Crystal structures of Hg-Sr-Ca-Cu-O superconductors with enhanced flux pinning: Hg{sub 1{minus}{ital x}}Re{sub {ital x}}Sr{sub 2}Ca{sub {ital n}{minus}1}Cu{sub {ital n}}O{sub 2{ital n}+2+{delta}} ({ital n}=2,3; {ital x}{approx_equal}0.2{endash}0.25)
- Materials Science Division and Science and Technology Center for Superconductivity, Argonne National Laboratory, Argonne, Illinois 60439 (United States)
- Institute for Chemical Research, Kyoto University, Uji, Kyoto-fu 611 (Japan)
- Department of Applied Chemistry, University of Tokyo, Bunkyo-ku, Tokyo 113 (Japan)
The crystal structures of Hg{sub 1{minus}{ital x}}Re{sub {ital x}}Sr{sub 2}Ca{sub {ital n}{minus}1}Cu{sub {ital n}}O{sub 2{ital n}+2+{delta}} ({ital n}=2,3; {ital x}{approx_equal}0.2{endash}0.25) (synthesized at high pressure) were refined using neutron powder diffraction and the Rietveld analysis technique. Superconductivity was not observed in the as-prepared {ital n}=2 compound while a {ital T}{sub {ital c}} of 107 K was measured for the {ital n}=3 sample. Postannealing in evacuated tubes results in creating superconductivity in the {ital n}=2 sample with a {ital T}{sub {ital c}} of 90 K and in enhancing it up to 120 K in the {ital n}=3 sample. The structures of both as-prepared and vacuum-annealed samples were investigated. In both compounds, Re substitutes at the Hg site. Four additional oxygen atoms are incorporated into the (Hg, Re) plane for each Re atom providing an octahedral environment for Re. Thus, for a composition of {ital x}{approx_equal}0.25, all available oxygen sites in the (Hg, Re) plane are filled. These oxygen atoms shift off the ideal position to form bonds of appropriate length (1.88 A) with Re. Vacuum-annealed samples show oxygen deficiency in the (Hg, Re) layer suggesting that the actual Re content is below the solubility limit. The enhanced flux pinning for these chemically substituted compounds could result from the observed shortening of the blocking layer by 0.8{endash}0.9 A and/or from increased interlayer coupling through the blocking layer by possible improvement in electrical conduction. Additionally, Hg-rich regions and/or planar defects (faults) separating domains where the Re-O{sub 6} octahedra are ordered in different ways could act as pinning centers. {copyright} {ital 1996 The American Physical Society.}
- DOE Contract Number:
- W-31-109-ENG-38
- OSTI ID:
- 284401
- Journal Information:
- Physical Review, B: Condensed Matter, Vol. 53, Issue 21; Other Information: PBD: Jun 1996
- Country of Publication:
- United States
- Language:
- English
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