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 (PO2). 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 °C and Torr. The superconducting properties of the sample heat treated at 820 °C were fully restored by an oxygenation annealing treatment for 15 h at 600 °C.

Electro-mechanical properties of REBCO coated conductors from various industrial manufacturers at 77 K, self-field and 4.2 K, 19 T

“…Challenges with REBCO tapes: REBCO coated conductors however exhibit very low transverse thermal conductivity [33, chapter 4.3.4] (roughly three orders of magnitude lower than in tape direction [34,35]) requiring higher soldering iron temperatures and leading to temperatures ≫ °200 C on the coated conductor surface. At these temperatures, the oxygen content in the superconducting layer is reduced, resulting in a degradation of the current carrying capabilities [36]. As the soldering is done by hand, along the length of the 1 m long sample, the temperatures and the exposure times vary.…”

Persistent current joints between technological superconductors

“…In a series of publications [9,71,74,86] Park et al have documented the successful development of a joint between GdBCO CCs that addresses all of the above problems. In their process, the GdBCO is first exposed for jointing by dissolving the Ag with a KI + I based etchant.…”

A superconducting joint for GdBa2Cu3O7−δ-coated conductors

“…In this process, the oxygen partial pressure (P O2 ) and temperature are the key parameters for ensuring thermodynamic stability of REBa 2 Cu 3 O 7 Àd (RE123). 17,18 For a direct GdBCO-GdBCO joint, an optimized etching method is necessary to eliminate the resistive stabilizers from the top of the GdBCO CC, because stabilizers between the two GdBCO CCs degrade conductivity. We used a chemical etching method to remove a predetermined length of the stabilizers covering the GdBCO to expose a portion of the bare GdBCO surface without degrading the superconductivity.…”