Comparative Study of Structural, Electrical, and Mechanical Properties of (Tl, Hg)-1223 High Temperature Superconducting Phase Substituted by Lead Oxide and Lead Dioxide.

To compare between the effect of partial substitution of lead ions (Pb4+ and Pb2+) at thallium (Tl) site in Tl0.8-xHg0.2PbxBa2Ca2Cu3O9−δ superconductor; two different compounds, lead (II) oxide (PbO) and lead (IV) oxide (PbO2), were used for the synthesis of the superconducting samples. Samples with nominal compositions Tl0.8-xHg0.2PbxBa2Ca2Cu3O9−δ, with x = 0.00, 0.05, 0.10, 0.15, and 0.20, were synthesized via solid state reaction technique. The x-ray diffraction (XRD) results showed that the partial substitution of both lead ions has not affected the tetragonal structure. Moreover, the volume fraction was increased from 75.95% to 90.38% and 89.41% as x increased up to 0.20 for PbO and PbO2 substitutions, respectively. The scanning electron microscopy (SEM) images demonstrated better grain connectivity and rectangular-shaped plates, supporting the phase formation of (Tl,Hg)-1223. The energy-dispersive x-ray (EDX) analysis revealed good agreement between the nominal and real compositions. Moreover, the elemental composition and oxidation states were proved by x-ray photoelectron spectroscopy (XPS). Both the superconducting transition temperature (Tc) and critical current (Jc) showed enhancement at x = 0.5 and 0.1 for PbO and PbO2 substituted samples, respectively. Vickers microhardness (Hv) measurements were used to examine the mechanical properties of the composites under a range of applied loads (0.49–9.8 N). All the prepared composites revealed the normal indentation size effect. The proportional sample resistance model proved to be the best model for interpreting the experimental data for the prepared samples. [ABSTRACT FROM AUTHOR]