Linking Oxides’ Structures to Their Properties

Zhenxing Feng

School of Chemical, Biological, and Environmental Engineering, Oregon State University

Oxides are an important class of functional materials that exhibit a wide range of physical, chemical, and electrochemical properties including oxygen electrocatalytic activity and electronic/ionic conductivity. The understanding of oxides’ atomic and electronic structures is critical to find out the intrinsic physics that govern their macroscopic properties. For this purpose, we study both epitaxial thin films and powder materials to explore the structure-properties relationship. In this talk, I will first discuss how we utilize Coherent Bragg Rod Analysis (COBRA) and recent-developed differential COBRA to directly reveal the 3-dimentional atomic structure as well as layer-by-layer elemental distribution of La_1-xSr_xCoO_3-δ epitaxial and (La_1-ySr_y)₂CoO_4±δ/La_1-xSr_xCoO_3-δ heteostructured thin films for solid oxide fuel cells (SOFCs) applications. We find that the unexpected depth-dependent strontium distributions of these oxide thin films are coupled with strong oxygen octahedral distortions and oxygen vacancy concentration, which are correlated with their electrochemical properties. Then I will focus on strongly correlated systems. By using resonant inelastic X-ray scattering (RIXS) and resonant X-ray emission spectroscopy (RXES), we have revealed how the electronic structure is responsible for the high-pressure induced metal-insulator transition in oxides (e.g., SmNiO₃ and Sr₃Ir₂O₇). These mechanistic studies help us figure out the fundamental physics in oxides, thus providing strategies to design new materials.