The crystal structure

local electron density and superconductivity were investigated by X-ray diffraction

positron annihilation and other methods for Fe-doped GdBa2Cu3-xFexO7-δ(x=0.00-0.30) systems.The results showed that the crystal structure of the samples evolved a phase transition from orthorhombic to tetragonal near x=0.10.The superconducting transition temperature Tc decreased with increasing Fe doping amounts

and the superconducting transition width changed strikingly for O-T phase transition samples.The width increased markedly for the tetragonal phase ones.The results from the positron experiments indicated that the local electron density displayed a noticeable change when the O-T phase transition took place in the systems.It was found that the superconducting transition temperature Tc decreased with the local electron density.These findings manifest that the crystal phase transition and the local electron density can strongly affect the superconductivity in the Fe doped GdBa2Cu3-xFexO7-δ systems.