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

Protonation can be used to tune diverse physical and chemical properties of functional oxides. Although protonation of nickelate perovskites has been reported, details on the crystal structure of the protonated phase and a quantitative understanding of the effect of protons on physical properties are still lacking. Therefore, in this work, we select NdNiO3 (NNO) as a model system to understand the protonation process from pristine NNO to protonated HxNdNiO(3) (H-NNO). We used a reliable electrochemical method with well-defined reference electrode to trigger the protonation-induced phase transition. We found that the protonated H-NNO phase showed a colossal similar to 13% lattice expansion caused by a large tilt of NiO6 octahedra and displacement of Nd cations. Importantly, we further designed a novel device configuration to induce a gradient of proton concentration into a single NNO thin film to establish a quantitative correlation between the proton concentration and the lattice constant and transport property of H-NNO.

Automated summary

This work investigates the effects of protonation on nickelate perovskites and establishes a quantitative correlation between proton concentration, lattice constant, and transport properties.