Directing the synthesis of complex materials from metal fluxes

在材料研究部固态和材料化学项目的支持下，Susan Latturner教授和她的研究小组研究了使用熔融金属作为溶剂合成磁性和电子材料的方法。元素在熔融金属助熔剂中发生反应的温度高于在水中进行反应的温度，低于传统固态合成中使用的温度。这种不寻常的温度范围和溶液化学性质允许形成全新的材料，以及通过故意在通量反应中添加少量氢或碳原子而形成的新化合物。研究人员还研究了这些化合物的性质是否可以通过添加这些小原子而改变。例如，所得到的金属氢化物或金属碳化物产品可能具有有用的磁性。另一个相关的研究重点是利用金属熔剂反应用另一种元素部分取代化合物中的一种元素。这种方法可能会产生复杂的半导体化合物，这些化合物可能对太阳能电池或废热转化为电能等应用有用。此外，参与这项跨学科研究的学生在合成、各种表征技术和批判性思维方面获得了宝贵的培训，并与化学、物理和材料工程领域的科学家合作。他们还利用国家实验室的设施。该研究由材料研究部固态和材料化学项目支持，研究了熔融金属溶液中反应合成新的金属间化合物，并探索了在这些反应中可能发生的取代和间隙化学。在金属熔剂中合成允许反应在熔融溶液中进行，温度低于传统固态合成中通常使用的温度。这种液相法可以形成新的亚稳相，并将它们分离成大晶体。通量中存在的间隙或掺杂元素源可能引发新结构的形成，或通过改变载流子浓度来调整已知母体化合物的电子性质。通量化学这方面的研究很少；因此，本项目进一步加深了对该合成技术的认识和利用。Susan Latturner教授和她的研究小组探索了两个特定的系统：一个是在存在间隙元素（H， C， N， O， F）来源的情况下，在镧系/过渡金属（Ln/T）共晶通量中合成富镧系金属间相。它们决定了间隙是否被加入，以及它们如何影响产品的结构和磁性能。第二个领域研究了富镁熔剂混合物中金属硅化物相的合成以及通过控制掺杂优化其热电性能。三价（Sc， Y, Dy）或一价（Li, Na）金属在Mg位点上的取代被探索来改变电子性质。用x射线和中子衍射测定产物的结构。计算工作揭示了间隙或取代掺杂如何影响化合物的电子结构。磁性和输运特性是与国家强磁场实验室的研究人员合作研究的。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。

Non-technical Summary With this project, supported by the Solid State and Materials Chemistry program in the Division of Materials Research, Professor Susan Latturner and her research group investigate the synthesis of magnetic and electronic materials using molten metals as solvents. Reactions of elements in molten metal fluxes take place at temperatures above those used for reactions carried out in water, and below those used in traditional solid state synthesis. This unusual temperature range and solution chemistry allows for formation of entirely new materials as well new compounds that are formed by deliberately adding a small amount of hydrogen or carbon atoms to flux reactions. The researchers also study if the properties of these compounds can be changed by addition of such small atoms. For example, the resulting metal hydride or metal carbide products may have useful magnetic behavior. Another related research thrust focuses on using metal flux reactions to partially substitute one element in a compound by another. This approach could lead to complex semiconducting compounds that may be useful for applications such as solar cells or conversion of waste heat to electricity. Additionally, students involved in this interdisciplinary research gain valuable training in synthesis, a variety of characterization techniques, and critical thinking, and collaborate with scientists in the chemistry, physics, and materials engineering fields. They also make use of National Laboratory facilities. Technical Summary The research, supported by the Solid State and Materials Chemistry program in the Division of Materials Research, investigates the synthesis of new intermetallic compounds from reactions in molten metal solutions, and explores the substitution and interstitial chemistry that is possible in these reactions. Synthesis in metal flux allows reactions to take place in a molten solution, at temperatures below those typically used in traditional solid state synthesis. This liquid state method enables the formation of new metastable phases and their isolation as large crystals. The presence of sources of interstitial or dopant elements in the flux may trigger the formation of new structures, or enable the tailoring of electronic properties of known parent compounds by modifying charge carrier concentration. This aspect of flux chemistry has been little studied; therefore, this project furthers the understanding and utilization of this synthetic technique. Professor Susan Latturner and her research group explore two specific systems: One is the synthesis of lanthanide-rich intermetallic phases in lanthanide/transition metal (Ln/T) eutectic fluxes, in the presence of sources of interstitial elements (H, C, N, O, F). They determine whether interstitials are incorporated and how they impact the structures and magnetic properties of the products. The second area investigates the synthesis of metal silicide phases in magnesium-rich flux mixtures and the optimization of their thermoelectric properties by controlled doping. Substitution of trivalent (Sc, Y, Dy) or monovalent (Li, Na) metals on Mg sites is explored to modify electronic properties. X-ray and neutron diffraction are used to determine the structures of products. Computational work sheds light on how interstitial or substitutional doping affects the electronic structure of the compounds. Magnetic and transport properties are studied in collaboration with researchers at the National High Magnetic Field Laboratory.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.