The High-Tc Phase with a New Modulation Mode in the Bi, Pb-Sr-Ca-Cu-O System

Abstract
The preparation and characterization of Bi1.73Pb0.35Sr1.89Ca1.86Cu3O9.91, a lead-rich high-T c phase, were studied (T c(ρ=0)=105 K). This compound crystallized in a pseudotetragonal structure with a t=0.541 nm and c t=3.709 nm, while a unique one-dimensional modulation with a wavelength of 4.7 nm (≃8.7a) was found along the b axis using transmission electron microscopy. Such a lead-rich phase and a lead-free (or very poor) phase crystallizing in the well-known modulated structure (2.7 nm≃5a) were intergrown at intermediate compositions, such as Pb/Bi=1/9. Effects of annealing under different oxygen pressures were studied.