Oxygen-stoichiometry dependence of the electronic structure of YBa/sub 2/Cu/sub 3/O/sub 7/. sqrt. /sub delta/ with delta(0<0. 7): Possibility of a highly correlated mixed-valent state
YBa/sub 2/Cu/sub 3/O/sub 7/..sqrt../sub delta/ is obtained over a wide range of stoichiometry (0<0.7) by proper thermal treatment in O/sub 2/. Samples are carefully characterized by x-ray powder diffraction and thermogravimetry. Their superconducting properties are investigated mainly by measuring the susceptibility (chi/sub dc/) in low fields (Meissner effect). The main part of this paper is devoted to an x-ray photoemission spectroscopy study of core levels (mainly O 1s and Cu 2p) with the aim of elucidating the change of the electronic structure on passing from the semiconducting (delta>0.5) to the superconducting metallic state (deltaapprox. =0). On the basis of our experimental results, we argue that the superconducting state is obtained from a mixture of configurations chemically bond3d/sup 9/> and chemically bond3d/sup 9/Lk> in the ground state of copper (L stands for a hole in the O-Cu ligand and k for a conduction electron). We find that the ratio of the chemically bond3d/sup 9/Lk> configuration is directly related to the magnitude of T/sub c/. The charge-neutrality rule is approximatively followed, provided that the Cu/sup 3 +/ state is identified as a chemically bond3d/sup 9/Lk> configuration. We discuss also the presence of the 3d/sup 10/ configuration (i.e., Cu/sup +/) in the ground state. A possible consequence of these Cu/sup +/ would be to increase the number of formal Cu/sup 3 +/ (here 3d/sup 9/Lk)
- Research Organization:
- Laboratoire de Physique des Solides, Universite de Nancy I, Boi-italic-circumflexte Postale 239, 54506 Vandoeuvre-les-Nancy, Cedex, France
- OSTI ID:
- 5220975
- Journal Information:
- Phys. Rev. B: Condens. Matter; (United States), Vol. 37:13
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
75 CONDENSED MATTER PHYSICS
SUPERCONDUCTIVITY AND SUPERFLUIDITY
BARIUM OXIDES
ELECTRONIC STRUCTURE
COPPER OXIDES
YTTRIUM OXIDES
COPPER
GROUND STATES
MAGNETIC SUSCEPTIBILITY
OXYGEN
PHOTOELECTRON SPECTROSCOPY
POWDERS
STOICHIOMETRY
SUPERCONDUCTORS
THERMAL GRAVIMETRIC ANALYSIS
X RADIATION
X-RAY DIFFRACTION
ALKALINE EARTH METAL COMPOUNDS
BARIUM COMPOUNDS
CHALCOGENIDES
CHEMICAL ANALYSIS
COHERENT SCATTERING
COPPER COMPOUNDS
DIFFRACTION
ELECTROMAGNETIC RADIATION
ELECTRON SPECTROSCOPY
ELEMENTS
ENERGY LEVELS
GRAVIMETRIC ANALYSIS
IONIZING RADIATIONS
MAGNETIC PROPERTIES
METALS
NONMETALS
OXIDES
OXYGEN COMPOUNDS
PHYSICAL PROPERTIES
QUANTITATIVE CHEMICAL ANALYSIS
RADIATIONS
SCATTERING
SPECTROSCOPY
THERMAL ANALYSIS
TRANSITION ELEMENT COMPOUNDS
TRANSITION ELEMENTS
YTTRIUM COMPOUNDS
360204* - Ceramics
Cermets
& Refractories- Physical Properties
656100 - Condensed Matter Physics- Superconductivity