Recent studies suggest that the apical oxygen plays an important role in high-${\mathit{T}}_{\mathit{c}}$ superconductivity of mercury-based superconductors ${\mathrm{HgBa}}_2$${\mathrm{Ca}}_{\mathit{n}\mathrm{-}1}$${\mathrm{Cu}}_{\mathit{n}}$${\mathrm{O}}_{2\mathit{n}+2+\mathrm{\delta }}$ [Hg-12(n-1)n]. Among strong Raman peaks at ∼570 and ∼ 585 ${\mathrm{cm}}^{\mathrm{-}1}$, the mode at ∼ 585 ${\mathrm{cm}}^{\mathrm{-}1}$ has been determined to be the ${\mathit{A}}_{1\mathit{g}}$ mode of the apical oxygen. However, the origin of the mode near 570 ${\mathrm{cm}}^{\mathrm{-}1}$ is still in question. In order to clarify the origin of the 570 ${\mathrm{cm}}^{\mathrm{-}1}$ mode, we have carried out Raman measurements on the ${\mathrm{Hg}}_{1\mathrm{-}\mathit{x}}$${\mathrm{Tl}}_{\mathit{x}}$${\mathrm{Ba}}_2$(${\mathrm{Ca}}_{0.86}$${\mathrm{Sr}}_{0.14}$${)}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_{8+\mathrm{\delta }}$ systems, where the amount of the oxygen in the Hg/Tl-O plane is controlled by the doping level of Tl ions. The results show that the 570 ${\mathrm{cm}}^{\mathrm{-}1}$ peak does not arise from the modes of the interstitial oxygens in the Hg/Tl-O plane, but from the ${\mathit{A}}_{1\mathit{g}}$-type mode of the apical oxygen. From our analysis, it is shown that the 570 ${\mathrm{cm}}^{\mathrm{-}1}$ mode arises from the apical oxygen ${\mathrm{O}}_{\mathit{A}}$ with the neighboring interstitial oxygen ${\mathrm{O}}_{\mathrm{\delta }}$, while the 585 ${\mathrm{cm}}^{\mathrm{-}1}$ mode is from the ${\mathrm{O}}_{\mathit{A}}$ without the nearest ${\mathrm{O}}_{\mathrm{\delta }}$ neighbor. We conclude that the apical oxygens in the Hg-12(n-1)n systems can have two distinctive sets of ${\mathrm{O}}_{\mathrm{\delta }}$ environment.

• Received 13 July 1995

DOI:https://doi.org/10.1103/PhysRevB.52.15078