Center for Functional Nanomaterials Seminar

Grain boundaries in oxide materials often have different properties compared to the grain interior, which can lead to either advantageous or detrimental consequences. One effective way to manipulate the grain boundary properties is through the doping of impurity elements. Such techniques (e.g. sintering) have long been implemented using trial and error methods without much consideration of the changes to the grain boundary structure on the atomic scale. The development of a general understanding of the role that impurity doping plays on the atomic structure of the grain boundary will provide the framework for predicting how particular dopants will affect the overall grain boundary. In this talk, results from the combination of scanning transmission electron microscopy (STEM) and theoretical calculations will be presented.
With recent advancements in STEM yielding resolutions on the scale of 0.1nm, we can now directly observe the impact of impurity doping on the grain boundary atomic structure. Z-contrast images obtained from STEM intrinsically contain chemical information due the acquisition conditions employed, and thus, the location of the dopants can often be determined from the image alone. This technique is most useful for detecting the location of heavy elements. On the other hand, the simultaneous use of high spatial resolution electron energy loss spectroscopy (EELS) can extend the range of chemical sensitivity to the lighter elements. Additionally, EELS can provide information on the changes of the local bonding and/or electronic environments, which is indispensable for modeling the resulting changes in the grain boundary properties due to impurity doping.
The atomic structure of the grain boundary is often rather complicated and the use of atomic simulations is required to interpret the experimental results, in order to predict the properties of the structures observed from STEM/EELS. Simpler theoretical methods are based on pair potentials a