Electron Irradiation Effects in YBa2Cu3O7_δ Single Crystals
Defect structures in YBa2Cu3O7_δ produced by electron irradiation at 300 K, were investigated by transmission electron microscopy. Threshold energies for the production of visible defects were determined to be 152 keV and 131 keV (± 7 keV) in directions near the a- and b-axes, respectively (b > a, both perpendicular to c, the long axis in the orthorhombic structure) During above — threshold irradiations in an electron flux of 3 × 1018 cm−2s−1, extended defects were observed to form and grow to sizes of 10–50 nm over 15 minutes, in material thicknesses varying between 20 and 200 nm. Upon irradiation between the a- and b-thresholds, movement of twin plane boundaries and shrinkage of twinned volume were observed. All these findings suggest oxygen atom displacements in the basal plane with recoil energies near 20 eV. Above — threshold irradiations also show the collapse of c-axis long range order into a planar faulted defect structure with short range order peaks at 1.2 c and 1.07 c, depending on the irradiation direction.
KeywordsThreshold Energy Twin Boundary Electron Flux Recoil Energy Defect Production
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