Bulk and Interface Bonding in Ceramics and Intermetallics

提出了一项为期三年的晶体、界面和缺陷原子键的研究计划。陶瓷和金属间化合物将采用从头算量子分子动力学计算、自一致计算和定量会聚束电子衍射法键电荷分布的实验测量相结合的方法进行研究。亚利桑那州立大学高分辨率电子显微镜中心的蔡司Omega能量过滤电子显微镜将用于实验工作。主要投资者提出了一种基于透射几何金属-陶瓷界面反射的镜面电子束的新技术，用于反射成像，微分析和埋藏界面的键合研究。这项工作是与C.P.弗林合作完成的。对于最近才首次“看到”键的完美晶体，Principal Investors建议测量钛铝和一系列离子晶体中的键电荷分布，以测试基于局部密度近似的自一致计算的准确性。将测量的键分布与未掺杂锰的钛铝进行比较，发现锰可以降低脆性。在铁电晶体中，主要研究人员计划比较钛酸锶和钛酸钡氧中钛和氧之间的电荷转移，以了解为什么一个是铁电的，而另一个不是。提出的研究旨在调查晶体、界面和缺陷中原子键合的起源。陶瓷和金属间化合物将通过定量技术结合理论计算和键电荷分布的实验测量来研究。＊＊＊

Spence 9412146 A three year program of research is proposed of atomic bonding in crystals, at interfaces and at defects. Ceramics and intermetallic compounds will be studied using a combination of ab-initio quantum molecular dynamics computations, self-consistent calculations and experimental measurements of bond charge distributions by quantitative convergent beam electron diffraction method. The Zeiss Omega energy-filtering electron microscope at the Arizona State University center for High Resolution Electron Microscopy will be used for the experimental work. Principal Investors propose a new technique based on the specular electron beam reflected from a metal-ceramic interface in the transmission geometry for reflection imaging, microanalysis and bonding studies of buried interfaces. This work is collaborative with C.P. Flynn. For perfect crystals, in which bonds have been "seen" for the first time only recently, Principal Investors propose bond charge distribution measurements in titanium-aluminum and a series of ionic crystals in order to test the accuracy of self-consistent computations based on the local density approximation. Measured bond distributions will be compared for titanium-aluminum with and without manganese doping, which is found to reduce brittleness. In ferroectric crystal Principal Investigators plan comparisons of charge transfer between titanium and oxygen in strontium titanate and isostructural barium titanate oxygen in order to understand why one is ferroelectric and the other not. %%% The proposed research seeks to investigate the origins of atomic bonding in crystals, at interfaces and defects. Ceramics and intermetallic compounds will be studied using a combination of theoretical calculations and experimental measurements of bond charge distributions by quantitative techniques. ***