Ryan T. Hart

ORCID Identifier(s)

0000-0002-4056-2388

Graduation Semester and Year

2018

Language

English

Document Type

Thesis

Degree Name

Master of Science in Materials Science and Engineering

Department

Materials Science and Engineering

First Advisor

Ye Cao

Abstract

In this study, thermodynamic analysis and phase field simulation are utilized to study the polarization, phase transitions, and phase coexistence in BFO thin films. The effect of temperature, substrate strain, and electrical bias on the phase stability and the phase transformation pathways were studied. Existing thermodynamic analysis methods are supplemented by a phase destrain model, which determines free energy minima as a function of biaxial strain and the fractions of BFO’s ferroelectric phases in a thin film. The results of this methodology are compared with phase field modeling. The phase de-strain model shows reasonable accuracy in determining boundaries at which BFO’s phase mixtures and morphotropic phase boundaries can form. Increasing temperature is shown to favor phases that occur at lower strains, and increase the strain required to induce formation of high-strain phases of BFO. Thermodynamic analysis and phase field modeling are further used to predict the coercive field and its dependence on the biaxial strain, and temperature. Both models show reasonable agreement. As temperature increases, the coercive field required to induce electrical switching decreases under given substrate strain. Depending on the relative stability of phases at a given strain, the phase transformation can occur as a part of the electrical switching process.

Keywords

BiFeO3, Bismuth ferrite, Ferroelectricity, Ferroelectrics, Multiferroic, Morphotropic phase boundary, PE hysteresis, Electrical switching, Phase-field modeling, Thermodynamic analysis

Disciplines

Engineering | Materials Science and Engineering

Comments

Degree granted by The University of Texas at Arlington

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