Phonon characterization of YBa2(Cu1-xAlx)3O7- delta by Raman spectroscopy.

We present new Raman scattering data on high-temperature superconducting materials with composition YBa/sub 2/(Cu/sub 1-//sub x/Al/sub x/)/sub 3/O/sub 7//sub -//sub delta/. In YBa/sub 2/Cu/sub 3//sub 7-//sub delta/ we observe new high-frequency peaks greater than 700 cm/sup -1/ that we associate with two phonon interactions of the first-order Cu-O Raman vibrations that occur at 337, (450 +- 10) and 502 cm/sup -1/. The intensity of these new peaks suggest that anomalous phonon interactions are taking place. Results on Al substitution are consistent with a unit-cell change from orthorhombic to tetragonal. The observation of superconductivity in the tetragonal structure means that it is not possible to simply assign superconductivity to the orthorhombic structure.