Raman spectroscopy and normal mode assignments for Ba sub 2 MCu sub 3 O sub x (M = Gd,Y) single crystals.

We present a polarization study and normal mode analysis of the Raman spectra of Ba sub 2 MCu sub 3 O sub x single crystals (6 = x = 7) in the orthorhombic and tetragonal phase. Our results give a definitive assignment of the highest A sub g mode, which is due to the O (1) axial symmetric stretch vibration, to a band at 500 cm sup (-1) in the orthorhombic (O) and at 472 cm sup (-1) in the tetragonal (T) phase. In addition four other A sub g modes are observed at 435, 335, 230 (O)/220 (T) and 140 cm sup (-1), all of which are assigned. A broad feature between 500 and 650 cm sup (-1) is ascribed to a defect - (O vacancies) induced mode.