title: Electron microscopy study of twin behavior in GdBa2Cu3Ox and YBa2Cu3Ox.
abstract: Twins are ubiquitous in the perovskite superconductors. They form during cooling from high temperatures through the tetragonal-to-orthorhombic phase transformation. Their behavior has been studied by transmission electron microscopy using a liquid-nitrogen-cooled specimen holder. It is observed that extra twins sometimes form in coarse-twinned regions to give a "refined" twin structure; this is thought to be induced by thermal stresses from the electron beam. Prolonged electron irradiation (with little beam heating) results in transformation to tetragonal with a loss of the twin structure; this is probably due to disordering of the oxygen sublattice by knock-on displacement. The same transformations can be induced by deliberate electron beam heating. In both cases the twinned orthorhombic structure can be restored by re-ordering of the oxygen ions, in the first case by removing the beam and in the second case by allowing the specimen to cool.
authors.affiliation: Center for Materials Science, Los Alamos National Laboratory, New Mexico.
authors.forename: T E
authors.initials: TE
authors.lastname: Mitchell
authors.forename: T
authors.initials: T
authors.lastname: Roy
authors.forename: R B
authors.initials: RB
authors.lastname: Schwarz
authors.forename: J F
authors.initials: JF
authors.lastname: Smith
authors.forename: D
authors.initials: D
authors.lastname: Wohlleben
mesh_terms: D001464:Barium / Q000032:analysis; D003300:Copper / Q000032:analysis; D004553:Electric Conductivity; D005682:Gadolinium / Q000032:analysis; D006358:Hot Temperature; D008670:Metals / Q000032:analysis*; D008854:Microscopy, Electron / Q000379:methods*; D008968:Molecular Conformation; D010087:Oxides / Q000032:analysis*
chemical_list: D008670:Metals; D010087:Oxides; D001464:Barium; D003300:Copper; D005682:Gadolinium