Superconducting and Structural Features of Tl-1223

TL;DR

This paper investigates the synthesis, structural modifications, and superconducting properties of Tl-1223, revealing how annealing conditions influence Tc and local atomic arrangements, with detailed structural and magnetic analyses.

Contribution

It provides new insights into how annealing in different gases affects the structural and superconducting properties of Tl-1223, combining bulk and local structural investigations.

Findings

Tc increased from 106 K to 125 K after annealing.

Structural changes are subtle and vary with annealing atmosphere.

Local atomic arrangements show Tl substitution and non-uniform Ca layers.

Abstract

This study provides an account of the bulk preparation of TlBa2Ca2Cu3O9-{\delta} (Tl-1223) superconductor at ambient pressure, and the Tc features under thermal-annealing conditions. The as-prepared Tl-1223 (Tc =106 K) presents a significantly higher Tc = 125 K after annealing the polycrystalline material in either flowing Ar+4% H2, or N2 gases. In order to understand the fundamental reasons for a particular Tc, we refined the average bulk structures using powder X-ray diffraction data. Although Ar+4%H2 annealed Tl-1223 shows an increased c lattice parameter, it is approximately unchanged upon N2-anneal. Due to such indeterminate conclusions on the average structural changes, local structures were investigated at using aberration-corrected scanning-transmission electron microscopy technique. Similar compositional changes in the atomic arrangements of both annealed-samples of Tl-1223 were detected in which the plane containing Ca atomic layer gives a non-uniform contrast, due to substitution of some heavier Tl. In this report, extensive bulk properties are summarized through temperature-dependent resistivity, and shielding and Meissner fractions of magnetic susceptibility results; the bulk and local structures are investigated to correlate to properties.