A Single Crystal High Temperature X-Ray Study of Orthorhombic Ba₂YCu_3-xO_7-y Superconductor

Abstract

An orthorhombic superconductor with composition Ba 2 YCu 3- x O 7- y was investigated at the temperature range of 24°C-600°C by single crystal X-ray diffraction method. All of the `single crystals' examined showed twinning of which the law can be explained by the point symmetry, suggesting the origin of the twinning is a transition from a tetragonal phase in cooling process. Through heating experiments, it was confirmed that these crystals show reversible orthorhombic-tetragonal transition at 575°C.