Masters Theses

Abstract

This thesis presents an investigation of the conduction mechanism in the La1-yCayAl1-xMnxO3 perovskite system. This system allows a detailed study of site percolation in which small polarons hop among nearest neighbor Mn sites because the small polarons are restricted to the Mn sites as the Al ions are incapable of supporting small polarons.

Electrical conductivity and Seebeck coefficient measurements were carried out as a function of temperature for the LaAl1-xMnxO3 series and the La0.79Ca0.2Al1-xMnxO3 series in which 20 mol% Ca was substituted for La. The conductivity results for both series indicate that this system can be related to a site percolation model in which conduction occurs via hopping of small polarons among the Mn sites. The Seebeck data indicates that thermally activated Mn2+- Mn4+ pairing occurs from the Mn3+ state in these systems. Measured high temperature Seebeck coefficients for these systems were near zero for Mn concentrations above the percolation limit. Reproducible, but unexplained, results were observed for Mn concentrations below the percolation threshold in the Ca-doped series.

Advisor(s)

Anderson, H. U. (Harlan U.)

Committee Member(s)

Sparlin, Don M.
Nasrallah, Magdi M.

Department(s)

Materials Science and Engineering

Degree Name

M.S. in Ceramic Engineering

Publisher

University of Missouri--Rolla

Publication Date

Fall 1991

Journal article titles appearing in thesis/dissertation

Conduction Mechanism in the La(Al,Mn)O3 System

Pagination

vii, 68 pages

Note about bibliography

Includes bibliographical references.

Rights

© 1991 Michael Joseph DeBarr, All rights reserved.

Document Type

Thesis - Restricted Access

File Type

text

Language

English

Thesis Number

T 6277

Print OCLC #

25344455

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