## Abstract

The phonon Raman spectra of (Formula presented)(Formula presented)(Formula presented)(Formula presented)(Formula presented)(Formula presented) (x=0-1) have been investigated in a number of well-defined single-crystal and polycrystalline samples. From the polarization and Y-doping dependence, and from a comparison with previous reports on Bi-based cuprates, we identify the (6(Formula presented)+1(Formula presented)) symmetry modes that are Raman allowed within the ideal body-centered-tetragonal unit cell. A large number of extra “disorder-induced” phonon bands are observed in the ab-plane polarized spectra. In contrast to most previous reports, we argue that the c-axis polarized phonon band around 629 (Formula presented) is due to the O(2(Formula presented) vibration, while the exclusively ab-plane polarized band around 463 (Formula presented) is induced by the O(3(Formula presented) vibration. With increasing Y doping we find that the vibrational modes involving atoms in the (Formula presented) planes rapidly increase in intensity as a result of the reduced metallic screening in the hole-depleted Y-doped samples. We also find that Y substitution gives rise to a substantial hardening of the O(1(Formula presented) and (Formula presented) phonons by ∼40 (Formula presented), whereas the O(2(Formula presented) phonon is found to soften by ∼20 (Formula presented), when x increases from 0 to 1. The phonon frequency changes can be explained by the “internal pressure” induced by the decrease in the average Ca/Y ion size and an additional “charge-transfer” induced by the change in the Cu and Bi valences with Y doping.

Original language | English |
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Pages (from-to) | 11796-11806 |

Number of pages | 11 |

Journal | Physical Review B - Condensed Matter and Materials Physics |

Volume | 53 |

Issue number | 17 |

DOIs | |

Publication status | Published - 1996 |

Externally published | Yes |

## ASJC Scopus subject areas

- Electronic, Optical and Magnetic Materials
- Condensed Matter Physics