Doctoral Dissertations

Jen-Ho Kuo

Abstract

"Undoped LaMnO₃, Sr-doped LaMnO₃ and Mg-doped LaMnO₃ showed reversible oxidation-reduction behavior. These perovskites can be excess, stoichiometric or deficient in oxygen content depending on the specific conditions. Under very reducing conditions these oxides will decompose into new phases. Phase stabilities for these oxides were determined. The results showed that both Sr and Mg doping caused the LaMnO₃ to dissociate at higher oxygen activities than for undoped LaMnO₃.

Defect models were proposed to interpret the TG results, in which metal vacancies are assumed for the oxygen excess condition and oxygen vacancies are assumed for the oxygen deficient condition. Thermodynamic properties were calculated which supported the model. Results for both dc and ac electrical conductivities showed p-type behavior. The Sr dopant enhanced the conductivity while Mg dopant lowered the conductivity.

The measured Seebeck coefficients confirmed that the conduction was due to holes. The small polaron hopping model was used to interpret the electrical and Seebeck data. Calculations of the carrier concentrations, activation energies and mobilities were also performed. The results suggested that the electrical conductivity for these perovskites was dominated by the mobility rather than by the carrier concentration"--Abstract, page ii.

Advisor(s)

Anderson, H. U. (Harlan U.)

Committee Member(s)

Moore, Robert E., 1930-2003
Ownby, P. D.
Sparlin, Don M.
Tang, Min-Ming

Department(s)

Materials Science and Engineering

Degree Name

Ph. D. in Ceramic Engineering

Publisher

University of Missouri--Rolla

Publication Date

Spring 1987

Pagination

xi, 139 pages

Note about bibliography

Includes bibliographical references (pages 124-129).

Rights

© 1987 Jen-Ho Kuo, All rights reserved.

Document Type

Dissertation - Open Access

File Type

text

Language

English

Thesis Number

T 5521

Print OCLC #

17499801

Electronic OCLC #

1044759218

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