Directing the synthesis of complex materials from metal fluxes

Florida State University, Tallahassee FL

Investigators

Abstract

PART 1:   NON-TECHNICAL SUMMARY This 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 SUMMARY This 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.