Oxygen Diode Formed in Nickelate Heterostructures by Chemical Potential Mismatch

Abstract

Deliberate control of oxygen vacancy formation and migration in perovskite oxide thin films is important for developing novel electronic and iontronic devices. Here, it is found that the concentration of oxygen vacancies (V ) formed in LaNiO (LNO) during pulsed laser deposition is strongly affected by the chemical potential mismatch between the LNO film and its proximal layers. Increasing the V concentration in LNO significantly modifies the degree of orbital polarization and drives the metal-insulator transition. Changes in the nickel oxidization state and carrier concentration in the films are confirmed by soft X-ray absorption spectroscopy and optical spectroscopy. The ability to unidirectional-control the oxygen flow across the heterointerface, e.g., a so-called "oxygen diode", by exploiting chemical potential mismatch at interfaces provides a new avenue to tune the physical and electrochemical properties of complex oxides.

Tuning Bifunctional Oxygen Electrocatalysts by Changing the A‐Site Rare‐Earth Element in Perovskite Nickelates

“…Due to the strong overlap of the La M 4 edge with the Ni L 3 edge (Figure S2, Supporting Information), only the Ni L 2 ‐edge spectra are used for the analysis. The spectral shape of the Ni L 2 edge strongly varies with the Ni oxidation state in Ni oxides, providing insight into the Ni valence in our films. As shown in Figure a, the Ni L 2 ‐ edge spectra from different films are clearly different, revealing their difference in Ni valence states.…”

Metal Oxide Nanocomposites: A Perspective from Strain, Defect, and Interface

“…Oxygen vacancy is one of the most common defects in oxide thin films. Oxygen vacancy formation and ordering have been discussed in lateral heterostructures to accommodate the strain relaxation and compensate for the chemical potential mismatch . Three main approaches have been mostly used to accommodate oxygen vacancies: I) by generating corresponding vacancies in cation sites, II) by altering the valence state of cations without altering cation stoichiometry, and III) by incorporating both cation vacancies and change of valence state.…”

Directional ionic transport across the oxide interface enables low-temperature epitaxy of rutile TiO2

“…As an analogy to the reversible control of electric charge transfer at an interface with discontinuity, (electro-)chemical potential mismatch for oxygen (Δμ O ) between two materials (μ I O < μ II O ) may give rise to charged ionic transfer to bring the equilibrium of the system with heterogeneous junction at the interface (Fig. 1a) 5,[8][9][10][11][12] . In particular, charged ionic defects migrate by ionic diffusion (e.g., diffusion of oxygen ions through vacancies) to mitigate Δμ O at the interface; 9-14 charged ions, in principle, are transferred to adjacent materials and reconfigured by the redox reaction across the chemically-reacting interfaces in oxide heterostructure until the chemical potentials of the layers match (μ I O ¼ μ II O in Fig.…”

“…In this case, instead of electric charge transfer, charged oxygen ions outdiffused to the IL to equilibrate the (electro-)chemical potential between VO 2 and IL; the formation of oxygen vacancies (V O ) by oxygen ion migration are responsible for the reversible insulatorto-metal transition and giant lattice expansion in VO 2 films under the positive bias 15 . Furthermore, V O concentrations that develop in LaNiO 3 , LaTiO 3 , and In 2 O 3 can be modulated by the directional oxygen flow to the adjacent layers [10][11][12] .…”

“…At interfaces where ionic flux (J O 2À in Fig. 1a) is directional, the dynamics of charged ions may be important by assembling other metal oxides that have different μ O 10,11,14 . The redistribution of charged vacancies can screen the electric fields that Δμ O causes.…”