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Sol-gel synthesis and characterization of superconducting REBa 2 Cu 4 O 8 (RE = Y, Eu, Gd, Yb and Lu) oxides

In this study superconducting REBa 2 Cu 4 O 8 (RE–Y, Eu, Gd, Yb and Lu) cuprates have been synthesized by an aqueous sol–gel method. The superconducting YBa 2 Cu 4 O 8 (Y-124), EuBa 2 Cu 4 O 8 (Eu124), GdBa 2 Cu 4 O 8 (Gd-124), YbBa2Cu4O8 (Yb-124) and LuBa 2 Cu 4 O 8 (Lu-124) compounds have been characterized by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), resistivity and magnetic susceptibility measurements. The X-ray diffraction patterns showed that single phase compounds formed in all the cases. The results of resistivity measurements for the REBa 2 Cu 4 O 8 samples showed that the onset critical temperature of superconductivity is in a good correlation with changes in the orthorhombicity of the RE-124 unit cell and ionic radius of lanthanide ion. However, no correlation between the T C (onset) of RE-124 superconducting oxides and the superconducting volume fraction was observed.