Valence fluctuations in the YBa/sub 2/Cu/sub 3/O/sub 7-x/ superconductor
Journal Article
·
· Inorg. Chem.; (United States)
The electronic structures of copper oxide clusters representing the new superconducting materials YBa/sub 2/Cu/sub 3/O/sub 7-x/ and La/sub 2-x/M/sub x/CuO/sub 4/ (M = Ba, Sr) have been calculated by semiempirical molecular orbital methods. For YBa/sub 2/cu/sub 3/O/sub 7-x/ the orbital energies indicate that the Cu's located in the CuO/sub 3/ chains are primarily trivalent, while the Cu's in the CuO/sub 2/ dimpled planes are primarily divalent. The effects of the oxygen breathing mode on the charge distributions and orbital energies are investigated for different electronic configurations. The results indicate that the oxygen breathing modes can cause significant charge fluctuations on the Cu's in the clusters. For certain electron configurations, a double-well type potential may exist for oxygen movement between Cu's in the chains. This may cause an instability at oxygen stoichiometries near 6.75 and result in a phase separation. A phase diagram is proposed for YBa/sub 2/Cu/sub 3/O/sub 7-x/, which suggests that the 94 K high-temperature superconducting phase is characterized by an oxygen stoichiometry near 7.0. The phase diagram predicts that a plateau should exist for T/sub c/ in the region x = 0.0-0.25 and that in this region two phases are present which are characterized by compositions having oxygen stoichiometries either in the range 6.5-6.75 or close to 7.0. 24 refs., 5 figs., 4 tabs.
- Research Organization:
- Argonne National Lab., IL (USA)
- DOE Contract Number:
- W-31109-ENG-38
- OSTI ID:
- 5709587
- Journal Information:
- Inorg. Chem.; (United States), Journal Name: Inorg. Chem.; (United States) Vol. 27:8; ISSN INOCA
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
36 MATERIALS SCIENCE
360204* -- Ceramics
Cermets
& Refractories-- Physical Properties
ALKALINE EARTH METAL COMPOUNDS
BARIUM COMPOUNDS
COPPER COMPOUNDS
DATA
ELECTRIC CONDUCTIVITY
ELECTRICAL PROPERTIES
ELECTRONIC STRUCTURE
EXPERIMENTAL DATA
INFORMATION
LANTHANUM COMPOUNDS
NUMERICAL DATA
OXYGEN COMPOUNDS
PHYSICAL PROPERTIES
RARE EARTH COMPOUNDS
STRONTIUM COMPOUNDS
SUPERCONDUCTIVITY
TRANSITION ELEMENT COMPOUNDS
YTTRIUM COMPOUNDS
360204* -- Ceramics
Cermets
& Refractories-- Physical Properties
ALKALINE EARTH METAL COMPOUNDS
BARIUM COMPOUNDS
COPPER COMPOUNDS
DATA
ELECTRIC CONDUCTIVITY
ELECTRICAL PROPERTIES
ELECTRONIC STRUCTURE
EXPERIMENTAL DATA
INFORMATION
LANTHANUM COMPOUNDS
NUMERICAL DATA
OXYGEN COMPOUNDS
PHYSICAL PROPERTIES
RARE EARTH COMPOUNDS
STRONTIUM COMPOUNDS
SUPERCONDUCTIVITY
TRANSITION ELEMENT COMPOUNDS
YTTRIUM COMPOUNDS