The effect of Gd diffusion-doped on structural and superconducting properties of YBa 2Cu 3O 7− x superconductors

Abstract

The effect of Gd diffusion on structural evolution and superconducting properties of YBa 2Cu 3O 7− 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 ( D 1) and over the grain boundaries ( D 2) are described by the relations: D 1 = 8.9 × 10 −6 exp(−1.25/ kT) and D 2 = 2.3 × 10 −5 exp(−1.09/ kT). For the Gd diffused-doped samples, magnetization and resistivity measurements show that the critical transition temperature, T c, increased from 88 to 91 K and the critical current density, J c, 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 T c and J c 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.