Title page for ETD etd-04132004-101822

Type of Document

Dissertation

Author

Su, Jianhua

URN

etd-04132004-101822

Title

Fabrication and Characterization of Mercurocuprate superconductors on Silver Substrates

Degree

Doctor of Philosophy

Department

Mechanical Engineering, Department of

Advisory Committee

Advisor Name	Title
Jim Zheng	Committee Member
Justin Schwartz	Committee Member
Simone Peterson Hruda	Committee Member
Steven W. Van Sciver	Committee Member

Keywords

Superconductor
Hg-1212
Hg-1223
silver substrate
film
pulsed laser deposition

Date of Defense

2004-03-15

Availability

unrestricted

Abstract

This research studies the fabrication and characterization of doped Hg-1212 and Hg-1223 superconductors grown on silver substrates using dip-coating and pulsed laser deposition (PLD) techniques. The main goal of this thesis is to optimize the synthesis parameters, understand the growth mechanism, and investigate the influences of the silver interface on the microstructure and superconducting properties of doped Hg-1212/Hg-1223 films.
A process methodology is firstly developed to fabricate Pb and Re doped Hg-1223 thick films using the dip-coating method. The phase content, microstructure, irreversibility behavior, and critical current density of the dip-coated films are investigated. The Re-doped films showed the dominant phase of (Hg,Re)-1223, characterized by an onset critical temperature (Tc) of 131 K. The transport critical current (Ic) is measured at 4.2 K, self-field and the corresponding transport critical current density (Jc) is ~ 3000 A/cm2. The limitations to the critical currents are discussed in detail.
The comparison of Pb and Re doping effects on microstructure and irreversibility are studied. The Pb-doped films have much larger colony size, whereas the Re-doping significantly decreases the structural anisotropy gamma, which consequently increases the vortex line stiffness and enhances flux pinning.
(Hg,Re)-1212 thin films are also synthesized on silver substrates using the PLD method. The films exhibit c-axis orientation but without in-plane texture, which mainly results from the polycrystalline structure of silver. Although the average transport Jc (4.2 K, self-field) of the PLD thin films, ~ 30,000 A/cm2, is about one order of magnitude higher than that of the dip-coated thick films, it is about two orders of magnitude lower than its magnetization Jc. The lower Jc value is explained in terms of grain connectivity, film texture, and defects in the films.
The studies of the laser deposited (Hg,Re)-1212 film/silver interface microstructure show that the substrate surface morphology significantly affect the film nucleation and growth. The (Hg,Re)-1212 film growth mechanism is investigated by Atomic Force Microscopy (AFM). A two-stage growth mode is also proposed.

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