Three generations of infinite-layer nickelate crystals

Abstract Topotactic transformations between related crystal structures represent a powerful method for synthesizing novel quantum materials. In particular, the groundbreaking discovery of superconductivity in nickelates with the infinite-layer (IL) crystal structure—achieved through the topotactic oxygen reduction of the perovskite phase—has sparked recent interest in topotactic methods. However, while most topotactic reductions of nickelates were performed on polycrystalline powders or thin films, single-crystalline samples, which are the gold standard for physical property measurements in quantum materials, remain underexplored. Here, we summarize our progress in synthesizing IL nickelate bulk crystals. We review both breakthroughs and limitations encountered, and also discuss critical insights into the microstructural effects of the topotactic transformation of bulk crystals provided by scanning transmission electron microscopy. Graphical abstract