Oriented BSCCO thick film coatings on polycrystalline MgO
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Oriented BSCCO thick film coatings on polycrystalline MgO J. R. Spann,a) L. E. Toth, I. K. Lloyd,b) M. Kahn, M. Chase,c> and B. N. Das Composites and Ceramics Branch, Naval Research Laboratory, Washington, DC 20375
T. L. Francavilla and M. S. Osofsky Materials Physics Branch, Naval Research Laboratory, Washington, DC 20375 (Received 29 June 1989; accepted 27 February 1990) Highly oriented 2212 BSCCO thick films were prepared on polycrystalline MgO substrates using a melt/crystallization technique. Results compare very favorably with those on single crystal materials.1'2 The melting, quenching, and annealing processes were all found to be important in the development of a good microstructure and good superconducting properties. The best results (Jc ~ 2000 A/cm2 at 64 K and 6000 A/cm2 at 4.2 K) were obtained on films which had been melted, quenched to room temperature, heated to 860 °C where they were annealed before slow cooling to room temperature in oxygen, lightly polished, and reannealed at 860 °C.
ing of highly oriented platelets. In many BSCCO compositions melting begins around 860-880 °C.10'24 Thick BSCCO (BiaSTbCa.cCudOx) has been of great inter- films processed above the melting temperature tend to est since it was first reported that it was possible to be highly oriented,1'2'9"12 while films sintered below this prepare oriented materials1 which were much less sensi- range tend to be more randomly oriented.916 Quenchtive to atmospheric conditions than the Ba2YCu3O7 ing, as discussed later, and by Oka et al.,u appears to type materials.3 Oriented BSCCO has been prepared by suppress the formation of the 2201 phase, allowing roller quenching and annealing ribbons4 and as thin more of the 2212 BSCCO phase to form. Annealing can films5"8 and thick films.1'2-9"12 The advantages of thick increase the R = 0 temperature and the critical curand thin films are as follows: they assume the shape of rent.1'2'9"12 We believe that the improvement in behavior their substrate, minimizing forming requirements; their after annealing is related to increased homogeneity and substrates provide mechanical support; and they are 2212 content in the films. much smaller dimensionally than bulk materials, which The research effort in oriented films has been inenhances their compatibility with various levels of inte- tense because the superconducting transport properties grated circuitry. Numerous recent reports have de- of BSCCO are highly anisotropic and the critical curscribed the processing of highly oriented thick and thin rents in oriented films are much higher than those in films of BSCCO on MgO single crystal substrates. Ag unaligned materials. However, highly oriented BSCCO foil, Ni foil, Cu plate, SrTiO3, and stabilized zirconia films on polycrystalline MgO substrates have not been have also been used6'11"16 as substrate materials, alreported. The use of polycrystalline MgO substrates is though in general, MgO is reported to give the best important practically, since single crystal substrates are films. Many different proces
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