High Voltage Electron Microscopy of Crack Tip Dislocations in MgO

Crack tip dislocations in a (001) MgO thin plate introduced by (010) cleavage were investigated using high voltage transmission electron microscopy. The stress concentration at a crack tip was modified by the multiplication of (a) (011)[011] and (011)[011] screw dislocations or (b) (110)[110] edge dislocations. The former case was dominantly observed in a thin plate sample as predicted by Wahn's model