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- Nikiforova, Yulia A., et al.
(författare)
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Crystal structure and phase transitions at high pressures in the superconductor FeSe0.89S0.11
- 2021
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Ingår i: Journal of Alloys and Compounds. - : Elsevier. - 0925-8388 .- 1873-4669. ; 860
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Tidskriftsartikel (refereegranskat)abstract
- We report on the structural phase transitions in the FeSe0.89S0.11 superconductor with T-C = 11 K observed by powder synchrotron X-ray diffraction at high pressures up to 18.5 GPa under compression and decompression modes. It was found that at ambient pressure and room temperature, FeSe0.89S0.11 has a tetragonal structure (space group NM). Under compression, in the region of 10 GPa, a phase transition from the tetragonal into the orthorhombic structure (sp. gr . Pnma) is observed, which persists up to 18.5 GPa. Our results strongly suggest that, at decompression, as the applied pressure decreases to 6 GPa and then is completely removed, most of the sample recrystallizes into the hexagonal phase of the structural type NiAs (sp. gr . P6(3)/mmc). However, the other part of the sample remains in the high pressure orthorhombic phase (sp. gr . Pnma), while the tetragonal phase (sp. gr . P4/n) is not restored. These observations illustrate a strong hysteresis of the structural properties of FeSe0.89S0.11 during a phase transition under pressure. (C) 2020 Elsevier B.V. All rights reserved.
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| 2. |
- Michnowski, S., et al.
(författare)
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Review of Relationships Between Solar Wind and Ground-Level Atmospheric Electricity : Case Studies from Hornsund, Spitsbergen, and Swider, Poland
- 2021
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Ingår i: Surveys in geophysics. - : Springer. - 0169-3298 .- 1573-0956. ; 42:3, s. 757-801
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Forskningsöversikt (refereegranskat)abstract
- This paper reviews individual cases of the relationships between variations of solar wind parameters and variations of the DC vertical atmospheric electric field, E-z, and current density, J(z), measured at ground level in the Arctic, at the S. Siedlecki Polish Polar Station Hornsund, Spitsbergen (Svalbard, Norway), and at the mid-latitude S. Kalinowski Geophysical Observatory in Swider (Poland). A considerable number of events from Hornsund confirmed previous observations of regularity of effects related to the station's position against the location of the potential bays of ionospheric convection and polar electrojets, observed in other polar locations, as well as effects of other polar cap current systems. This allowed us to conclude that the physical dependence of ground-level E-z and J(z) on solar wind changes produce measurable effects which do not require statistical analysis to be observed. We can also expect that the dependence does exist, especially in strongly disturbed circumstances, e.g., following solar flares and Earth-directed coronal mass ejections, at middle latitudes. However, further investigations of these physical relationships by this approach are practically almost impossible since a very large number of variable parameters simultaneously affect the recorded lower atmospheric variables. In addition, results of quantitative analysis of predicted and observed effects are not satisfactory. Future research studies require more efficient ways of investigation by theoretical treatment and modelling work using existing and novel observational data besides taking advantage of scientific progress in magnetospheric physics.
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