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440 results on '"Skrotzki, W."'

2. Emerging superconductivity with broken time reversal symmetry inside a superconducting $s$-wave state

Author

Grinenko, V., Sarkar, R., Kihou, K., Lee, C. H., Morozov, I., Aswartham, S., Büchner, B., Chekhonin, P., Skrotzki, W., Nenkov, K., Hühne, R., Nielsch, K., Efremov, D. V., Drechsler, S. -L., Vadimov, V. L., Silaev, M. A., Volkov, P., Eremin, I., Luetkens, H., and Klauss, H. H.

Subjects
Condensed Matter - Superconductivity, Condensed Matter - Materials Science, Condensed Matter - Strongly Correlated Electrons
Abstract

In general, magnetism and superconductivity are antagonistic to each other. However, there are several families of superconductors, in which superconductivity may coexist with magnetism, and only a few examples are known, when superconductivity itself induces spontaneous magnetism. The most known compounds are Sr$_2$RuO$_4$ and some noncentrosymmetric superconductors. Here, we report the finding of a narrow dome of a novel $s+is'$ superconducting (SC) phase with broken time-reversal symmetry (BTRS) inside the broad $s$-wave SC region of the centrosymmetric multiband superconductor Ba$_{\rm 1-x}$K$_{\rm x}$Fe$_2$As$_2$ ($0.7 \lesssim x \lesssim 0.85$). We observe spontaneous magnetic fields inside this dome using the muon spin relaxation ($\mu$SR) technique. Furthermore, our detailed specific heat study reveals that the BTRS dome appears very close to a change in the topology of the Fermi surface (Lifshitz transition). With this, we experimentally demonstrate the emergence of a novel quantum state due to topological changes of the electronic system., Comment: 28 pages, 11 figures

Published
2018
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9. Strain induced superconductivity in the parent compound BaFe2As2

Author

Engelmann, J., Grinenko, V., Chekhonin, P., Skrotzki, W., Efremov, D. V., Oswald, S., Iida, K., Hühne, R., Hänisch, J., Hoffmann, M., Kurth, F., Schultz, L., and Holzapfel, B.

Subjects
Condensed Matter - Superconductivity
Abstract

The discovery of superconductivity (SC) with a transition temperature, Tc, up to 65K in single-layer FeSe (bulk Tc =8K) films grown on SrTiO3 substrates has attracted special attention to Fe-based thin films. The high Tc is a consequence of the combined effect of electron transfer from the oxygen-vacant substrate to the FeSe thin film and lattice tensile strain. Here we demonstrate the realization of SC in the parent compound BaFe2As2 (no bulk Tc) just by tensile lattice strain without charge doping. We investigate the interplay between strain and SC in epitaxial BaFe2As2 thin films on Fe-buffered MgAl2O4 single crystalline substrates. The strong interfacial bonding between Fe and the FeAs sublattice increases the Fe-Fe distance due to the lattice misfit which leads to a suppression of the antiferromagnetic spin density wave and induces SC with bulk-Tc ?10K. These results highlight the role of structural changes in controlling the phase diagram of Fe-based superconductors., Comment: http://www.nature.com/ncomms/2013/131206/ncomms3877/full/ncomms3877.html

Published
2013
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28. Phase Transformation Induced by High Pressure Torsion in the High-Entropy Alloy CrMnFeCoNi

Author

Chulist, R., Pukenas, A., Chekhonin, P., Hohenwarter, A., Pippan, R., Schell, N., Skrotzki, W., Chulist, R., Pukenas, A., Chekhonin, P., Hohenwarter, A., Pippan, R., Schell, N., and Skrotzki, W.

Abstract

The forward and reverse phase transformation from face-centered cubic (fcc) to hexagonal close-packed (hcp) in the equiatomic high-entropy alloy (HEA) CrMnFeCoNi has been investigated with diffraction of high-energy synchrotron radiation. The forward transformation has been induced by high pressure torsion at room and liquid nitrogen temperature by applying different hydrostatic pressures and large shear strains. The volume fraction of hcp phase has been determined by Rietveld analysis after pressure release and heating-up to room temperature as a function of hydrostatic pressure. It increases with pressure and decreasing temperature. Depending on temperature, a certain pressure is necessary to induce the phase transformation. In addition, the onset pressure depends on hydrostaticity; it is lowered by shear stresses. The reverse transformation evolves over a long period of time at ambient conditions due to the destabilization of the hcp phase. The effect of the phase transformation on the microstructure and texture development and corresponding microhardness of the HEA at room temperature is demonstrated. The phase transformation leads to an inhomogeneous microstructure, weakening of the shear texture, and a surprising hardness anomaly. Reasons for the hardness anomaly are discussed in detail.

Published
2022

48. Microstructure, texture and hardness of a metastable β-titanium alloy after bar-rolling and annealing

Author

Gu, B., Chekhonin, P., Schaarschuch, R., Oertel, C.-G., Xin, S. W., Ma, C. L., Zhou, L., Gan, W. M., and Skrotzki, W.

Subjects
Bar-rolling, Microhardness, Texture, Metastable β-titanium alloy, Microstructure
Abstract

The microstructure and texture evolution of a metastable Ti-5Al-3V-3Mo-2Cr-2Zr-1Nb-1Fe alloy during bar-rolling and after various thermal treatments was investigated by high-energy synchrotron diffraction and electron backscatter diffraction. Bar-rolling is applied in the (α+β)-phase field in order to achieve a bi-modal (duplex) microstructure. The effect of dynamic recrystallized and recovered zones on texture of Ti5321was analyzed separately, as well as the texture of primary α-precipitates and secondary α-lamellae. The texture of the recovered zones is characterized by a cube component ({001}) plus α- and γ-fibre with dominant {100}, {112}, {111} components, while the texture of the recrystallized zones is a strong cube texture. After aging or recrystallization plus aging, this texture component remains, while it disappears after solution treatment. The primary α-precipitates have their c-axes perpendicular to the rolling direction and do not follow the Burgers orientation relationship. This texture characteristics remains after various thermal heat treatments. Secondary α-lamellae obey the Burgers orientation relationship. Moreover, a variant selection of secondary α-lamellae occurs. The mechanism of texture formation of the β-phase and the precipitation behavior of the α-phase is discussed. The hardness increase can be attributed to size, shape and volume fraction of the α-precipitates. Different combinations of primary α- and secondary α-precipitates make an increase in hardness of about 11%.

Published
2020

50. Strengthening of ods silver wires

Author

Wasserbäch, W., Skrotzki, W., Chekhonin, P., Wasserbäch, W., Skrotzki, W., and Chekhonin, P.

Abstract

The present work is part of an experimental program in which the mechanical behavior and the evolution of microstructure and texture of different industrially manufactured oxide-dispersion strengthened silver alloys upon different processing steps like hot-extrusion, cold-working and further annealing have been investigated. The investigations reveal that the incoherent oxide particles strongly influence the evolution of microstructure and texture during processing and consequently the deformation behavior at room temperature. Small oxide particles cause a high strengthening of the material but only a small change of the microstructure and texture. Increasing the oxide particle size subsequently reduces the strength and changes the original microstructure and texture in a more pronounced way. The yield strength at room temperature can be explained with a linear superposition of the Orowan stress for bypassing of oxide particles by dislocations and grain boundary strengthening according to Hall-Petch. The impact of texture of the materials on the yield strength is accounted for.

Published
2020

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