Temperature dependence of the local structure of YBa/sub 2/Cu/sub 3/O/sub 7-//sub delta/ with varying oxygen content: An x-ray-absorption study

Journal Article · Sat Apr 01 00:00:00 EST 1989 · Phys. Rev. B: Condens. Matter; (United States)

DOI:https://doi.org/10.1103/PhysRevB.39.6555· OSTI ID:6408453

Boyce, J B; Bridges, F; Claeson, T; Nygren, M

The local structure of YBa/sub 2/Cu/sub 3/O/sub y/ determined using x-ray-absorption fine structure (XAFS) agrees well with the long-range order given by diffraction results for both oxygen-rich, orthorhombic (y = 6.98 and 6.87) and oxygen-deficient, tetragonal (y = 6.15) compounds. The x-ray-absorption near-edge structure supports the conclusion that, as y = 7 goes to y = 6, the O is removed from the chains and the chain Cu atoms, Cu(1), becomes monovalent with a linear O-Cu-O structural configuration and a 3d/sup 10/ electronic configuration, as in Cu/sub 2/O. For the XAFS analysis, structural standards were determined, and these standards worked well not only for the Cu first-neighbor O environment but also for the Cu second-neighbor metal-atom environment out to 4 A. A detailed multipeak analysis reproduced the XAFS spectra well and yielded structural parameters that agree with diffraction. The temperature dependence of the structural parameters shows only a smooth variation, with no significant anomalies. The Cu-X distances have a negligible to a small positive change with temperature, consistent with the lattice expansion. The exception is the Cu-Ba distances which change substantially; the Cu(1)-Ba distance increases and the Cu(2)-Ba distance decreases. This indicates that the Ba moves away from the Cu(1)-O chains and toward the Cu(2)-O planes with increasing temperature and that anharmonicity plays a role. This motion is larger for the oxygen-depleted compound than for the fully oxygenated material. The in-plane Cu-O first-neighbor vibrations exhibit no significant softening with temperature.

• Research Organization: Xerox Palo Alto Research Center, Palo Alto, California 94304
• OSTI ID: 6408453
• Journal Information: Phys. Rev. B: Condens. Matter; (United States), Vol. 39:10
• Country of Publication: United States
• Language: English

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ABSORPTION SPECTROSCOPY
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