Abstract
The present work is devoted to explaining the role of epitaxialstrain in the structure and the metal–insulator (MI) transition inSmNiO3 (SNO) filmsdeposited on LaAlO3 (LAO) and SrTiO3 (STO) substrates. X-ray reciprocal space mapping and valence bond calculationsallow us to show that in-plane compressive strain (for SNO/LAO) stabilizesNi3+ inthe orthorhombically distorted structure with the result that films exhibit a sharp MI transition at120 °C, whereas in-plane tensile strain (for SNO/STO) stabilizesNi2+, implying the creation of oxygen vacancies, which is accompanied by a ‘flattening’ of theresistivity curves together with a huge increase of the overall resistivity. As SNO films aredeposited on STO, we demonstrate that strain relaxation acts like the temperature orthe rare-earth size, increasing the Ni–O–Ni bond angles. Hence in-plane tensilestrain shifts the MI transition towards high temperatures. The flattening of theresistivity curve observed for SNO/STO can be understood by taking into account theinhomogeneous strain distribution across the film thickness (strain gradient) while theincrease in resistivity has been ascribed to the homogeneous part of the strain.
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