Influence of lead fluoride on the mechanical properties of ($\text{Cu}_{0.5} \text{Tl}_{0.5}$): 1223 Phase

Abstract

This work reveals the influence of lead fluoride substitution and liquid nitrogen immersion on the mechanical properties of high-temperature superconductor samples $\left( {{\text{Cu}}_{0.5 - x} {\text{Tl}}_{0.5} {\text{Pb}}_{x} } \right){\text{Ba}}_{2} {\text{Ca}}_{2} {\text{Cu}}_{3} {\text{O}}_{10 - \delta - y} {\text{F}}_{y}$, with (0.00 ≤ x ≤ 0.10). The samples under investigation were synthesized by solid-state reaction method at normal pressure. The samples were characterized using X-ray powder diffraction (XRD) and scanning electron microscope (SEM). The X-ray data have indicated that the partial replacement of ${\text{Cu}}^{2 + }$ ions by Pb²⁺ ions and oxygen by fluorine in the reservoir layer do not alter the tetragonal structure of the samples. On the other hand, the values of the lattice parameters a and c were found to be varied with x according to the difference in the ionic radii of ${\text{Pb}}^{2 + } {\text{and Cu}}^{2 + }$ as well as to the oxygen content. SEM analysis has revealed that lead fluoride substitutions improve the inter-grains connectivity of the prepared samples. The values of the superconducting transition temperature ($T_{\text{c}}$) were determined using ac magnetic susceptibility measurements. Vickers microhardness $(H_{\text{v}} )$ was measured as a function of applied loads and the immersion time in liquid nitrogen (t). It was found that $H_{\text{v}}$ values have recorded enhancements after one-hour immersion in liquid nitrogen. Moreover, the variation of $H_{\text{v}}$ has shown an enhancement about 34% for x = 0.06. Furthermore, various models were employed to interpret the load dependence behavior of H_v.