Effect of thermal treatments on the superconductivity of undoped and WO3 doped Y-Ba-Cu-O system

Undoped and WO3-doped Y-Ba-Cu-O ceramics have been slowly cooled in flowing oxygen or quenched in air from 900°C to room temperature, after sintering at 900°C for 30h in flowing oxygen. The ac susceptibility measurements show that the Tc of the quenched WO3-doped Y-Ba-Cu-O superconductor can reach 88K, while the undoped Y-Ba-Cu-O ceramic quenched in air is a non-superconductor. X-ray diffraction data show that WO3 does not enter into the YBa2Cu3O7-x lattice but forms an impurity phase. The WO3-doped YBCO specimens quenched in air consist of orthorhombic YBa2Cu3O7-x phase and an impurity phase which increases with increasing WO3 content. Raman spectra show that oxygen contents are different for undoped and WO3-doped samples. It is suggested that suitable doping with WO3 can change the oxygen content and reduce the effect of thermal treatments on the superconductivity of Y-Ba-Cu-O system.