Directing the synthesis of complex materials from metal fluxes

第一部分： 该项目由NSF材料研究部的固态和材料化学计划资助，探索使用熔融金属作为溶剂合成新的磁性和电子材料。熔融金属助熔剂中的元素的反应在高于水中反应所用的温度和低于传统固态合成所用的温度下发生。这种不寻常的温度范围促进了新材料的发现。金属助熔剂反应也促进了新化合物作为大晶体的生长，这允许使用先进的表征技术，例如单晶X射线衍射来确定原子位置，以及定向磁性和输运测量来探索磁性和电子行为的方向性。主要研究人员的研究小组探索使用镧系元素和过渡金属的低熔点混合物作为助熔剂合成新的磁性材料。硅与熔融镁合金中的其他元素的反应被进行以合成可用于诸如太阳能电池的应用的复杂半导体化合物。进一步了解金属助熔剂化学对合成科学的进步和下一代磁性和半导体材料的发现至关重要。参与这项跨学科研究的学生获得了合成，各种表征技术和批判性思维的宝贵经验。他们与化学，物理和材料工程领域的科学家互动。 第二部分： 该项目由NSF材料研究部的固态和材料化学计划资助，研究了由两种元素组成的金属熔剂合成新的金属间化合物，这种方法能够形成新的亚稳相并将其分离为大晶体。用X射线和中子衍射确定晶体结构，并研究磁性和电子性质。探讨了两个领域：a）镧系元素/过渡金属共晶焊剂中的磁性金属间相的合成，和B）富镁焊剂混合物中的半金属相的合成。前者产生具有磁性的新化合物，这些磁性来自镧系元素和过渡金属元素的组合贡献。开发控制过渡金属结构单元形成的合成能力允许定制磁性和改善对复杂现象的理解，例如自旋玻璃行为和长程磁有序。镁基助熔剂被证明是金属硅化物的有效生长介质，金属硅化物具有作为热电材料的潜力。二价金属（Ca，Sr，Ba，Eu，Yb）与Si在Mg/Al熔体中的反应产生电荷平衡的半导体或半金属相复合结构类型，这是碲化物热电材料的潜在替代物。此外，研究人员还探索了不同加热曲线的影响，以便在转化为更有利的产品之前分离中间相，以及反应性的趋势，元素替代对常见结构构建块形成的影响以及结构-性能关系。此外，这项工作扩展了对金属熔剂化学的理解，目标是控制这些反应的过程和目标化合物。学生获得合成，各种表征技术和批判性思维的宝贵经验。他们通过与化学、物理和材料工程领域的科学家的互动，接触到现代科学的跨学科性质。该奖项反映了NSF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 SUMMARYThis project, funded by the Solid State and Materials Chemistry Program in the Division of Materials Research at NSF, explores the synthesis of new 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 in water, and below those used in traditional solid state synthesis. This unusual temperature range promotes the discovery of new materials. Metal flux reactions also facilitate the growth of new compounds as large crystals, which allows for the use of advanced characterization techniques such as single crystal X-ray diffraction to determine atomic positions, and oriented magnetic and transport measurements to explore the directionality of magnetic and electronic behavior. The principle investigator's research group explores the synthesis of new magnetic materials using low melting mixtures of lanthanide and transition metals as a flux. Reactions of silicon with other elements in molten magnesium alloys are carried out to synthesize complex semiconducting compounds that may be useful for applications such as solar cells. Further understanding of metal flux chemistry is crucial to the advancement of synthesis science and the discovery of the next generation of magnetic and semiconducting materials. Students involved in this interdisciplinary research gain valuable experience in synthesis, a variety of characterization techniques, and critical thinking. They interact with scientists in the chemistry, physics, and materials engineering fields. PART 2:   TECHNICAL SUMMARYThis project, funded by the Solid State and Materials Chemistry Program in the Division of Materials Research at NSF, investigates the synthesis of new intermetallics from metal fluxes comprised of two elements, a method that enables the formation of new metastable phases and their isolation as large crystals. Crystal structures are determined using X-ray and neutron diffraction, and magnetic and electronic properties are studied. Two areas are explored: the synthesis of a) magnetic intermetallic phases in lanthanide/transition metal eutectic fluxes, and b) semimetallic phases in magnesium-rich flux mixtures. The former produce new compounds with magnetic properties stemming from the combined contributions of both the lanthanide and the transition metal element. Developing the synthetic ability to control the formation of transition metal building blocks allows tailoring magnetic properties and improved understanding of complex phenomena such as spin glass behavior and long range magnetic ordering. Magnesium-based fluxes are proving to be fruitful growth media for metal silicides, which have potential as thermoelectric materials. Reactions of divalent metals (Ca, Sr, Ba, Eu, Yb) with silicon in Mg/Al melts yield charge-balanced semiconducting or semimetallic phases complex structure types, which are potential alternatives to telluride thermoelectrics. Additionally, researchers explore effects of varying heating profiles in order to isolate intermediate phases before their conversion to more thermodynamically favored products, as well as trends in reactivity, effects of element substitution on formation of common structural building blocks, and structure-property relationships. Furthermore, this work expands the understanding of metal flux chemistry, with the goal to control the process of these reactions and target desired compounds. Students gain valuable experience in synthesis, a variety of characterization techniques, and critical thinking. They are exposed to the interdisciplinary nature of modern science through interactions with scientists in the chemistry, physics, and materials engineering fields.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.