Influence of the incommensurate-modulation structure on the Raman spectra for La- and Pb-doped ${\mathrm{Bi}}_2$${\mathrm{Sr}}_2$${\mathrm{CuO}}_{\mathit{y}}$ systems

Raman measurements were performed on single-phase samples of ${\mathrm{Bi}}_{2.1}$${\mathrm{Sr}}_{1.9\mathrm{-}\mathit{x}}$${\mathrm{La}}_{\mathit{x}}$${\mathrm{CuO}}_{\mathit{y}}$ (0≤x≤1.0) and ${\mathrm{Bi}}_{2\mathrm{-}\mathit{x}}$${\mathrm{Pb}}_{\mathit{x}}$${\mathrm{Sr}}_2$${\mathrm{CuO}}_{\mathit{y}}$ (0.05≤x≤0.6). Significant modifications of the spectra, becoming more pronounced with increasing x, are noted with respect to the undoped ${\mathrm{Bi}}_2$${\mathrm{Sr}}_2$${\mathrm{CuO}}_{\mathit{y}}$ in the energy ranges of 450–465 ${\mathrm{cm}}^{\mathrm{-}1}$ and 610–650 ${\mathrm{cm}}^{\mathrm{-}1}$. The experimental results provide important data related to the origin of the incommensurate modulation structure and its relation to the superconductivity of the ${\mathrm{Bi}}_2$${\mathrm{Sr}}_2$${\mathrm{CuO}}_{\mathit{y}}$ system.