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Superconductivity in high-entropy alloy system containing Th

Research Square (Research Square), 2023

Th-containing superconducting high entropy system with the nominal composition (NbTa)0.67(MoWTh)0.33 was synthesized. Its structural and physical properties were investigated by X-ray diffraction, scanning electron microscopy, energy dispersive X-ray spectroscopy, specific heat, resistivity and magnetic measurements. Two main phases of alloy were observed: major bcc structure and minor fcc. The experimental results were supported by numerical simulation by the DFT Korringa-Kohn-Rostoker method with the coherent potential approximation (KKR-CPA).

Superconductivity in a new hexagonal high-entropy alloy

Physical Review Materials

High entropy alloys (HEAs) are the new class of materials with an attractive combination of tunable mechanical and physicochemical properties. They crystallize mainly in cubic structures, however, for practical applications, HEAs with hexagonal close-packed (hcp) structure are highly desirable in connection to their in general high hardness. Herein, we report the synthesis, structure and detailed superconducting properties of Re0.56Nb0.11Ti0.11Zr0.11Hf0.11-the first hexagonal superconducting high entropy alloy (HEA) composed of five randomly distributed transition-metals. Combination of room temperature precession electron diffraction, precession electron diffraction tomography and powder X-ray diffraction is utilized to determine the room temperature crystal structure. Transport, magnetic and heat capacity measurements show that the material is a type-II superconductor with the bulk superconducting transition at Tc = 4.4 K, lower critical field Hc1(0) = 2.3 mT and upper critical field Hc2(0) = 3.6 T. Low-temperature specific heat measurement indicates that Re0.56Nb0.11Ti0.11Zr0.11Hf0.11 is a phonon-mediated superconductor in the weak electron-phonon coupling limit with a normalized specific heat jump ∆C el γnTc = 1.32. Further, hexagonal to cubic structural transition is observed by lowering the valence electron counts and Tc follows crystalline-like behaviour.

Enhanced Superconducting Critical Parameters in a New High-Entropy Alloy Nb0.34Ti0.33Zr0.14Ta0.11Hf0.08

Materials

The structural and physical properties of the new titanium- and niobium-rich type-A high-entropy alloy (HEA) superconductor Nb0.34Ti0.33Zr0.14Ta0.11Hf0.08 (in at.%) were studied by X-ray powder diffraction, energy dispersive X-ray spectroscopy, magnetization, electrical resistivity, and specific heat measurements. In addition, electronic structure calculations were performed using two complementary methods: the Korringa–Kohn–Rostoker Coherent Potential Approximation (KKR-CPA) and the Projector Augmented Wave (PAW) within Density Functional Theory (DFT). The results obtained indicate that the alloy exhibits type II superconductivity with a critical temperature close to 7.5 K, an intermediate electron–phonon coupling, and an upper critical field of 12.2(1) T. This finding indicates that Nb0.34Ti0.33Zr0.14Ta0.11Hf0.08 has one of the highest upper critical fields among all known HEA superconductors.

Study of Superconducting State Parameters of Alloy Superconductors

2009

The theoretical study of the superconducting state parameters (SSP) viz. electron-phonon coupling strength λ, Coulomb pseudopotential μ * , transition temperature T C , isotope effect exponent α and effective interaction strength N O V of Pb-Tl-Bi alloys viz. Tl 0.90 Bi 0.10 , Pb 0.40 Tl 0.60 , Pb 0.60 Tl 0.40 , Pb 0.80 Tl 0.20 , Pb 0.60 Tl 0.20 Bi 0.20 , Pb 0.90 Bi 0.10 , Pb 0.80 Bi 0.20 , Pb 0.70 Bi 0.30 , Pb 0.65 Bi 0.35 and Pb 0.45 Bi 0.55 have been made extensively in the present work using a model potential formalism for the first time. A considerable influence of various exchange and correlation functions on λ and μ * is found from the present study. The present results of the SSP are found in qualitative agreement with the available experimental data wherever exist.

Boron based new high entropy alloy superconductor Mo0.11W0.11V0.11Re0.34B0.33

Superconductor Science and Technology, 2022

Superconducting high entropy alloys (HEAs) are new members of disordered superconductors. We report the synthesis and investigation of a new superconducting high entropy alloy Mo$_{0.11}$W$_{0.11}$V$_{0.11}$Re$_{0.34}$B$_{0.33}$ (MWVRB). It crystallized in the tetragonal CuAl$_2$ crystal structure with space group (I4/$mcm$). Comprehensive transport, magnetization and heat capacity measurements confirmed bulk type-II superconductivity having transition temperature T$_{C}$ = 4.0 K. The low temperature electronic specific heat suggests a fully gapped superconducting state in weak coupling limit.

Superconducting in Equal Molar NbTaTiZr-Based High-Entropy Alloys

Natural Science, 2018

Superconducting (SC) in equal molar NbTaTiZr-based high-entropy alloys (HEAs) that were added with Fe, Ge, Hf, Si, and/or V was observed. According to investigation on crystal structure, composition, and the relationship between critical temperature and e/a ratio, as indicated in Matthias' empirical rule, the main superconducting phase was that enriched with Nb and Ta. The coherence length (ξ) that was calculated from the carrier density reveals that ξ value has the same order of magnitude of several hundreds of Angstroms as those binary Nb-Ti and Nb-Zr alloys showed.

Relation between Crystal Structure and Transition Temperature of Superconducting Metals and Alloys

Metals, 2020

Using the Roeser–Huber equation, which was originally developed for high temperature superconductors (HTSc) (H. Roeser et al., Acta Astronautica 62 (2008) 733), we present a calculation of the superconducting transition temperatures, T c , of some elements with fcc unit cells (Pb, Al), some elements with bcc unit cells (Nb, V), Sn with a tetragonal unit cell and several simple metallic alloys (NbN, NbTi, the A15 compounds and MgB 2 ). All calculations used only the crystallographic information and available data of the electronic configuration of the constituents. The model itself is based on viewing superconductivity as a resonance effect, and the superconducting charge carriers moving through the crystal interact with a typical crystal distance, x. It is found that all calculated T c -data fall within a narrow error margin on a straight line when plotting ( 2 x ) 2 vs. 1 / T c like in the case for HTSc. Furthermore, we discuss the problems when obtaining data for T c from the lite...

Superconductivity in equimolar Nb-Re-Hf-Zr-Ti high entropy alloy

Journal of Alloys and Compounds

Herein, we report the synthesis and detailed superconducting properties of a new high entropy alloy superconductor with nominal composition Nb20Re20Zr20Hf20Ti20 using powder X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDX), magnetization, transport, and thermodynamic measurements. The room temperature powder XRD confirms that the alloy is arranged on a simple body centered cubic crystal lattice with lattice parameter a = 3.38 (1) Å. EDX measurement yields an average composition of Nb21Re16Zr20Hf23Ti20 (in atomic %). Transport, magnetic and heat capacity measurements reveal that the material is a type-II superconductor with the bulk superconducting transition at Tc = 5.3 K, lower critical field Hc1(0) = 33 mT and upper critical field Hc2(0) = 8.88 T. Low temperature specific heat measurement indicates that the sample is a moderately coupled superconductor, and the electronic specific heat data fits well with the single-gap BCS model.

The theory of strong coupling superconductivity in disordered transition metal alloys

Journal of Low Temperature Physics, 1983

The equations of strong coupling superconductivity in disordered transition metal alloys have been derived by means of "'irreducible" Green's functions and on the basis of the alloy version of the Bari~id-Labbd-Friedel model for electron-ion interaction. The configurational averaging has been performed by means of the coherent potential approximation. Making some approximations, we have obtained the formulas for the transition temperature Tc and the electron-phonon coupling constant A. These depend on the alloy component and total densities of states, the phonon Green's function, and the parameters of the model

Progress in Calculations of the Superconducting Properties of Transition Metals

Superconductivity in D- and F-Band Metals, 1980

This report wai prepared as an account of work sponsored by the Unmd States Government. Neither the United Slates nor the Uniied Statef Department of Energy, noi any of their employees, nor any cf then contractors subcontractors, or their employeei. makes any warranty, express or implied, or assume* any legal liability or reiponsibifffy for the accmcy. compkun 01 usefulness of any information, apparatus, product piocess disclosed, 01 rep.eienu ihjt us use wauld not infringe privately owned nghts. Research sponsored by the Materials Sciences DivisionÛ .S. Department of Energy under contract W-7405-eng-?,6 with the Union Carbide Corporation.