Superconductivity in thermally annealed Ta-Nb-Hf-Zr- Ti high-entropy alloys
Superconductivity in thermally annealed Ta-Nb-Hf-Zr- Ti high-entropy alloys
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DOI：
10.1016/j.jallcom.2016.11.417
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发表时间：
2017-02-25
影响因子：
6.2
通讯作者：
Dolinsek, J.
中科院分区：
文献类型：
--
作者：
Vrtnik, S.;Kozelj, P.;Dolinsek, J.
我们通过研究四种不同原子浓度（等摩尔和非等摩尔）和成分数量（4 和 5）并经过不同热处理的样品，对 Ta-Nb-Hf-Zr-Ti 高熵合金 (HEA) 的超导性进行了研究。样品的结构在均匀随机固溶体和部分有序纳米结构之间变化，部分有序纳米结构的形式是在长时间退火过程中形成的富含 Zr 和 Hf 的短程有序原子簇的三维网格。人们发现超导是一种强大的现象，对材料的实际结构非常不敏感。所有研究的样品在其整个体积内都是超导的。样品的超导转变温度 TC 分散在 5.0 至 7.3 K 范围内，这种分散可能与样品的结构和化学不均匀性程度有关。在具有部分有序纳米结构的样品中，短程原子团簇的 TC 与富 Ta 和 Nb 基体的 TC 略有不同。我们的结果还证明了一个重要事实，即规则（非理想）HEA 混合物的形成、稳定性和结构是由有利于局部原子有序的混合焓的最小化和有利于随机固溶体的混合熵的最大化两者决定的。通过原子扩散进行长时间热退火过程中达到的实际平衡状态通常是部分有序的，并且所得的纳米结构是构成HEA的组分数量、它们的浓度、原子半径的差异以及退火温度和时间的敏感函数。这种纳米结构本质上决定了 HEA 材料的电子特性。 (C) 2016 Elsevier B.V. 保留所有权利。
We present a study of superconductivity in Ta-Nb-Hf-Zr-Ti high-entropy alloys (HEAs) by investigating four samples of different atomic concentrations (equimolar and off-equimolar) and number of components (4 and 5), subjected to different thermal treatments. The structure of the samples varied between a homogeneous random solid solution and a partially ordered nanostructure in the form of a three-dimensional grid of short-range ordered atomic clusters enriched in Zr and Hf that has developed during long-time annealing. Superconductivity was found to be a robust phenomenon, being quite insensitive to the actual structure of the material. All investigated samples were superconducting in the entirety of their volumes. The superconducting transition temperatures TC of the samples are scattered in the range between 5.0 and 7.3 K and this scatter could be related to the degree of structural and chemical inhomogeneity of the samples. In the samples with partially ordered nanostructure, short-range atomic clusters possess a slightly different TC than the Ta- and Nb-rich matrix. Our results also demonstrate the important fact that the formation, stability and structure of a regular (non-ideal) HEA mixture are determined by both, the minimization of the mixing enthalpy that favors local atomic ordering and the maximization of the mixing entropy that favors a random solid solution. The actual equilibrium state achieved during long-time thermal annealing via the atomic diffusion is generally partially ordered, and the resulting nanostructure is a sensitive function of the number of components constituting the HEA, their concentrations, the differences in the atomic radii and the annealing temperature and time. This nanostructure essentially determines the electronic properties of HEA materials. (C) 2016 Elsevier B.V. All rights reserved.