Discussion of x-ray-absorption near-edge structure: Application to Cu in the high-Tc superconductors La1.8Sr0.2CuO4 and YBa2Cu3O7
Farrel W. Lytle, Robert B. Greegor, Armand J. Panson
DOI 10.1103/PhysRevB.37.1550 · Physical Review B
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Abstract
A model for interpretation of x-ray-absorption near-edge structure (XANES) in transition-metal compounds is presented based on λ=R backscattering from nearby atoms. The model allows identification of XANES features with specific lattice distances. Reference to spectra from model compounds of simple structure allows construction of a calibration curve of ΔE vs R from 1.5 to 3.5 Å with an accuracy of ±0.1 Å. Specific multiscattering paths were also identified in MO4 molecules. The Cu K spectra of La1.8Sr0.2CuO4 and YBa2Cu3O7 were examined using the model. A unique feature in the spectra was identified with a (Cu—O) bond distance of ∼2.6 Å and confirmed with analysis of the extended x-ray-absorption fine structure. This distance is evidence of antisite disorder in these compounds with 0.2–0.3 mole fraction of Cu substituting into the Y or La site. We also find evidence of simultaneous Cu2+ and Cu3+ valences. The structural implications of these findings are discussed.
Source-reported materials — not catalogue approval
| Formula | Reported Tc (K) | Pressure (GPa) | Type |
|---|---|---|---|
| YBa2Cu3O7 Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula. | 94 | Pressure not reported | midpoint |
| La1.8Sr0.2CuO4 Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula. | 36.5 | Pressure not reported | midpoint |
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