Synthesis and characterization of doped YBa₂Cu₄ O₈ superconductor by Cd⁺²

In this study, the effect of yttrium substitution by cadmium in the YBa₂Cu₄O₈ superconductor was investigated. A series of superconducting oxide ceramics of (Y_1-x Cd_x )Ba₂Cu₄O₈ with a different Cd content (x=0.00-0.18 mol) were prepared by an aqueous sol-gel method using aqueous mixtures of the metal acetates. Homogeneous precursor gels were obtained by complexing copper ions with tartaric acid. The obtained gel powders and end products were characterized by X-ray powder diffraction analysis, infrared spectroscopy, thermal gravimetric analysis, differential thermal analysis, scanning electron microscopy, energy of dispersive X-ray analysis, DC-electrical resistivity, and magnetic susceptibility measurements. The gel synthesized was amorphous and highly homogeneous. Single-phase bulk samples were obtained after annealing at 1108 K for 100 h, in an atmosphere of flowing O₂ gas. XRD measurements indicated that the crystal structure remains orthorhombic (up to x=0.12 mol). With a further increase of the cadmium substitutional level, peaks of Y-124 phase disappeared. Doping the YBa₂Cu₄O ₈ phase with cadmium showed a strong effect on the superconducting properties increasing the critical temperature (T_c) from 80 K (for the nonsubstituted sample) to 92 K (for the (Y_0.88Cd _0.12)Ba₂Cu₄O₈), and T_c decreases with a further increase of the cadmium substitutional level. Also prepared was a series of (Y_1-x Cd_x Ba₂Cu ₄O₈) samples with (0.0≤x≤0.08 mol), via the ceramic method and annealed at 1123 K for 132 h in an atmosphere of flowing O ₂ gas. The characterization of the final products was conducted by X-ray diffraction, scanning electron microscopy, and energy dispersive X-ray analysis. We have not observed any trace of the superconducting Y-124 phase in any of our Cd doped samples.