Preparation of 110k Superconductor in Bi-Sr-Ca-Cu-O System
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PREPARATION OF 110K SUPERCONDUCTOR IN Bi-Sr-Ca--Cu-O SYSTEM
Chen Zuyao, Lin Rong, Chen Xianhui, Qian Yitai (Laboratory of Crystal Chemistry and Functional Materials, Department of Applied Chemistry, Univ. of Science and Technology of China, Hefei, Anhui 230026, P.R.China) Xia Jiansheng, Wang Shunxi (Department of Physics, Univ. of Science and Technology of China)
ABSTRACT To explore high T in Bi-Sr-Ca-Cu-O system, many different nominal compositions have been prepared by using the traditional solid state reactions and using the method of crystallizion from glass samples. The better results are as follows: single high-T -phase and essentially single high-T phase have been obtained from Bi 1.803.2 7 1 8 b Sr Ca Cu , 0 and Bi 2Sr Ca Cu7O respectively, by solid reaction. Basica ly single hign-T phase material with nominal composition Bi Sr Ca Cu 4 O has been produced by the method of crystallizion from glass samples. The relationship between the starting composition heat treatment, preparation methods and high T is briefly disGussed. ce
INTRODUCTION The discovery of superconducting Bi-Sr-Ca-Cu-O phases (1,2) has encouraged effort to isolate the high-T superconducting phase in this system. Many reports (3) show that the zero resistant temperature T c of bulk samples are never more than lOOK, although its Meissner fraction reaches sixty percent. Recently, a preparation procedure where Pb is partially substituted for Bi has been shown to be effective for obtaining a 110K superconductor (4), although the a.c. susceptibility vs temperature curve has shown two superconducting phases (5). It is well known that the formation of high-T superconducting phase and its superconductivity are extremely sensitive to preparation conditions, espcially annealing temperature, time and starting composition..In this study, we concentrate on the comparision of preparation methods with the aim of synthesizing single high-T phase materials of Pb-doped and undoped Bi-base compound. Many samples wits different nominal composition have been investigated by using traditional solid state reaction and quenching molten samples following crystallization in a flowing oxygen atmosphere.
EXPERIMENTAL Samples with the nominal compositions Bi Sr Ca Cu 0 (2223), Bi Sr Ca Cu 0 (3223), Bi Sr2Ca3Cu40 (2234), Bi2SrCa Khe u7 3V2297ý, Bi.Sr Ca.8u 6 i43g5h and Bi 2- PxSr2Ca 2Cu 3 were prepare. s~arting materias were Kighpurity powders of Bi3O', SrCO3 , CaCO3 , CuO and PbO2 . The powders are mixed and ground for several hours. All mixture are precalcined in air at 8000C for about 20 hrs. For 3223, the samples are sintered at 855-8680C for 60-80 hrs. For 2223-a, 2267, the samples are sintered at 850-8700C for 72-96 hrs. and for Bi Pb Sr Ca Cu 0 , the pellets are sintered at 850-880C for 80120 hrs, finally t~e samples are quenched in air . All samples are sintered in oxygen with slowly increasing temperature followed by annealing at 5OO°C in the same atmosphere for 24 hours. In searching for the Pb-doped single high-T superconductor, the nominal " compositions Bi
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