|Ph.D Student||Zamir Shlomit|
|Subject||Dopant Effect on the Grain Boundary Mobility of|
|Department||Department of Materials Science and Engineering||Supervisors||ASSOCIATE PROF. Rachman Chaim|
|PROF. Boaz Pokroy|
|Full Thesis text|
The mechanism of grain boundary (GB) motion is one of the classical unresolved issues in materials science. Despite years of research on GB motion, there is persistent and even an increasing interest in this matter. The main reason is that the GB motion controls the evolution of polycrystalline solids’ microstructure which in turn determines their physical, chemical and mechanical properties.
Solutes can have enormous effect on GB mobility. Even very minute amounts of solute can dramatically affect the mobility of the GB.
Yttrium Aluminum Garnet (Y3Al5O12), YAG, is the most important solid-state laser host material. Sintered polycrystalline YAG gained intensive interest in recent years, since YAG powders can be sintered to optical transparency and have similar properties to the single crystal YAG.
In this research, measurements on the intrinsic GB mobility of YAG and the effect of different cation dopants (aliovalent and isovalent) on the GB mobility will be presented. In order to discuss the mechanism of GB motion in SiO2 doped YAG, the Si solubility in YAG at 17000C and vacuum was measured. A unique quenching furnace enabling the quenching of specimens from 1700°C in vacuum directly into cold water was constructed. For the first time, Si solubility limit in YAG at the most common sintering temperature and atmosphere was experimentally determined. Analytical transmission electron microscopy and atom probe tomography were employed for determining the dopant concentration profiles at the GBs. An excess of Si at the GBs in SiO2 doped YAG was observed. Finally, the Lücke and Detert model of solute drag was modified to account for the conditions of the present experiments, The modified model demonstrated a good agreement with the experimental results.
These findings offer a new explanation for the effect of Si as a dopant which is frequently used for Nd:YAG sintering for high power lasers, and may improve the development process of such lasers in the future.