Growth Mechanism During Firing Process of Single-Coated Thick YBCO Films by TFA-MOD

Single-coating technology for metal organic deposition using trifluoroacetate has various advantages: no inhomogeneous interface in the case of multilayers, no random orientation from the interface, and no deterioration of material through two or more heat treatments. However, single-coated thick film inevitably has many voids. In order to minimize voids, both a calcining process and a firing process are required. This paper focuses on the firing process. During the firing process, balance of V_d and V_g is important. V_d and V_g are the drop rate of quasi-liquid and the growth rate of YBa₂Cu₃O_{7 -}x, respectively. We found that the volume of voids can be reduced in the condition of V_d > V_g, where gas flow is low, temperature high, and humidity low. We prepared gel films whose thickness was about 50 μm and calcined them to realize thick calcined films. The films are fired to realize 5.2-μm-thick superconductor on LaAlO₃ single crystal. Transmission electron microscopy observation revealed oriented layers. The film is still 20% void by volume. However, the film must be 40% void by volume without optimal firing process based on a quasi-liquid network model. The quasi-liquid network model is effective for reducing voids. Optimization of the calcining process will spur further development.