Infrared spectra and normal modes of orthorhombic Bi₂Sr₂(Ca_1-x Y_x)Cu₂O_8+y

Abstract

IR absorption spectra have been recorded for the series of high-T_c compounds Bi₂Sr₂(Ca_1-xY_x)Cu₂O _8+y at 300 K and 85 for x = 0.0 (T_c = 81 K), x = 0.4 (T_c = 24 K) and x = 1.0 (non-superconducting). The spectra have been discussed and analysed for the x = 0.0 and x = 1.0 compounds with the help of normal mode computations by fitting the available infared and Raman bands. The vibrational analysis for the non-superconducting compound helps to form an initial force field and thus generates all the vibrational modes for the superconducting compound Bi₂Sr₂(Ca_1-xY_x)Cu₂O_8+y. The computation generates the potential energy distribution and the eigenvectors for both the compounds and thus gives a precise description of all the normal modes. This helps to establish a correlation between the vibrational modes of the two compounds.