Operando electrical transport during topotactic reduction of nickelate superconductors

The use of topotactic reduction reactions has enabled the exploration of new classes of quantum materials. However, the reduction process remains largely unexplored due to the limited accessibility of characterization techniques during the reaction. To address this, we have developed an apparatus allowing operando measurement of (magneto-)electrical transport properties throughout the topotactic reduction process, spanning temperatures from 620 K to 2 K. Using this tool, we successfully synthesized superconducting infinite-layer nickelates via topotactic reduction from perovskite nickelate thin films. Guided by electrical transport, we have identified distinct structural phases during the reduction reactions, tracked the evolution of superconductivity with changing oxygen stoichiometry, and determined optimal reduction conditions. Our method offers a versatile approach applicable to a growing family of metastable materials accessible via topochemistry.