Electrochemical Doping and Electronic Phase Transition of Thin-Film Perovskite LaNiO3 at Room Temperature

Rare-earth nickelates ( R NiO 3 ) offer great promise for applications in emergent electronic devices owing to their tunable electrical properties. LaNiO 3 offers processing and operational advantages over heavier R NiO 3 due to its easier synthesis and superior stability. However, the experimental exploration of modulation strategies and the mechanistic understanding of electronic phase transition in thin-film LaNiO 3 remain incomplete. Herein, we demonstrate the electrochemical doping of cations (Li + , Zn 2+ , Mg 2+ , and Al 3+ ) with different radii and valence states into LaNiO 3 thin films prepared by magnetron sputtering and air annealing. A significant increase of resistivity was observed upon ion intercalation into LaNiO 3 under a positive gate voltage (3 V). X-ray photoelectron spectroscopy (XPS) and synchrotron radiation-based X-ray absorption near-edge structure (XANES) have been conducted to unveil the effect of electrochemical doping on the electronic structure change. Specifically, the peak intensity ratio change of Ni L-edge XAS confirms the reduction of the nominal valence of nickel from +3 to +2 after electrochemical doping. The decrease of the relative intensity of the oxygen K-edge pre-edge also confirms the increased electron occupation in Ni 3d–O 2p orbitals and suggests enhanced electron localization. Moreover, first-principles density functional theory (DFT) calculations reveal that the metal–insulator transition of LaNiO 3 was attributed more to the Coulombic repulsion caused by electron doping rather than to the structure distortion.