Melt Growth of YBa2Cu3O7-δ by Using BaCu2O2 and Y2BaCuO5 in Ag-Sheath

REBa ₂ Cu ₃ O _7-δ (REBCO; RE = Y or rare earth) wires with high critical current density (J _c ) are developed as coated conductors because REBCO crystals must be oriented to achieve high J _c . To create biaxially textured REBCO films, REBCO is deposited as a thin film on an oriented substrate. However, REBCO-coated conductors exhibit problems of hotspots, delamination etc. Because these problems can be eliminated in round wires, the development of round REBCO wires is necessary. Silver is a suitable sheath material for Powder-in-Tube (PIT)-processed REBCO wires because it does not react with REBCO, is not oxidized at high temperatures in the air, and is permeable to oxygen. In addition, the melting point of silver is 961°, which is lower than that of YBa ₂ Cu ₃ O _7-δ (1000°). However, with other materials having low melting points, the melt growth method must be used. In this study, BaCu ₂ O ₂ and Y ₂ BaCuO ₅ were prepared as raw materials to fabricate round YBCO wires. The melting point of BaCu ₂ O ₂ is approximately 880° in low oxygen partial pressure. A round wire comprising BaCu ₂ O ₂ and Y ₂ BaCuO ₅ was fabricated by utilizing the PIT method. Microstructural observation and measurement of superconducting properties were performed. The critical current density of the wire reached 5200 A/cm ² at 4.2K in self-field.