Development of advanced EBSD techniques for high temperature superconductors
Electron backscatter diffraction (EBSD) is a well-established technique that probes the local crystallography near the surface of bulk materials in a scanning electron microscope (SEM). Diffraction patterns are rapidly collected at each pixel, as the incident electron beam is rastored across the sample. Conventionally, these are indexed automatically using a technique that identifies the positions of the diffraction bands to ascertain the local crystallographic orientation of each pixel. EBSD is a valuable technique for characterising high temperature superconductors, such as REBa2Cu3O7-d (REBCO, where RE=rare earth element) because high angle grain boundaries severely limit superconducting current transport in these materials. However, it is challenging to accurately index REBCO diffraction patterns because the orthorhombic unit cell is very similar to a stack of three cubic cells. This leads to the diffraction patterns for a, b and c-axis aligned grains to be indistinguishable by the standard indexing algorithm. This project will explore novel pattern analysis techniques, based on template matching to a library of patterns, and/or measuring small shifts in pattern features as is done in HR-EBSD. The Oxford Micromechanics Group has pioneered innovation in EBSD methods.
A variety of commercial bulk and tape samples as well as thin films grown in-house will be studied. Since REBCO is the material of choice for fusion magnet applications, this project will explore the suitability of EBSD for assessing the effects of irradiation damage on the crystalline perfection of REBCO. This aligns with other research being undertaken on irradiation damage of superconductors in the Oxford Centre for Applied Superconductivity.
