Effects of alloying and deposition temperature on phase formation and superconducting properties of TiZrTaNb-based high entropy-alloy films

Abstract

A variety of bulk high-entropy alloy superconductors have been recently discovered; however, for thin films, only the TaNbHfZrTi high-entropy alloy system has been investigated for its superconducting properties. Here, (TiZrNbTa)1−xWx and (TiZrNbTa)1−xVx superconducting films have been produced by DC magnetron sputtering at different growth temperatures. The phase formation and superconducting behavior of these films depend on the content of alloying x and deposition temperature. A single body-centered cubic (bcc) phase can be formed in the low x range with enough driving energy for crystallinity, but phase transition between amorphous or two bcc structures is observed when increasing x. The highest superconducting transition temperature Tc reaches 8.0 K for the TiZrNbTa film. The superconducting transition temperature Tc of these films deposited at the same temperature decreases monotonically as a function of x. Increasing deposition temperature to 400 °C can enhance Tc for these films while retaining nearly equivalent compositions. Our experimental observations suggest that Tc of superconducting high entropy alloys relate to the atomic radii difference and electronegativity difference of involved elements beyond the valence electron number.

Stoichiometry Effects on the Chemical Ordering and Superconducting Properties in TiZrTaNbNx Refractory High Entropy Nitrides

“…A maximum T c of 10 K was achieved for the (TiZrNbTa)N 1.08 film with a nearly stoichiometric nitrogen content. The T c for the x = 0 film is ≈8 K, which is equal to the values of the TiZrNbTa film produced by a compound target [ 15 ] and the non‐equiatomic Ti 15 Zr 15 Nb 35 Ta 35 bulk synthesized by arc melting. [ 27 ] It meets the general understanding that T c of early transition metal nitrides are higher than their pure elements.…”

“…These compositions lead to a combination of mechanical, electrical, and chemical properties that are interesting for a range of potential applications as thin films. Furthermore, there is an increasing interest to explore new high-entropy superconducting thin films, [14][15][16][17] after the first observation of superconductivity in Ti-Zr-Nb-Ta-Hf with a superconducting transition temperature of T c = 7.3 K. [18] However, no superconducting highentropy nitride has been reported. Therefore, the effect of nitrogen stoichiometry on the superconducting properties needs to be explored.…”

Superconductivity in the bcc‐Type High‐Entropy Alloy TiHfNbTaMo

“…Nonetheless, a scarce bcc HEA superconductor with a VEC of 4.8 or higher has solely been documented in NbTaTiZrFe, Nb 20 Re 20 Zr 20 Hf 20 Ti 20 , and (TiZrNbTa) 1-x W x . [19,20,41] In combination with late-transition metals, predominantly Cr, Mo, and W, achieving a VEC equal to 4.8 is possible. Furthermore, the bcc-type HEA superconductors with a VEC larger than or equal to 4.8 will provide more material platforms for studying the relationship between VEC and superconducting properties.…”

Superconductivity and hardness of the equiatomic high-entropy alloy HfMoNbTiZr

“…Several interesting superconducting properties have been reported, such as the robustness of superconductivity against extremely high pressure [43] or magnetism [44] and the cocktail effect in enhancing bulk superconductivity [41]. The fabrication of HEA thin-film superconductors is one of the frontier studies [45,46]. It is also attractive that HEA superconductors display a high critical current density by improving the thermal treatment [47] or sample preparation method [48,49] when viewed from their applicability.…”