Impact of electric fields on microstructure evolution in functional ceramics

电场对功能陶瓷微观结构演变的影响

• 批准号: 436250027
• 负责人: Professor Roger De Souza, Ph.D.
• 金额: --
• 依托单位: Fraunhofer-Institut für Werkstoffmechanik (IWM)
• 依托单位国家: 德国
• 项目类别: Priority Programmes
• 资助国家: 德国
• 项目状态: 未结题
• 来源: https://gepris.dfg.de/gepris/projekt/436250027?language=en
• 关键词: Impact; electric; fields; microstructure; evolution

Sintering in an electric field is a new and promising field of materials science. It resulted in the discovery of flash sintering, which has proved to be a versatile technique for powder densification. However, as many processes are active during field assisted sintering, the specific influence of the electric field is difficult to isolate. In the first period of the priority programme, we investigated the origin of microstructural gradients during microstructure evolution in electric fields for strontium titanate (STO). We placed the emphasis on flash sintering, field assisted grain growth, and atomistic simulations of defect formation energies and migration barriers of point defects. Grain growth in STO was studied by analyzing the microstructure evolution of seeded polycrystals at different temperatures, heating times and electric field strengths. We identified changes in space charge characteristics, induced by electromigration of oxygen vacancies, as the probable mechanism for the formation of microstructural gradients. A model was introduced that suggests redistribution of oxygen vacancies at the negative electrode causes a decrease of the electrostatic potential and the intrinsic drag on a moving grain boundary (GB), thereby locally accelerating grain growth. These findings are supported by TEM observations and continuum-level thermodynamic modelling of space charge layers. Classical atomistic calculations were used to establish a computational simulation framework for the formation and migration of point defects at grain boundaries.The results have led to detailed insights into the dependence of microstructure evolution on defect chemistry even beyond field assisted sintering and grain growth. The findings contribute to a better understanding of the manipulation of mater by electric fields.On the basis of the knowledge acquired, the focus of the second period, experimentally, will be on altering the defect chemistry and defect migration kinetics of strontium titanate and other perovskite materials by introducing dopants, changing atmospheres and applying AC electric fields. The theoretical part will focus on building a more efficient workflow to predict macroscopic diffusion constants for the relevant defect species based on master equations and to implement the electric field effects directly (migration and vacancy formation energies) and indirectly (field driven configurational changes of the grain boundaries).

电场烧结是材料科学的一个新领域。这导致了闪速烧结的发现，闪速烧结已被证明是一种用于粉末致密化的通用技术。然而，由于许多过程在场辅助烧结期间是活跃的，电场的具体影响难以隔离。在优先计划的第一阶段，我们研究了钛酸锶（STO）在电场中微观结构演变过程中微观结构梯度的起源。我们把重点放在闪速烧结，场辅助晶粒生长，和原子模拟的缺陷形成能和迁移障碍的点缺陷。通过分析不同温度、加热时间和电场强度下籽晶多晶的微观结构演变，研究了STO中晶粒的生长。我们确定的空间电荷特性的变化，诱导的氧空位的电迁移，作为可能的机制形成的微结构梯度。引入了一个模型，该模型表明在负电极处的氧空位的再分布引起移动晶界（GB）上的静电势和固有阻力的降低，从而局部加速晶粒生长。这些发现得到了TEM观测和空间电荷层的连续级热力学模型的支持。采用经典的原子计算方法建立了晶界点缺陷形成和迁移的计算模拟框架，研究结果揭示了场辅助烧结和晶粒生长过程中缺陷化学对微观结构演化的影响。这些发现有助于更好地理解电场对物质的操纵。在所获得的知识的基础上，第二阶段的重点将是通过引入掺杂剂、改变气氛和施加交流电场来改变钛酸锶和其他钙钛矿材料的缺陷化学和缺陷迁移动力学。理论部分将侧重于建立一个更有效的工作流程来预测宏观扩散常数的基础上的主方程的相关缺陷物种和实现电场效应直接（迁移和空位形成能量）和间接（场驱动的配置变化的晶界）。