MICRO-RAMAN SPECTROSCOPY OF BI2SR2CACU2O8+DELTA INTERCALATED WITH NICKEL PHTHALOCYANINE BENZENE

Micro-Raman measurements on pure Bi2Sr2CaCu2O8+delta (host) intercalated with conjugated ring-shaped molecules (guest) like nickel phthalocyanine (NiPc) and benzene have been carried out. Drastic changes due to intercalation have been observed in the peak frequencies, intensities and band widths of several vibrational modes of both the guest and the host species. The anomalous variations in the peak frequencies and intensities of C = N aza group stretching and C-C pyrrole ring stretching vibrations of the NiPc molecule as well as the vibrational modes of oxygen in the Cu-O planes of the host material reveal the possibility of charge transfer processes in the intercalated compounds from the guest to the host species. The large increase in the bandwidths of many vibrational modes has been related to local distortions and to the inhomogeneous distribution of guest species in the intercalated samples. The contention of charge transfer due to intercalation is also substantiated from STM/STS studies. The suppression of the superconductivity due to intercalation has been explained in terms of the charge transfer mechanism.