钛酸铋钠体系氧离子电导率与晶体平均/局域结构的相关性研究

钛酸铋钠(NBT)是一种新型氧离子导体，在中温固态氧化物燃料电池等领域具有广泛应用潜力。目前受困于受主离子在NBT中的固溶度过低，平均结构、局域结构及掺杂离子特性对氧离子传导的关键影响机制尚未准确描述，材料设计依据匮乏。针对此问题，本项目提出通过NBT固溶体分别在A、B位引入较多掺杂离子，有效“放大”平均结构与局域结构的变化。利用不同氧分压下的交流阻抗谱结合电动势测量揭示电导机理与电导率，建立缺陷化学模型，阐明A、B位掺杂离子与氧空位相互作用机制；利用高温XRD、中子衍射及拉曼光谱揭示固溶体的晶体结构、鞍点关键半径、晶胞自由体积等平均结构参数以及八面体倾斜角、金属-金属及金属-氧键长、键角、配位数等局域结构参数随成分与温度的变化规律；通过耦合电学性能与结构信息建立氧离子电导率与各结构参数的定量关系，揭示影响氧离子传导的关键因素，为发展基于NBT的新型氧离子导体提供缺陷化学设计的理论依据。

Sodium bismuth titanate, NBT, is a recently discovered oxide-ion conductor. It has great potential as electrolyte for intermediate-temperature solid oxide fuel cells (IT-SOFCs). Limited by the extremely low solubility of acceptor-type dopants in NBT, it is difficult to reveal the impact of average and local crystal structure, as well as the characteristics of dopants (i.e., ionic size, polarizability, bonding-strength) on the oxide-ion conduction. This project aims to solve the above problem by utilizing NBT-based solid solutions to introduce large amount of acceptor-type dopants into NBT to magnify the variation of average and local structure. The conduction mechanism and the oxide-ion conductivity of the solid solutions will be investigated by impedance spectroscopy under various pO2 combined with electromotive force (EMF) to establish the defect chemistry model and to reveal the interaction mechanism between A- or B-site dopants and oxygen vacancies. Variable-temperature XRD (both laboratory and synchrotron high-energy X-ray), neutron powder diffraction (NPD) and Raman spectroscopy will be employed to investigate the average structure parameters (i.e., crystal structure, critical radius at the saddle point and specific free volume), as well as the local structure parameters (i.e., octahedral tilting angle, length, angle and coordination number of metal-metal and metal-oxygen bonds). Couple the electrical properties and the structural information to explore the relationship between oxide-ion conductivity and each structural parameter to reveal the key factor(s) that influence(s) the oxygen migration in NBT. Completion of this project will provide strategy for developing NBT-based oxide-ion conductors with high conductivity by defect chemistry design.