The effect of Fe diffusion on structural and superconducting properties of YBaCuO

The Fe diffusion in superconducting YBa2Cu3O7 (YBaCuO) ceramic has been studied over the temperature range 615-880 degrees C by the energy dispersive X-ray fluorescence (EDXRF) technique. The temperature dependences of iron diffusion coefficient in grains (D-1) and over the grain boundaries (D-2) are described by the relations D-1 = 1.5 x 10(-4) exp(-1.25/kT) and D-2 = 1.8 x 10(-5) exp(-0.90/kT). Effects of iron diffusion and cooling rate on the crystal structure and superconducting properties of YBaCuO have been investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and resistivity measurements. It is found that iron diffusion is accompanied by the formation of iron oxides in YBaCuO, The fast cooling of iron-doped samples stimulates the formation of predominantly orthorhombic phase, while the undoped sample, employing the same cooling rate, remained tetragonal.