Speaker
Description
High-entropy alloys (HEAs) consist of several (typically $5$ or more) different types of randomly mixed constituent atoms displaying a high degree of disorder and thus high configurational entropy. Our recent research shown that main factors that influence their superconducting properties include crystal structure, valence electron count (VEC) and mixing entropy [1-3]. Thanks to possibility to prepare HEAs in form of films it is possible to prepare nitrides of such films within very wide range of N concentration. We have shown that with concentration of N the crystal structure can be changed from $bcc$ to $fcc$ and moreover VEC is modified. By appropriate combination of constituent atoms and by nitriding it is possible to tune VEC and mixing entropy in order to find relationship between them and superconducting properties of a given HEAs. Recent investigation of N incorporation into TiNbMoTaW high-entropy alloy (HEA) films has shown that in corresponding (TiNbMoTaW)$_{1.0}$N$_x$ nitrides this leads to a dome-like transition temperature $T_c$ vs concentration $x$ dependence with eightfold $T_c$ enhancement [2]. Here, we report about the impact of N incorporation into NbTaTiZrHf films that exhibit a lower configuration entropy and lower VEC than that of TiNbMoTaW. The obtained results show that the $T_c$ vs $x$ dependence in (NbTaTiZrHf)$_{1.0}$N$_x$ shows a significantly different course. In this contribution we will discuss influence of various parameters on superconductivity in HEAs.
Acknowledgements
This work was supported by projects Mobility Slovakia-Austria, AT-SK 2023-03-15-003, APVV-23-0624, and VEGA 2/0091/24. Liquid nitrogen for experiments was sponsored by U.S. Steel Košice, s.r.o. The thin film synthesis was supported by the Austrian Research Promotion Agency (FFG) under project number 871687.
References
[1] G. Pristáš et al., “Superconductivity in medium- and high-entropy alloy thin films: Impact of thickness and external pressure,” Physical Review B, vol. 107, no. 2. American Physical Society (APS), Jan. 17, 2023. https://doi.org/10.1103/physrevb.107.024505
[2] G. Pristáš et al., “Multiple transition temperature enhancement in superconducting TiNbMoTaW high entropy alloy films through tailored N incorporation,” Acta Materialia, vol. 262. Elsevier BV, p. 119428, Jan. 2024. https://doi.org/10.1016/j.actamat.2023.119428
[3] G. Pristáš et al., “Impact of annealing and hydrogenation on the superconducting transition temperature of (TiNbMoTaW)Nx high entropy alloy nitride films,” Solid State Sciences, vol. 161. Elsevier BV, p. 107851, Mar. 2025. https://doi.org/10.1016/j.solidstatesciences.2025.107851
