High-Entropy Alloy Superconductors under High Pressures

超导体在美国经济的各个部门发挥着至关重要的作用，从能量传输、医学成像、用于聚变能产生的磁约束等离子体、高速运输，以及量子计算和信息技术。超导材料是特殊的，因为它们对电流表现出零电阻，并在低于临界转变温度时自发地排出磁场。高熵合金是一类特殊的金属，通常含有五种或五种以上的元素，数量接近相等，而传统的合金通常在一种基体中添加少量的几种元素（如铁、镍、钴）。高熵合金代表了超导体家族的新成员，因为它们表现出强大的超导现象，即使材料受到非常高的压力，超导转变温度也不受影响。这项工作揭示了对高熵合金中超导现象的基本理解，目的是利用3d打印技术定制其微观结构，以进一步提高其产生实际应用所需的更高磁场的能力。该项目支持在国家实验和计算设施接受培训的研究生和本科生，为学术界、国家实验室和工业界提供全面发展的材料科学毕业生。阿拉巴马大学伯明翰分校与东南地区的传统黑人学院和大学合作，共同努力扩大代表性不足的群体在科学和工程领域的参与。在这个项目中，需要理论和实验相结合的专业知识来研究高压和低温下高熵合金的鲁棒超导现象。对体心立方相（TiZrHfTaNb）、六方密排相（TiZrHfReNb）和氯化铯型相（RhPdScZrNb）结晶的三种高熵合金超导体进行了四探针电阻和磁化率测量。超导测量正在扩展到1.9 K的低温和高达200 GPa的压力，使用定制的金刚石砧和嵌入探针进行电传输和磁化率测量。利用同步x射线源研究了高温低温下高熵合金超导体的晶体结构。本研究基于密度泛函理论、电子-声子计算和三种高熵合金的随机结构作为外部压力的函数，提供了相应的第一性原理计算。由此产生的结构、电子和超导特性的模拟将直接与实验进行比较，这有助于对计算框架进行基准测试。目前3d打印高熵合金超导体的研究提供了独特的微结构控制，提高了超导体的上临界磁场，这对超导体的实际应用具有重要意义。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

PART 1: NON-TECHNICAL SUMMARYSuperconductors play a vital role in various sectors of the US economy ranging from energy transmission, medical imaging, magnetically confined plasma for fusion energy generation, high-speed transportation, as well as quantum computing and information technology. Superconducting materials are special because they exhibit zero resistance to current flow and spontaneously expel magnetic fields below a critical transition temperature. High-entropy alloys are a special class of metal that has near equal amounts of typically five or more elements as opposed to more conventional alloys that usually add small amounts of several elements to one base (e.g. Iron, Nickel, Cobalt). High-entropy alloys represent a new addition to the family of superconductors as they show a phenomenon of robust superconductivity, where the superconducting transition temperature is unaffected even when the material is subjected to very high pressure. This work is uncovering a fundamental understanding of the superconducting phenomenon in high-entropy alloys for the purposes of tailoring their microstructure using 3-D printing techniques to further enhance their ability to generate higher magnetic fields required for practical applications. This project supports graduate and undergraduate students who are receiving training at national experimental and computational facilities, leading to a pipeline of well-rounded materials science graduates for employment in academia, national laboratories, and industry. The University of Alabama at Birmingham in partnership with the Historically Black Colleges and Universities in the southeastern region jointly undertake efforts in broadening participation of underrepresented groups in the science and engineering fields.PART 2: TECHNICAL SUMMARYIn this project, combined theoretical and experimental expertise is called upon to investigate the phenomenon of robust superconductivity in high-entropy alloys at high-pressures and low-temperatures. Four-probe electrical resistance and magnetic susceptibility measurements on three classes of high-entropy alloy superconductors crystallizing in body-centered cubic phase (TiZrHfTaNb), hexagonal close-packed phase (TiZrHfReNb), and Cesium-Chloride type phase (RhPdScZrNb) are being conducted. The superconducting measurements are being extended to low temperatures of 1.9 K and pressures as high as 200 GPa using a custom diamond anvil with embedded probes for electrical transport and magnetic susceptibility measurements. The crystal structures of high-entropy alloy superconductors under high-pressures and low temperatures are also being examined using a synchrotron x-ray source. This study is providing corresponding first-principles calculations based on density functional theory, electron-phonon calculations, and stochastic random structures across three classes of high-entropy alloys as a function of external pressure. The resulting simulations of structural, electronic, and superconducting properties are being compared directly with experiments, which are helping benchmark the computational frameworks. Current studies on 3-D printed high-entropy alloy superconductors are offering unique microstructural control that increases the upper critical magnetic field which is of importance for practical applications of superconductors.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.