An advanced low-fluorine solution route for fabrication of high-performance YBCO superconducting films

Abstract

We have developed a new low-fluorine solution consisting of non-fluorine (F-free) barium and copper salts, and fluorine-containing yttrium trifluoroacetate. Using this new low-fluorine solution, the BaCO3 phase was avoided in the pyrolyzed precursor films. Instead, CuO, Y and Ba fluorides (YF3 and BaF2) were formed in the precursor films pyrolyzed at 450 °C, which was the same as when an All-TFA solution (prepared using Y, Ba, Cu trifluoroacetates as precursors) or other fluorine-reduced solutions were used. This new kind of low-fluorine solution has only 23% of the fluorine content in an All-TFA solution, and the fluorine content was lower than any other fluorine-reduced solution. Thus, rapid production of YBa2Cu3O7−x (YBCO) films can be easily realized. Using a heating rate of 10 °C min−1 in the pyrolysis process, a high critical current density (Jc) of 5 MA cm−2 (at 77 K, 0 T) was obtained in YBCO films fabricated on LaAlO3 (LAO) single crystal substrates from the new starting solution.

High-efficiency preparation of high-quality YBCO superconducting films using an ultralow-fluorine sol–gel method

“…Figure 4a shows the dependence of the J c on applied magnetic field for a YBCO sample with size of 2 mm 9 3 mm. The single-coated film annealed at 760°C shows a J c of 5.09 MA/cm 2 (77 K, 0 T), which is comparable to the one derived from sols with higher fluorine content [7]. Figure 4b shows the R-T curve for the YBCO film.…”

“…Here, 10 % Cu excess was adopted to compensate for Cu loss during pyrolysis process. And the fluorine content (F/Ba = 2) was about 44 % of that in our recently reported advanced low-fluorine solution (F/ Ba & 4.5) [7].…”

“…However, it was found that in the TFA solution route, the fluorine content of the sol showed great influence on the processing and final properties of the YBCO films. In the past decade, precursor sols with F/Ba = 9:1, 6:1, 4.5:1 have been respectively reported [5][6][7]. Results indicated that using the fluorinereduced precursor solutions, the coated gel films became more stable in air.…”

An All Sol-Gel Process for the Heteroepitaxial Growth of YBa2Cu3O7−x/LaNiO3/YBa2Cu3O7−x Tri-layer

“…The process for preparing YBCO and LaNiO 3 films can be found elsewhere [12,13]. Starting from these previous reports, the solution and heat treatment temperatures were slightly modified to prepare the YBCO/LaNiO 3 /YBCO tri-layer.…”

“…The gel coating and pyrolysis processes can be found in references [12] and [13]. The heat treatment temperature is a key factor in preparing the tri-layer.…”