A comparative study of (Ce) and (Gd) doping influence on the superconducting properties of YBCO ceramics

Abstract

This work is devoted to investigate the structural and electrical properties of the Ce, Gd-doped YBCO superconductors bulk ceramics. YBa2-xRExCu3O7−δ (x = 0, 0.01, 0.05, 0.1) (RE = Gd, Ce) samples were prepared by means of conventional solid-state reaction. X-ray diffraction analysis was carried out to identify the present phases in the as-prepared samples followed by the determination of their lattice parameters. Fourier Transform Infrared Spectroscopy (FTIR) was used to identify the functional groups. Furthermore, the morphology and the surface roughness of the studied samples were characterized using Scanning Electronic Microscopy (SEM) and Atomic Force Microscopy (AFM). Vickers Micro-hardness of the as-prepared samples was examined. Besides, the electrical resistivity measurements were achieved to determine the critical transition temperature TC and the critical current density JC.The effect of Ce and Gd additions is clearly noticed in the obtained results, where all the prepared samples are superconductors with the presence of Y123 as a major polycrystalline phase. From the XRD patterns, the intensities of the Y123 corresponding peaks decrease with further increasing the Ce and Gd contents. In addition, the variation of the cell parameters was significant after additions of both Ce and Gd, which affect the grain size and the oxygen content of the YBa2-xRExCu3O7−δ system. An improvement of the structure and surface roughness is observed on SEM and AFM images. Likewise, Vickers micro-hardness has increased after the Ce and Gd additions. Although, the critical transition temperature TC was not further increased upon Ce or Gd additions compared to the undoped YBCO samples. Nevertheless, an exception has been recorded with an increase of TC for YBa2-xRExCu3O7−δ with (RE = Gd, x=0.01) to reach 88 K. In contrary, an improvement of the deduced critical current density JC was achieved for all Ce-doped YBCO samples unlike those of Gd-doped samples.