Phase Transformation in the Superconductor Ba-Y-Cu-O and La-Sr-Cu-O Compounds

The change of microstructure with phase transformation in the superconductor Ba-Y-Cu-O and La-Sr-Cu-O compounds are studied by in situ observation using a transmission electron microscope equipped with heating and cooling goniometer stages. It is confirmed in the Ba-Y-Cu-O system that tetragonal phase is transformed to the orthorhombic phase with (110) internal twins. In the La-Sr-Cu-O system, twins are also observed to appear on cooling, accompanied by the phase transformation, while they disappear reversibly on heating.