Chromium clustering and ordering in Hg{sub 1{minus}{ital x}}Cr{sub {ital x}}Sr{sub 2}CuO{sub 4+{delta}}
- Materials Science Division and Science and Technology Center for Superconductivity, Argonne National Laboratory, Argonne, Illinois 60439 (United States)
- Department of Materials Science and Engineering and Science and Technology Center for Superconductivity, Northwestern University, Evanston, Illinois 60208 (United States)
- Physics Department, Northern Illinois University, DeKalb, Illinois 60115 (United States)
Solid-solution compounds where Cr, Re, and other metals are substituted for Hg in Hg-Ca-Ba-Cu-O superconductors have been reported to exhibit enhanced flux-pinning behavior. We have determined the structural modifications resulting from the incorporation of Cr in Hg{sub 1{minus}{ital x}}Cr{sub {ital x}}Sr{sub 2}CuO{sub 4+{delta}} (for {ital x}{approx}0.4) using neutron powder diffraction, electron diffraction, and lattice imaging. Cr substitutes at the Hg site, but is displaced to allow tetrahedral coordination by oxygen atoms. Additional oxygen is incorporated to provide four oxygen atom neighbors for each Cr atom. These CrO{sub 4} units cluster to form a supercell of approximate dimensions 5{ital a}{times}5{ital a}{times}2{ital c} in which Cr-rich and Hg-rich regions alternate in all three crystallographic directions. Because the Cu-O apical bond associated with the CrO{sub 4} unit is lengthened to 3.13 A, the superconducting planes are best viewed as consisting of CuO{sub 5} pyramids, oriented up or down as dictated by the supercell ordering, rather than CuO{sub 6} octahedra. Local structural constraints associated with individual Cr sites require that considerable disorder is present, even in the supercell. Extended defects in this supercell (e.g., columns of CuO{sub 6} octahedra associated with Hg-rich regions) may contribute to the enhanced flux pinning.
- DOE Contract Number:
- W-31-109-ENG-38
- OSTI ID:
- 132878
- Journal Information:
- Physical Review, B: Condensed Matter, Vol. 52, Issue 21; Other Information: PBD: 1 Dec 1995
- Country of Publication:
- United States
- Language:
- English
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