TWIN FORMATION DUE TO IRRADIATION OF ENERGETIC ELECTRON-BEAM IN HIGH-TEMPERATURE SUPERCONDUCTORS OF IN-DOPED AND SB-DOPED YBCO

Twins and twin boundaries existing in the YBCO and In- and Sb-doped YB CO high-T(c) ceramic superconductors were observed by means of a trans mission electron microscope. The orientation of the twins was determin ed from the electron diffraction pattern using the operation voltage o f 160 kV. By the conventional extinction method the image of twins cou ld be revealed with a better contrast, so that they might be observed more clearly. Based on the TEM observation, we have proposed a model f or twin formation in the perovskite structure. The energy for twin bou ndary formation has also been roughly estimated to be 44.0 mJ/m2.