Directing the synthesis of complex materials from metal fluxes

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.