XPS study of the dependence on stoichiometry and interaction with water of copper and oxygen valence states in the YBa sub 2 Cu sub 3 O sub 7-x compound

Journal Article · Tue Aug 01 00:00:00 EDT 1989 · Journal of Solid State Chemistry; (USA)

DOI:https://doi.org/10.1016/0022-4596(89)90011-X· OSTI ID:6884859

Salvador, P; Fierro, J L.G. ^[1]; Amador, J; Cascales, C; Rasines, I ^[2]

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1. Instituto de Catalisis y Petroleoquimica, Madrid (Spain)
2. Instituto de Ciencia de Materiales, Madrid (Spain)

In order to elucidate the valence states of both copper and oxygen in YBa{sub 2}Cu{sub 3}O{sub 7-x} as a function of the oxygen content, their O{sub 1s} and Cu{sub 2p} core-level X-ray photoelectron spectra were studied at room temperature for 0.9 {ge} {times} {ge} 0.1. No evidence of the Cu{sup 3+} (i.e., 3d{sup 8}) configuration was found for the ground state of a superconducting sample (x {approx} 0.1). Rather, the ground state for this composition can be described as a mixture of two configurations: mainly 3d{sup 9}KL (i.e., Cu{sup 2+}-O{sup {minus}} hybridization), where K represents an electron of the conduction band and L stands for a hole in the oxygen bonded to a virtually divalent copper, and some 3d{sup 10} (i.e., Cu{sup +}). The amount of monovalent copper was found to increase with x, as oxygen (O{sup {minus}} species) from Cu{sub 1}-O chains parallel to the crystallographic b axis leave the lattice and electrons are transferred to the adjacent Cu{sup 2+} ions. Simultaneously, the concentration of holes delocalized in the oxygen valence band decreases, the Fermi level goes upward, and the material's behavior at room temperature changes from quasi-metallic (degenerated p-type semiconductor) to p-type semiconducting. For x {approx} 0.9 the amount of Cu{sup +} predominates over that of Cu{sup 2+}. The high reactivity of the superconducting material with water is evidenced by the special characteristics of its O{sub 1s} core-level spectrum. The presence of OH{sup {minus}} ions indicates dissociative adsorption of water molecules from the air. The XPS signal due to OH{sup {minus}} species is higher than that of the O{sup 2{minus}} lattice ions, even when the sample was preserved from exposure to air. Moreover, when the superconducting sample was contaminated by prolonged exposition to air, the O{sup 2{minus}} signal could hardly be observed.

• OSTI ID: 6884859
• Journal Information: Journal of Solid State Chemistry; (USA), Vol. 81:2; ISSN 0022-4596
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
SUPERCONDUCTING COMPOSITES
PHOTOELECTRON SPECTROSCOPY
BARIUM
COPPER
DATA ANALYSIS
EXPERIMENTAL DATA
MEASURING INSTRUMENTS
MEASURING METHODS
OXYGEN
VALENCE
WATER
YTTRIUM
ALKALINE EARTH METALS
COMPOSITE MATERIALS
DATA
ELECTRON SPECTROSCOPY
ELEMENTS
HYDROGEN COMPOUNDS
INFORMATION
MATERIALS
METALS
NONMETALS
NUMERICAL DATA
OXYGEN COMPOUNDS
SPECTROSCOPY
TRANSITION ELEMENTS
360000* - Materials
360600 - Other Materials
360602 - Other Materials- Structure & Phase Studies