Twinning of High-Tc Ba2YCu3O7-x Oxides

Abstract

Orthorhombic crystallites of the high-Tc superconductor Ba₂YCu₃O_7-x oxide prepared by the standard sintering technique are heavily laminated by twinning on (110) lattice planes. Upon heating these crystals under a vacuum in an electron microscope, the orthorhombic structure transformed irreversibly to a tetragonal one. Between these two forms, a transitional orthorhombic form was observed. This irreversible transformation seems to be caused by a lack of oxygen in the evacuated microscope.