Doctoral Dissertations

Abstract

"Solid state reaction of Bi2O3 · Fe2O3 mixtures was shown to yield impure bismuth ferrate, BiFeO3, containing Bi2Fe4O9 and residual Bi2O3; this places the results of much of the literature based on BiFeO3 prepared by this technique in suspect. Single phase polycrystalline BiFeO3 was prepared by multiple nitric acid leaching of sintered samples which contained excess Bi2O3 to prevent the formation of Bi2Fe4O9 during sintering. X-ray and neutron powder diffraction data indicate that BiFeO3 possesses superstructure, probably resulting from a puckering of the oxygen octahedra. A rhombohedrally distorted unit cell containing two ABO3 formula units generates all superstructure peaks but a final atomic model could not be developed by trial and error methods.

The room temperature phase diagram of the pseudo-ternary BiFeO3-PbZrO3-PbTiO3 system was refined to the limit consistent with sample homogeneity. It consists primarily of one tetragonal and two rhombohedral phase regions. The tetragonal structure of PbTiO3 exists over an extensive region of the phase diagram and shows a high degree of distortion (c/a > 1.15) near the tetragonal-rhombohedral phase boundary in the PbTiO3- BiFeO3 system. The rhombohedral phases of BiFeO3 and the Pb(ZrTi)O3 system extend far into the ternary diagram with decreasing angular distortion. As shown by x-ray analysis the orthorhombic structure of PbZrO3 reverts to pseudocubic symmetry with the addition of approximately 25 mole per cent BiFeO3 and retains this pseudocubic nature for compositions containing up to about 80 mole per cent BiFeO3. Neutron diffraction studies of this region reveal that the oxygen octahedra are highly distorted in the pseudocubic phase and thereby account structurally for the high Curie temperatures of these compositions. All phases in the central region of the ternary diagram are of low distortion which prevents precise delineation of phase boundaries by x-ray methods.

The simple G-type antiferromagnetic structure of BiFeO3, in which each iron magnetic dipole is surrounded by six anti-parallel aligned dipoles, exists throughout the ternary system. Magnetic ordering is visible at room temperature in PbZrO3 · BiFeO3 samples containing as little as 20 mole per cent BiFeO3. The temperature dependence of magnetic ordering follows Van Vleck's model at low temperatures. Residual short-range ordering persists at temperatures above the Neel temperature as determined by magnetic susceptibility studies "--Abstract, pages i-ii.

Advisor(s)

James, William Joseph

Committee Member(s)

Johnson, James W., 1930-2002
Lorey, G. Edwin
Park, Efton
Gerson, Robert, 1923-2013

Department(s)

Chemical and Biochemical Engineering

Degree Name

Ph. D. in Chemical Engineering

Sponsor(s)

U. S. Atomic Energy Commission
Shell Oil Company
National Science Foundation (U.S.)

Publisher

University of Missouri at Rolla

Publication Date

1967

Pagination

ix, 176 pages

Note about bibliography

Includes bibliographical references (pages 122-127).

Rights

© 1967 Gary David Achenbach, All rights reserved.

Document Type

Dissertation - Open Access

File Type

text

Language

English

Library of Congress Subject Headings

Bismuth compounds -- Analysis
Ferroelectric crystals
Antiferromagnetism

Thesis Number

T 1991

Print OCLC #

5981478

Electronic OCLC #

922583558

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