NEW APEX-OXYGEN RELATED MODE IN PR-BA-CU-O FROM IR-EXCITED RAMAN-SCATTERING

In this communication, we present IR-excited Raman scattering of singl e crystals of PrBa2Cu3O7-y. In contrast with Raman scattering excited in the visible, we find the presence of two different Raman modes with energy around 500 cm(-1). Comparison with visible excitation and with the band associated with the apex oxygen local modes in low-oxygen Pr xY1-xBa2Cu3O6+y indicates that there are two separate vibrational mode s associated with the apex oxygen position in the high oxygen phase of PrBa2Cu3O6+y. We interpret this as due to the existence of two differ ent sites for apex oxygen atoms and in terms of polaronic states in th e chain sites.