Interfacial Segregation in Oxide Ceramics: Atomic-Scale Experimental and Theoretical Studies

晶界和界面偏析对许多陶瓷材料有着深远的影响。本研究旨在通过互补的实验和理论研究来阐明离子材料中界面偏析的原子尺度方面。该研究计划的最终目标是发展预测原则，从这些原则中可以设计界面化学来定制界面物理性质。这样的预测原理将需要对界面原子结构、点缺陷化学和化学键的相关方面的偏析的理解。最初要探索的材料系统将是α -氧化铝，因为这种陶瓷被很好地理解和表征。此外，广泛的研究表明，偏析剂，特别是稀土元素，对氧化铝的蠕变和晶界迁移等物理性质有深远的影响。大多数实验分析将基于电子成像，衍射和光谱技术，因为晶体学，原子结构和化学可以同时研究，因此是相关的。多晶材料的偏析研究将以探索完整的多维热力学相空间为目的进行。对于那些有利于原子尺度结构分析的特殊边界，我们将研究掺杂后晶界原子结构和空间电荷的特定位置偏析和变化。原子结构将通过高分辨率电子显微镜和z -对比度成像进行量化。电子能量损失谱将逐柱进行，以获得特定位点的化学和电子结构信息。特殊对称倾斜边界将通过从头算电子结构计算和使用半经验势的蒙特卡罗模拟并行研究。传输机制将使用结合从头算、从头算分子动力学模拟和半经验分子动力学模拟的过渡态理论进行建模。通过进行这一系列系统的实验，将获得陶瓷中界面偏析及其对晶界扩散和粘附的影响的基本知识。这些信息可以对结构陶瓷（如用于飞机发动机的陶瓷）和功能陶瓷（如用于手机和电脑的陶瓷）的设计产生重大影响。

9976851DickeyGrain boundary and interfacial segregation have far reaching ramifications for many ceramic materials. The proposed research aims to elucidate atomic-scale aspects of interfacial segregation in ionic materials by complementary experimental and theoretical studies. The ultimate goal of the research program is to develop predictive principles from which interfacial chemistry can be designed to tailor interface physical properties. Such predictive principles will require an understanding of segregation on the interrelated aspects of interface atomic structure, point defect chemistry and chemical bonding. The initial material system to be explored will be alpha-alumina since this ceramic is well understood and characterized. Moreover, it has been widely demonstrated that segregants, particularly rare earth elements, have profound effects on physical properties of alumina such as creep and grain boundary transport. Most of the experimental analyses will be based on electron imaging, diffraction and spectroscopy techniques since crystallography, atomic structure and chemistry can be studied simultaneously and therefore correlated. Segregation studies on polycrystalline materials will be carried out with the aim of exploring the complete multidimensional thermodynamic phase space. For special boundaries, those conducive to atomic-scale structure analysis, we will investigate site-specific segregation and changes in grain boundary atomic structure and space charge upon doping. Atomic structures will be quantified by high-resolution electron microscopy and Z-Contrast imaging. Electron energy loss spectroscopy will be performed on a column-by-column basis to obtain site-specific chemical and electronic structure information. Special symmetric tilt boundaries will be studied in parallel by ab initio electronic structure calculations and Monte Carlo simulations using semi-empirical potentials. Transport mechanisms will be modeled using transition state theory combined with ab initio calculations, ab initio molecular dynamics simulations, and semi-empirical molecular dynamics simulations.%%%By performing this systematic series of experiments, fundamental knowledge will be gained about interfacial segregation in ceramics and the effects on grain boundary diffusion and adhesion. This information can have a large impact on the design of both structural ceramics, such as those used in aircraft engines, as well as on functional ceramics, such as those used in cell phones and computers.