THE EFFECT OF FE DIFFUSION ON STRUCTURAL AND SUPERCONDUCTING PROPERTIES OF YBACUO

The Fe diffusion in superconducting YBa2Cu3O7 (YBaCuO) ceramic has bee n studied over the temperature range 615-880 degrees C by the energy d ispersive X-ray fluorescence (EDXRF) technique. The temperature depend ences 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) ex p(-1.25/kT) and D-2 = 1.8 x 10(-5) exp(-0.90/kT). Effects of iron diff usion and cooling rate on the crystal structure and superconducting pr operties 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 oxi des in YBaCuO, The fast cooling of iron-doped samples stimulates the f ormation of predominantly orthorhombic phase, while the undoped sample , employing the same cooling rate, remained tetragonal.