KUKU

KU ScholarWorks

  • myKU
  • Email
  • Enroll & Pay
  • KU Directory
    • Login
    View Item 
    •   KU ScholarWorks
    • Dissertations and Theses
    • Dissertations
    • View Item
    •   KU ScholarWorks
    • Dissertations and Theses
    • Dissertations
    • View Item
    JavaScript is disabled for your browser. Some features of this site may not work without it.

    Mechanism of Cation Exchange Process for Epitaxy of Superconducting HgBa2CaCu2O6 Films and Passive Microwave Devices

    Thumbnail
    View/Open
    umi-ku-2301_1.pdf (2.150Mb)
    Issue Date
    2007-12-17
    Author
    Zhao, Hua
    Publisher
    University of Kansas
    Format
    129 pages
    Type
    Dissertation
    Degree Level
    PH.D.
    Discipline
    Physics & Astronomy
    Rights
    This item is protected by copyright and unless otherwise specified the copyright of this thesis/dissertation is held by the author.
    Metadata
    Show full item record
    Abstract
    The record high superconducting transition temperature (Tc) in Hg-based High temperature superconducting (HTS) cuprates make them very promising for both fundamental physics and practical applications. The high volatile nature of Hg presents a major challenge in epitaxy of high quality Hg-based HTS films. In a novel cation exchange process developed by our group recently, epitaxial HgBa2CaCu2O6+δ (Hg-1212) films can be obtained by diffusing volatile Tl cations out of, and simultaneously diffusing Hg cations into, the lattice of epitaxial Tl2Ba2CaCu2O8 (Tl-2212) or TlBa2CaCu2O7 (Tl-1212) precursor films. Aiming at the remained issues in understanding the mechanism of the cation exchange (CE) process, this thesis work has studied the reversibility of CE. We have found that the CE process is completely reversible between Hg-1212 and Tl-2212, confirming further the thermal perturbation diffusion model. One of the experimental works unveiled that the conversion from Hg-1212 to Tl-2212 involves two steps: conversion from Hg-1212 to Tl-1212 via CE followed by Tl intercalation to form double Tl-O plans in each unit cell. Two improvements have been made in raising the quality of the Hg-1212 films. First, by successfully introducing micro-channels in Tl-1212 precursor with reversible CE, purer HTS Hg-1212 thin films have been obtained. Secondly, by pinning lattice with nonvolatile Re atoms, the surface morphology of Hg-1212 films have been improved. In addition to making the high quality Hg-1212 films, we have fabricated a two-pole X-band Hg-1212 microstrip filter and then investigated its nonlinearity by measuring the third-order intermodulation (IM3) signals since the major limitation for real application still comes from the nonlinearity. By a comparison between different structural materials of Hg-1212, Tl-2212 and YBa2Cu3O7 (YBCO), the third-order intercept (IP3) of the Hg-1212 filter is consistently higher than that in the YBCO and Tl-2212. The surprising similarity in the curves of dc critical current density Jc and the rf JIP3 derived from the IP3 against reduced temperature suggests that the magnetic vortex depinning in HTS materials dominates the microwave nonlinearity at elevated temperatures. These encouraging results have marked Hg-1212 out as a promising alternative material for passive microwave devices at above 77 K operating temperature.
    URI
    http://hdl.handle.net/1808/4117
    Collections
    • Dissertations [4475]
    • Physics & Astronomy Dissertations and Theses [121]

    Items in KU ScholarWorks are protected by copyright, with all rights reserved, unless otherwise indicated.


    We want to hear from you! Please share your stories about how Open Access to this item benefits YOU.


    Contact KU ScholarWorks
    785-864-8983
    KU Libraries
    1425 Jayhawk Blvd
    Lawrence, KS 66045
    785-864-8983

    KU Libraries
    1425 Jayhawk Blvd
    Lawrence, KS 66045
    Image Credits
     

     

    Browse

    All of KU ScholarWorksCommunities & CollectionsThis Collection

    My Account

    LoginRegister

    Statistics

    View Usage Statistics

    Contact KU ScholarWorks
    785-864-8983
    KU Libraries
    1425 Jayhawk Blvd
    Lawrence, KS 66045
    785-864-8983

    KU Libraries
    1425 Jayhawk Blvd
    Lawrence, KS 66045
    Image Credits
     

     

    The University of Kansas
      Contact KU ScholarWorks
    Lawrence, KS | Maps
     
    • Academics
    • Admission
    • Alumni
    • Athletics
    • Campuses
    • Giving
    • Jobs

    The University of Kansas prohibits discrimination on the basis of race, color, ethnicity, religion, sex, national origin, age, ancestry, disability, status as a veteran, sexual orientation, marital status, parental status, gender identity, gender expression and genetic information in the University’s programs and activities. The following person has been designated to handle inquiries regarding the non-discrimination policies: Director of the Office of Institutional Opportunity and Access, IOA@ku.edu, 1246 W. Campus Road, Room 153A, Lawrence, KS, 66045, (785)864-6414, 711 TTY.

     Contact KU
    Lawrence, KS | Maps