Wm. Bian et al., THE INTERMEDIATE PHASE DURING (BI,PB)(2)SR2CACU2O8-TRANSFORMATION(DELTA TO (BI,PB)(2)SR2CA2CU3O10+DELTA PHASE), Physica. C, Superconductivity, 248(1-2), 1995, pp. 119-126
We report our observations on and identification of an intermediate ph
ase, (Bi,Pb)(4)Sr4Ca3Cu5O18 (+) (delta) (denoted as Bi/4435), during t
he phase transformation of (Bi,Pb)(2)Sr2CaCu2O8+delta (Bi/2212) to (Bi
,Pb)(2)Sr2Ca2Cu3O10+delta (Bi/2223) in powder-in-tube processed tapes.
The unit cell of the phase consists of one half each of the Bi/2212 a
nd the Bi/2223 cell, with lattice parameters of a approximate to b = 5
.4 Angstrom and c = 33.9 Angstrom. The space group of the new phase wa
s determined to be Pbmn using the extinction rule of the selected-area
electron diffraction, as well as convergent beam electron diffraction
and high-resolution electron microscopy. The presence of the Bi/4435
phase and the abundance of its local structure during the early stage
of the transformation suggests that the Bi/2223 phase is formed by the
rapid insertion of two extra Ca/CuO bi-layers, one at a time, into th
e two identical CuO/Ca/CuO building blocks of the Bi/2212 matrix. This
finding may shed light on the mechanism of structural phase transform
ation in layered cuprate superconductors.