Raman spectra of Sr14-xCaxCu24O41 have been investigated in a number of well-defined single-crystal and polycrystalline samples. From the polarization and doping dependence, and from a comparison with previous reports on isostructural compounds, we identify the (4Ag + 4B1g + 3B2g + B3g) modes that are Raman allowed within the simple Fmmm structure, consisting of two Cu-O sub-lattices. With increasing Ca content, we observe the intensity decrease in the modes involving the atoms of the ladders. This effect, analogous to the CuO2-plane phonons in the high-Tc cuprates, can be attributed to the hole transfer from the chains to the ladders.
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