Controllable Strongly Electron-Correlated Properties of NdNiO₃ Induced by Large-Area Protonation with Metal–Acid Treatment

Abstract

Unlike normal hydrogen doping in a H2 gas atmosphere assisted by precious metal catalysts at high temperatures, the cost-effective hydrogenation of rare-earth nickelate (RNiO3) thin films in acid solution with abundant protons supplies a tunable protonation-induced phase transition via the internal mechanism of electron–proton synergistic co-doping under ambient conditions. Here, we report the first ever large-area hydrogenation of a millimeter-scale NdNiO3 film by metal–acid treatment, which leads to marked changes in optical and electrical transport properties corresponding to the hydrogen-induced electronic phase transition. We found that reflectance and conductance modulations are governed by the concentration of protons in NNO, which is controlled by the crystal facet orientation, which in turn affects the proton doping speed. The effect of the crystal orientation on the speed of protonation may be due to anisotropic hydrogen diffusion owing to the existence of an energetically favored channel along the [001] direction in the NdNiO3 film. Our work provides a green route for the development of electronic devices based on nickelates with hydrogenation.

Strain-Induced Uphill Hydrogen Distribution in Perovskite Oxide Films

“…Therefore, the uphill distribution does not necessarily depend on the method to introduce hydrogen, which can be maintained in the absence of an electric field. This is also the first successful attempt of hydrogenation to perovskite oxides via metal-alkaline treatment, which avoids the use of electric gating or H 2 gas at high temperatures. , Note that metal-acid processing can also inject hydrogen into NNO via proton–electron codoping, but acid will inevitably corrode the surface of oxides. , Since most perovskite oxides are stable in alkaline conditions, the metal-alkaline protocol provides opportunities for exploring new hydrogenated phases of perovskite oxides.…”

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

“…Except the electrochemical intercalation and chemical reduction methods, [ 16,24 ] H‐spillover with Pt catalyst also can be used to realize the hydrogenation of perovskite nickelates. [ 15,17,25 ] In order to comprehensively study the hydrogenation phenomenon, we also formed hydrogenated NNO using the Pt catalytic method.…”

“…Moreover, through the gate voltage (V G )dependent in situ XRD measurement, the threshold voltage for the phase transition is determined to be between 1.2 V and 1.3 V (Note 2 and Figure S5, Supporting Information), which is also consistent with the water hydrolysis mechanism in ionic liquid gating. [4] Except the electrochemical intercalation and chemical reduction methods, [16,24] H-spillover with Pt catalyst also can be used to realize the hydrogenation of perovskite nickelates. [15,17,25] In order to comprehensively study the hydrogenation phenomenon, we also formed hydrogenated NNO using the Pt catalytic method.…”

Protonation-Induced Colossal Chemical Expansion and Property Tuning in NdNiO3 Revealed by Proton Concentration Gradient Thin Films

“…Protons play an important role in tuning the physical and chemical properties of perovskite nickelates ( R NiO 3 ), including transport properties, optical properties, ion migration and ionic conductivity, (electro-)­catalytic activity, etc. Tuning the proton concentration via an ionic liquid gating technique has already attracted a great deal of attention from the functional oxide community, due to its ease of implementation and wide range of tunability in oxide properties .…”

“…The electron transport of NNO at different stages of protonation is still under intense exploration. , A detailed picture of electron transport from pristine NNO to protonated H-NNO remains elusive. Therefore, utilizing the continuous proton concentration in the graded thin film can provide us with more insight.…”