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Naohiro Hara and Tsuyoshi Tateishi Kobelco Institute Co., Wakinohama Chuo-Ku, Kobe 651, Japan (Received 1 February 1992; accepted 26 May 1992) Using Bi-based oxide superconductors of the Bio.96Pbo.24-^SbxSri oCaijCui ^Oy

composition which were prepared by the sol-gel method, production of the high-Tc phase and also microstructures of the high-J c and the low-Tc phases were investigated using the XRD method and the TEM technique. Two superconducting phases showed good linearities of shrinkages of the a, b, and c lattice parameters as the Sb content increased, and so it has been found that Sb can be included in superconducting crystal structures. However, all shrinkages were below 1%. The activation energy of Sb diffusion was estimated from time dependence of changes of the lattice parameters using the Arrhenius plots. Its energy was from 510 to 593 KJ/mol.

I. INTRODUCTION 1>2

Since Hongbao et al. investigated the effects of Sb doping together with Pb into Bi-based high-Tc superconductor (described as high-r c phase or 2223 phase) and found that the Bij^Pb^SboiSraCa^usOj, (x = 0.3—0.4) composition shows a superconducting critical temperature (Tc) of 132 K, many studies have been carried out on the Sb-doped superconductors.3^6 Various methods, among them the conventional solids mixing method, the melting method, and the solution method, have been applied for production of these materials. We prepared the Sb-doped materials by the sol-gel method.7-8 It was reported that a melt was generated at a low temperature, so that the high-J c phase was produced effectively by doping Sb.4'8-9 In our previous study,8 it was found that a partial melting occurred at about 804 °C in the Bi0.96Pbo.24_^SbxSri.oCa1.1Cui.6Oy system, and it was presumed that the high-J c phase is increased by the melt produced in the partial melting, which may be composed of Pb-Sb-(Ca, S r ) - C u - O . In order to investigate whether Sb actually diffuses into the crystal structures and replaces some components of the Bi-based superconductors of both highrc phase and low-Tc phase (2212 phase), studies of the microstructures of the superconductors have been undertaken in detail.

B. Production quantity of the superconducting phases Phases produced by firing were identified by the x-ray diffraction (XRD) method using CuK a radiation. The XRD equipment used was Rigakudenki RINT-1500. The quantity of the high-Tc phase was calculated from x-ray peak heights of the high-r c phase and the lowTc phase, using the equation shown below.10 The peaks from the (002) and the (115) planes of both the high-r c and the low-r c phases were used for this calculation. *H(002) 'H(002)

A. Preparation

/L(H5):

An aqueous solution of acetates was prepared using BiO(OCOCH3), Sr(OCOCH 3 ) 2 • 1/2H2O, Ca(OCOCH 3 ) 2 • H 2 O, Cu(OCOCH3)2 • H 2 O, and Pb(OCOCH 3 ) 2 • 2H 2 O as starting materials. Metal Sb was dissolved by J. Mater. Res., Vol. 7, No. 10, Oct 1992

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'L(002)

X 100 *L{H5)J

_ (1)

IH(IIS):

II. EXPERIMENTAL

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