X-ray diffraction and transmission electron microscopy studies on the structure of the ''Pb''-1223 superconductor

A nearly single phase ''Pb''-1223 sample with a nominal composition of Pb: Sr: Ca: Cu = 0.5:2.8:1.7:3.0 has been prepared by using a high pressure technique. The sample showed superconductivity at 104 K with a Meissner superconducting volume fraction of about 35% at 5 K. A micro-composition analysis by energy dispersive X-ray (EDX) measurement indicated that the ratio of cations in the final product was Pb:Sr:Ca:Cu = 0.55:2.42:1.73:3.30. The basic structure of the present sample was determined by X-ray Rietveld refinement. This compound has a tetragonal symmetry with space group P4/mmm and lattice parameters a = 3.831(3) Angstrom and c = 15.30(1) Angstrom. An electron diffraction (ED) study indicated the presence of an orthorhombic B-face centered superlattice with lattice parameters a(s) = 3.1a, b(s) = a and c(s) = 2c. Based on a high-resolution transmission electron microscopic (HRTEM) study, a structural model is proposed.