Mixed Molten Metals as Solvents for Materials Synthesis

本研究项目探索通过使用熔融金属作为溶剂进行反应来合成新的半导体和磁性材料。金属助熔剂中的合成允许在溶液中发生反应；这种液态方法使晶体生长和形成不寻常的新化合物。这项工作中发现的新材料可能具有有用的磁性和电学性质，它们的研究有助于加深对磁性合金、太阳能电池材料和储氢合金性质的理解。这个跨学科的研究项目培养材料化学的本科生和研究生研究人员。这项工作涉及与不同领域(如化学、物理和工程)的科学家合作，以及使用国家实验室的先进设施，如橡树岭国家实验室和国家强磁场实验室。这使学生能够了解现代科学日益复杂和协作的性质。技术摘要材料研究部固态和材料化学项目的支持使研究团队能够探索两个领域：在稀土/过渡金属(Ln/T)共晶熔剂中合成磁性合金，以及在富碱土(AE)熔剂中合成轻质复杂盐状化合物。这些反应的产物用X射线衍射、磁化率测量、输运测量、能带结构计算和其他技术进行了表征。研究了反应性、常见的结构构件和结构-性能关系的趋势。Ln/T助熔剂合成的新化合物具有来自镧系元素和过渡金属元素的磁性。产品结构通常包含过渡金属簇或层；这些构建块的磁性行为将揭示随着过渡金属簇尺寸的增大，磁矩是如何发展的。可能出现的磁性行为包括磁性有序、自旋玻璃行为、超导、磁阻、混合价和重费米子行为。使用钙、锶或钡的富碱土助熔剂会强烈还原大多数主族元素，形成新的锌相和复杂的盐。这些包括新的金属氢化物和次氢化物相，它们可能对储氢感兴趣。使用富镁熔剂可以产生更多的边界产品，这些产品不会表现出完全的电荷转移，而且通常是半金属的；它们可能作为热电材料的潜在用途，或者可能显示出金属到绝缘体的转变。

Non- Technical AbstractThis research project explores the synthesis of new semiconductors and magnetic materials by carrying out reactions using molten metals as solvents. Synthesis in metal flux allows reactions to take place in a solution; this liquid state method enables crystal growth and the formation of unusual new compounds. The new materials discovered in this work may possess useful magnetic and electronic properties, and their study contributes to increasing understanding of the nature of magnetic alloys, solar cell materials, and hydrogen storage alloys. This interdisciplinary research project educates undergraduate and graduate student researchers in materials chemistry. The work involves collaboration with scientists in a variety of areas (such as chemistry, physics, and engineering), as well as the use of advanced facilities at national labs such as Oak Ridge National Laboratory and the National High Magnetic Field Laboratory. This allows the student participants to understand the increasingly complex and collaborative nature of modern science.Technical AbstractSupport from the Solid State and Materials Chemistry program in the Division of Materials Research allows the research team to explore two areas: the synthesis of magnetic alloys in lanthanide/transition metal (Ln/T) eutectic fluxes, and the synthesis of lightweight complex salt-like compounds in alkaline earth-rich (AE) flux mixtures. Products of these reactions are characterized by X-ray diffraction, magnetic susceptibility measurements, transport measurements, band structure calculations, and other techniques. Trends in reactivity, common structural building blocks, and structure-property relationships are investigated. The Ln/T flux syntheses yield new compounds with magnetic properties stemming from both the lanthanide and the transition metal element. Product structures often contain clusters or layers of transition metals; the magnetic behavior of these building blocks will shed light on how magnetic moments develop as transition metal clusters increase in size. Magnetic behavior that may arise includes magnetic ordering, spin glass behavior, superconductivity, magnetoresistance, mixed valence and heavy fermion behavior. Alkaline earth-rich flux mixtures using calcium, strontium, or barium will strongly reduce most main group elements to form new Zintl phases and complex salts. These include new metal hydride and subhydride phases which may be of interest for hydrogen storage. Using magnesium-rich fluxes yields more borderline products which do not exhibit complete charge transfer and are often semimetallic; they may be of potential use as thermoelectric materials, or may show metal-to-insulator transitions.