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arXiv · 2306.02809

Topotactically induced oxygen vacancy order in nickelate single crystals

Yu-Mi Wu·Pascal Puphal·Hangoo Lee·Jürgen Nuss·Masahiko Isobe·Bernhard Keimer·Matthias Hepting·Y. Eren Suyolcu·Peter A. van Aken
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Abstract

The strong structure-property coupling in rare-earth nickelates has spurred the realization of new quantum phases in rapid succession. Recently, topotactic transformations have provided a new platform for the controlled creation of oxygen vacancies and, therewith, for the exploitation of such coupling in nickelates. Here, we report the emergence of oxygen vacancy ordering in Pr$_{0.92}$Ca$_{0.08}$NiO$_{2.75}$ single crystals obtained via a topotactic reduction of the perovskite phase Pr$_{0.92}$Ca$_{0.08}$NiO$_{3}$, using CaH$_2$ as the reducing agent. We unveil a brownmillerite-like ordering pattern of the vacancies by high-resolution scanning transmission electron microscopy, with Ni ions in alternating square-pyramidal and octahedral coordination along the pseudocubic [100] direction. Furthermore, we find that the crystal structure acquires a high level of internal strain, where wavelike modulations of polyhedral tilts and rotations accommodate the large distortions around the vacancy sites. Our results suggest that atomic-resolution electron microscopy is a powerful method to locally resolve unconventional crystal structures that result from the topotactic transformation of complex oxide materials.

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Yu-Mi Wu, Pascal Puphal, Hangoo Lee, Jürgen Nuss, Masahiko Isobe, Bernhard Keimer, Matthias Hepting, Y. Eren Suyolcu, Peter A. van Aken. 2023-06-05. Topotactically induced oxygen vacancy order in nickelate single crystals. https://doi.org/10.1103/physrevmaterials.7.053609

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