There are few physical properties of matter that show as much variation across different materials as electrical conductivity. Materials can be insulators, semiconductors, and metals, and indeed the distinctive abilities of different materials to carry electronic charge underpin most aspects of modern technology. A relatively rare class of materials comprises solids that abruptly switch from being insulators to metals in response to an applied external stimulus such as an increase in temperature, application of a voltage, illumination with a light source, or being subjected to a tensile strain. Rarer still are materials that undergo such dramatic switching of properties close to room temperature. With support from the Solid State and Materials Chemistry program in the Division of Materials Research, this project focuses on deciphering the changes in atomic structure and chemical bonding across these abrupt transformations with a view towards rationally designing materials that can be induced to switch their conductivity across many orders of magnitude in response to external stimuli. The activity takes advantage of the structural versatility of transition metal oxides, a class of materials where the chemical composition and the precise details of the atomic structure can be finely controlled. The project is anticipated to greatly expand the available repertoire of materials that show such technologically relevant switchability of properties close to room temperature while also addressing fundamental science related to the interaction between electrons in such solids. The principal investigator is focused on engaging students transferring from community colleges in research early on in their college careers to better tap into this often overlooked talent pool. Finally, the project is developing inspirational material to provide elementary school students a flavor of the technological possibilities of nanoscience.
The project is focused on the intriguing phenomenon of metal-insulator transitions wherein the electrical conductivity of a material abruptly switches from insulating to metallic behavior in response to temperature, pressure, voltage, photo-excitation, or change in chemical composition. Such an abruptly discontinuous change in electrical conductivity arises from the transformation of localized valence electrons to itinerant electrons in the material, and is often underpinned by electron-electron interactions. Understanding and tuning electron correlation remains one of the grand challenges of the physical sciences. The fundamental premise of the research activity is the idea that inter-atomic distances, charge-ordering motifs, and dopant ratios can be precisely modulated in complex transition metal oxides through variation of the size, charge, stoichiometry, and polarizability of intercalating cations. The activity spans chemical synthesis of complex oxides with precise control of composition and structure, correlation of structural and compositional characteristics to metal-insulator transitions, the application of diffraction and spectroscopic tools to probe the mechanistic basis for these transitions, and modulation of the transitions by defining intercalation gradients. A summer research activity will engage undergraduates transferring to Texas A&M from community colleges. Graphical novels focused on nanoscience and designed to motivate elementary school students will be developed and disseminated at public science events.
