Effects of heat-treatment conditions on microstructure of multi-coating Y123 films deposited by advanced TFA-MOD method

YBa2Cu3O7-delta (Y123) films were deposited under various water partial pressures (P-H2O) in the crystallization process by the advanced metalorganic deposition (MOD) method using trifluoroacetates. Microstructures of the films were evaluated by means of transmission electron microscopy. As a result, in the Y123 film crystallized under lower P-H2O, such as 2.1%, large pores were remarkably observed. Furthermore, there were many amorphous layers of a non-superconducting phase in this film. In contrast, small pores were distributed in the films deposited under higher P-H2O. Considering that the critical current (I-C) values become higher as P-H2O increases, existence of large pores and non-superconducting phase crystals causes to reduce I-C. Through the investigation of the microstructure of the films quenched during the crystallization process, it was found that the pores in the film are generated by reaction of the non-superconducting phases, which are trapped in the growing Y123 film afterwards, to transform to Y123 with accompanied by the volume reduction of about 30%. The sizes of the entrapped phase crystals in Y123 film depend on the P-H2O,o and it may determine the pore sizes in the final film. (C) 2004 Elsevier B.V. All rights reserved.