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


von Rohr, Fabian O; Cava, Robert J (2018). Isoelectronic substitutions and aluminium alloying in the Ta-Nb-Hf-Zr-Ti high-entropy alloy superconductor. Physical Review Materials, 2:034801.

Abstract

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.

Abstract

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.

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Additional indexing

Item Type:Journal Article, refereed, original work
Communities & Collections:07 Faculty of Science > Department of Chemistry
Dewey Decimal Classification:540 Chemistry
Language:English
Date:21 March 2018
Deposited On:06 Mar 2019 16:55
Last Modified:25 Sep 2019 00:23
Publisher:American Physical Society
ISSN:2475-9953
OA Status:Green
Publisher DOI:https://doi.org/10.1103/physrevmaterials.2.034801
Project Information:
  • : FunderSNSF
  • : Grant IDPZ00P2_174015
  • : Project TitleChemistry and Physics of Nitride Based Materials

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