Raman Study of Tb-doped YBCO and Ce-doped GdBCO

The phase formation and the variation of the normal phonon frequencies of high temperature superconductors YBa2Cu3O7−δ and GdBa2Cu3O7−δ upon doping Tb and Ce for Y and Gd, respectively, have been investigated using XRD and Raman spectroscopy measurements. It is found that the increase of doping content causes the formation of impurity phases that can be detected in the XRD and Raman spectra, and results in the suppression of superconductivity. Moreover, analysis of the Raman peaks reveals that substitutions of Tb and Ce for Y and Gd in the parent structure are restricted to low concentrations in favor of impurity island formation.