Ln. Wang et al., NANOPHASE PRECURSORS FOR HIGH-J(C) AG-CLAD SUPERCONDUCTING BIPBSRCACUO TAPES, Superconductor science and technology, 8(2), 1995, pp. 94-100
A controlled coprecipitation technique has been used to synthesize pre
cursors of superconducting BiPbSrCaCuO ceramics. The oxalate precursor
s were nano-sized powders with high homogeneity, low crystallinity, an
d well-defined stoichiometry. These precursors have been used to fabri
cate superconducting tapes by the powder-in-tube technique, which invo
lves the use of Ag sheaths. The nano-sized homogeneous powders require
considerably reduced tape-processing (sintering) times for Bi-2223 fo
rmation, and provide 'clean' intergrain boundaries within the sintered
tapes. As a result, high critical transport current density, J(c), ca
n be obtained even in multiphase composites that do not necessarily ex
hibit a high degree of texture. To gain further insight into the role
of microstructural details at each step of the tape fabrication, exten
sive x-ray diffraction analyses and scanning electron microscopy measu
rements have been made. The influence of homogeneity and grain size di
stribution on the superconducting properties of the Ag-clad tapes is d
iscussed. We have reproducibly achieved, within 60 h of the thermal pr
ocessing, J(c) values as high as 4.4 x 10(4) A cm(-2) at 77 K in zero
applied magnetic field.