Tomotaka Goto

Progress in R&D for coated conductors by TFA-MOD processing

Recent progress in the research and development of the TFA-MOD processing for the coated conductors in Japan was reviewed. For the higher Ic performance, the optimizations both in the calcinations and crystallization steps have taken place. Consequently, the extremely high Ic value of 413 A was achieved by the combination of the information from the above investigations and the use of highly textured CeO/sub 2/ cap layered substrates. Concerning the development of long tapes, a 8.6-m-long tape with its end-to-end Ic value of 119 A was successfully grown by a reel-to-reel system. Additionally, improvement of the production rate in the calcination step was realized by designing a multi-turn system.

Optimization of Process Parameters for Calcination in TFA-MOD Method

We have investigated the influence of the H2O vapour inlet temperature in the calcination on both the microstructure and superconducting properties of YBa2Cu3O7-x, (YBCO) films fabricated by the TFA-MOD method, from the viewpoint of the process control in the reel-to-reel system. Low critical current (Jc) values were obtained in the films prepared by introducing the H2O vapour at temperatures less than 200degC. XRD measurements and cross-sectional TEM observations suggest that the YBCO films calcined with the H2O vapour inlet temperature below 200degC revealed a random orientation without the epitaxial growth of the YBCO phase grains. Consequently, it is necessary to introduce H2O vapour from temperatures higher than 250degC in calcination for fabrication of high performance YBCO tapes. In reel-to-reel system, it is important that the humidity management in a low temperature range in the furnace.