HIGH-TEMPERATURE STUDY OF THE RAMAN-ACTIVE PHONON MODES OF YBA2CU3O7-DELTA

We have accomplished Raman scattering measurements on a polycrystalline sample of YBCO in the temperature range 25-600 degrees C and in oxygen atmosphere. In the spectra at high temperature, we observe, new vibrational structures at 360, 585, and 605 cm(-1). The usual Raman modes at 335, 440, and 500 cm(-1) showed a trend to broaden and flatten with increasing temperature. We attribute the peaks observed at high temperature to IR-active vibrational modes which become Raman-active as a result of temperature induced disorder in the YBCO unit cell. In this perspective, we discuss how the migration of oxygen atoms might account for the observed phenomena.