Raman spectra of iodide species in intercalated IBi₂Sr₂CaCu₂O_8+δ

We report Raman spectra of pristine Bi₂Sr₂CaCu₂O_8+δ single crystals. Low frequency spectra of the intercalated crystal taken at room and liquid nitrogen temperatures with the 488 nm Ar⁺ excitation line exhibit a strong band at 105 cm^-1 and weaker bands at ≈ 73 and ≈ 150 cm^-1. The results are confirmed by using the 647 nm Kr⁺ excitation line. These bands characterize the fundamental vibrations of I₃-molecular anions embedded in the lattice. Drastic change of the micro-Raman scattering in the 200–700 cm^-1 region is observed between pristine and iodinated crystals. A factor group analysis of stage-1 IBi₂Sr₂CaCu₂O_8+δ is presented based on possible structures and predicts that iodine vibrations can be Raman active in a non-centrosymmetric lattice.