The Influence of Gas Flow Rate on the Growth of YBCO Films Prepared by TFA-MOD

As reported by some authors, during the high temperature firing heat treatment step of TFA-MOD process, the gas flow rate on film surfaces, which is directly related to the transfers of water and the product HF gas, is one of the most important parameters influencing YBCO film nucleation and growth. In our experiments, this influence was investigated by a rotating method rather than changing the volume gas flow directly. As the rotating speed of the sample holder increased, relative gas flow rate on film surfaces increased, and quite high values could be reached without consumption of much gas. It was found that microstructure, texture, superconducting properties of YBCO films were evidently dependent on the rotating speed. With increasing the rotating speed, critical current density of YBCO films converted from precursor films in different quality could be enhanced to around 3 MA/cm², the c-axis lattice parameter of YBCO unit cell was slightly reduced and the texture of the epitaxial films was improved, while the ratio of a-axis/c-axis oriented grains first increased and then decreased again.