Authors

Abstract

Hydrogen donor doping has been exploited as a strategy to manipulate the electronic structure and electrical properties of functional oxide systems. Especially, the development of synthetic methods to achieve electron doping of perovskite rare-earth nickelate thin films utilizing interstitial hydrogen is highly desirable considering the rich electronic phase diagram hosting several functional properties. In this work, we present the hydrogenation of NdNiO3 (NNO) thin films using CaH2 annealing and the resulting giant modulation of electrical resistivity in hydrogenated NNO (HNNO) thin films. Magnetron sputtering was employed to deposit epitaxial 60 nm-thin NNO films on single crystal LaAlO3 (LAO) substrates. The formation of the pristine perovskite NNO phase was realized after annealing the films at 500 C for 24 h. CaH2 annealing of NNO thin films for time durations ranging from 1 to 6 h was performed in a vacuumed ampule with two interconnected chambers at 280 C. The two-chamber design enables a simple and clean approach for hydrogen doping without physical contact between the powder and sample of interest. X-ray diffraction and Raman spectroscopy revealed the formation of NNO in pristine samples, and the subsequent hydrogen incorporation upon CaH2 annealing without forming any impurity phases. The conversion of the oxidation state of Ni towards +2 upon CaH2 annealing was probed using X-ray photoelectron spectroscopy and X-ray absorption spectroscopy. Consequently, a substantial increase in the room-temperature resistivity was observed upon CaH2 annealing indicating the formation of a strongly correlated electronic configuration of Ni in HNNO due to electron doping. Overall, the findings of this study highlight the versatility of CaH2 annealing as an electron doping method to tune the electrical properties of correlated oxides at low temperatures.