Synthesis and Para-conductivity of (Tl$_{1-x}$Ti$_{x}$)Ba$_{2}$Ca$_{2}$Cu$_{3}$O$_\mathrm{y}$ (x $=$ 0, 0.2, 0.4, 0.6, 0.8) Superconductors

Abstract

We have synthesized Ti-doped (Tl$_{1-x}$Ti$_{x})$Ba$_{2}$Ca$_{2}$Cu$_{3}$O$_{y}$ (x = 0, 0.2, 0.4, 0.6, 0.8) superconductors at normal pressure. The samples have shown $T_\mathrm{c}$ onset at 117, 118, 113, 110, and 115 K and the $T_\mathrm{c}$ $(R=0)$ at 103, 96, 94, 97, and 106 K and the onset of diamagnetism around 109, 100, 98, 111, 100 K, respectively. The apical oxygen-related phonon modes are observed around 485 and 540 cm$^{-1 }$, and the planar oxygen modes at 600 cm$^{-1}$. These phonon modes are softened with the increase concentration of Ti in the final compound showing that Ti is incorporated into the (Tl$_{1-x}$Ti$_{x})$Ba$_{2}$Ca$_{2}$Cu$_{3}$O$_{y}$ (x = 0, 0.2, 0.4, 0.6, 0.8) samples. The excess conductivity analysis of these samples has shown an enhancement in the values of the parameters such as $\xi _{\mathrm{c}(0)}$, J, and $V_\mathrm{F}$ with the doping of Ti. We proposed that the doping of Ti in the $( {\mathrm{Tl}_{1-{\textit{x}}} \mathrm {Ti}_{{x}} })\mathrm{Ba}_2 \mathrm{O}_{4-\delta }$ charge reservoir layer facilitates the charge transfer mechanism for conducting CuO$_{2}$ planes which in turn enhance the values of aforementioned superconductivity parameters. The values of superconductivity parameters such as $B_\mathrm{c(0), }$ $B_\mathrm{c1(0), }$ $B_\mathrm{c2(0)}$, and $J_\mathrm{c}$(0) are, however, suppressed with Ti doping. We suggested this to be arising from the weakening of flux pinning character in the final compound. These results have shown that the oxygen defect density in (Tl$_{1-x}$Ti$_{x})$Ba$_{2}$Ca$_{2}$Cu$_{3}$O$_{y}$ samples is significantly suppressed with Ti doping.