Doctoral Dissertations

Abstract

"The stability of BaTiO3-type insulators to DC fields has long been recognized as one of the important factors in determining the quality of a capacitor which uses such a material as its dielectric. The slow increase of the electrical conductivity of an insulator which is stressed by DC fields at levels below the breakdown strength is normally termed degradation. Since degradation is a very common malady to the ceramic capacitor manufacturers, many studies have been conducted over the past two decades in efforts to learn how to remedy the problem.

The results of previous studies have shown that certain dopants (present both as intentional additives and as impurities), the Ba:Ti ratio, and hydroxyl content greatly influence the degradation process. Since all of the studies have been carried out on ill-defined commercial materials, no correlation between defect structure and degradation has been possible. It was the intent of this present investigation to study degradation in well-defined BaTiO3 (both high purity and intentionally doped) with the intent of developing a defect model which can be used to explain the influence of dopants and Ba:Ti ratio upon degradation.

High purity BaTiO3 powder was prepared by a chemical preparation technique which allows the ratio of cations and dopant levels to be precisely controlled. The DC current-voltage characteristics of sintered discs were measured as a function of both time and temperature.

Undoped BaTiO3 with a Ba:Ti ratio less than unity had the greatest tendency to degrade. Undoped and acceptor doped material with a Ba:Ti ratio greater than unity had a high resistance to degradation. Donor and acceptor doping with a Ba:Ti ratio less than unity improved the degradation resistance while donor doping with a Ba:Ti ratio greater than one increased the degradation.

To explain the observed behavior, a model is presented that includes the effect of acceptors, donors, and the Ba:Ti ratio on the degradation process"--Abstract, pages ii-iii.

Advisor(s)

Anderson, H. U. (Harlan U.)

Committee Member(s)

Wuttig, Manfred
Sorrell, Charles A.
James, William Joseph
Lewis, Gordon

Department(s)

Materials Science and Engineering

Degree Name

Ph. D. in Ceramic Engineering

Publisher

University of Missouri--Rolla

Publication Date

1976

Pagination

ix, 119 pages

Note about bibliography

Includes bibliographical references (pages 103-106).

Rights

© 1976 Jeffrey Duncan Keck, All rights reserved.

Document Type

Dissertation - Open Access

File Type

text

Language

English

Thesis Number

T 4106

Print OCLC #

5985380

Electronic OCLC #

1086609022

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