Raman study of hydrogenated RBa 2Cu 3O 7-δ ( R = Y, Gd)

Single crystal Raman spectra of various scattering geometries were obtained from ceramic H _1.0YBa ₂Cu ₃O _6.7 and H _1.0GdBa ₂Cu ₃O _y using the microprobe technique. Apart from the five prominent A _g Raman lines being characteristic for YBa ₂Cu ₃O ₇, three more lines at 210 cm ^-1, 248 cm ^-1 and 610 cm ^-1 with exact A _g symmetry are observed in H _1.0YBa ₂Cu ₃O _6.7. The lowest frequency extra Raman lines are unambiguously attributed to IR vibrations ofY and Cu(1), respectively. The line at 610 cm ^-1 arises from oxygen vibrations but can not be conclusively assigned. Hydrogen occupies the interstitial sites around Cu(1) and Cu(2) (within the Y-plane) and perturbs the vibrations of its nearest-neighbours. The experimental results imply that the modes involving otherwise only odd parity vibrations become Raman active under hydrogen doping. The Raman scattering evidence is given that the hydrogen doping decreases the free holes concentration in YBa ₂Cu ₃O _7-δ.