Mixed metal melts as solvents for materials synthesis

Florida State University, Tallahassee FL

Investigators

Abstract

TECHNICAL SUMMARY: This research is supported by the Solid State and Materials Chemistry program of the NSF Division of Materials Research. This project will investigate the synthesis of new intermetallics, Zintl phases, and complex salts from metal fluxes comprised of two elements. Synthesis in metal flux allows reactions to take place in a molten solution; this liquid state method enables crystal growth and the formation of unusual new metastable phases. Combining two different metals to act as a mixed solvent allows for lower reaction temperatures due to eutectic formation, and improved solubility of a wider range of reactants. Two areas will be explored: the synthesis of magnetic intermetallic phases in lanthanide/transition metal (Ln/T) eutectic fluxes, and the synthesis of lightweight Zintl phases and complex salt-like compounds in alkaline earth-rich (AE) flux mixtures. The Ln/T flux syntheses will yield new compounds with complex crystal structures and magnetic properties stemming from magnetic moments of both the lanthanide and the transition metal element. Possible magnetic behavior that may arise includes magnetic ordering, spin glass behavior, superconductivity, magnetoresistive behavior, mixed valence and heavy fermion behavior. Reactions in alkaline earth rich fluxes will produce a wide range of classes of materials, depending on the flux metals used. Fluxes rich in highly electropositive Ca, Sr, or Ba will strongly reduce main group elements to form new Zintl phases and complex salts. These include new complex hydride phases which may be of interest for hydrogen storage. Using Mg-rich fluxes will yield more borderline products which do not exhibit complete charge transfer and may as a result show metal-to-insulator transitions. NON-TECHNICAL SUMMARY: The Solid State and Materials Chemistry program of the NSF Division of Materials Research supports exploration of unusual synthetic methods which may lead to discovery of new compounds with useful properties. The metal flux technique uses molten metals as solvents for synthesis and crystal growth of alloys and intermetallics. Magnetic compounds are being sought by carrying out reactions of a variety of elements in flux mixtures of two magnetic metals (a lanthanide metal and a transition metal). Light weight alloys for hydrogen storage and potential aerospace applications are being sought from reactions of elements in flux mixtures comprised of lightweight metals such as Li, Mg, and Ca. Flux growth often yields products in the form of large crystals; this allows for use of a large suite of characterization techniques which will lead to a better understanding of how magnetic and electronic properties are derived from the structure and composition of the compounds. This research will educate undergraduate, graduate and postdoctoral researchers in materials chemistry, which will strengthen the developing program in materials science at Florida State University. This highly interdisciplinary project involves collaboration with scientists in a variety of areas (such as chemistry, physics, and engineering); this will allow the participants to understand the increasingly complex nature of modern science.