Chain-Oxygen Vibrations and Phonon Anomalies Above Tc in RBa2Cu3O7 and YBa2Cu4O8
The modes of B1u -symmetry observed in the infrared spectra of YBa2Cu3O7−δ and YBa2Cu4O8 at v ≈ 277 cm−1 and 500 cm−1, respectively, are assigned to vibrations of the chain-oxygens. This assignment is reached by analysis of the corresponding eigenvectors, influence of Au, Pr, 18O doping on these frequencies and comparison of infrared spectra of both materials. Anomalous softenings of oxygen-related phonon frequencies with decreasing temperature are found starting above T c , the most pronounced ones occuring for YBa2Cu4O8.
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