改良型TFA-MOD法におけるY123膜組織形成機構と水蒸気分圧の影響

抄録

YBa₂Cu₃O_7-δ (Y123) films were deposited under various water vapor partial pressures (P(H₂O)) in the crystallization process by an 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 non-superconducting phases in the film. In contrast, small pores were distributed in the films deposited under higher P(H₂O) of 4.2, 6.3 and 13.5%. Considering that the critical current (I_c) values become higher as P(H₂O) increases, the existence of large pores and non-superconducting phase compounds causes a reduction in I_c. By investigating the microstructures of the films quenched during the crystallization process, it was found that the pores in the films are generated by the reaction of the non-superconducting phases trapped in the growing Y123 film, which then transform to Y123 afterwards accompanied by volume reduction of about 30%. The sizes of the entrapped phase crystals in the Y123 film depend on the P(H₂O), and this may determine the pore sizes in the final film.