| 1. |
- Korzhavyi, Pavel A., 1966-, et al.
(författare)
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Exploring monovalent copper compounds with oxygen and hydrogen
- 2012
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Ingår i: Proceedings of the National Academy of Sciences of the United States of America. - : National Academy of Sciences. - 0027-8424 .- 1091-6490. ; 109:3, s. 686-689
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Tidskriftsartikel (refereegranskat)abstract
- New important applications of copper metal, e.g., in the areas of hydrogen production, fuel cell operation, and spent nuclear fuel disposal, require accurate knowledge of the physical and chemical properties of stable and metastable copper compounds. Among the copper(I) compounds with oxygen and hydrogen, cuprous oxide Cu(2)O is the only one stable and the best studied. Other such compounds are less known (CuH) or totally unknown (CuOH) due to their instability relative to the oxide. Here we combine quantum-mechanical calculations with experimental studies to search for possible compounds of monovalent copper. Cuprous hydride (CuH) and cuprous hydroxide (CuOH) are proved to exist in solid form. We establish the chemical and physical properties of these compounds, thereby filling the existing gaps in our understanding of hydrogen- and oxygen-related phenomena in Cu metal.
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| 2. |
- Korzhavyi, Pavel A., 1966-, et al.
(författare)
-
Thermodynamics of stable and metastable Cu-O-H compounds
- 2011
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Konferensbidrag (refereegranskat)abstract
- We apply density functional perturbation theory together with experimental studies in order to investigate the structure and physical properties of possible stable and metastable copper(I) compounds with oxygen and hydrogen. Copper(I) hydride, CuH, is found to be a metastable phase which decomposes at ambient conditions and exhibiting a semiconducting gap in the electronic spectrum. The calculated structure and phonon spectra are found to be in good agreement with experimental data. The phonon spectra of a novel metastable phase, copper(I) hydroxide, are also determined.
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| 3. |
- Soroka, Inna, et al.
(författare)
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Element-specific magnetic moments in bcc Fe81Ni19/Co superlattices
- 2005
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 72:13, s. 134409-
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Tidskriftsartikel (refereegranskat)abstract
- The magnetic moments in bcc Fe81Ni19/Co(001) superlattices with the individual layer thickness of 2-6 monolayers were studied by means of soft x-ray magnetic circular dichroism. It was found that the magnetic moment was enhanced in the Fe81Ni19 layer by about 0.35 mu(B)/atom as compared to the bulk value, while the Co moment remained unaffected by the presence of interfaces. The extension of the region with the high Fe81Ni19 moment in our samples was found to be at least 3 monolayers from the interfaces. Possible sources of the Fe81Ni19 moment enhancement were considered in ab initio calculations, and it was concluded that the enhanced moment may be explained by intermixing and formation of a B2-type short-range order at the interfaces.
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| 4. |
- Soroka, Inna, 1966-
(författare)
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Magnetic Heterostructures : The Effect of Compositional Modulation on Magnetic Properties
- 2005
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The effect of compositional modulation on structural and magnetic properties of magnetic heterostructures was explored. The systems under focus were ferromagnetic superlattices Fe81Ni19/Co, metal-insulator multilayers Al2O3/Ni81Fe19, nanoparticles and artificial multilayered pillars. The heterostuctures were grown by magnetron sputtering in a state-of-the-art ultra-high vacuum system. The structural characterization was done by X-ray diffraction and reflectivity, as well as by transmission electron microscopy. Magneto-optical Kerr effect, SQUID and XMCD magnetometry and magnetic force microscopy were used for magnetic characterization. The bilayer thickness, ratio of the constituents and the interface quality influence the magnetic properties (magnetic moments and anisotropy) of metallic heterostructures. In particular, magnetic moments in bcc Fe81Ni19/Co superlattices were found to scale with the interface density thus, implying different magnetic moments at the interfaces as compared to the interior part of the layers. The easy direction of magnetization can be rotated from in-plane to out-of-plane, by increasing the bilayer thicknesses, keeping other parameters unchanged. Consequently, the anisotropy strength is strongly dependent on the repeat distance. Stripe domains appear in the films that possess an out-of-plane magnetization. The average domain period was found to be dependent on the applied in-plane magnetic field and on the total thickness of the films. The structural and magnetic properties of Al2O3/Ni81Fe19 multilayers depend strongly on the individual layers thicknesses. By increasing the amount of the magnetic deposits one can change the obtained film structure, from superparamagnetic nanoparticles to ferromagnetic multilayers. By increasing the oxide layer thickness the magnetic behavior of the nanoparticles can be altered from ferromagnetic, via spin glass like, to a superparamagnetic character.
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| 5. |
- Yang, Yi, et al.
(författare)
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Tuning Catalytic Activity of Ni-Co Nanoparticles Synthesized by Gamma-Radiolytic Reduction of Acetate Aqueous Solutions
- 2023
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Ingår i: Advanced Materials Interfaces. - : Wiley-Blackwell. - 2196-7350. ; 10:17
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Tidskriftsartikel (refereegranskat)abstract
- Transition metal-based catalysts show great potential to replace Pt-based material in energy conversion devices thanks to their low cost, reasonable intrinsic activity, thermodynamic stability, and corrosion resistance. The electrochemical performance of such catalysts is sensitive to their composition and structure. Here, it is demonstrated that homogeneous alloy nanoparticles with varying Ni-to-Co ratio and controlled structure can be synthesized from aqueous Ni(Co) acetate solutions using a facile gamma-radiolytic reduction method. The obtained samples are found to possess defects that are ordered to form polytypes structures. The concentration of these defects depends on the Ni-to-Co ratio, as supported by the results of ab initio calculations. It is found that structural defects may influence the activity of catalysts toward the oxygen evolution reaction, while this effect is less pronounced with respect to the oxygen reduction reaction. At the same time, the activity of Ni-Co catalysts in the hydrogen evolution reaction is affected by formation of Ni-OH bonds on the surface rather than by the presence of structural defects. This study demonstrates that the composition of Ni-Co nanoparticles is an essential factor affecting their structure, and both composition and structure can be tuned to optimize electrochemical performance with respect to various catalytic reactions.
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