The ability to design and control the atomic structure of materials in order to achieve a desired macroscopic property is a grand challenge of materials research. The complex oxides are an ideal family of compounds for addressing this challenge due to their ubiquity, societal importance, and strong dependence of structure on properties. For instance, properties including magnetism, ferroelectricity, catalytic behavior, and electronic conductivity are known to couple directly to atomic structure in oxides. This project aims to stabilize complex oxide thin films in non-equilibrium atomic structures in order to control electronic properties relevant to applications ranging from solar energy conversion to optoelectronics. Outreach and educational activities, with particular emphasis on the importance of structure/property relationships in materials, are incorporated in the project.
TECHNICAL DETAILS: The goal of the project is to control electronic properties such as the band gap and carrier mobilities in semiconducting perovskite films by enforcing non-equilibrium atomic structures. While a dominant theme in oxide research has been to develop an understanding of interfacial charge transfer, the use of interfaces to finely tune local structure and bonding environments has yet to be fully explored as a means to control physical properties. In ABO3 perovskites, the distortions and rotations of the corner-connected BO6 octahedra, which determine the B-O bond lengths and B-O-B angles, are known to couple directly to electronic structure. While approaches to control octahedral behavior in bulk perovskites are limited to compositional changes, oxide heterostructures offer new routes to engineering octahedral behavior independent of composition. In this project, local atomic structure in isocompositional perovskite films is systematically varied via strain or substrate-film coupling. Structural and electronic properties are probed using a combination of synchrotron diffraction, spectroscopy, and electronic transport measurements. By directly comparing octahedral behavior and electronic properties, the project isolates structure as a single independent variable and provides a direct study of how mobility and band gap can be controlled by the local bond environment. The fundamental insights gained into these atomic structure/electronic properties relationships can be used to guide materials design for applications in energy conversion and oxide electronics. The participating graduate and undergraduate students receive hands-on training with advanced materials synthesis and characterization techniques, including molecular beam epitaxy and synchrotron-based scattering.
