Degree Type

Thesis

Date of Award

2010

Degree Name

Master of Science

Department

Materials Science and Engineering

First Advisor

Xiaoli Tan

Abstract

Widespread adoption of renewable energy sources, such as wind and solar power, will necessitate an efficient way to interface with energy storage devices in order to ensure around-the-clock energy delivery during off-peak hours. Energy storage devices implementing linear dielectric capacitors offer exceptional power density (i.e. rate of charge/discharge), but cannot match the energy density (i.e. storage capacity) of batteries. However, replacing the linear dielectric in capacitors with an antiferroelectric material has the potential to increase the energy density by approximately one order of magnitude. Since the energy is stored via a reversible and diffusionless antiferroelectric-to-ferroelectric phase transformation, the high power density is maintained.

In this study, the response of antiferroelectric Pb0.99Nb0.02[(Zr0.57Sn0.43)1-yTiy]0.98O3 ceramics with compositions near an antiferroelectric/ferroelectric phase boundary were systemically characterized in the presence of electric fields. By altering the titanium content (y in the chemical formula) the phase boundary was incrementally approached, allowing for detailed study of the electric field-induced phase transformation in this region of structural instability. The key parameters of polarization, longitudinal strain, and transverse strain were simultaneously recorded as a function of externally applied electric fields on all compositions. It was found that the volume expansion and polarization developed during the antiferroelectric-to-ferroelectric phase transformation remained ~0.4% and ~30 μC/cm2, respectively, regardless of the composition in the range of 0.060 ≤ y ≤ 0.075. However, the critical field strengths associated with the phase transformation varied in a linear fashion with y, supporting the suggestion that increasing the titanium content strengthens the ferroelectric ordering of the system.

Application of axial and radial compressive pre-stresses to samples with composition y = 0.060 were observed to increase the critical field magnitude necessary to induce the ferroelectric phase, but the manners in which they suppressed the phase transformation were distinctively different. Axial pre-stresses resulted in an abrupt, uniform suppression while radial pre-stresses caused a gradual, non-uniform suppression of the phase transformation. The results were interpreted based on different textures in the ceramic developed by each pre-stress condition. In the absence of mechanical confinement, the induced ferroelectric phase in compositions y ≥ 0.069 became metastable and the ferroelectric-to-antiferroelectric phase transformation did not occur during the unloading of the applied field. This reverse phase transformation occurred partially when electric fields with reversed polarity were applied, though the extent of the antiferroelectric phase recovered diminished with increasing titanium content. Through the use of in-situ X-ray diffraction, an electric field-induced ferroelectric-to-antiferroelectric phase transformation was confirmed for the first time.

Copyright Owner

Joshua Cody Frederick

Language

en

Date Available

2012-04-30

File Format

application/pdf

File Size

85 pages

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