Physica C: Superconductivity and its applications

Raman spectra and normal mode assignments of superconducting YBa2Cu4O8 single crystals

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Single crystals of YBa2Cu4O8 high temperature superconductors with well characterized structural, magnetic, and transport properties have been studied by Raman microprobe spectroscopy in various polarization geometries. The unique orthorhombic structure, spacegroup Ammm, with double linear CuO chains along the a-axis gives rise to two additional modes of Ag symmetry that are not present in the single chain YBa2Cu3O7(1:2:3) structure. Comparison of the observed spectra with YBa2Cu3O7 shows four modes at nearly identical positions and with comparable strengths to the known 1:2:3 Ag modes as expected from the similar structure. Two additional peaks observed at 250 cm-1 and 600 cm-1 in the YBa2Cu4O8 spectrum have no corresponding modes in the spectrum of fully oxygenated 1:2:3. This suggests their assignment to Ag modes associated with CuO bending and stretching motion in the double chains as predicted by factor group analysis. © 1989.