Growth and Domain Structures of Ba2YCu3O7-y Single Crystals

Crystallographic and superconducting properties of single crystals of Ba2YCu3O7-y grown by the flux method are studied. The single crystals were superconductors in as-grown atates. Domain observation by an interference microscope revealed that there were a few kinds of single crystals with a single domain and a few with several domains. A single-domain crystal had a tetragonal structure and a Tc onset of ∼45 K while a multidomain crystal had an orthorhombic structure and a Tc onset of ∼95 K. The latter crystal with no twins had several rectangular shape domains. It is thought that long one-dimensional chains of oxygens with a few 100 µm in length were realized in each domain of the crystal. The reason for the appearance of such domain structures is discussed.