Electrochemical oxidation for ultra high critical currents

Superconductors are unique materials, as - below a certain, critical temperature - they can carry current without dissipation. This enables novel, highly efficient applications in the fields of modern electric power industry (generation, transport, fault control), medicine (MRI) and research. To date, so-called high temperature superconductors are best suited for these purposes, in particular the complex perovskite compound Y-Ba-Cu-O. In this oxide, the oxygen content is key: incorporated oxygen ions release free electrical charge (holes), which govern the superconducting critical temperature, as well as the dissipation free, critical current density. The standard procedure to set the oxygen content is based on thermal treatments under defined oxygen atmosphere, which renders a cheap and simple approach, but with detrimental limitations on flexibility and precise control. In this research action, we will investigate a novel methodology to pump oxygen electrochemically into the superconducting structure by deploying a similar concept as for fuel cells or batteries, which is based on the separation of electronic and ionic currents using a solid electrolyte. This novel approach to superconductivity not only allows the oxygen incorporation reaction to be decoupled from the slow and vulnerable surface of the superconductor and the incorporated oxygen ions to be determined very precisely by simultaneously measuring the transported electrical charge, but also extends the possible equilibrium concentration of oxygen to previously unattainable values. This is highly interesting, as previous research has demonstrated that an increase in oxygen concentration of less than 1% can result in the doubling of the maximum loss-free current. However, the exploration of this so-called over-doped region is also essential for a better understanding of superconductivity, as in this region of the phase diagram the electronic structure is free of competing phases. Thanks to this unprecedented control over the hole doping state, we can systematically investigate its influence on superconducting properties with the aim of pushing the critical current to its intrinsic physical limitation. In parallel, we will explore innovative ways to integrate this electrochemical approach into the commercial production of superconducting tapes to enable conductor optimization and application specific customization. This research work encompasses the synthesis, electrochemical modification and in-depth analysis of superconducting thin films at TU Wien in collaboration with international partners in Barcelona and Grenoble, combining expertise from the fields of materials science, electrochemistry and superconductivity with the overall goal of deepen our understanding of the superconducting state.