Twinning dislocations in yba₂cu₃o_7−δ superconductor

Abstract

Structural images of twinning steps associated with an |a — b|[ — 10] twinning dislocation at a (110) twin boundary of YBa₂Cu₃O_{7 −δ} (δ ≈ 0·0) were observed for the first time. High-resolution electron microscopy (HREM) studies suggest that there are two types of twin boundaries: one with a lattice translation along the boundary for fully oxygenated YBa₂Cu₃O_{7 −δ}, and the other, without a lattice translation, for the oxygen-deficient one. High resolution in situ experiments indicate that the structure of the twin boundary changes from one type to the other under electron beam irradiation. Dislocations were observed from regions where the two types of twin boundary merge together. Dislocation models are proposed for interpreting the kinetics of the transition of the boundary structures. The geometry of the twin boundary and twinning dislocation using the concepts of coincidence site lattice (CSL) and of displacement shift complete lattice (DSCL) is also demonstrated.