Investigations of Local Structure in High Entropy Oxides

Many properties we observe in materials are a direct consequence of their composition and local structure. High entropy oxides are a unique class of systems that do not have a primary composition; rather they contain a near-equimolar distribution of several elements— where no single element serves as host. Such compositional disorder is accompanied by a unique distribution of localized structural distortions which may affect properties such as thermal conductivity, magnetic interaction, diffusion, and more. A key point of interest in these high entropy systems is the implied breadth of property tunability, which ranges in compositionally dependent functionalities from amorphous-like thermal conductivities to exotic magnetic states. In this talk, we review the beginnings of high entropy oxides then present ongoing work on the local characterization of several high entropy compositions exhibiting numerous crystal structures. X-ray absorption fine structure (XAFS), both near-edge and extended, is demonstrated to aid in understanding such chemical and structural disorder. The strengths and challenges of such characterization are discussed.