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This work raises a fundamental question about the “real” structure of molecular compounds containing three different metals: whether they consist of genuine hetero tri metallic species or of a mixture of parent hetero bi metallic species. Heterotrimetallic complex Li 2 CoNi(tbaoac) 6 ( 1 , tbaoac = tert -butyl acetoacetate) has been designed based on the model tetranuclear structure featuring two transition metal sites in order to be utilized as a molecular precursor for the low-temperature preparation of the LiCo 0.5 Ni 0.5 O 2 battery cathode material. An investigation of the structure of 1 appeared to be very challenging, since the Co and Ni atoms have very similar atomic numbers, monoisotopic masses, and radii as well as the same oxidation state and coordination number/environment. Using a statistical analysis of heavily overlaid isotope distribution patterns of the [Li 2 MM′L 5 ] + (M/M′ = Co 2 , Ni 2 , and CoNi) ions in DART mass spectra, it was concluded that the reaction product 1 contains both heterotrimetallic and bimetallic species. A structural analogue approach has been applied to obtain Li 2 MMg(tbaoac) 6 (M = Co ( 2 ) and Ni ( 3 )) complexes that contain lighter, diamagnetic magnesium in the place of one of the 3d transition metals. X-ray crystallography, mass spectrometry, and NMR spectroscopy unambiguously confirmed the presence of three types of molecules in the reaction mixture that reaches an equilibrium, Li 2 M 2 L 6 + Li 2 Mg 2 L 6 ↔ 2Li 2 MMgL 6 , upon prolonged reflux in solution. The equilibrium mixture was shown to have a nearly statistical distribution of the three molecules, and this is fully supported by the results of theoretical calculations revealing that the stabilization energies of hetero tri metallic assemblies fall exactly in between those for the parent hetero bi metallic species. The LiCo 0.5 Ni 0.5 O 2 quaternary oxide has been obtained in its phase-pure form by thermal decomposition of heterometallic precursor 1 at temperatures as low as 450 °C. Its chemical composition, structure, morphology, and transition metal distribution have been studied by X-ray and electron diffraction techniques and compositional energy-dispersive X-ray mapping with nanometer resolution. The work clearly illustrates the advantages of heterometallic single-source precursors over the corresponding multi-source precursors.
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Bi-continuous pattern formation in thin films via solid-state interfacial dealloying studied by multimodal characterization
Bicontinuous-nanostructured materials with a three-dimensionally (3D) interconnected morphology offer unique properties and potential applications in catalysis, biomedical sensing and energy storage. The new approach of solid-state interfacial dealloying (SSID) opens a route for fabricating bi-continuous metal–metal composites and porous metals at nano-/meso-scales via a self-organizing process driven by minimizing the system's free energy. Integrating SSID and thin film processing fully can open up a wide range of technological opportunities in designing novel functional materials; to-date, no experimental evidence has shown that 3D bi-continuous films can be formed with SSID, owing to the complexity of the kinetic mechanisms in thin film geometry and at nano-scales, despite the simple processing strategy in SSID. Here, we demonstrate that a fully-interconnected 3D bi-continuous structure can be achieved by this new approach, thin-film-SSID, using Fe–Ni film dealloyed by Mg film. The formation of a Fe–Mg x Ni bi-continuous 3D nano-structure was visualized and characterized via a multi-scale, multi-modal approach, combining electron transmission microscopy with synchrotron X-ray fluorescence nano-tomography and absorption spectroscopy. Phenomena involved with structural formation are discussed. These include surface dewetting, nano-size void formation among metallic ligaments, and interaction with a substrate. This work sheds light on the mechanisms of the SSID process, and sets a path for manufacturing of thin-film materials for future nano-structured metallic materials.
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- Award ID(s):
- 1752839
- PAR ID:
- 10100219
- Date Published:
- Journal Name:
- Materials Horizons
- ISSN:
- 2051-6347
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract Solid‐state metal dealloying (SSMD) is a promising method for fabricating nanoscale metallic composites and nanoporous metals across a range of materials. Thin‐film SSMD is particularly attractive due to its ability to create fine features via solid‐state interfacial reactions within a thin‐film geometry, which can be integrated into devices for various applications. This work examines a new dealloying couple, namely the Nb–Al alloy with the dealloying agent Sc, as previously predicted in the machine‐learning (ML) models. Prior ML predictions aimed to guide the design of nanoarchitectured materials through dealloying, relying on intuition‐driven discovery within a large parameter space. However, this work reveals that at the nanoscale, the involvement of oxygen in thin film processing may instead drive the dealloying process, resulting in the formation of bicontinuous nanostructures similar to those formed by metal‐agent dealloying. The phase evolution, as well as chemical and morphological changes, are closely analyzed using a combination of X‐ray absorption spectroscopy, diffraction, and scanning transmission electron microscopy to understand the mechanisms behind nanostructure formation. The findings suggest a potential pathway for utilizing oxygen to drive the formation of bicontinuous metal–metal oxide nanocomposites, paving the way for further development of functional nanoporous materials in diverse fields.more » « less
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1039/c9mh00669a
