High Entropy Alloys HEA
In November 2022 an article titled „Superconductivity in the high-entropy alloy (NbTa)0.67(MoHfW)0.33” (Phys. Rev. B 106, 184512) authored by Piotr Sobota, Rafał Topolnicki, Tomasz Ossowski, and Rafał Idczak from the Institute of Experimental Physics, in cooperation with Adam Pikul from ILTSR PAS and Tomasz Pikula from the Lublin University of Technology, was published in the acclaimed journal Physical Review B.
High entropy alloys (HEA) are made up of five or more elements mixed at a minimum of 5%at. of each component. Despite the complex chemical composition, they form homogenous, simple structures. They exhibit high toughness and resistance to corrosion.
Superconductive HEA alloys are promising candidates for new, resistant for mechanical damage, superconductive electromagnets with a potential application in science, medicine, and industry. Currently there is no cohesive theoretical description that allows prediction of both the formation of uniform HEA alloys and their superconductive properties. A significant goal of the study is finding the correlation between the chemical composition of the alloys, method of synthesis, and thermal/mechanical processing and the critical parameters of their superconductive state, i.e. critical temperature (Tc) or upper critical field (Hc2).
The work describes the synthesis, structural and physical properties of a new superconductive alloy with the sum formula (NbTa)0.67(MoHfW)0.33. It crystallises in the bcc structure and features critical parameters Tc = 4.3 K and μ0Hc2 ≈ 1.45 T. In theoretical calculations two DFT methods were used: the commonly used for studying HEA alloys KKR-CPA (Korringa-Kohn-Rostoker method with the coherent potential approximation) method and the PAW (projector augmented wave) method. The electron-phonon coupling constant, an important parameter in the description of materials exhibiting superconducting properties, obtained from calculations using the PAW = 0.63 method turned out to be, within the limits of uncertainty, equal to the constant determined from experimental tests.
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