X-ray-absorption studies of YBa/sub 2/Cu/sub 3/O/sub 7-//sub delta/ and GdBa/sub 2/Cu/sub 3/O/sub 7-//sub delta/ superconductors

Journal Article · Thu Oct 01 00:00:00 EDT 1987 · Phys. Rev. B: Condens. Matter; (United States)

DOI:https://doi.org/10.1103/PhysRevB.36.5251· OSTI ID:6197903

Boyce, J B; Bridges, F; Claeson, T; Howland, R S; Geballe, T H

X-ray-absorption measurements of the high-T/sub c/ superconductors YBa/sub 2/Cu/sub 3/O/sub 7-//sub delta/ and GdBa/sub 2/Cu/sub 3/O/sub 7-//sub delta/ show that their near edge and extended fine structures (EXAFS) are essentially identical over the temperature range of 4.2 to 688 K. The results indicate that not only are YBa/sub 2/Cu/sub 3/O/sub 7-//sub delta/ and GdBa/sub 2/Cu/sub 3/O/sub 7-//sub delta/ very similar to each other in local bonding and electronic structure, but also remain virtually unchanged, electronically and structurally, over this wide range in temperature, from far below to well above T/sub c/. The positions of the Cu near-edge spectra for these superconductors indicate a Cu valence between that of Cu in CuO, which has a formal valence of II, and that in KCuO/sub 2/, with a formal valence of III. Our EXAFS structural results agree well with those from neutron diffraction data. Recently proposed alternate structures are shown to be inconsistent with our data. The characteristic vibration frequencies of the near-neighbor atoms show that the two-dimensional Cu: O planes and the one-dimensional Cu: O chains form the most rigid parts of the structure, and these layers are bound more weakly along the c axis via the Ba and Y planes. These oscillator frequencies are identified with specific near-neighbor pairs, and the values are consistent with those for some of the modes seen by inelastic neutron scattering as well as by infrared and Raman spectroscopy. No evidence of phonon softening is apparent in any of the phonon modes studied, providing evidence against a strong electron-phonon coupling mechanism.

• Research Organization: Xerox Palo Alto Research Center, Palo Alto, California 94304
• OSTI ID: 6197903
• Journal Information: Phys. Rev. B: Condens. Matter; (United States), Vol. 36:10
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
75 CONDENSED MATTER PHYSICS
SUPERCONDUCTIVITY AND SUPERFLUIDITY
BARIUM OXIDES
ABSORPTION SPECTRA
CRYSTAL STRUCTURE
X-RAY SPECTRA
COPPER OXIDES
GADOLINIUM OXIDES
YTTRIUM OXIDES
ELECTRONIC STRUCTURE
HIGH TEMPERATURE
LOW TEMPERATURE
MEDIUM TEMPERATURE
PHONONS
SUPERCONDUCTORS
TEMPERATURE DEPENDENCE
TRANSITION TEMPERATURE
ULTRALOW TEMPERATURE
VERY LOW TEMPERATURE
ALKALINE EARTH METAL COMPOUNDS
BARIUM COMPOUNDS
CHALCOGENIDES
COPPER COMPOUNDS
GADOLINIUM COMPOUNDS
OXIDES
OXYGEN COMPOUNDS
PHYSICAL PROPERTIES
QUASI PARTICLES
RARE EARTH COMPOUNDS
SPECTRA
THERMODYNAMIC PROPERTIES
TRANSITION ELEMENT COMPOUNDS
YTTRIUM COMPOUNDS
360204* - Ceramics
Cermets
& Refractories- Physical Properties
656100 - Condensed Matter Physics- Superconductivity