Raman-scattering study of high- Tc films of the ordered defect structure YBa sub 2 Cu sub 4 O sub 8 minus. delta
- Department of Physics, The Ohio State University, Columbus, OH (USA)
We report Raman-scattering measurements on superconducting YBa{sub 2}Cu{sub 4}O{sub 8{minus}{delta}} (1:2:4) films ({ital T}{sub {ital c}}=80 K) grown on (110) and (001) surfaces of SrTiO{sub 3}. In contrast to YBa{sub 2}Cu{sub 3}O{sub 7{minus}{delta}}, phonons associated with CuO chain atoms are Raman active in YBa{sub 2}Cu{sub 4}O{sub 8{minus}{delta}}. Four Raman-active phonons are identified with the CuO chains in addition to five phonons corresponding to the five well-studied {ital A}{sub {ital g}} modes in YBa{sub 2}Cu{sub 3}O{sub 7{minus}{delta}}. The 337-cm{sup {minus}1} mode associated with out-of-phase vibrations of the CuO{sub 2} planar oxygens softens by about 2 cm{sup {minus}1} below {Tc} just as is observed in YBa{sub 2}Cu{sub 3}O{sub 7{minus}{delta}} films. A new result is that the phonon associated with in-phase vibrations of the CuO{sub 2} planar oxygens at 435 cm{sup {minus}1} hardens about 2 cm{sup {minus}1} below {Tc}. This nonthermal hardening has also been reported very recently in YBa{sub 2}Cu{sub 3}O{sub 7{minus}{delta}}. Interpreted with a recent theory for phonon energies that includes coupling to superconducting electrons, the hardening and softening of phonons with relatively close frequencies (337 and 435 cm{sup {minus}1}) indicates that the energy gap is 2{Delta}=280 cm{sup {minus}1}{plus minus}10% so 2{Delta}/{ital kT}{sub {ital c}}=5{plus minus}0.5. The 150-cm{sup {minus}1} mode associated with CuO{sub 2} planar Cu motion and the four new chain modes behave normally with temperature. We attempt to deplete oxygen from some of the YBa{sub 2}Cu{sub 4}O{sub 8{minus}{delta}} films by annealing in Ar up to 700 {degree}C. The films change crystal structure to YBa{sub 2}Cu{sub 3}O{sub 7{minus}{delta}} before significant amounts of oxygen are removed.
- OSTI ID:
- 5942381
- Journal Information:
- Physical Review, B: Condensed Matter; (USA), Journal Name: Physical Review, B: Condensed Matter; (USA) Journal Issue: 16 Vol. 42:16; ISSN PRBMD; ISSN 0163-1829
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
360202* -- Ceramics
Cermets
& Refractories-- Structure & Phase Studies
ALKALINE EARTH METAL COMPOUNDS
BARIUM COMPOUNDS
BARIUM OXIDES
CHALCOGENIDES
COPPER COMPOUNDS
COPPER OXIDES
CRYSTAL DEFECTS
CRYSTAL STRUCTURE
ENERGY GAP
FILMS
HIGH-TC SUPERCONDUCTORS
OXIDES
OXYGEN COMPOUNDS
PHONONS
QUASI PARTICLES
RAMAN SPECTRA
SPECTRA
SUPERCONDUCTING FILMS
SUPERCONDUCTORS
TEMPERATURE DEPENDENCE
TRANSITION ELEMENT COMPOUNDS
YTTRIUM COMPOUNDS
YTTRIUM OXIDES