Modeling oxygen isotope shifts and line-broadening effects of the 502-cm sup minus 1 Raman mode of YBa sub 2 Cu sub 3 O sub 7 minus x
- Department of Physics, Simon Fraser University, Burnaby, British Columbia, Canada V5A1S6 (CA)
- Department of Physics, University of Alberta, Edmonton, Alberta (Canada)
Raman scattering experiments have been carried out on sintered pellets of YBa{sub 2}Cu{sub 3}{sup 18}O{sub 7{minus}{ital x}} and YBa{sub 2}Cu{sub 3}{sup 16}O{sub 7{minus}{ital x}}, obtained both by gas exchange and by growth with substituted oxides. The frequencies of the modes at 340, 435, and 500 cm{sup {minus}1}, which involve motion of the oxygen atoms and which shift significantly upon oxygen-isotope substitution, have been measured for several sets of samples. The 500-cm{sup {minus}1} line of the {sup 18}O samples is observed to be isotope shifted to a lesser degree than the 340- and 435-cm{sup {minus}1} phonons, and is significantly broadened. To model the observed behavior of the 500-cm{sup {minus}1} mode, a linear chain of O and Cu atoms is used to compute first-order {ital k}{congruent}0 Raman cross sections from 400 to 600 cm{sup {minus}1}. Disorder is introduced by randomly substituting {sup 18}O atoms for {sup 16}O atoms at positions in the chain corresponding to O(4) in the YBa{sub 2}Cu{sub 3}O{sub 7} lattice. Comparison of computed and experimental spectra suggest that the maximum linewidth in the 500-cm{sup {minus}1} peak occurs for a relative {sup 18}O concentration ({sup 18}O(4))/({sup 16}O(4)) between 24% and 36%. In addition, the 502-cm{sup {minus}1} peak position is found to depend nonlinearly on the relative {sup 18}O concentration. The implications of these results are discussed in terms of the currently accepted models for oxygen-isotope exchange in YBa{sub 2}Cu{sub 3}O{sub 7}
- OSTI ID:
- 5885839
- Journal Information:
- Physical Review, B: Condensed Matter; (USA), Journal Name: Physical Review, B: Condensed Matter; (USA) Vol. 43:4; ISSN PRBMD; ISSN 0163-1829
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
360204* -- Ceramics
Cermets
& Refractories-- Physical Properties
ALKALINE EARTH METAL COMPOUNDS
BARIUM COMPOUNDS
BARIUM OXIDES
CHALCOGENIDES
COPPER COMPOUNDS
COPPER OXIDES
HIGH-TC SUPERCONDUCTORS
ISOTOPES
LATTICE VIBRATIONS
OXIDES
OXYGEN COMPOUNDS
RAMAN SPECTRA
SPECTRA
SPECTRAL SHIFT
STRUCTURAL MODELS
SUPERCONDUCTORS
TRANSITION ELEMENT COMPOUNDS
YTTRIUM COMPOUNDS
YTTRIUM OXIDES