| 1. |
- Menushenkov, V. P., et al.
(författare)
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Effect of heat treatment on the microstructure and magnetic properties of as-cast SmCo 5-based alloys
- 2012
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Ingår i: Magnetism and Magnetic Materials V. - : Trans Tech Publications Inc.. - 9783037854365 ; , s. 204-207
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Konferensbidrag (refereegranskat)abstract
- Local and crystalline structures of as-cast SmCo 5±x alloys subjected to various heat treatments were studied using EXAFS, X-ray diffraction, and metallographic analyses. XRD and EXAFS analyses of SmCo 5-x alloys show the evidence of the Sm-enrichment of the SmCo 5 phase. The behavior of the lattice parameters of SmCo 5 phase in Sm-rich alloys during aging between 1120°C and 700°C can be related to the phase transformation of SmCo 5 into SmCo 5-x phases.
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| 2. |
- Khubbutdinov, Ruslan, et al.
(författare)
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High spatial coherence and short pulse duration revealed by the Hanbury Brown and Twiss interferometry at the European XFEL
- 2021
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Ingår i: Structural Dynamics. - : American Institute of Physics (AIP). - 2329-7778. ; 8:4
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Tidskriftsartikel (refereegranskat)abstract
- Second-order intensity interferometry was employed to study the spatial and temporal properties of the European X-ray Free-Electron Laser (EuXFEL). Measurements were performed at the soft x-ray Self-Amplified Spontaneous Emission (SASE3) undulator beamline at a photon energy of 1.2 keV in the Self-Amplified Spontaneous Emission (SASE) mode. Two high-power regimes of the SASE3 undulator settings, i.e., linear and quadratic undulator tapering at saturation, were studied in detail and compared with the linear gain regime. The statistical analysis showed an exceptionally high degree of spatial coherence up to 90% for the linear undulator tapering. Analysis of the measured data in spectral and spatial domains provided an average pulse duration of about 10 fs in our measurements. The obtained results will be valuable for the experiments requiring and exploiting short pulse duration and utilizing high coherence properties of the EuXFEL.
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| 3. |
- Menushenkov, A. P., et al.
(författare)
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Direct evidence of real-space pairing in BaBiO3
- 2024
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Ingår i: Physical Review Research. - : American Physical Society. - 2643-1564. ; 6:2
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Tidskriftsartikel (refereegranskat)abstract
- The parent compound BaBiO3 of bismuthate high-temperature superconductors (HTSCs) BaBi(Pb)O3 and Ba(K)BiO3 with perovskitelike structure exhibits unusual electronic and structural properties, which can be satisfactorily explained if we assume that all charge carriers are in the paired state. However, the prior experiments and the first-principle calculations only indirectly indicate the existence of paired charge carriers in BaBiO3. In this work, we report the direct evidence of initially paired electrons and holes in the upper antibonding Bi 6s-O 2p sigma* orbital of the neighboring octahedral complexes in the ground state of BaBiO3 using the time-resolved x-ray absorption spectroscopy (XAS) to monitor the electron dynamics after the femtosecond resonant 633 nm laser excitation. We observe strong changes in the oxygen K-edge XAS preedge region, defined by the Bi 6s-O 2p sigma* orbitals. We interpret them as a fast (<= 0.3 ps) breaking of charge carrier pairs and slower (0.3-0.8 ps) lattice rearrangement from the distorted monoclinic structure into the new metastable state with a cubic lattice, which persists at least up to 60 ps after the excitation. Analysis of the intermediate state at the fast excitation shows that the bond disproportionation and monoclinic distortion of BaBiO3 structure are energetically favorable due to the charge carrier pairing. Thus the compound BaBiO3 forms a new quantum state that we define as a local pair density wave. Taking into account a large number of similarities between bismuthate and cuprate high-temperature superconductors, we believe that our work will give a new impetus to understanding the nature of superconductivity in perovskite HTSCs.
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| 4. |
- Purans, J., et al.
(författare)
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Local electronic structure rearrangements and strong anharmonicity in YH3 under pressures up to 180 GPa
- 2021
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Ingår i: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723. ; 12:1
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Tidskriftsartikel (refereegranskat)abstract
- The discovery of superconductivity above 250 K at high pressure in LaH10 and the prediction of overcoming the room temperature threshold for superconductivity in YH10 urge for a better understanding of hydrogen interaction mechanisms with the heavy atom sublattice in metal hydrides under high pressure at the atomic scale. Here we use locally sensitive X-ray absorption fine structure spectroscopy (XAFS) to get insight into the nature of phase transitions and the rearrangements of local electronic and crystal structure in archetypal metal hydride YH3 under pressure up to 180 GPa. The combination of the experimental methods allowed us to implement a multiscale length study of YH3: XAFS (short-range), Raman scattering (medium-range) and XRD (long-range). XANES data evidence a strong effect of hydrogen on the density of 4d yttrium states that increases with pressure and EXAFS data evidence a strong anharmonicity, manifested as yttrium atom vibrations in a double-well potential.
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| 5. |
- Ivanov, A. A., et al.
(författare)
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Studying the effect of oxygen content on the electron structure of Nd1.85Ce0.15CuO4 by means of photoelectron spectromicroscopy
- 2007
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Ingår i: Journal of Experimental and Theoretical Physics. - 1063-7761. ; 105:1, s. 241-245
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Tidskriftsartikel (refereegranskat)abstract
- Changes in the electron structure of the surface layer of Nd1.85Ce0.15CuO4 (NCCO) epitaxial films, which were caused by variation of the oxygen content and modification of the crystal structure of samples as a result of Ar+ ion etching and annealing, have been studied by means of photoelectron spectromicroscopy. A method is proposed for the cleaning the surface of oxygen-containing superconductors, which includes sequential stages of deep ion etching, high-temperature annealing in an oxygen-containing atmosphere (for the structural recovery and saturation with oxygen), a short-term ion etching (for the removal of an adsorbed layer of the oxidizer), and the final vacuum annealing of radiation-induced effects. The application of this procedure to NCCO films allowed an electron structure to be obtained, which was identical to that inherent in the surface of single crystals cleaved in situ in the measurement chamber.
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| 6. |
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| 7. |
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| 8. |
- Menushenkov, V. P., et al.
(författare)
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Crystalline structure of SmCo5 based alloys
- 2009
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Ingår i: METAL 2009 - 18th International Conference on Metallurgy and Materials, Conference Proceedings. - 9788087294109 ; , s. 394-400
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Konferensbidrag (refereegranskat)abstract
- Microstructure and crystalline structure of SmCo5 based alloys after various heat treatments were studied using X-ray diffraction and metallographic methods. It was established that complicated microstructure of hyperstoichiometric alloys forms in nonequilibrium conditions during crystallization of the ingots and the subsequent cooling to room temperature. XRD study of the lattice parameters of SmCo5 phase in as-cast SmCo5 based alloys after different heat treatments shows evidence of the Sm enrichment of the SmCo5 phase. The behavior of the lattice parameters of SmCo5 phase in Sm-rich alloys when subjected to aging between 1220°C and 700°C can be related to the phase transformation of SmCo5 into SmCo5-x phases.
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| 9. |
- Tsetlin, M. B., et al.
(författare)
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Investigation of Epitaxial Nd1.85Ce0.15CuO4-y Film Surface by Low Energy Electron Diffractometry
- 2008
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Ingår i: Journal Of Surface Investigation-X-Ray Synchrotron And Neutron Techniques. - 1027-4510. ; 2:6, s. 928-930
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Tidskriftsartikel (refereegranskat)abstract
- The surface of epitaxial Nd1.85Ce0.15CuO4-y(001) (NCCO) film has been studied by low energy electron diffractometry (LEED) and photoelectron spectroscopy. Ar+ ion etching of a surface with subsequent annealing in oxygen at atmosphere pressure has been found to lead to the ordered structure restoration of surface layers with the symmetry type and lattice parameters corresponding to the NCCO phase. Annealing in vacuum at temperatures close to the boundary of thermodynamic phase stability results in the formation of epitaxial Ce0.5Nd0.5O1.75 phase on a surface that is indicated in the LEED pattern as additional spots corresponding to the surface lattice (root 2 x root 2) R45 degrees.
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