Bulk and surface exsolution produces a variety of Fe-rich and Fe-depleted ellipsoidal nanostructures in La0.6Sr0.4FeO3 thin films

Syed, Komal; Wang, Jiayue; Yildiz, Bilge; Bowman, William J.

doi:10.1039/d1nr06121f

Cited by 13 publications

(9 citation statements)

References 67 publications

(112 reference statements)

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“…This potentially indicates that at such high particle concentration levels other effects, besides strain, for example, interfacial point defects, may also contribute to increasing conductivity, as observed recently. [ 31,32 ] Another aspect to note is that this plot shows that the maximum oxide ion conductivity enhancement factor of ≈8.5 observed experimentally in this system is accounted for by a volumetric strain of ≈2.2%. The magnitude of this strain value may appear to be relatively large, however, it is consistent with other literature values observed for thin‐film perovskites, where 2–2.5% strain can increase conductivity several folds up to an order of magnitude, at temperatures similar to the current study.…”

Section: Resultsmentioning

confidence: 73%

A Model for Modulating Oxide Ion Transport with Endo‐Particles for Application in Energy Conversion

Dalton

Neagu

2022

Adv Energy and Sustain Res

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Oxide ion transport in oxides is instrumental for enabling various energy conversion technologies including, but not limited to solid oxide fuel cells and electrolyzers, oxygen separation membranes, and chemical looping. [1][2][3][4][5] For example, in solid oxide cells (Figure 1a), oxide ion conduction is required not only in the electrolyte, which ensures the selective transport of oxide ions between electrodes, preventing the reactants from mixing directly, but also within the electrodes responsible for electrochemically breaking down the reactants into respective ions and transporting them to the electrolyte. [2,4] In chemical looping (Figure 1b), an oxygen carrier material reversibly exchanges oxygens, by reacting successively with a reducing stream (e.g., CH 4 ), during which oxide ions are supplied to form the products (e.g., syngas), and then an oxidizing stream (e.g., O 2 ), where the oxide ions are replenished (cations also undergo redox changes to preserve charge neutrality). [5,6] Oxide ion transport is typically controlled and enhanced by chemical substitution, doping, or crystal lattice engineering. Notable examples include yttria-substituted zirconia (YSZ), the "classic" ion conductor, magnesium-doped lanthanum strontium gallates (LSGM), a perovskite ion conductor with a relatively high conductivity at intermediate temperatures, and also more recently ferroelectric and hexagonal perovskite oxide structures. [4,[7][8][9][10] A more exotic form of ion transport modulation is through strain, the artificial distortion of a crystal lattice. [11][12][13][14][15][16][17] Tensile strain, for example, involves "stretching" the crystal lattice, which seemingly allows more space for ion transport and lowers the activation energy for ion migration. [11,13] Generally, strain is induced by depositing the material of interest as a thin film upon a substrate, which results in a mismatch in lattice parameters between the two crystalline phases (ε i ), causing an artificial expansion or contraction of the thin-film layer. [12,13,15] Elastic relaxation, and potentially the formation of interfacial dislocations, then confines strain and its effects to a small region near the interface, which extends to no more than 100 nm. [12,13,18] Therefore, strain effects are generally limited to thin films and the nanoscale.However, two recent studies from the fields of solid oxide cells (SOC) and chemical looping (CL) suggest that strain might be induced in macroscopic systems by dispersing nanoparticles within the oxide ion conductor matrix, i.e., as internal or "endo-particles" (Figure 1c). This would effectively introduce a dense distribution of spherical interfaces, thus propagating the interface misfit ε i throughout the volume. The SOC study prepared such a system by assembling and sintering gold (Au) nanoparticles with a double perovskite oxide matrix Pr 1.9 Ni 0.71 Cu 0.41 Ga 0.05 O 4þδ (PNCO) and measured up to %2.5-fold increase in ion conductivity for an Au to PNCO matrix content of 1-3 mol%. [19] The CL study employe...

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Section: Resultsmentioning

confidence: 73%

A Model for Modulating Oxide Ion Transport with Endo‐Particles for Application in Energy Conversion

Dalton

Neagu

2022

Adv Energy and Sustain Res

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“…It should be noted that for cases where exsolution takes place in the bulk, 48 the bulk chemistry of the host oxide can also evolve after bulk exsolution. For example, we have recently observed percolating Fe-deficient channels 41 (∼2 nm wide) and other Fe-deficient nanostructures 49 near the exsolved Fe 0 nanoparticles in the La 0.6 Sr 0.4 FeO 3 film after bulk exsolution. The similarities between these two cases (i.e., surface and bulk exsolutions) suggest that the formation of nanoscale regions that are depleted in the to-be-exsolved cations near the exsolved nanoparticles can be a general phenomenon in exsolution.…”

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confidence: 99%

Exsolution-Driven Surface Transformation in the Host Oxide

et al. 2022

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Exsolution synthesizes self-assembled metal nanoparticle catalysts via phase precipitation. An overlooked aspect in this method thus far is how exsolution affects the host oxide surface chemistry and structure. Such information is critical as the oxide itself can also contribute to the overall catalytic activity. Combining X-ray and electron probes, we investigated the surface transformation of thin-film SrTi0.65Fe0.35O3 during Fe0 exsolution. We found that exsolution generates a highly Fe-deficient near-surface layer of about 2 nm thick. Moreover, the originally single-crystalline oxide near-surface region became partially polycrystalline after exsolution. Such drastic transformations at the surface of the oxide are important because the exsolution-induced nonstoichiometry and grain boundaries can alter the oxide ion transport and oxygen exchange kinetics and, hence, the catalytic activity toward water splitting or hydrogen oxidation reactions. These findings highlight the need to consider the exsolved oxide surface, in addition to the metal nanoparticles, in designing the exsolved nanocatalysts.

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“…Although it may challenge the implementation of CaTi 1– x Fe x O 3−δ in OTMs, chemical instability presents an exciting opportunity in other contexts. For instance, the process of cation exsolutionwhich is akin to oxide phase decompositionprovides a finely tunable in situ synthesis route to durable metal nanoparticle catalysts embedded in the surface of various oxide supports. − Perovskite oxides readily incorporate transition metals into the lattice during material synthesis under oxidizing conditions; when subsequently exposed to reducing conditions, the oxide undergoes a controllable phase decomposition, and transition metals can be selectively exsolved as dispersed catalytically active nanoparticles. The exsolution method is increasingly popular as it can overcome typical drawbacksincluding nanoparticle agglomeration and deactivationwhich are typical of traditional nanoparticle catalyst synthesis methods such as impregnation or vapor deposition.…”

Section: Introductionmentioning

confidence: 99%

Nanoscale Iron Redistribution during Thermochemical Decomposition of CaTi_1–xFe_xO_3−δ Alters the Electrical Transport Pathway: Implications for Oxygen-Transport Membranes, Electrocatalysis, and Photocatalysis

Luong

Wang

Tsung

et al. 2023

ACS Appl. Nano Mater.

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Potential applications of the earth-abundant, low-cost, and non-critical perovskite CaTi1–x Fe x O3−δ in electrocatalysis, photocatalysis, and oxygen-transport membranes have motivated research to tune its chemical composition and morphology. However, investigations on the decomposition mechanism(s) of CaTi1–x Fe x O3−δ under thermochemically reducing conditions are limited, and direct evidence of the nano- and atomic-level decomposition process is not available in the literature. In this work, the phase evolution of CaTi1–x Fe x O3−δ (x = 0–0.4) was investigated in a H2-containing atmosphere after heat treatments up to 600 °C. The results show that CaTi1–x Fe x O3−δ maintained a stable perovskite phase at low Fe contents while exhibiting a phase decomposition to Fe/Fe oxide nanoparticles as the Fe content increases. In CaTi0.7Fe0.3O3−δ and CaTi0.6Fe0.4O3−δ, the phase evolution to Fe/Fe oxide was greatly influenced by the temperature: Only temperatures of 300 °C and greater facilitated phase evolution. Fully coherent Fe-rich and Fe-depleted perovskite nanodomains were observed directly by atomic-resolution scanning transmission electron microscopy. Prior evidence for such nanodomain formation was not found, and it is thought to result from a near-surface Kirkendall-like phenomenon caused by Fe migration in the absence of Ca and Ti co-migration. Density functional theory simulations of Fe-doped bulk models reveal that Fe in an octahedral interstitial site is energetically more favorable than in a tetrahedral site. In addition to coherent nanodomains, agglomerated Fe/Fe oxide nanoparticles formed on the ceramic surface during decomposition, which altered the electrical transport mechanism. From temperature-dependent electrical conductivity measurements, it was found that heat treatment and phase decomposition change the transport mechanism from thermally activated p-type electronic conductivity through the perovskite to electronic conduction through the iron oxide formed by thermochemical decomposition. This understanding will be useful to those who are developing or employing this and similar earth-abundant functional perovskites for use under reducing conditions, at elevated temperatures, and when designing materials syntheses and processes.

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Bulk and surface exsolution produces a variety of Fe-rich and Fe-depleted ellipsoidal nanostructures in La_0.6Sr_0.4FeO₃ thin films

Abstract: Bulk & surface exsolution of Fe produces various nanostructures in Lanthanum Strontium Ferrite (LSF) thin films.

Cited by 13 publications

References 67 publications

A Model for Modulating Oxide Ion Transport with Endo‐Particles for Application in Energy Conversion

A Model for Modulating Oxide Ion Transport with Endo‐Particles for Application in Energy Conversion

Exsolution-Driven Surface Transformation in the Host Oxide

Nanoscale Iron Redistribution during Thermochemical Decomposition of CaTi_1–xFe_xO_3−δ Alters the Electrical Transport Pathway: Implications for Oxygen-Transport Membranes, Electrocatalysis, and Photocatalysis

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Bulk and surface exsolution produces a variety of Fe-rich and Fe-depleted ellipsoidal nanostructures in La0.6Sr0.4FeO3 thin films

Abstract: Bulk & surface exsolution of Fe produces various nanostructures in Lanthanum Strontium Ferrite (LSF) thin films.

Cited by 13 publications

References 67 publications

A Model for Modulating Oxide Ion Transport with Endo‐Particles for Application in Energy Conversion

A Model for Modulating Oxide Ion Transport with Endo‐Particles for Application in Energy Conversion

Exsolution-Driven Surface Transformation in the Host Oxide

Nanoscale Iron Redistribution during Thermochemical Decomposition of CaTi1–xFexO3−δ Alters the Electrical Transport Pathway: Implications for Oxygen-Transport Membranes, Electrocatalysis, and Photocatalysis

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Bulk and surface exsolution produces a variety of Fe-rich and Fe-depleted ellipsoidal nanostructures in La_0.6Sr_0.4FeO₃ thin films

Nanoscale Iron Redistribution during Thermochemical Decomposition of CaTi_1–xFe_xO_3−δ Alters the Electrical Transport Pathway: Implications for Oxygen-Transport Membranes, Electrocatalysis, and Photocatalysis