Utilizing Electrochemical Transformations and Enhancing Carrier Doping in Functional Oxides by Electrolyte Gating*

The very high charge density induced by an electric double layer formed at the solid-liquid interface has recently been used to induced or "gate" exotic phase transitions, therefore electronic ground states of multifunctional oxides in the interfacial region, via the subtle interplay between electrostatic doping (electronic phenomena) and chemical redox effects (field-driven ionic motion) depending on field polarity and defect instability. In this talk, we will present two developing frontiers of ionic electrolyte gating within two contrasting mechanistic frameworks by illustrating most recent in-situ and real-time X-ray studies to deliver fundamental understanding of structural and chemical basis and their inherent links during gating on representative functional oxide heterostructures. In one end, we drive forward the limits of electrochemically emergent transformations by manipulating ionic defects during gating. For example, a combination of electronic and ionic doping processes across the interface of perovskite nickelate heterostructure (e.g. NdNiO3) by switching between positive and negative ionic gating voltages can be utilized in realizing electrochemical transistors. [1] Moreover, ionic gating process can induce dynamically manipulating oxygen octahedra-controlled properties in the complex oxides (e.g. WO3) for the design of highly responsive multifunctional materials. [2] In the other end, we create a new paradigm of highly efficient ionic gating toward sub-voltage operation regime (e.g. enhancing carrier doping but without defect generation across the interface) by designing redox actuatable poly-ionic-liquids. [3]