Epitaxial superlattices as a framework for stabilizing different LaNiO3 structures

Targeted material design is at the center of research efforts on epitaxial, complex oxide heterostructures. Due to the strong electron-lattice coupling, small structural modifications are often decisive for the resulting macroscopic, physical properties of artificially layered materials. Here we report on a detailed structural analysis of a set of differently stacked <a:math xmlns:a="http://www.w3.org/1998/Math/MathML"><a:mrow><a:msub><a:mi>LaNiO</a:mi><a:mn>3</a:mn></a:msub><a:mtext>−</a:mtext><a:msub><a:mi>LaGaO</a:mi><a:mn>3</a:mn></a:msub></a:mrow></a:math> superlattices by transmission electron microscopy. We find that the relative thickness ratio of the two superlattice sublayers affects the structural network, resulting in different Ni–O bond lengths and Ni–O–Ni angles under the same epitaxial strain conditions. Whereas the bond length values depend mainly on the <b:math xmlns:b="http://www.w3.org/1998/Math/MathML"><b:msub><b:mi>LaNiO</b:mi><b:mn>3</b:mn></b:msub></b:math> layer thickness, bond angles are mainly influenced by the <c:math xmlns:c="http://www.w3.org/1998/Math/MathML"><c:msub><c:mi>LaGaO</c:mi><c:mn>3</c:mn></c:msub></c:math> layer thickness. The orbital polarization determined from x-ray absorption spectroscopy measurements shows that the superlattice with the smallest deviation of both values compared to bulk shows the highest orbital polarization. Therefore, the thickness ratio of the two superlattice components can be regarded as an additional effective tool to tune the functional properties of nickelates. Published by the American Physical Society 2024