Structure-Property Relationships in Transition-Metal Pnictides Confined to Nanoscale Dimensions

Wayne State University, Detroit MI

Investigators

Abstract

TECHNICAL SUMMARY In this NSF Solid State and Materials Chemistry funded project, key steps towards establishing how confinement of dimensions to the nanometer scale impacts structure-property relationships in transition metal pnictides of increased complexity (ternary formulations) will be undertaken. Three systems will be studied, chosen based on the prior experience of the Brock group with related binary phases, and the expectation of unique size-dependent physical properties: (MM')2P (M, M' = Mn, Fe, Co, Ni), Mn1-xFexAs, and Na1-xFeAs. The (MM')2P phases are ternary derivatives of binary phases for which syntheses have been established. The motivation for targeting these phases is based on the expectation that they will have ferromagnetic transitions at elevated temperatures, relative to the binaries, making them potentially suitable for room-temperature applications (magnetic refrigeration, data storage). Mn1-xFexAs phases were chosen because they represent Fe-doped analogs of MnAs nanoparticles, a system wherein thermodynamic phase transitions, characteristic of bulk MnAs phases, are suppressed on the nanoscale. It is expected that phase transformation phenomena can be controlled through incorporation of chemical defects, such as Fe, and this will be explicitly tested. Finally, Na1-xFeAs will be pursued because these phases will enable a new range of synthesis space to be charted, enabling nanomaterials combining ionic and covalent/metallic bonding to be prepared. Moreover, the preparation of nanoscale Na1-xFeAs will enable the effect of size confinement on the superconducting transition to be probed in this novel class of materials. In the course of the project, graduate and undergraduate researchers will develop critical thinking and communication skills, and will learn cutting-edge research techniques, including electron microscopy. The project will also introduce Detroit-area middle and high school girls, many of which are minorities, to nano- and materials science through the GO-GIRL (Gaining Options-Girls Investigate Real Life) outreach project. NON-TECHNICAL SUMMARY The unique properties attained when solids are prepared with dimensions of just 10-1000 times the diameter of an individual atom (nanomaterials) promise to revolutionize a wide range of technologies from data storage to energy conversion. However, the exploitation of nanomaterials in actual devices is limited by progress in a number of fundamental areas, including established methods for making functional nanomaterials and a developed understanding of how properties change when the size is varied in this critical regime. This NSF Solid State and Materials Chemistry funded project will establish how size, structure, and chemical composition affect the magnetic or superconducting properties of a series of phases called transition metal pnictides. In the course of the research, key factors that underpin material preparation on this lengthscale will be discovered. The development of a rationale for the synthesis of transition metal pnictides on the nanoscale has potential to impact fields such as catalysis, energy conversion, and energy storage (batteries). Moreover, insight gained from the study of materials proposed here is expected to impact use of these phases in magnetic recording, refrigeration, and so-called "spintronic" devices. In the course of the project, graduate and undergraduate students will develop the necessary critical thinking and technical skills, as well as hands-on experience with cutting-edge techniques, for developing the next generation of advanced technologies. The project will also introduce Detroit-area middle and high school girls, many of which are minorities, to nano- and materials science through the GO-GIRL (Gaining Options-Girls Investigate Real Life) outreach project. This program addresses perennially underrepresented groups in Science, Technology, Education, and Math (STEM) fields and seeks to develop these untapped assets by empowering them with positive STEM experiences and by providing them (and their parents) with the resources and information needed to ensure they get the most out of the educational system.