Characterization of nickelate-based short-period superlattices using transmission electron microscopy

Abstract

RMO3 perovskites (R = rare-earth metal, M = transition metal) represent a board spectrum of intriguing functionalities such as metal-insulator transitions, multiferroicity, colossal magnetoresistance and superconductivity owing to the strong correlation between charge, spin and orbital degrees of freedom. In recent years, heterostructures and superlattices formed by two or more different RMO3 perovskites have received intense research interest. Due to the electronic and structural reconstructions at the heterointerfaces, novel phenomena may emerge opening the way to novel functionalities that are not accessible in their bulk counterparts. In RMO3 perovskites, the magnetic and electronic states are strongly coupled to the M-O-M bond angles and M-O bond lengths. Therefore, precise control of the MO6 octahedral rotations and distortions via epitaxial strain and interfacial octahedral connectivity offers a promising route to tailoring the material properties in a controllable way. In this work, the atomic structures of epitaxial-strained short-period RNiO3/RMO3 superlattices (R = La, Pr, and M = Ga, Al) have been systematically studied. By using aberration-corrected high-resolution transmission electron microscopy (AC-HRTEM), the effects of interfacial octahedral connectivity, as well as the formation mechanism of crystal defects in short-period RNiO3/RMO3 superlattices have been elucidated with atomic resolution. In addition, by using energy-dispersive X-ray (EDX) mapping in aberration-corrected scanning transmission electron microscopy (AC-STEM), the chemical abruptness at heterointerfaces has been probed with atomic-scale precision.