Displacement Waves of Oxygen Atoms in Bi,Pb-2223 Lattice of Composites Annealed in Oxygen Reduced (O2+N2) Atmosphere

TL;DR

This study investigates how annealing Bi,Pb-2223 superconducting composites in a reduced oxygen atmosphere affects the lattice structure, revealing oxygen displacement waves likely caused by oxygen deficiency, which impacts superconductivity.

Contribution

It provides new insights into lattice changes and oxygen deficiency effects in Bi,Pb-2223 superconductors annealed in oxygen-reduced atmospheres.

Findings

Displacement waves of oxygen atoms observed in the lattice.

Oxygen content decreases below stoichiometric levels.

Nitrogen does not penetrate or interact with the lattice.

Abstract

Annealing of Bi,Pb-2223/Ag composites in (O2+N2) atmosphere at 820-780C is believed to reduce the number of the accompanying phases, to make contacts between crystallites closer and to increase the critical current. The goals of this study were to reveal the changes in the 2223 lattice at annealing in the reduced oxygen atmosphere, to elucidate the reasons of these changes and to discuss their effect on the ceramics superconductivity. After the annealing the transversely-polarized displacement waves of oxygen atoms in [010]2223 direction have been found in the 2223 phase by electron diffraction analysis. These waves could appear due to the lack of oxygen in the 2223 lattice or to the nitrogen penetration in it. As demonstrated by the X-ray photo-electron spectroscopy and nuclear microanalysis, nitrogen does not interact with the 2223 lattice, and the oxygen index decreases to 9.67, which is lower than the stoichiometric. Thus, the atomic displacement waves result from the lack of oxygen in Bi-O bilayers.