| 1. |
- Gačnik, Darja, et al.
(författare)
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Structure and superconductivity of tin-containing hftizrsnm (M = cu, fe, nb, ni) medium-entropy and high-entropy alloys
- 2021
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Ingår i: Materials. - : MDPI AG. - 1996-1944. ; 14:14
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Tidskriftsartikel (refereegranskat)abstract
- In an attempt to incorporate tin (Sn) into high-entropy alloys composed of refractory metals Hf, Nb, Ti and Zr with the addition of 3d transition metals Cu, Fe, and Ni, we synthesized a series of alloys in the system HfTiZrSnM (M = Cu, Fe, Nb, Ni). The alloys were characterized crystallographically, microstructurally, and compositionally, and their physical properties were determined, with the emphasis on superconductivity. All Sn-containing alloys are multi-phase mixtures of intermetallic compounds (in most cases four). A common feature of the alloys is a microstructure of large crystalline grains of a hexagonal (Hf, Ti, Zr)5Sn3 partially ordered phase embedded in a matrix that also contains many small inclusions. In the HfTiZrSnCu alloy, some Cu is also incorporated into the grains. Based on the electrical resistivity, specific heat, and magnetization measurements, a superconducting (SC) state was observed in the HfTiZr, HfTiZrSn, HfTiZrSnNi, and HfTiZrSnNb alloys. The HfTiZrSnFe alloy shows a partial SC transition, whereas the HfTiZrSnCu alloy is non-superconducting. All SC alloys are type II superconductors and belong to the Anderson class of “dirty” superconductors.
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| 2. |
- Krnel, Mitja, et al.
(författare)
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The Effect of Scandium on the Structure, Microstructure and Superconductivity of Equimolar Sc-Hf-Nb-Ta-Ti-Zr Refractory High-Entropy Alloys
- 2022
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Ingår i: Materials. - : MDPI AG. - 1996-1944. ; 15:3
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Tidskriftsartikel (refereegranskat)abstract
- In this study, we investigate the scandium-containing Sc-Hf-Nb-Ta-Ti-Zr system of refractory high-entropy alloys (HEAs). Using the arc-melting method, we synthesized nine equimolar alloys (five 4-, three 5-and one 6-component), with all of them containing Sc. The alloys were characterized by XRD, electron microscopy and EDS, while superconductivity was investigated via electrical resistivity, specific heat and the Meissner effect. The results were compared to the parent Hf-Nb-Ta-Ti-Zr refractory HEAs, forming a single-phase body-centered cubic (bcc) structure and quite homogeneous microstructure. The addition of Sc produces a two-phase structure in the Sc-Hf-Nb-Ta-Ti-Zr alloys, with one phase being bcc and the other hexagonal close-packed (hcp). The hcp phase absorbs practically all Sc, whereas the Sc-poor bcc phase is identical to the bcc phase in the Hf-Nb-Ta-Ti-Zr parent system. Upon the Sc addition, the microstructure becomes very inhomogeneous. Large bcc dendrites (10–100 µm) are homogeneous in the central parts, but become a fine dispersion of sub-micron precipitates of the bcc and hcp phases close to the edges. The interdendritic regions are also a fine dispersion of the two phases. Superconductivity of the Sc-Hf-Nb-Ta-Ti-Zr alloys originates from the bcc phase fraction, which demonstrates identical superconducting parameters as the bcc Hf-Nb-Ta-Ti-Zr parent alloys, while the Sc-containing hcp phase fraction is non-superconducting.
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| 3. |
- Petrović, Julia, et al.
(författare)
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The Kondo Effect in Ce x LaLuScY (x = 0.05–1.0) High-Entropy Alloys
- 2023
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Ingår i: Materials. - 1996-1944. ; 16:24
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Tidskriftsartikel (refereegranskat)abstract
- In the search for electronic phenomena in high-entropy alloys (HEAs) that go beyond the independent-electron description, we have synthesized a series of hexagonal rare earth (RE)-based HEAs: CexLaLuScY (x = 0.05–1.0). The measurements of electrical resistivity, magnetic susceptibility and specific heat have shown that the CexLaLuScY HEAs exhibit the Kondo effect, which is of a single impurity type in the entire range of employed Ce concentrations despite the alloys being classified as dense (concentrated) Kondo systems. A comparison to other known dense Kondo systems has revealed that the Kondo effect in the CexLaLuScY HEAs behaves quite differently from the chemically ordered Kondo lattices but quite similar to the RE-containing magnetic metallic glasses and randomly chemically disordered Kondo lattices of the chemical formula RE1xRE21−xM (with RE1 being magnetic and RE2 being nonmagnetic). The main reason for the similarity between HEAs and the metallic glasses and chemically disordered Kondo lattices appears to be the absence of a periodic 4f sublattice in these systems, which prevents the formation of a coherent state between the 4f-scattering sites in the (Formula presented.) 0 limit. The crystal-glass duality of HEAs does not bring conceptually new features to the Kondo effect that would not be already present in other disordered dense Kondo systems. This study broadens the classification of HEAs to correlated electron systems.
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| 4. |
- Wencka, Magdalena, et al.
(författare)
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Al 27 NMR local study of the Al0.5TiZrPdCuNi alloy in high-entropy alloy and metallic glass forms
- 2022
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Ingår i: Physical Review B. - 2469-9969 .- 2469-9950. ; 105:17
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Tidskriftsartikel (refereegranskat)abstract
- We report a Al27 nuclear magnetic resonance (NMR) local spectroscopic study of the NMR lineshape and Knight shift of a six-component Al0.5TiZrPdCuNi metallic alloy that can be prepared either as a crystalline high-entropy alloy (HEA) or as an amorphous metallic glass (MG) at the same chemical composition. For both structural modifications of the material (HEA and MG), we have determined the distribution of electric-field-gradient (EFG) tensors and the local electronic density of states (DOS) g(ϵF) at the Fermi level at the position of Al27 nuclei. A theoretical I=52 quadrupole-perturbed NMR spectrum, pertinent to both cubic HEAs and amorphous MGs, has been derived using the Gaussian isotropic model of the EFG tensor distribution, and excellent fits of the experimental spectra were obtained. The EFG distribution function of the MG state is about twice broader than that of the HEA state, reflecting the existence of a (distorted) crystal lattice in the latter and its absence in the former. The T2 dependence of the Knight shift indicates that the DOS is changing rapidly with energy within the Fermi level region for both structural modifications. The local DOS at the Al27 sites of the HEA sample is ∼10% larger than that of the MG state, indicating comparable degrees of disorder.
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| 5. |
- Wencka, Magdalena, et al.
(författare)
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Electronic transport properties of the Al 0.5 TiZrPdCuNi alloy in the high-entropy alloy and metallic glass forms
- 2022
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Ingår i: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322 .- 2045-2322. ; 12:1, s. 2271-
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Tidskriftsartikel (refereegranskat)abstract
- High-entropy alloys (HEAs) are characterized by a simultaneous presence of a crystal lattice and an amorphous-type chemical (substitutional) disorder. In order to unravel the effect of crystal-glass duality on the electronic transport properties of HEAs, we performed a comparative study of the electronic transport coefficients of a 6-component alloy Al0.5TiZrPdCuNi that can be prepared either as a HEA or as a metallic glass (MG) at the same chemical composition. The HEA and the MG states of the Al0.5TiZrPdCuNi alloy both show large, negative-temperature-coefficient resistivity, positive thermopower, positive Hall coefficient and small thermal conductivity. The transport coefficients were reproduced analytically by the spectral conductivity model, using the Kubo-Greenwood formalism. For both modifications of the material (HEA and MG), contribution of phonons to the transport coefficients was found small, so that their temperature dependence originates predominantly from the temperature dependence of the Fermi-Dirac function and the variation of the spectral conductivity and the related electronic density of states with energy within the Fermi-level region. The very similar electronic transport coefficients of the HEA and the MG states point towards essential role of the immense chemical disorder.
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