Hydrogen-Mediated, Voltage-Tunable Modulation of the Metal–Insulator Transition in SmNiO3 at Room Temperature

The broad interest in proton (or hydrogen) doping of strongly correlated oxides, such as perovskite nickelates (RNiO3), stems from their extraordinary modulation of electronic properties that lead to dramatic changes in electrical resistivity. However, the mechanism by which this occurs is not well understood. In this work, in situ X-ray diffraction (XRD), neutron reflectivity (NR), and electrical measurements are utilized to probe the mechanism for a voltage-tunable metal-insulator transition in SmNiO3 (SNO) thin films and memristive devices in hydrogen-rich environments. The SNO films show an immediate expansion of the c-axis lattice parameter at room temperature upon hydrogen exposure, which saturates at a massive value of ∼8%. NR measurements confirm for the first time that this expansion arises from hydrogen incorporation at a ratio of 1:4. In situ current-voltage (IV) measurements reveal that hydrogenation induces a dramatic resistivity change of more than three orders of magnitude, and the protonated Pt/SNO device exhibits a bipolar resistive switching (RS) hysteresis. The RS effects in this system arise from an interfacial Schottky barrier height modulation where proton migration at the Pt/SNO interface and within the SNO film serves as the main driver for the analog IV hysteresis. The dynamics of hydrogen incorporation and desorption are systematically studied in the Pt/SNO device with temperature-dependent electrical characterizations and Avrami model. These results for the first time demonstrate the mechanism by which hydrogen drives electronic transitions in SmNiO3 and, mediated by voltage control, can be used to manipulate the electronic character of neuromorphic devices.