The Effect of Fe Diffusion on Some Physical and Superconducting Properties of MgB2

The iron (Fe) diffusion in superconducting MgB2 bulk samples has been studied over the temperature range of 650-900 degrees C for 1 h. Fe coating on bulk polycrstalline superconducting MgB2 samples was performed in two ways, i.e., on pressed pellets without sintering (set(2)) and on pressed and sintered pellets (set(1)). For both sets, a 50 mu m thick Fe layer was coated on MgB2 by evaporation in vacuum. Effects of Fe diffusion on the crystal structure and superconducting properties of MgB2 have been investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), and resistivity measurements. Fe diffusion coefficients were determined from lattice parameter c and room temperature resistivity values. The temperature dependence of the Fe diffusion coefficient in this temperature range is described by the Arrhenius relation. It has been found that the Fe diffusion coefficient increases with increasing sintering temperature, as expected. The plausible explanations for the observed improvement in microstructure and superconducting properties of the samples due to Fe diffusion are discussed.