Phase-selective route to high T sub c superconducting Tl sub 2 Ba sub 2 Ca sub n minus 1 Cu sub n O sub 2 n +4 films: Combined metalorganic chemical vapor deposition using an improved barium precursor and stoichiometry-controlled thallium vapor diffusion
- Science and Technology Center for Superconductivity and the Materials Research Center, Northwestern University, Evanston, Illinois 60208 (US)
Films of the Tl{sub 2}Ba{sub 2}Ca{sub {ital n}{minus}1}Cu{sub {ital n}}O{sub 2{ital n}+4} high {ital T}{sub {ital c}} superconductors ({ital n}=2 or 3) can be prepared with a high degree of phase selectivity using a combination of metalorganic chemical vapor deposition (MOCVD) and vapor diffusion. Ba-Ca-Cu-O films are first prepared by MOCVD using the volatile metalorganic precursors Ba(hexafluoroacetyl- acetonate){sub 2}(tetraglyme), Ca(dipivaloylmethanate){sub 2}, and Cu(acetylacetonate){sub 2}. The second-generation'' barium precursor exhibits significantly improved thermal stability and volatility over previously used compounds. Thallium is then incorporated into these films by vapor diffusion using a Tl-Ba-Ca-Cu oxide mixture of controlled composition as the source of volatile thallium oxides. Phase control is achieved by a combination of improved stoichiometry of the deposited film, a result of the new Ba source, and annealing with the appropriate oxide mixture. The resultant films consist predominantly of the Tl{sub 2}Ba{sub 2}Ca{sub 2}Cu{sub 3}O{sub {ital x}} or Tl{sub 2}Ba{sub 2}CaCu{sub 2}O{sub {ital x}} phase, each having preferential orientation of the crystallite Cu-O planes parallel to the substrate surface. The films exhibit superconducting onset temperatures of {similar to}115 K with zero resistance by 93 and 85 K, respectively. Critical current densities for a number of films, estimated by the Bean method, are in the range 10{sup 4}--10{sup 5} A/cm{sup 2} at 5 K.
- OSTI ID:
- 6258448
- Journal Information:
- Applied Physics Letters; (USA), Journal Name: Applied Physics Letters; (USA) Vol. 58:2; ISSN APPLA; ISSN 0003-6951
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
360202 -- Ceramics
Cermets
& Refractories-- Structure & Phase Studies
360204* -- Ceramics
Cermets
& Refractories-- Physical Properties
ALKALINE EARTH METAL COMPOUNDS
BARIUM COMPOUNDS
BARIUM OXIDES
CALCIUM COMPOUNDS
CALCIUM OXIDES
CHALCOGENIDES
CHEMICAL COATING
CHEMICAL VAPOR DEPOSITION
COPPER COMPOUNDS
COPPER OXIDES
DEPOSITION
DIFFUSION
ELECTRIC CONDUCTIVITY
ELECTRICAL PROPERTIES
FILMS
HIGH-TC SUPERCONDUCTORS
ORGANIC COMPOUNDS
ORGANOMETALLIC COMPOUNDS
OXIDES
OXYGEN COMPOUNDS
PHYSICAL PROPERTIES
STOICHIOMETRY
SUPERCONDUCTING FILMS
SUPERCONDUCTIVITY
SUPERCONDUCTORS
SURFACE COATING
THALLIUM COMPOUNDS
THALLIUM OXIDES
TRANSITION ELEMENT COMPOUNDS