High-Frequency Raman Scattering in the Superconducting and Semiconducting Phases of Ba2YCu3Ox-Type Single Crystals and Ceramics

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We report the high-frequency Raman spectra (>1000 cm-1) of Ba2YCu3Ox and various analogs, measured at room temperature. In semiconducting single crystals and ceramics of Ba2YCu3Ox (x6) and semiconducting single crystals of Sr2YCu2.4Al0.6Ox we find a peak at 1220 cm-1 (A1g symmetry) and a broadband at 2600 cm-1 (B1g). The 1220-cm-1 peak can be interpreted as scattering from excitations of single spins near defects or two-phonon scattering. The 2600-cm-1 band is attributed to scattering from spin-pair excitations. In the spectra of superconducting Ba2YCu3Ox crystals and ceramics (x7) these bands are not present. In all samples, semiconductors and superconductors, we observe flat and featureless spectral intensity (A1g symmetry) extending up to =5000 cm-1, the origin of which is not understood at present. The similarity between the high-frequency spectra of Ba2YCu3Ox (x6) and Sr2YCu2.4Al0.6Ox [Al on Cu(1)-chain sites] shows that the magnetic scattering is determined by the structure of the Cu(2)-O planes and is not affected by the distance between the planes or by the Cu(1)-chain structure.



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