The effect of electron beam irradiation on electron diffraction patterns of Bi-Sr-Ca-Cu-O high-T-c superconductors

The effect of electron irradiation having the energy of 75, 100, and 200 ke V on structural modifications of Bi-2212 superconducting samples has been s tudied. For the last energy, the irradiation time from zero to 150 min was used. At a constant energy of the electrons, the observed phenomena consist in the disappearance of the incommensurate unidimensional modulation, in t he decreasing of spots intensity and their elongation along the equivalent crystallographic axis a, and even spot splitting with the occurrence of dou ble extra spots, with the increase of the irradiation time. After electron irradiation with energy of 75 and 100 keV, the structural mo difications lead to some spot patterns consisting of some planar lattices ( in some cases a pseudotetragonal one) that are twisted on each other at dif ferent angles (8 degrees, 13.6 degrees, 19 degrees, etc.) around the axis o f the incident electron beam. For the irradiation at increased doses of thi n microcrystals having reduced lateral dimensions, the electron diffraction spots were arranged in discrete or partial continuous Debye rings or conti nuous concentric Debye rings characteristic for the polycrystalline state. After electron irradiation with energy of 200 keV, the effects of electron irradiation on Bi-2212 samples depend strongly on irradiation fluence rate and time and consisted in the following: disordering defects in the diffrac tion patterns (disappearance of some spots, spot intensity modification, st reaks occurrence, spot elongation); alteration and disappearance of incomme nsurate structural modification; conversion of single crystal particle area s into polycryslalline material; and quasi-amorphization. A simple approach based on the evaluation of the displacement yield of in-p lane oxygen atoms vs. irradiation time for the different incident energy an d electron fluence rates could explain the general trend of irradiation dam age in HTS materials.