Electron Irradiation Effects in YBa₂Cu₃O_{7_δ} Single Crystals

Abstract

Defect structures in YBa₂Cu₃O_{7_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.

Work supported by the U.S.Department of Energy, BES-Materials Sciences, under contract W-31-109-Eng-38.