Orientation Change of an Infinite-Layer Structure LaNiO₂ Epitaxial Thin Film by Annealing with CaH₂

Abstract

Low-temperature annealing with CaH2 reduced a perovskite LaNiO3 thin film to a c-axis oriented LaNiO2 thin film with an infinite-layer structure. X-ray diffraction and X-ray absorption spectroscopy measurements revealed that a further annealing caused oxygen rearrangement that changed the c-axis oriented LaNiO2 to an a-axis oriented LaNiO2 thin film consisting of a twin structure without changing the monovalent Ni oxidation state. The NiO2 infinite-layer planes in the a-axis oriented and c-axis oriented LaNiO2 thin films are perpendicular to each other.