In situ observation of oxygen deficiency occurring during electron irradiation in high T-c superconductor YBa2Cu3Oy

The decreasing process of oxygen in YBa2Cu3Oy is investigated through high resolution electron microscopy (HREM) and convergent beam electron diffract ion (CBED). Measurements of the axial length in HREM images show that oxyge n content y decreases faster near a twin boundary than at the inner part of a twin lamella. The transformation from an orthorhombic to a tetragonal ph ase starts at a twin boundary and the transformed region propagates to an i nner region of lamella. Lattice strains are observed near boundaries betwee n transformed and nontransformed regions. The transformation is almost comp lete within 30 s during observation of HREM images at 400 kV and at room te mperature. A value of y was quantitatively measured by analysing observed i ntensities of energy-filtered CBED patterns with the dynamical theory. The value of y decreases from 6.9 to 6.5 when 200 kV electrons are irradiated f or 160 s in a microscope at 108 K. More precise analysis of the intensities provides information on charge distribution along the c-axis as well as lo cal oxygen content at a spatial resolution of several nanometres.