The effect of Gd diffusion-doped on structural and superconducting properties of YBa2Cu3O7−x superconductors

The effect of Gd diffusion on structural evolution and superconducting properties of YBa2Cu3O7−x (Y123) prepared in the bulk polycrystalline form were studied. The gadolinium (Gd) diffusion in superconducting Y123 ceramic has been studied over the temperature range of 600-900 °C by energy dispersive X-ray fluorescence technique (EDXRF). The temperature dependence of Gd diffusion coefficient in grains (D1) and over the grain boundaries (D2) are described by the relations: D1 = 8.9 × 10−6 exp(−1.25/kT) and D2 = 2.3 × 10−5 exp(−1.09/kT). For the Gd diffused-doped samples, magnetization and resistivity measurements show that the critical transition temperature, Tc, increased from 88 to 91 K and the critical current density, Jc, which was calculated from M-H loops taken at 77 K, increased from 55 to 122 A cm−2 in comparison with those of undoped Y123. The possible reasons for the observed increases in Tc and Jc due to Gd diffusion were discussed. In addition, magnetic hysteresis curves of the Gd900, Gd800, Gd700 and undoped Y123 are presented for temperature of 5 K. It was found that the hysteresis is enhanced by the Gd diffusion. Such enhancement, which is considered to represent a characteristic strength of intergrain coupling, is more clearly recognized when critical current densities are compared.