The influence of heat-treatment and oxygenation annealing on the superconducting properties of YBCO coated conductors

Abstract

The superconducting properties of YBCO (yttrium barium copper oxide) coated conductors (CCs) are strongly dependent on their oxygen content. Degradation of the superconducting properties of a YBCO CC can occur due to a phase/structure transition caused by the oxygen diffusion out of the YBCO during heat-treatment or soldering, which is an inevitable process during the creation of a superconducting joint. Such variations in phase/structure are generally functions of temperature and oxygen partial pressure (P-O2). Therefore, in order for a superconducting joint of YBCO CC to be feasible, it is important to examine the changes in the microstructure and oxygen diffusion behavior for YBCO CCs. This study examined the superconducting properties of YBCO CCs before and after a heat-treatment under a reduced PO2 followed by an oxygenation annealing process in an oxygen rich environment. Partial melting of YBCO without melting of the silver stabilizer layer was obtained for a sample heat treated for 60 s at 820 degrees C and P-O2 similar or equal to 1 x 10(-2) Torr. The superconducting properties of the sample heat treated at 820 degrees C were fully restored by an oxygenation annealing treatment for 15 h at 600 degrees C.