Application of Nano-Scale Eels Spectrum Lines To Grain Boundaries

Extract

Polycrystals containing small quantities of impurity can exhibit dramatically different properties from that of the pure material. One example of this is the tenfold increase in the creep resistance of Y or La doped alumina relative to ultra-pure alumina. Such changes are correlated to grain boundary segregation, however the segregant’s potency to influence properties remains unexplained. Determining the driving force to segregation only partially addresses this issue. A full understanding must take account of the chemical bonding and structural changes occurring at the boundary after segregation. The purpose of this study is to observe the electronic structure associated with the segregating species using EELS spectrum-line profiling. This is accomplished by monitoring the segregation profile along with the characteristic near edge absorption fine structures which reflect changes in the localized density of unoccupied states along that profile. In these experiments a finely focused beam was sequentially stepped across the boundary of interest and a spectrum recorded at each step.