Atomic-resolution imaging of radiation-induced defects in high temperature superconductors for fusion applications

Rare-earth barium copper oxides (REBCO) are the only class of high-temperature superconducting (HTS) materials that have been developed into commercial wires with an engineering performance good enough for use in the high field magnet for small fusion tokamaks like the one being designed in the STEP programme ( https://ccfe.ukaea.uk/research/step/ ). One of the critical aspects we must understand before deploying these expensive materials in a fusion reactor is how their superconducting properties are affected by exposure to high energy neutrons and a significant flux of gamma rays to ensure that they can retain adequate performance for the lifetime of the magnets. Atomic-resolution imaging and spectroscopy in an aberration-corrected electron microscope can directly reveal the local structure and bonding arrangement associated with lattice defects.  We have developed a technique known as electron ptychography that allows the oxygen atoms, which only weakly scatter electrons, to be imaged.  This is particularly important for this project because radiation is known to generate defects on the oxygen sublattice that have a strong influence on the superconducting transition temperature.  Alongside this, electron energy-loss spectroscopy (EELS) will reveal the disruption to the electronic structure of the material due to the introduction of defects.  The project will involve sample preparation and operation of advanced electron microscope instruments followed by data processing and modelling allow a full understanding to be developed.