2, Universidad Complutense de Madrid, Madrid, Madrid, Spain
Tuning the Metal-Insulator transition (MIT) of nikelate perovskites, RENiO3, where RE refers to a rare-earth, is possible by changing the Rare-earth cation of the structure [1,2]. Alternatively, this transition can also be shifted by other mechanisms, for instance, inducing structural distortions via epitaxial strain . However, it still remains unclear how the ReNiO3 films accommodate when they are epitaxially grown onto different substrates. Here, we use the aberration corrected Scanning transmission Electron Microscope (STEM) to precisely characterize the atomic structure of tensile and compressive strained LaNiO3 (LNO) and NdNiO3 (NNO) thin films grown by chemical solution deposition (CSD) processes. Firstly, we discuss the influence of the selected substrate on the final defect landscape, which is different in each case. Secondly, we elucidate a fundamental link between strain and the commonest defect observed in nikelate films, the Ruddlesden-Popper fault (RPF), which will ultimately impinge on the electrical properties of the films. Finally, we identify the exact position of each atomic column by applying a center of mass refinement routine, enabling us to locally quantify, with subatomic resolution, any atomic-atomic spacing or displacement, with which we unveiled unforeseen polar-like distortions appearing on either side of the RPF’s rock salt fault.
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Authors acknowledge the MICIN (NANOSELECT, CSD2007-00041 and MAT2014-51778-C2-1-R), Severo Ochoa SEV-2015-0496 grant, the RyC-2012–11709 contract of J.G. and the Generalitat de Catalunya (2014SGR 753 and Xarmae) project. The STEM microscopy work was conducted in the ICTS-CNME at UCM as well as at the Laboratorio de Microscopias Avanzadas (LMA) at Instituto de Nanociencia de Aragon (INA) at the University of Zaragoza. Authors acknowledge the ICTS-CNME for offering access to their instruments and expertise.