Unraveling nano-scale effects of topotactic reduction in LaNiO$_2$ crystals

TL;DR

This study investigates the nano-scale structural changes during the topotactic reduction of LaNiO₂ crystals, revealing grain boundary formation, disordered phases, and internal strain accommodation crucial for understanding the synthesis of superconducting nickelates.

Contribution

It provides detailed nano-scale insights into the lattice transformation process from perovskite to infinite-layer phase in LaNiO₂, using advanced microscopy and spectroscopy techniques.

Findings

Identification of grain boundaries and twin boundaries induced by reduction

Discovery of an oxygen-rich disordered transition phase around impurities

Observation of internal strain relief via grain boundary formation

Abstract

Infinite-layer nickelates stand as a promising frontier in the exploration of unconventional superconductivity. Their synthesis through topotactic oxygen reduction from the parent perovskite phase remains a complex and elusive process. This study delves into the nano-scale effects of the topotactic lattice transformation within LaNiO$_2$ crystals. Leveraging high-resolution scanning transmission electron microscopy and spectroscopy, our investigations uncover a panorama of structural alterations, including grain boundaries and coherent twin boundaries, triggered by reduction-induced transformations. In addition, our analyses unveil the formation of an oxygen-rich disordered transition phase encircling impurities and pervading crystalline domains, and the internal strain is accommodated by grain boundary formation. By unraveling these nano-scale effects, our findings provide insights into the microscopic intricacies of the topotactic reduction process elucidating the transition from the perovskite to the infinite-layer phase within nickelate bulk crystals.