Raman measurements were carried out on the high-Tc superconductor $RBa_2Cu_3O_{7-y}$ ( R = Y, Gd, Tm, Eu, Sm, Nd, Pr, La ).
It seems that the high-Tc superconductor $RBa_2Cu_3O_{7-y}$ has no lattice instability as suggested from the temperature dependence of the frequencies investigated in the temperature range from 15 to 300K.
By substituting different rare earth R, it was found that the frequencies of the bending and stretching mode vibrations depended linearly on the ionic radius of the rare earth R. Similar results were also shown with $Y_{1-x}Pr_xBa_2Cu_3O_{7-y}$ ( 0 ≤ x ≤ 1 ).
The evidence that the electron-phonon interaction in $RBa_2Cu_3O_{7-y}$ series except R=Nd was confirmed, whereas any significant electron-phonon interaction was not observed in the case of the non-superconducting $PrBa_2Cu_3O_{7-y}$ having the same structure.
Crystal field effect seems to be significant in $Y_{1-x}Nd_xBa_2Cu_3O_{7-y}$ ( 0 ≤ x ≤ 1 ) where the electron-phonon interaction was also observed to be effective.
