[Paper Review] Trial of a search for a face-centered-cubic high-entropy alloy superconductor

Naoki Ishizu, Jiro Kitagawa|arXiv (Cornell University)|Jul 1, 2020

High Entropy Alloys Studies26 references4 citations

TL;DR

This study investigates the synthesis of face-centered-cubic (fcc) high-entropy alloy (HEA) superconductors using Nb- and Pb-containing multi-component systems. Despite successful formation of fcc phases in Nb-based alloys via XRD, no superconductivity was observed down to 3 K; however, new Nb-containing HEA phases were identified, and challenges in Pb-based HEA formation were attributed to large atomic size and crystal structure mismatches, providing critical insights for future HEA superconductor design.

ABSTRACT

With the aim of the discovery of face-centered-cubic (fcc) high-entropy alloy (HEA) superconductor, we have carried out materials research on Nb or Pb-containing multi-component alloys. Although the X-ray diffraction (XRD) patterns of some Nb-containing samples exhibited the dominant fcc phases, no superconducting signals were observed down to 3 K. Examination with an energy dispersive X-ray spectrometer revealed that all samples were multi-phase, but the existence of several new Nb-containing HEA phases was found in them. It was confirmed that the synthesis of Pb-containing an HEA or quaternary alloy would be difficult, probably due to the large differences in the crystal structure and atomic radius among constituent elements, low reaction temperature and the lack of a rapid cooling process in the synthesis. Despite the negative results in this research, some hints for an improved strategy for the search for an fcc HEA superconductor are provided. Moreover, our results are useful as fundamental data for future HEA predictions or for studies of phase relations in Nb or Pb-containing multi-component alloys based on the CALPHAD (calculation of phase diagram) method.

Motivation & Objective

• To explore the feasibility of discovering face-centered-cubic (fcc) high-entropy alloy (HEA) superconductors.
• To investigate the synthesis of Nb- and Pb-containing multi-component HEAs as potential fcc superconducting candidates.
• To identify phase formation challenges in HEAs with large atomic radius and crystal structure differences.
• To provide foundational data for future HEA predictions and phase diagram modeling using the CALPHAD method.

Proposed method

• Synthesis of multi-component Nb- and Pb-containing alloys via arc-melting and subsequent annealing to promote solid solution formation.
• X-ray diffraction (XRD) analysis to identify crystal structures and phase composition of synthesized samples.
• Energy dispersive X-ray spectrometry (EDS) to assess elemental distribution and detect multi-phase microstructures.
• Low-temperature electrical resistivity measurements down to 3 K to search for superconducting transitions.
• Systematic evaluation of phase stability and formation limits in HEAs with elements of differing atomic radii and crystal structures.
• Use of CALPHAD-based phase diagram calculations to interpret experimental results and guide future alloy design.

Experimental results

Research questions

• RQ1 Can a face-centered-cubic high-entropy alloy superconductor be synthesized using Nb- and Pb-based multi-component systems?
• RQ2 What are the phase formation limitations in HEAs with large differences in atomic radius and crystal structure between components?
• RQ3 Why is the synthesis of Pb-containing HEAs particularly challenging despite high configurational entropy?
• RQ4 To what extent do XRD and EDS data reveal the presence of new Nb-containing HEA phases in multi-component systems?
• RQ5 How can experimental results inform future CALPHAD-based predictions of phase stability in complex HEA systems?

Key findings

• XRD patterns confirmed the presence of dominant face-centered-cubic (fcc) phases in several Nb-containing multi-component alloys.
• No superconducting transition was observed in any sample down to 3 K, despite successful fcc phase formation.
• Energy dispersive X-ray spectrometry revealed multi-phase microstructures, with evidence of several new Nb-containing high-entropy alloy phases.
• The synthesis of Pb-containing HEAs or quaternary alloys was found to be difficult, likely due to large atomic size and crystal structure mismatches.
• Low reaction temperature and absence of rapid cooling during synthesis hindered complete solid solution formation in Pb-based systems.
• The study provides essential experimental data for future CALPHAD-based modeling of phase equilibria in Nb- and Pb-containing multi-component systems.