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 -Tl-0.8-xHg(0.2)PbxBa(2)Ca(2)Cu(3)O(9)- d 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 -Tl-0.8-xHg(0.2)PbxBa(2)Ca(2)Cu(3)O(9)-d, 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 (T-c) and critical current (J(c)) 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.