Investigation of some superconducting properties of ytterbium diffusion-doped YBa2Cu3O7−x superconductors

The effect of Yb diffusion on structural evolution and superconducting properties of YBa2Cu307−x (Y123) prepared in the bulk polycrystalline form were studied. The ytterbium (Yb) diffusion in superconducting Y123 ceramic has been studied over the temperature range 800-900 °C by energy dispersive X-ray fluorescence technique (EDXRF). The temperature dependences of the Yb diffusion coefficient in grain (D1) and over the grain boundaries (D2) are described by the relations: D1 = 4.8 × l0−6 exp(−1.15/kT) and D2 = 2.2 × l0−5 exp(−1.05/kT). For the Yb-doped sample, critical current density was increased from 1.64 × 104 to 1.91 × 104 A/cm2 at 5 K and 56 to 135 A/cm2 at 77 K in comparison with those of undoped Y123 sample. In addition, the critical transition temperature increases by about 3 K compared with the pure Y123. It is found that Jc can be improved by the diffusion doping of Yb in Y123, which may be due to improving the structural quality at the grain boundaries and stress-field pinning effect.