Charge States in Ceramics

[9973894] spence新型功能陶瓷的性能是由组成离子的电荷状态的微小变化所控制的。这种状态现在可以通过定量会聚束电子微衍射（QCBED）来确定。该项目延续了PI之前的工作（DMR9412146），即测量和使用电荷状态来建模和预测陶瓷性能。计划进行三项任务：(i)测量过渡金属氧化物中的电荷密度，以便在困难系统中测试从头算算法。（ii）利用QCBED绘制氧化物超导体的三维电荷密度和空穴分布。弹性过滤静态漫射散射也将用于确定掺杂原子周围的应变。通过将测量到的基态电荷密度与abinitio晶体计算进行比较，可以确定最成功的理论近似，并用于预测改性（例如不同掺杂）材料的性质。这项工作可以很容易地扩展到CMR锰矿，其中类似的小极化子是重要的。在这两种情况下，我们感兴趣的是离子的电荷状态和由此产生的晶格弛豫之间的关系。（三）对电子衍射反转问题的新解决办法进行实验测试，该办法使晶体电荷密度图能够直接根据实验微衍射图样计算出来。与x射线晶体学一样，这些图揭示了单细胞中每个原子的位置和类型，并且可以从纳米尺寸的材料区域获得。该衍射方法求解微相晶体结构的空间分辨率不受成像透镜的限制。微相识别是了解晶间相、烧结或沉淀硬化材料和新型纳米相复合材料以及许多其他应用的重要要求。所有这些工作都是基于亚利桑那州立大学现有的Leo/Zeiss Omega-filter电子显微镜。将获得一台新的CCD相机和液氦冷级。这项工作提高了我们对原子间键（它控制着材料的性能）的认识，并进一步努力设计和合成具有所需性能的新材料。* * *

9973894SpenceThe properties of new functional ceramics are controlled by small changes in the charge state of the constituent ions. This state can now be determined by quantitative convergent-beam electron microdiffaction (QCBED). This project continues the PI's previous work (DMR9412146) on the measurement and use of charge state to model and predict ceramic properties. Three tasks are planned: (i) Charge-density measurement in transition metal monoxides for the purpose of testing ab-initio algorithms in difficult systems. (ii) Mapping of the three-dimensional charge-density and hole distribution in oxide superconductors using QCBED. Elastically filtered static diffuse scattering will also be used to determine the strain around dopant atoms. By comparing this measured ground-state charge density with ab-initio crystal computations, the most successful theoretical approximations can be identified and used to predict the properties of modified (e.g. differently doped) material. This work may readily be extended to the CMR manganites, where similar small polarons are important. In both cases we are interested in the relationship between the charge state of ions and the resulting lattice relaxation. (iii) Experimental tests of a new solution to the inversion problem of electron diffraction, which allows crystal charge density maps to be computed directly from experimental microdiffraction patterns. As in X-ray crystallography, these maps reveal the position and type of every atom in the unit cell, and may be obtained from nanometer sized regions of material. The spatial resolution of this diffraction method for solving microphase crystal structures is not limited by imaging lenses. Microphase identification is an important requirement for understanding the properties of intergranular phases, sintered or precipitation hardened materials and the new nanophase composites, amongst many other applications. All this work is based on the existing Leo/Zeiss Omega-filter electron microscope at ASU. A new CCD camera and liquid-helium cold stage will be acquired. %%%This work advances our knowledge of bonds between atoms (which control the properties of materials) and furthers the effort to design and synthesize new materials with wanted properties. ***