High-Frequency Raman Scattering in the Superconducting and Semiconducting Phases of Ba sub 2 YCu sub 3 Ox-type Single Crystals and Ceramics.

We report the high-frequency Raman spectra (DELTA omega > 1000 cm sup (-1)) of Ba sub 2 YCu sub 3 O sub x and various analogues, measured at room temperature. In semiconducting single crystals and ceramics of Ba sub 2 YCu sub 3 O sub x (x ~ 6) and semiconducting crystals of Sr sub 2 YCu sub (2.4) Al sub (.6) O sub x we find a peak at 1220 cm sup (-1) (A sub (1g) symmetry) and a broad band at 2600 cm sup (-1) (B sub g ). The 1220 cm sup (-1) peak can be interpreted as scattering from excitations of single spins near defects or two-photon scattering. The 2600 cm sup (-1) band is attributed to scattering from spin-pair excitations. In the spectra of superconducting Ba sub 2 YCu sub 3 O sub x crystals and ceramics (x ~ 7) these bands are not present.