Zhonghui Wang

Publication Date

1994

Document Type

Dissertation/Thesis

First Advisor

Dąbrowski, Bogdan

Degree Name

M.S. (Master of Science)

Legacy Department

Department of Physics

LCSH

High temperature superconductors; Copper oxide superconductors

Abstract

In this thesis, the synthesis, structure and properties of Ca-substituted La[sub 2]CuO[sub 4]-based single layer high-T[sub c] superconducting copper oxides will be presented. Homogeneous single phase samples of La[sub 2-x]Ca[sub x]CuO[sub 4] and La[sub 1.85-y]Nd[sub y]Ca[sub 0.15]CuO[sub 4] were synthesized through nitride method and high oxygen pressure technique. The calcium solid-solubility limit in La[sub 2-x]Ca[sub x]CuO[sub 4] has been extended from x~0.10 for air-synthesized material to x=0.2 using synthesis at an oxygen pressure of 600 atm and lllO °C . Under the same synthesis conditions, the neodymium solid-solution in La[sub 1.85-y]Nd[sub y]Ca[sub 0.15]CuO[sub 4] has been extended to y=1.0. The tetragonal-to-orthorhombic transition for Ca-substituted materials occurs at higher temperatures, or larger doping levels, than for the isostructural Srsubstituted material. The superconducting transition temperature increases with doping to 34K at x=0.15 and is suppressed for x>0.15, similar to the Sr-substituted material. Comparison of structures and superconducting properties for Ca- and Sr-substituted materials along with Nd-doped compounds indicates that (1) both orthorhombic and tetragonal structures are superconducting; (2) at a fixed doping level, the optimum superconducting properties (the highest T[sub c]) are found for flat and square CuO[sub 2] planes; and (3) T[sub c] is suppressed by the distortion of the CuO[sub 2] planes or by overdoping, which results in a maximum of T[sub c] found at x=0.15.

Comments

Includes bibliographical references (pages [80]-84).

Extent

ix, 84 pages

Language

eng

Publisher

Northern Illinois University

Rights Statement

In Copyright

Rights Statement 2

NIU theses are protected by copyright. They may be viewed from Huskie Commons for any purpose, but reproduction or distribution in any format is prohibited without the written permission of the authors.

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