a varies from 5.466 35(13) Å to 5.507 10(13) Å, b from 7.7018(2) to 7.561 75(13) Å, c from 5.443 38(10) to 5.292 00(8) Å, and unit-cell volume V from 229.170(9) Å 3 to 220.376(9) Å 3 , respectively. While the trend of V follows the trend of the lanthanide contraction, the lattice parameter “ a ” increases as the ionic radius r ( R 3+ ) decreases. X-ray diffraction (XRD) and transmission electron microscopy confirm that Fe and Co are disordered over the octahedral sites. The structure distortion of these compounds is evidenced in the tilt angles θ, ϕ , and ω , which represent rotations of an octahedron about the pseudocubic perovskite [110] p , [001] p , and [111] p axes. All three tilt angles increase across the lanthanide series (for R = Pr to R = Gd: θ increases from 12.3° to 15.2°, ϕ from 7.5° to 15.8°, and ω from 14.4° to 21.7°), indicating a greater octahedral distortion as r ( R 3+ ) decreases. The bond valence sum for the sixfold (Fe/Co) site and the eightfold R site of R (Fe 0.5 Co 0.5 )O 3 reveal no significant bond strain. Density Functional Theory calculations for Pr(Fe 0.5 Co 0.5 )O 3 support the disorder of Fe and Co and suggest that this compound to be a narrow band gap semiconductor. XRD patterns of the R (Fe 0.5 Co 0.5 )O 3 samples were submitted to the Powder Diffraction File.more » « less
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Abstract Chemical looping air separation (CLAS) is a promising technology for oxygen generation with high efficiency. The key challenge for CLAS is to design robust oxygen sorbents with suitable redox properties and fast redox kinetics. In this work, perovskite-structured Sr1-xCaxFe1-yCoyO3oxygen sorbents were investigated and demonstrated for oxygen production with tunable redox properties, high redox rate, and excellent thermal/steam stability. Cobalt doping at B site was found to be highly effective, 33% improvement in oxygen productivity was observed at 500 °C. Moreover, it stabilizes the perovskite structure and prevents phase segregation under pressure swing conditions in the presence of steam. Scalable synthesis of Sr0.8Ca0.2Fe0.4Co0.6O3oxygen sorbents was carried out through solid state reaction, co-precipitation, and sol-gel methods. Both co-precipitation and sol-gel methods are capable of producing Sr0.8Ca0.2Fe0.4Co0.6O3sorbents with satisfactory phase purity, high oxygen capacity, and fast redox kinetics. Large scale evaluation of Sr0.8Ca0.2Fe0.4Co0.6O3, using an automated CLAS testbed with over 300 g sorbent loading, further demonstrated the effectiveness of the oxygen sorbent to produce 95% pure O2with a satisfactory productivity of 0.04 gO2gsorbent−1h−1at 600 °C.
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Abstract Super‐Earths ranging up to 10 Earth masses (ME) with Earth‐like density are common among the observed exoplanets thus far, but their measured masses and radii do not uniquely elucidate their internal structure. Exploring the phase transitions in the Mg‐silicates that define the mantle‐structure of super‐Earths is critical to characterizing their interiors, yet the relevant terapascal conditions are experimentally challenging for direct structural analysis. Here we investigated the crystal chemistry of Fe3O4as a low‐pressure analog to Mg2SiO4between 45–115 GPa and up to 3000 K using powder and single crystal X‐ray diffraction in the laser‐heated diamond anvil cell. Between 60–115 GPa and above 2000 K, Fe3O4adopts an 8‐fold coordinated Th3P4‐type structure (
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