Designing materials to function in harsh environments, such as conductive aqueous media, is a problem of broad interest to a range of technologies, including energy, ocean monitoring and biological applications1,2,3,4. The main challenge is to retain the stability and morphology of the material as it interacts dynamically with the surrounding environment. Materials that respond to mild stimuli through collective phase transitions and amplify signals could open up new avenues for sensing. Here we present the discovery of an electric-field-driven, water-mediated reversible phase change in a perovskite-structured nickelate, SmNiO35,6,7. This prototypical strongly correlated quantum material is stable in salt water, does not corrode, and allows exchange of protons with the surrounding water at ambient temperature, with the concurrent modification in electrical resistance and optical properties being capable of multi-modal readout. Besides operating both as thermistors and pH sensors, devices made of this material can detect sub-volt electric potentials in salt water. We postulate that such devices could be used in oceanic environments for monitoring electrical signals from various maritime vessels and sea creatures.
S.R. thanks K. Catania (Vanderbilt University) for discussions on bioelectric fields in marine organisms and B. Robinson and K. Benoit-Bird of the Monterey Bay Aquarium Research Institute for technical discussions on electroreception in sharks. We acknowledge financial support from the Army Research Office (W911NF-16-1-0289, W911NF-16-1-0042), National Science Foundation (DMR-1609898, DMR-1610215), Defense Advanced Research Projects Agency (grant D15AP00111), Office of Naval Research (grants N00014-16-1-2442 and N00014-12-1040) and Air Force Office of Scientific Research (grants FA9550-16-1-0159 and FA9550-14-1-0389). Use of the Center for Nanoscale Materials, an Office of Science user facility, was supported by the US Department of Energy (DOE), the Office of Science, Office of Basic Energy Sciences under contract number DE-AC02-06CH11357. This research used resources of the Advanced Photon Source, a US DOE Office of Science User Facility operated by Argonne National Laboratory under contract number DE-AC02-06CH11357. This research used resources of the National Energy Research Scientific Computing Center, which is supported by the Office of Science of the US DOE under contract number DE-AC02-05CH11231. An award of computer time was provided by the Innovative and Novel Computational Impact on Theory and Experiment (INCITE) programme. This research used resources of the Argonne Leadership Computing Facility at Argonne National Laboratory, which is supported by the Office of Science of the US DOE under contract DE-AC02-06CH11357. S.S.N. acknowledges support from the University of Massachusetts-Amherst through start-up funding. Part of the research described in this paper was performed at the Canadian Light Source, which is supported by the Canada Foundation for Innovation, Natural Sciences and Engineering Research Council of Canada, the University of Saskatchewan, the Government of Saskatchewan, Western Economic Diversification Canada, the National Research Council Canada and the Canadian Institutes of Health Research.
Extended data figures
MD trajectory highlights the dissociation of water molecules near the oxide-water interface into free protons and OH- ions. A fraction of the protons migrates to the oxide surface and binds to surface oxygen of the SNO. The spheres shown here represent nickel (green), samarium (purple), oxygen (red), and hydrogen (cyan) atoms.
The mechanism of protonation of the SNO surface is similar to that observed at 300 K. Note that the surface of SNO maintains its structural integrity even at elevated temperatures. The spheres shown here represent nickel (green), samarium (purple), oxygen (red), and hydrogen (cyan) atoms.
AIMD video showing proton hopping between two neighboring O atoms belonging to a NiO6 octahedron in bulk SNO at 300 K.
Only a selected region of bulk SNO is shown, wherein proton hopping occurs within ~1.5 ps. The spheres shown here represent nickel (green), samarium (purple), oxygen (red), and hydrogen (cyan) atoms.