BAF(2) POST-DEPOSITION REACTION PROCESS FOR THICK YBCO FILMS.

[摘要] The basic processes of the so-called BaF(sub 2) process for the formation of YBa(sub 2)Cu(sub 3)O(sub 7), YBCO, films as well as its advantages over the in situ formation processes are discussed in the previous chapter. The process and the properties of YBCO films by this process were also nicely described in earlier articles by R. Feenstra, et al. Here, we will discuss two pertinent subjects related to fabrication of technologically viable YBCO conductors using this process. These are (1) the growth of thick (>> 1 (micro)m) c-axis-oriented YBCO films and (2) their growth rates. Before the detail discussions of these subjects are given, we first briefly discuss what geometrical structure a YBCO-coated conductor should be. Then, we will provide examples of simple arguments for how thick the YBCO films and how fast their growth rates need to be. Then, the discussions in the following two sections are devoted to: (1) the present understanding of the nucleation and the growth process for YBCO, and why it is so difficult to grow thick c-axis-oriented films (> 3 (micro)m), and (2) our present understanding of the YBCO growth-limiting mechanism and methods to increase the growth rates. The values of critical-current densities J(sub c) in these films are of primary importance for the applications,. and the above two subjects are intimately related to the control of J(sub c) of the films. In general, the lower the temperatures of the YBCO formation are the higher the values of J(sub c) of the films. Thus, the present discussion is limited to those films which are reacted at (approx)735 C. This is the lowest temperature at which c-axis-oriented YBCO films (1-3 (micro)m thick) are comfortably grown. It is also well known that the non-c-axis oriented YBCO platelets are extremely detrimental to the values of J(sub c) such that their effects on J(sub c) dwarf essentially all of other microstructural effects which control J(sub c). Hence, the discussion given below is mainly focused on how to avoid the growth of these crystallites when the films are thick and/or the growth rates are high.

[发布机构] Technical Information Center Oak Ridge Tennessee

[学科分类] 工程和技术（综合）

[关键词] Thin films;Yttrium oxides;Barium oxides;Copper oxides;Critical current