Electronic Instabilities by Design: Defining Pathways for Diffusing Electrons and Ions in Vanadium Oxide Bronzes

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PART 1:?? NON-TECHNICAL SUMMARYMany aspects of modern technology, spanning the range from computer chips to batteries, rely on moving charge, either electrons or ions, across the length of solids. Precisely controlling the flow of ions and electrons is of great importance for these technologies, and it depends on the pathways defined by the structural arrangement of atoms within the material as well the manner in which the atoms are bonded together. The project, funded by the Solid State and Materials Chemistry program in the Division of Materials Research at NSF, explores the way in which rearranging atoms and changing pathways within a versatile class of compounds (built from atoms of vanadium, oxygen, and a variable third metal) alters the flow of electrons and ions. By adjusting the distance between atoms and the width of the conduits, the researchers can make a material insulating, metallic, or bring it to a point where it can be switched between insulating and metallic behavior when applying external stimuli. Such materials are of great interest for designing new ways to process information. Alternately, tuning conduits for storage and movement of ions holds promise for enabling the design of new types of batteries. As such, the project advances national prosperity and welfare by unravelling basic mechanisms and guiding the design of new materials for electronics and energy storage. Understanding the specific manner in which atoms need to be connected to realize effective paths for charge flow paves the way to creating new precisely designed compounds exhibiting unprecedented function in terms of tunable electrical conductance and the ability to store ions. In order to further the objective of US global leadership in education, the principal investigator engages a diverse group of students in his research through summer internship programs and workshops, with an emphasis on students transferring from community colleges. ??PART 2:?? TECHNICAL SUMMARY?As electrons and holes propagate across extended solids, the velocity, energy, and effective mass of the charge carriers are determined by the specific pathways that they traverse. The ability to precisely and continuously tune orbital overlap and modulate bandwidths through specific alterations of atomistic structure is a long-desired goal in the chemistry and physics of solids, but it is exceedingly difficult to achieve in practice given difficulties in independently controlling structure and composition. The project, funded by the Solid State and Materials Chemistry program in the Division of Materials Research at NSF, seeks to precisely define electronic and ionic conduction pathways using a versatile palette of compounds with the formula MxV2O5 (where M denotes a cation and x its stoichiometry) by alteration of composition, framework connectivity, and cation stoichiometry. The project comprises two thrusts: the first thrust is focused on developing design rules for tuning electronic conductivity based on modulation of structure, composition, and stoichiometry with an emphasis on designing new materials that are at the cusp of undergoing electronic transitions. The second thrust is focused on designing intercalation hosts for Li-, Mg-, Ca-, and Al-ions based on a systematic understanding of specific structural motifs that allow for diffusion of each of the cations. Both thrusts bring together theory, synthesis, characterization of average and local structure, measurements of electronic structure, and the search for descriptors to design new electron correlated materials and multivalent insertion cathodes.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.