Rare Earth Nickelate Epitaxial Heterostructure Preparation And Metal-insulator Transformation Performance Research

Metal-insulator transition?MIT?in oxides is a topic of long-standing interest in condensed matter materials sciences,due to the complex coupling between electron,spin,and lattice.One series of such correlated materials is the rare-earth nickelates ReNiO₃?where Re is trivalent rare-earth ion but not La?.As temperature increase above the metal-insulator transition temperature(T_MI),the material transfers to metallic state.The change in resistivity around T_MI is quite large,usually 2³ orders of magnitude across a narrow temperature window?¹0K?.Thus,more studies are needed to ravel the correlations between the MIT transition and the structure change.In this work,we adopt Pulsed Laser Deposition?PLD?to prepare the NdNiO₃/LaAlO₃ and SmNiO₃/LaAlO₃ heterostructures,and then carry out systematic investigation on the MIT characteristics by controlling film thickness,oxygen pressure,strain,and orientation.We find that the MIT effect can be achieved in the?001?-oriented substrates whatever the high and the low of the oxygen pressure.The MIT performance can be modulated by both the mismatch induced by the lattice strain and the oxygen pressure during the PLD growth.In addition,both the tensile and compressive strains suppress the MIT behaviors.It was found that the T_MI of films is decreased remarkably when the oxygen pressure is decreased.These may be due to the competition between the changes of Ni valence,elongation of Ni-O band length and bending of Ni-O-Ni angle.However,the MIT effect in the?111?-oriented substrates shows different results due to the interfaces and substrate calmping effect.Furthermore,in order to study the flexible metal-insulator transition effect film behaviors under bending conditions,the NdNiO₃ thin films are grown on lattice-mismatched mica?001?substrate along the pseudocubic?111?direction via the van der Waals heteroepitaxy,in which the MIT behaviors are induced and modulated by carefully controlling the lattice strain and the ionic valence state with SrTiO₃ and LaAlO₃ buffering layers.Enhanced MIT properties with sharp transition and significant resistivity change between the metallic and the insulating states are achieved in the NdNiO₃/LaAlO₃/SrTiO₃/mica heterostructures with appropriate in-plane tensile strain and suppressed concentration of Ni²⁺ions.In addition,the proposed NdNiO₃-based heterostructures exhibit excellent flexibility with reliable MIT characteristics not only in statically concave/convex bending but also in dynamically bending cycling up to1000 times.The present work provides a platform to design and fabricate new flexible devices integrated with the MIT effect.