Electric Field Induced Ion Migration and Property Tuning in Functional Oxides

ConspectusThe manipulation of functional oxide materials' properties through energy-efficient means is of great importance in materials science. Electric field-driven ionic control of functional oxides presents a versatile and effective approach for tailoring material properties, including insulator–metal transitions, superconductivity, magnetism, and optical characteristics, through spin, orbit, charge, and lattice degrees of freedom. This approach introduces a dynamic means of tuning these properties, allowing for real-time adjustments through external stimuli such as electric fields. The ability to modify material characteristics through ionic means is promising for both scientific exploration and practical applications, owing to its energy efficiency and compatibility with room temperature operation. Traditionally, this was primarily explored for energy storage applications, but it has now found broad utility in optoelectronics, nanoelectronic memory, and computing.Controlling charge carriers is a pivotal aspect of advancing the electronic functionalities of oxide materials. The substantial accumulation of charge carriers via electric field-induced electric double layers at oxide–electrolyte interfaces prompts extremely large electric fields, leading to different phenomena such as chemical reactions, phase transitions, and magnetic ordering. The mechanisms involved in electric field-controlled ionic motion using ionic liquids and gels range from primarily electrostatic to completely electrochemical. The electrostatic effect involves the induction of electrons or holes, and ionic motion is specific to the electrolyte side of the interface. In contrast, the electrochemical effect involves ionic motion occurring on both sides of the interface and across it. Through the application of electric fields, the insertion or extraction of ions in functional oxide materials enables the control of various phases and properties. In the electrostatic mechanism, carrier density modulation is primarily driven by band bending, whereas the electrochemical mechanism can completely reshape electronic band structures due to exceptionally high carrier densities. The electrolyte nature and target material properties significantly influence both the electrostatic and electrochemical effects. Recent advancements in characterization techniques and theoretical simulations have improved our understanding of the gating mechanisms in various material systems.In this Account, we provide a concise summary of recent advancements in manipulating the properties of various transition metal oxide material systems using electrolyte-based ionic motion through an electric field. We begin by exploring the detailed mechanisms that underlie how electric field gating can bring about substantial changes in the material properties. These changes encompass alterations in crystal and electronic structures as well as modifications in electrical, optical, and magnetic properties. Additionally, we assess the potential applications of functional oxide devices made possible through these ionic control mechanisms, particularly their relevance to neuromorphic computing. Finally, we address the primary challenges in this field and suggest future research directions to further its progress.