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 T_c 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 YBa₂Cu₃O_7-x lattice but forms an impurity phase. The WO₃-doped YBCO specimens quenched in air consist of orthorhombic YBa₂Cu₃O_7-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.