INFLUENCE OF COBALT SUBSTITUTION ON THE RAMAN-SPECTRUM OF YBA2CU3O7-DELTA

We have investigated the influence of cobalt substitution on the Raman spectrum of YBa2Cu3O7-δ and have revealed similarities between this system and oxygen-deficient YBa2Cu3O7-δ samples. The variation of the Raman-modes frequencies at 440 cm-1 and 500 cm-1 with Tc is found to be very similar in both Co-substituted as well as oxygen-deficient samples. These changes in the mode frequencies can be explained by the strong influence of charge transfer from the Cu-O chains to the Cu-O planes on both Tc and mode frequencies in both systems. In addition the Raman spectrum shows with increasing cobalt content an increase in intensity near 580 cm-1. This scattering intensity is attributed to disorder-induced Raman scattering from the infrared-active Cu-O vibration along the chains. This gives an additional proof that the cobalt is substituted at the Cu(1) sites in the chains. © 1990.