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Sergueev, I.

Publications and source records attributed to Sergueev, I..

9 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2017

Rocking curve imaging of high quality sapphire crystals in backscattering geometry

Here, we report on the characterization of high quality sapphire single crystals suitable for high-resolution X-ray optics at high energy. Investigations using rocking curve imaging reveal the crystals to be of uniformly good quality at the level of ~10 -4 in lattice parameter variations, deltad/d. But, investigations using backscattering rocking curve imaging with lattice spacing resolution of deltad/d ~ 5.10 -8 shows very diverse quality maps for all crystals. Our results highlight nearly ideal areas with edge length of 0.2-0.5 mm in most crystals, but a comparison of the back re ection peak positions shows that even neighboring ideal areas exhibit a relative difference in the lattice parameters on the order of deltad/d = 10-20.10 -8 ; this is several times larger than the rocking curve width. Furthermore, the stress-strain analysis suggests that an extremely stringent limit on the strain at a level of ~100 kPa in the growth process is required in order to produce crystals with large areas of the quality required for X-ray optics at high energy.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Spin disorder in maghemite nanoparticles investigated using polarized neutrons and nuclear resonant scattering

The manuscript reports the investigation of spin disorder in maghemite nanoparticles of different shape by a combination of polarized small-angle neutron scattering (SANSPOL) and nuclear forward scattering (NFS) techniques. Both methods are sensitive to magnetization on the nanoscale. SANSPOL allows for investigation of the particle morphology and spatial magnetization distribution and NFS extends this nanoscale information to the atomic scale, namely the orientation of the hyperfine field experienced by the iron nuclei. The studied nanospheres and nanocubes with diameters of 7.4nm and 10.6 nm, respectively, exhibit a significant spin disorder. This effect leads to a reduction of the magnetization to 44% and 58% of the theoretical maghemite bulk value, observed consistently by both techniques.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2016

Elasticity and magnetocaloric effect in MnFe 4 Si 3

The room temperature magnetocaloric material MnFe 4 Si 3 was investigated with nuclear inelastic scattering (NIS) and resonant ultrasound spectroscopy (RUS) at different temperatures and applied magnetic fields in order to assess the infuence of the magnetic transition and the magnetocaloric effect on the lattice dynamics. The NIS data give access to phonons with energies above 3 meV, whereas RUS probes the elasticity of the material in the MHz frequency range and thus low energy, ~5 neV, phonon modes. A significant infuence of the magnetic transition on the lattice dynamics is observed only in the low energy region. Here, MnFe 4 Si 3 and other compounds in the Mn 5-x Fe x Si 3 series were also investigated with vibrating sample magnetometry, resistivity measurements and Moessbauer spectroscopy in order to study the magnetic transitions and to complement the obtained results on the lattice dynamics.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

The sapphire backscattering monochromator at the Dynamics beamline P01 of PETRA III

Here, we report on a high resolution sapphire backscattering monochromator installed at the Dynamics beamline P01 of PETRA III. The device enables nuclear resonance scattering experiments on M ossbauer isotopes with transition energies between 20 and 60 keV with sub-meV to meV resolution. In a first performance test with 119 Sn nuclear resonance at a X-ray energy of 23.88 keV an energy resolution of 1.34 meV was achieved. Moreover, the device extends the field of nuclear resonance scattering at the PETRA III synchrotron light source to many further isotopes like 151 Eu, 149 Sm, 161 Dy, 125 Te and 121 Sb.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2015

Quenching rattling modes in skutterudites with pressure

In this paper, a high-pressure study of the lattice dynamics in the filled skutterudite Eu 0.84 Fe 4 Sb 12 was carried out by means of x-ray powder diffraction and nuclear inelastic scattering. The anharmonicity of particular phonon modes was characterized by mode and element specific Grüneisen parameters. The large anharmonicity of the rattling optical mode that is hybridized with the acoustical phonons at ambient pressure is reduced at high pressure as the phonon modes decouple. Finally, this result suggests that anharmonic coupling between acoustic and optical phonon modes plays a central role in the reduced thermal conductivity.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Nuclear forward scattering of synchrotron radiation by 99 Ru

In this study, we measured nuclear forward scattering spectra utilizing the 99 Ru transition, 89.571(3) keV, with a notably mixed E2/M1 multipolarity. The extension of the standard evaluation routines to include mixed multipolarity allows us to extract electric and magnetic hyperfine interactions from 99 Ru-containing compounds. This paves the way for several other high-energy Mössbauer transitions, E~90 keV. Lastly, the high energy of such transitions allows for operando nuclear forward scattering studies in real devices.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗