New Method for Synthesizing Bi-Sr-Ca-Cu-O Superconductor
- PDF / 213,634 Bytes
- 4 Pages / 420.48 x 639 pts Page_size
- 66 Downloads / 200 Views
NEW METHOD FOR SYNTHESIZING Bi-Sr-Ca-Cu-O SUPERCONDUCTOR MASAHIRO TANAKA AND KAZUTAKA HABU SONY Corporation Research Center, Tokyo, Japan ABSTRACT Ceramics
of
the
phase
Bi 2 Sr 2 Ca2 Cu3 01 0
(2223)
synthesized by a modified conventional ceramic process. the absence of Pb is observed in the lattice constant.
without
Pb
are
The influence of
INTRODUCTION Research on the superconductivity of the complex copper oxides have been simultaneously done at many laboratories after the discovery of the superconductivity of (La, Ba) 2CuO4 by Bednorz and Miller[l]. The superconductivity of Bi-Sr-Ca-Cu-oxide (BSCCO) was discovered by Akimitsu et al.[2], Michel et al.[3], and Maeda et al.[4]. It is well known that there are three kinds of phases with superconducting properties, Bi 2 Sr 2 CuO6 (2201), Bi 2 Sr 2 Ca1 Cu2 08 (2212) and Bi 2 Sr 2 Ca2 Cu301 0 (2223) in the BSCCO family, and that these three phases usually coexist in the ceramics. Single phase ceramics with a Tc of about 107 K are fabricated only in BSCCO doped with Pb[5]. It seems that (2223) with Pb is the alloy with the composition of (Bi, Pb) 2 (Pb, Sr, Ca) 4 Cu3 01 0 [6]. The superconductivity of BSCCO seems to be effected by Pb dopant. We have been trying to make ceramics consisting of (2223) without Pb for the sake of clarifying the role of Pb dopant on the crystal growth of (2223) and on the properties of ceramics. We have obtained samples by means of modifying a conventional ceramic process. And our results suggest that it is possible to grow (2223) crystals selectively without Pb dopant. EXPERIMENTS AND RESULTS The powders CaCO 3, SrCO3 and CuO, each purity better than 0.999, were mixed in a ratio corresponding to the nominal composition and ground in a ball mill at 120 rpm for 24-30 hrs. The dried mixture was calcined in air at 1233 K for 10 hrs. The calcining process was repeated 2-4 times with regrinding. It was found by the thermogravimetric and differential thermal analysis (TG-DTA) and the x-ray diffraction(XRD) that carbonate radicals were completely decomposed and that reactions among Sr, Ca, Cu and oxygen were saturated. The calcined Sr-Ca-Cu-O precursor ceramics and Bi 2 03 were mixed such as the nominal composition ratio. The Bi-Sr-Ca-Cu-O mixture was shaped into a cylindrical plate about 2.5mm in thickness, 12mm in 2 diameter under a pressure of 700 kg/cm2. The shaped samples were repeatedly sintered under the suitable conditions. The crystal growth of (2223) was very sensitive to sintering conditions; the sintering temperature and the atmosphere. The suitable sintering temperature was determined by trial and error. Samples were sintered at various temperatures close to the melting point estimated by TG-DTA. Figure 1 shows the examples on the sintering conditions: The nominal composition was Bi2. 0 5 Sr 2 Ca2 Cu3 0y; the partial pressure of oxygen
Mat. Res. Soc. Symp. Proc. Vol. 169. ©1990 Materials Research Society
342
1A C o
..
(b)
0 IL t(b))
(C)
(C)
4.0 6.0 8.0 10.0 20 (degree) Fig. 1. XRD patterns (Cu Ka) of the samples sint
Data Loading...
