J(C) properties and microstructures of YBCO films fabricated by low temperature calcination in TFA-MOD method

摘要

YBa2Cu3O7-delta (YBCO) films were grown on LaAlO3 Substrates by a metal organic deposition using trifluoroacetates (TFA-MOD). In this study, effects of calcination condition such as temperature on microstructures and J(c) properties for the YBCO films were studied. The TFA starting solution was coated on a substrate by a spin-coating method. Then, a two-step heat treatment was applied to the coated films. In the calcination step, the coated film was calcined to form a homogeneous amorphous precursor by increasing the temperature which was varied from 300 degrees C to 500 degrees C at a constant heating rate of 2 degrees C/min. The prepared precursor films were crystallized at a constant condition. As a result,Jc value depended on the calcination temperature, YBCO film calcined at 400 degrees C showed the highest J(c) of 2.5 MA/cm(2). J(c)'s for the YBCO films calcined at 300 degrees C and 350 degrees C were 1.9 MA/cm(2) and 2.0 MA/cm(2), respectively. On the other hand, YBCO film calcined at 500 degrees C showed the lowest J(c) of 1.4 MA/cm(2). Cross-sectional TEM images showed that the YBCO film calcined at 400 degrees C had less pores and small size of pores in the crystallized film randomly throughout the film. Large pores were observed in the YBCO film calcined at 500 degrees C. Also, these large pores were existed near substrate in the YBCO film. It is considered that the differences of these pore formation mechanisms are the main cause of the difference of J(c) characteristic.