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Palazzolo A, Poucin C, Freitas AP, Ropp A, Bouillet C, Ersen O, Carenco S. The delicate balance of phase speciation in bimetallic nickel cobalt nanoparticles. NANOSCALE 2022; 14:7547-7560. [PMID: 35412546 DOI: 10.1039/d2nr00917j] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/14/2023]
Abstract
Bimetallic nickel-cobalt nanoparticles are highly sought for their potential as catalytic and magnetic nanoparticles. These are typically prepared in organic solvents in the presence of strong stabilizing ligands such as tri-n-octylphosphine (TOP). Due to the variety of cobalt crystallographic phases and to the strong interaction of the ligands with the metallic surfaces, forming fcc nanoparticles rather than a phase mixture is a challenging endeavor. Here, using a two-step synthesis strategy that aims at a core-shell nickel-cobalt morphology, we demonstrated that many parameters have to be adjusted: concentration of the metal precursors, stoichiometry of TOP, and heating program from room temperature to 180 °C. We found optimized conditions to form size-controlled fcc NiCo nanoparticles from preformed Ni nanoparticles, and the phase attribution was confirmed with a combination of X-Ray diffraction on powder and X-Ray absorption spectroscopy at the Co K edge. We then investigated the early stages of Co nucleation on the nickel using a lower stoichiometry of Co, down to 0.05 equiv. vs. Ni. Using X-ray photoelectron spectroscopy and scanning transmission electron microscopy coupled to energy-dispersive X-Ray spectroscopy and electron energy loss spectroscopy, we showed that cobalt reacts first on the nickel nanoparticles but easily forms cobalt-rich larger aggregates in the further steps of the reaction.
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Affiliation(s)
- Alberto Palazzolo
- Sorbonne Université, CNRS, Collège de France, Laboratoire de Chimie de la Matière Condensée de Paris, 4 place Jussieu, 75005 Paris, France.
| | - Cyprien Poucin
- Sorbonne Université, CNRS, Collège de France, Laboratoire de Chimie de la Matière Condensée de Paris, 4 place Jussieu, 75005 Paris, France.
| | - Alexy P Freitas
- Sorbonne Université, CNRS, Collège de France, Laboratoire de Chimie de la Matière Condensée de Paris, 4 place Jussieu, 75005 Paris, France.
| | - Anthony Ropp
- Sorbonne Université, CNRS, Collège de France, Laboratoire de Chimie de la Matière Condensée de Paris, 4 place Jussieu, 75005 Paris, France.
| | - Corinne Bouillet
- Institut de Physique et Chimie des Matériaux de Strasbourg (IPCMS), UMR 7504 CNRS-Université de Strasbourg, 23 rue du Loess, BP 43, Strasbourg Cedex 2, France
| | - Ovidiu Ersen
- Institut de Physique et Chimie des Matériaux de Strasbourg (IPCMS), UMR 7504 CNRS-Université de Strasbourg, 23 rue du Loess, BP 43, Strasbourg Cedex 2, France
| | - Sophie Carenco
- Sorbonne Université, CNRS, Collège de France, Laboratoire de Chimie de la Matière Condensée de Paris, 4 place Jussieu, 75005 Paris, France.
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Bisht A, Koju RK, Qi Y, Hickman J, Mishin Y, Rabkin E. The impact of alloying on defect-free nanoparticles exhibiting softer but tougher behavior. Nat Commun 2021; 12:2515. [PMID: 33947860 PMCID: PMC8096810 DOI: 10.1038/s41467-021-22707-x] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/03/2021] [Accepted: 03/19/2021] [Indexed: 12/05/2022] Open
Abstract
The classic paradigm of physical metallurgy is that the addition of alloying elements to metals increases their strength. It is less known if the solution-hardening can occur in nano-scale objects, and it is totally unknown how alloying can impact the strength of defect-free faceted nanoparticles. Purely metallic defect-free nanoparticles exhibit an ultra-high strength approaching the theoretical limit. Tested in compression, they deform elastically until the nucleation of the first dislocation, after which they collapse into a pancake shape. Here, we show by experiments and atomistic simulations that the alloying of Ni nanoparticles with Co reduces their ultimate strength. This counter-intuitive solution-softening effect is explained by solute-induced local spatial variations of the resolved shear stress, causing premature dislocation nucleation. The subsequent particle deformation requires more work, making it tougher. The emerging compromise between strength and toughness makes alloy nanoparticles promising candidates for applications.
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Affiliation(s)
- Anuj Bisht
- Department of Materials Science and Engineering, Technion-Israel Institute of Technology, Haifa, Israel
| | - Raj Kiran Koju
- Department of Physics and Astronomy, MSN 3F3, George Mason University, Fairfax, VA, USA
| | - Yuanshen Qi
- Department of Materials Science and Engineering, Technion-Israel Institute of Technology, Haifa, Israel
| | - James Hickman
- Materials Science and Engineering Division, National Institute of Standards and Technology, Gaithersburg, MD, USA
| | - Yuri Mishin
- Department of Physics and Astronomy, MSN 3F3, George Mason University, Fairfax, VA, USA.
| | - Eugen Rabkin
- Department of Materials Science and Engineering, Technion-Israel Institute of Technology, Haifa, Israel.
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