过渡金属氧化物是一类重要的功能性材料，涵盖铁电、磁性、超导、阻变、催化和离子传导等诸多功能特性，在电子信息、能源转换和凝聚态物理基础研究中具有重大且广泛的应用，成为近年来材料科学的关注重点。离子迁移作为过渡金属氧化物多种功能得以实现的基础，可以显著改变材料的晶体结构和电子结构，调控其物理化学性能，从而完成电子器件中的磁电开关和能量转换中的传质过程。因此，高效的离子迁移对于提升氧化物器件的综合性能、降低功耗，具有关键的意义。然而，离子迁移面临较大的动力学势垒，通常需要高温或外加电场的驱动，造成了额外的能量损耗。本文基于“势垒调控”的思想，致力于开发室温下无偏压驱动的离子迁移手段，并调控氧化物中氢离子的空间分布，同时探索离子迁移的微观机制，进而推动高效、低能耗的离子器件发展。针对氧离子从过渡金属氧化物中脱嵌势垒较高的问题，本文提出贵金属纳米层电荷转移活化“金属-氧”化学键，并作为中转站以促进氧离子迁移的设想。通过SrCoO3?δ（钙钛矿相）表面沉积的Au纳米点活化Co-O键，实现了室温下的拓扑相转变（向SrCoO2.5,BM相），薄膜由铁磁金属态转变为反铁磁绝缘态。进一步采用活性更高、电荷转移能力更强的贵金属层（Pt, Ag），使氧离子迁移速率大大提高。此方法也被推广至SrFeO3，使其氧离子脱嵌温度大幅降低。为克服氧/氢离子注入过渡金属氧化物的势垒，本文提出生成高能初始态以降低或消除势垒的策略。利用H+溶解SrCoO2.5表面所释放的活性氧，原位填充下层晶格中的氧空位通道，实现了室温下的拓扑相转变（至SrCoO3?δ）和磁电性能的显著提升。另一方面，利用OH?溶解Al覆盖层所生成的活性氢，分别注入SrCoO2.5和LaMnO3薄膜，可获得其质子化相，并对磁性产生明显的调控作用。以活性氢为中介，实现了Al对CuO的高效室温还原（至金属Cu），此过程在Al-KOH(aq)-CuO三相界面率先发生，揭示了活性氢注入与氧离子脱嵌的密切耦合与相互促进作用。为实现对过渡金属氧化物中氢离子分布的有效调控，本文基于“化学晶格应变”，探究了外延应变对氧化物（NdNiO3, La0.67Sr0.33MnO3）薄膜注氢后氢离子分布的影响。在拉应变下，氢离子浓度呈现由表面至界面的“上坡”分布特征，而压应变状态下则为相反趋势。理论计算揭示了应变对“氢离子嵌入位置-体系能量-晶格畸变”依赖关系的影响，为精准调控氧化物的微观结构及性能提供了重要启示。
Transition metal oxides (TMOs) are an important group of functional materials and involve numerous performances including ferroelectricity, magnetism, superconductivity， resistive switching, catalysis, ion conduction, etc. TMOs possess significant and extensive applications in electronic information, energy conversion, and the fundamental research of condensed matter physics, which have become the focus of material science in recent years. As the basis of realizing various functions, ion migration in TMOs can sharply change the crystal/electronic structures and regulate the physicochemical properties, further accomplish the magnetoelectric switching in electronic devices and the mass transport process in energy conversion. Therefore, efficient ion migration is necessary for improving the comprehensive performances and reducing power consumption of oxide devices. However, ion migration is faced with large kinetic barriers, usually requiring the driving force from high temperature or external electric field, resulting in extra energy loss. Based on the idea of “barrier modulation”, this dissertation focuses on developing methods of room-temperature ion migration without bias voltage, controlling the spatial distribution of hydrogen ions in oxides, and exploring the microscopic mechanisms of ion migration, which would promote the advancement of high-efficiency and low-power-consumption ionic devices.To deal with the high barrier of oxygen ion deintercalation from TMOs, metal-oxygen bond activation by charge transfer from noble metal nanolayer has been proposed, in which noble metal serves as a transfer station to facilitate oxygen ion migration. Through the activation of Co-O bond by Au nanodots deposited on the surface of SrCoO3?δ perovskite, the topotactic phase transition to SrCoO2.5 (BM phase) occurs at room temperature, accompanied by the variation from ferromagnetic metallic state to antiferromagnetic insulating state. Furthermore, the utilization of noble metals (Pt, Ag) with higher activity and stronger electron-donating ability dramatically enhances the rate of oxygen ion migration. This method can also be applied to SrFeO3, which greatly decreases the temperature of oxygen ion deintercalation.To overcome the barrier of oxygen/hydrogen ion injection into TMOs, a strategy of generating high-energy initial states to reduce or eliminate the kinetic barrier has been proposed. Active oxygen species are released during the dissolution of SrCoO2.5 surface layer by H+, which in-situ fill the oxygen vacancy channels in the lower lattice. In this process, the room-temperature topotactic phase transition (SrCoO2.5 → SrCoO3-δ) is realized with prominent enhancement of magnetoelectric performances. On the other hand, the dissolution of Al capping layer by OH─ generates active hydrogen, which can be injected into SrCoO2.5 and LaMnO3 films to obtain the protonated phases with significant modulation of magnetic properties. Mediated by the active hydrogen, room-temperature reduction of CuO (to metallic Cu) by Al has been achieved with high efficiency. The reaction is preferentially initiated at the Al-KOH(aq)-CuO triple phase boundary, revealing the tight coupling and mutual promotion between active hydrogen injection and oxygen ion deintercalation.To effectively control the hydrogen ion distribution in TMOs, based on the “chemical lattice strain”, the influence of epitaxial strain on the hydrogen ion distribution in oxide (NdNiO3, La0.67Sr0.33MnO3) films after hydrogen injection has been investigated. Under the tensile strain, the concentration of hydrogen ions exhibits an "uphill" distribution from surface to interface, while the compressive strain state leads to an opposite trend. Theoretical calculations reveal the influence of strain on “hydrogen ion intercalation position-system energy-lattice distortion” relationship, which provides valuable insights for precisely manipulating the structure and properties of oxides on microscopic scale.
