Unveiling Strong Ion–Electron–Lattice Coupling and Electronic Antidoping in Hydrogenated Perovskite Nickelate

Abstract

Despite being highly promising for applications in emergent electronic devices, decoding both the ion–electron–lattice coupling in correlated materials at the atomic scale and the electronic band structure remains a big challenge due to the strong and complex correlation among these degrees of freedom. Here, taking an epitaxial thin film of perovskite nickelate NdNiO3 as a model system, hydrogen‐ion‐induced giant lattice distortion and enhanced NiO6 octahedra tilting/rotation are demonstrated, which leads to a new robust hydrogenated HNdNiO3 phase with lattice expansion larger than 10% on a series of substrates. Moreover, under the effect of ion–electron synergistic doping, it is found that the proposed electronic antidoping, i.e., the doped electrons mainly fill the ground‐state oxygen 2p holes instead of changing the Ni oxidation state from Ni3+ to Ni2+, dominates the metal–insulator transition. Meanwhile, lattice modification with enhanced Ni–O–Ni bond tilting or rotation mainly modifies the orbital density of states near the Fermi level. Last, by electric‐field‐controlled hydrogen‐ion intercalation and its strong coupling to the lattice and electron charge, selective micrometer‐scale patterns with distinct structural and electronic states are fabricated. The results provide direct evidence for a strong ion–electron–lattice coupling in correlated physics and exhibit its potential applications in designing novel materials and devices.

Hydrogen-induced tunable remanent polarization in a perovskite nickelate

“…By proton doping, the shape of D - E loops for H-NNO becomes sloped due to the significantly increased resistance in H-NNO as an insulating phase (resistivity ~ 6 × 10 8 Ω⋅cm). This is consistent with previous research that proton doping can increase the resistance of perovskite rare-earth nickelates up to several orders of magnitude, such as SmNiO 3 8 , 9 , LaNiO 3 22 , and NdNiO 3 10 , 11 , 15 . When the electric field increases up to a large magnitude, the loop becomes more circular as the device is more lossy at a higher electric field (Fig.…”

Strain-Induced Uphill Hydrogen Distribution in Perovskite Oxide Films

“…53,54 As a control experiment, we performed a similar ILG treatment for NNO films grown on LaAlO 3 (LAO, a = 3.788 Å) substrates, in which NNO has a tiny compressive strain (−0.5%) and its out-of-plane lattice parameter is a out = 3.856 Å. Hydrogen doping in NNO/LAO also leads to the disappearance of NNO (002) pc diffraction, and a weak peak arises at ∼42.5°due to colossal lattice expansion (Figure 3a), consistent with previous results. 23,44 SIMS characterization of the ILG NNO/LAO sample (+3 V) shows a flat hydrogen concentration along depth with a negligible uphill feature, indicating different diffusion behavior under small compressive strain (−0.5%), as presented in Figure 3b. Besides, natural aggregation of hydrogen on the interface has not been observed for the pristine NNO/LAO film, also suggesting the absence of uphill proton diffusion.…”

“…By contrast, hydrogen distribution is mainly influenced by the relative energy of protons at different positions along depth, which will be supported by theoretical calculations below. Although higher hydrogen concentration appears near the interface under large tensile strain, the formation of a stable protonated phase with colossal lattice expansion on the LAO substrate 23,44 may lead to higher overall hydrogen content. Meanwhile, the microscopic structure of the NNO/LAO system was also investigated for comparison.…”

“…In this work, we introduce epitaxial tensile strain to prototypical perovskite oxides (NdNiO 3 and La 0.67 Sr 0.33 MnO 3 ) by growing films on SrTiO 3 (STO) single-crystalline substrates. Two methods [ionic liquid gating (ILG) , and metal-alkaline solution treatment have been applied for the hydrogenation of oxide films, and we observe uphill hydrogen distribution with the maximum hydrogen concentration appearing near the interface instead of the surface layer. Control experiments on the LaAlO 3 (LAO) substrate and first-principles calculations demonstrate the strain effect on lattice distortion and distribution behavior.…”

Electric Field Induced Ion Migration and Property Tuning in Functional Oxides

“…Beyond the mechanisms involving oxygen vacancy migration, significant research has been conducted in recent years into the use of alkali metal ions and proton-based ionic motion in TMOs systems. 39,40 Protons, or hydrogen ions, are notable for their remarkable mobility, which is attributed to their extremely small ionic radius. Furthermore, the introduction of H + ions into oxide materials leads to electron doping, resulting in significant changes in the fundamental electronic structure, including modifications to the bandgap and carrier density.…”