Twin Domain Fragmentation in YBa₂Cu₃ O_7-δ Under Electron Irradiation

Detwinning and retwinning processes in the orthorhombic YBa₂Cu₃ O_7-δ have been directly observed under appropriate electron irradiation by transmission electron microscope. These processes can be repeated many times and are accompanied by twin domain fragmentation and appreciable increase of twin interface density, which is a potential pinning center in YBa₂Cu₃ O_7-δ.The meaning of this effect in raising J_c of the material YBa₂Cu₃ O_7-δ is suggested and discussed.