Research Highlights
The discovery of hydrogen-induced electronic phase transitions in strongly correlated materials such as rare-earth nickelates has opened a new paradigm in regulating the material properties for both fundamental studies and technological applications. However, an understanding of how protons and electrons behave during a phase transition is lacking, mainly owing to the difficulty in the characterization of the hydrogen doping level. Herein, we demonstrate the quantification and trajectory of hydrogen in strain-regulated SmNiO3 using a nuclear reaction analysis.
We found that, despite the reduction in hydrogen concentration, a more significant hydrogen-induced enhancement of the resistivity has been observed for biaxial tensile strained SmNiO3 films as compared with slightly compressively strained SmNiO3 films. The results contradict previous explanations regarding the origin of a hydrogen-induced phase transition in rare-earth nickelate perovskite compounds. We also proved that the highly electron localized insulating state observed in a rare-earth nickelate perovskite compound is not directly related to hydrogen doping, and is more likely a consequence of a proton incorporation/removal-induced localized defect in a metastable state. The study offers substantial scientific value in the understanding of the mechanisms and origin of a hydrogen-induced metal-insulator phase transition of strongly d-orbital-band-correlated perovskites. The results were published in Nature Communications 10, 694 (2019).
Figure 1-1. Schematic illustration of the accelerator system for a nuclear reaction analysis (a). Working principle for the quantitative detection of a hydrogen composition as a function of the distribution depth through a nuclear reaction analysis (b). Source: Nat. Commun. 2019, 10, 694