Preparation of Bipbsrcacuo Superconductors by Laser Pedestal Growth Method
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PREPARATION OF BiPbSrCaCuO SUPERCONDUCTORS BY LASER PEDESTAL GROWTH METHOD K.Hayashi, H.Nonoyama, M.Ueyama, M.Nagata, H.Hitotsuyanagi Osaka Research Laboratories, Sumitomo Electric Industries, LTD. 1-1-3, Shimaya, Konohama-ku, Osaka, 554, Japan
ABSTRACT Bi-Pb-Sr-Ca-Cu-O superconductors were prepared by the laser pedestal growth method. The high Tc phase was created only by post annealing. As the growing speed increased, the annealing time necessary to obtain a Tc above lOOK decreased. When the low Tc phase was aligned with the growing direction, Tc was un2 der lOOK, but a Jc of 1560A/cm (77.3K, OT) was obtained. In this case, magnetic field dependence below 300 gauss was superior to that of Pb-free materials.
INTRODUCTION Because it is necessary to obtain wire-shaped materials with high critical current density (Jc) for application in electric power apparatuses, many efforts to prepare high Jc wire have been made. It is well-known that melt processed oxide superconductors have high density and highly oriented structures with high Jc,[lJ[2] and in the Bi-Sr-Ca-Cu-O system discovered by H.Maeda et al.[3], the superconducting phase is easy to prepare by melt process. Recently, R.S.Feigelson et al. applied the laser pedestal growth method to the Bi-Sr-Ca-Cu-O system and obtained wellaligned superconducting fiber.[4J The laser pedestal growth method is useful for producing single crystalline oxide fiber for optical devices uncontaminated by impurities. Additionally, Bi system oxide superconductors have a high Tc phase with a Tc above lOOK, and Pb stabilizes the formation of this phase. There have been few experiments that produced high Tc materials above lOOK by the melt process.[5] In this experiment, the laser pedestal growth method was applied to the Bi -Pb-Sr-Ca-Cu-O system. The relationship between superconducting properties (Tc,Jc), nominal compositions, crystal growth conditions and post annealing conditions was investigated.
EXPERIMENTAL PROCEDURE Bi 2 0 3 , PbO, SrC0 3 , CaC0 3 and CuO were mixed in a ratio of 1.4:0.6:2:2:3 and 1.84:0.34:1.91:2.03:3.06 (Bi:Pb:Sr:Ca:Cu) and calcined. The former is an ideal composition for the high Tc phase and the latter is the composition which was used successfully to obtain a single high Tc phase by T.Kawai et al.[6] Sintered rod under 4mm in diameter was used for the feed rod. Mat. Res. Soc. Symp. Proc. Vol. 169. ©'1990 Materials Research Society
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Figure 1 is a schematic illustration of the laser pedestal Growing
growth method.
The two beam
method was used. The top of the sintered rod was melted by CO2 laser and the crystals C02 Laser CO2 Las were grown from the molten zone. The seed crystal was Molten Zonethe same sintered rod as the feed rod. Growing speed and Feed Rod feed speed were controlled individually and the growing crystal and feed rod were rotated in opposite directions Fig.l. Apparatus of laser All the samin most cases. pedestal growth method. ples after crystal growth were cut into a size of about Imm XlmmXl5mm and annealed in air. The Tc's and Jc's
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