Topotactic transformations between related crystal structures are a powerful emerging route for the synthesis of novel quantum materials. Whereas most such "soft chemistry" experiments have been carried out on polycrystalline powders or thin films, the topotactic modification of single crystals -- the gold standard for physical property measurements on quantum materials -- has proven remarkably difficult. Here, we report the topotactic reduction of La1−xCaxNiO3 single-crystals to La1−xCaxNiO2+δ using CaH2 as the reducing agent. The transformation from the three-dimensional perovskite to the quasi-two-dimensional infinite-layer phase was thoroughly characterized by X-ray diffraction, electron microscopy, Raman spectroscopy, magnetometry, and electrical transport measurements. Our work demonstrates that the infinite-layer structure can be realized as a bulk phase in crystals with micrometer-sized single-domains. The electronic properties of these specimens resemble those of epitaxial thin films rather than powders with similar compositions.
@article{arxiv.2106.13171,
title = {Topotactic transformation of single-crystals: from perovskite to infinite-layer nickelates},
author = {Pascal Puphal and Yu-Mi Wu and Katrin Fürsich and Hangoo Lee and Mohammad Pakdaman and Jan A. N. Bruin and Jürgen Nuss and Y. Eren Suyolcu and Peter A. van Aken and Bernhard Keimer and Masahiko Isobe and Matthias Hepting},
journal= {arXiv preprint arXiv:2106.13171},
year = {2021}
}