Superconducting in Equal Molar NbTaTiZr-Based High-Entropy Alloys

Abstract

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.

Synthesis of new high-entropy alloy-type Nb3 (Al, Sn, Ge, Ga, Si) superconductors

“…This is consistent with the resistivity values of approximately 150 μΩ cm for samples #1 and #2. For previously reported conventional alloying superconductors such as HEA superconductors [3][4][5][6], the decrease in Tc is not remarkable because of the disorder due to the long coherence length. In contrast, when the superconductors have a short coherence length such as Nb3M, disorder, which potentially causes nanoscale phase separation and/or the formation of nanoscale domains, the superconducting pairing may be affected and hence result in a decrease in Tc.…”

“…HEAs have recently attracted much attention in the fields of materials science and engineering because of their tunable properties as structural materials, such as excellent mechanical performance under extreme conditions [1,2]. As HEA superconductors, simple alloys with bcc, α-Mn, CsCl, and hcp crystal structures have mainly been studied so far [3][4][5][6][7][8][9][10][11][12][13][14]. Among these, Ta0.34Nb0.33Hf0.08Zr0.14Ti0.11 with a superconducting transition temperature (Tc) of 7.3 K, exhibits robustness in the superconducting state under extremely high pressures up to 190 GPa [4].…”

Superconductivity in HEA-Type Compounds

“…After the discovery of Ref. 18, various HEA superconductors have been developed; material information [18][19][20][21][22][23][24][25][26] is listed in Table I.…”

On the Superconductivity in High-Entropy Alloy (NbTa)<sub>1-X</sub>(HfZrTi)<sub>X</sub>

“…Here, k and l are wave vector and mean-free path, respectively, of the electron in the solid. The meanfree path in this HEA is of the order of 10 −7 cm [6] and from the Ioffe-Regel criterion one obtains k < 10 7 cm −1 , which is fairly low compared to the typical value of k F in metals (~10 8 cm −1 ) [8]. Localization can give rise to mobility edges of electronic band.…”

“…Enhancement of T C is also expected in the approximate solution to the theory when E B ω 0 , which accounts for the cocktail effect in this HEA [7]. Superconductivity has been studied in (NbTaTiZr)-based HEA with the addition of Hf, Fe, Ge, Si and V [6]. The ionization energies of Hf, Fe, Ge, Si and V are comparable to that of Nb, Ta, Ti and Zr.…”