The effect of Co electrodiffusion on the properties of YBaCuO superconductors

Diffusion over the temperature range 600-850 °C, electrodiffusion at 30 °C and effect of the Co substitution on crystalline structure and electrical characteristics of YBa²Cu³O_7-y (YBaCuO) ceramic samples have been investigated by the energy dispersive X-ray fluorescence (EDX), X-ray diffraction (XRD), resistivity-temperature and current-voltage measurements. The temperature dependence of the cobalt diffusion coefficient (600-850 °C) via the grain boundaries has been described by the relation D=5.1×10^-4exp(-1.12/kT). It is shown that the Co-doping of YBaCuO causes depression of the critical temperature and the critical current density. At the room temperature Co migrates in d.c. electric field preferentially in the form of positively charged ions with an effective charge q0.6- Electrodiffusion-stimulated orthorhombic-tetragonal transition, decrease in critical temperature and critical current density and change of the form of resistivity-temperature dependence are discovered.