Cu-O vibrations of Ba2YCu3Ox

We present Raman and infrared absorption data for Ba2YCu3Ox with 7>x>6 for several samples with well-characterized oxygen content. Over this range the material has an oxygen-deficient tripled perovskite structure whose superconductivity properties depend critically on x. An orthorhombic-to-tetragonal transition occurs for x 6.5. We have examined both phases for the frequency range >400 cm-1 which contains the Cu-O bond-stretching vibrations. A force-constant model has been developed which allows us to assign the features in the spectra. Our results are consistent with the linear Cu-O-Cu-O chains in Ba2YCu3O7 being absent in the nonsuperconducting Ba2YCu3O6.