JC properties and microstructures of YBCO films fabricated by low temperature calcination in TFA-MOD method

Abstract

YBa 2Cu 3O 7− δ (YBCO) films were grown on LaAlO 3 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 °C to 500 °C at a constant heating rate of 2 °C/min. The prepared precursor films were crystallized at a constant condition. As a result, J c value depended on the calcination temperature, YBCO film calcined at 400 °C showed the highest J c of 2.5 MA/cm 2. J c’s for the YBCO films calcined at 300 °C and 350 °C were 1.9 MA/cm 2 and 2.0 MA/cm 2, respectively. On the other hand, YBCO film calcined at 500 °C showed the lowest J c of 1.4 MA/cm 2. Cross-sectional TEM images showed that the YBCO film calcined at 400 °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 °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.