Results of Raman scattering studies on the natural isotope superconductor ${\mathrm{YBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_{7\mathrm{-}\mathrm{x}}$ and the heavy isotope superconductor ${\mathrm{YBa}}_2^{65}$${\mathrm{Cu}}_3$${\mathrm{O}}_{7\mathrm{-}\mathrm{x}}$ are presented. The phonon at 148.6 ${\mathrm{cm}}^{\mathrm{-}1}$ down-shifted by 1.8 ${\mathrm{cm}}^{\mathrm{-}1}$ in ${\mathrm{YBa}}_2^{65}$${\mathrm{Cu}}_3$${\mathrm{O}}_{7\mathrm{-}\mathrm{x}}$ whereas the position of the phonon at 112.5 ${\mathrm{cm}}^{\mathrm{-}1}$ remains unchanged. This conclusively relates the phonon mode at 148.6 ${\mathrm{cm}}^{\mathrm{-}1}$ to the vibration of Cu(2) atoms and suggests that the phonon at 112.5 ${\mathrm{cm}}^{\mathrm{-}1}$ is independent of Cu vibrations.

• Received 9 November 1988

DOI:https://doi.org/10.1103/PhysRevB.39.4699