Raman-active phonons in Bi{sub 2}Sr{sub 2}Ca{sub 1{minus}{ital x}}Y{sub {ital x}}Cu{sub 2}O{sub 8+{ital d}} ({ital x}=0{endash}1): Effects of hole filling and internal pressure induced by Y doping for Ca, and implications for phonon assignments
- Research Laboratory of Engineering Materials, Tokyo Institute of Technology, 4259 Nagatsuta, Midori-ku, Yokohama 226 (Japan)
- Department of Solid State Physics, Riso/ National Laboratory, DK-4000 Roskilde (Denmark)
- Department of Applied Physics, Chalmers University of Technology, S412-92 Goeteborg (Sweden)
- Department of Mathematics and Physics, The National Defense Academy, 1-10-20 Hashirimizu Yokosuka 239 (Japan)
The phonon Raman spectra of Bi{sub 2}Sr{sub 2}Ca{sub 1{minus}{ital x}}Y{sub {ital x}}Cu{sub 2}O{sub 8+{ital d}} ({ital x}=0{minus}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{ital A}{sub 1{ital g}}+1{ital B}{sub 1{ital g}}) symmetry modes that are Raman allowed within the ideal body-centered-tetragonal unit cell. A large number of extra {open_quote}{open_quote}{ital disorder}-{ital induced}{close_quote}{close_quote} phonon bands are observed in the {ital ab}-plane polarized spectra. In contrast to most previous reports, we argue that the {ital c}-axis polarized phonon band around 629 cm{sup {minus}1} is due to the O(2){sub Sr} {ital A}{sub 1{ital g}} vibration, while the exclusively {ital ab}-plane polarized band around 463 cm{sup {minus}1} is induced by the O(3){sub Bi} {ital A}{sub 1{ital g}} vibration. With increasing Y doping we find that the vibrational modes involving atoms in the CuO{sub 2} 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){sub Cu} {ital A}{sub 1{ital g}} and {ital B}{sub 1{ital g}} phonons by {approximately}40 cm{sup {minus}1}, whereas the O(2){sub Sr} {ital A}{sub 1{ital g}} phonon is found to soften by {approximately}20 cm{sup {minus}1}, when {ital x} increases from 0 to 1. The phonon frequency changes can be explained by the {open_quote}{open_quote}{ital internal} {ital pressure}{close_quote}{close_quote} induced by the decrease in the average Ca/Y ion size and an additional {open_quote}{open_quote}{ital charge}-{ital transfer}{close_quote}{close_quote} induced by the change in the Cu and Bi valences with Y doping. {copyright} {ital 1996 The American Physical Society.}
- OSTI ID:
- 283889
- Journal Information:
- Physical Review, B: Condensed Matter, Journal Name: Physical Review, B: Condensed Matter Journal Issue: 17 Vol. 53; ISSN 0163-1829; ISSN PRBMDO
- Country of Publication:
- United States
- Language:
- English
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