Shift of the apical oxygen of the (formula presented) octahedron and the superconductivity in (formula presented) systems

The Raman scattering, electron diffraction (ED), and resistivity are measured for a nominal composition of (Formula presented) system. It is found that the peaks of (Formula presented) vibrational modes of the oxygen atom in a SrO layer along the c axis are broadened, the intensity is reduced, and the position of the peak shifts toward low frequency in Raman spectra as Sr content decreases. The reduction of the incommensurate modulation wavelength is observed by ED measurements with the decrease in Sr content. This suggests that the results in Raman spectra and ED are attributed to the shift of the apical oxygen in (Formula presented) octahedron induced by the decrease of Sr content in (Formula presented) system. The resistivity measurements show that the shift of the apical oxygen not only brings about the disappearance of superconductivity, but also induces a metal-semiconductor transition.