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Isoelectronic substitutions and aluminium alloying in the Ta-Nb-Hf-Zr-Ti high-entropy alloy superconductor

Author(s): Von Rohr, Fabian O.; Cava, Robert Joseph

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Abstract: © 2018 American Physical Society. High-entropy alloys (HEAs) are a new class of materials constructed from multiple principal elements statistically arranged on simple crystallographic lattices. Due to the large amount of disorder present, they are excellent model systems for investigating the properties of materials intermediate between crystalline and amorphous states. Here we report the effects of systematic isoelectronic replacements, using Mo-Y, Mo-Sc, and Cr-Sc mixtures, for the valence electron count 4 and 5 elements in the body-centered cubic (BCC) Ta-Nb-Zr-Hf-Ti high-entropy alloy (HEA) superconductor. We find that the superconducting transition temperature Tc strongly depends on the elemental makeup of the alloy, and not exclusively its electron count. The replacement of niobium or tantalum by an isoelectronic mixture lowers the transition temperature by more than 60%, while the isoelectronic replacement of hafnium, zirconium, or titanium has a limited impact on Tc. We further explore the alloying of aluminium into the nearly optimal electron count [TaNb]0.67(ZrHfTi)0.33 HEA superconductor. The electron count dependence of the superconducting Tc for (HEA)Alx is found to be more crystallinelike than for the [TaNb]1-x(ZrHfTi)x HEA solid solution. For an aluminum content of x=0.4 the high-entropy stabilization of the simple BCC lattice breaks down. This material crystallizes in the tetragonal β-uranium structure type and superconductivity is not observed above 1.8 K.
Publication Date: Mar-2018
Electronic Publication Date: 21-Mar-2018
Citation: Von Rohr, F.O., Cava, R.J. (2018). Isoelectronic substitutions and aluminium alloying in the Ta-Nb-Hf-Zr-Ti high-entropy alloy superconductor. Physical Review Materials, 2 (3), 10.1103/PhysRevMaterials.2.034801
DOI: doi:10.1103/PhysRevMaterials.2.034801
EISSN: 2475-9953
Pages: 2.3:034801-1 - 034801-7
Type of Material: Journal Article
Journal/Proceeding Title: Physical Review Materials
Version: Final published version. Article is made available in OAR by the publisher's permission or policy.
Notes: Physical Review Materials Volume 2, Issue 3, 21 March 2018, Article number 034801

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