Cu-O vibrations of Ba sub 2 YCu sub 3 O sub x.

We present Raman and infrared absorption data for Ba sub 2 YCu sub 3 O sub x 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 omega > 400 cm sup (-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 Ba sub 2 YCu sub 3 O sub 7 being absent in the nonsuperconducting Ba sub 2 YCu sub 3 O sub 6.