Date of Award

2015

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Materials Science and Engineering (PhD)

College, School or Department Name

Department of Materials Science and Engineering

Advisor

Yu U. Wang

Abstract

Ferroelectric materials, as a large family exploited for the application of sensors, transducers and random access memories, open up a remarkable ground both for fundamental science and industry. Dielectric and piezoelectric properties are of the most interest in ferroelectric materials, which motivate research to enhance ferroelectric properties based on various application purposes. Among the multitudinous candidates in ferroelectric family, pseudo binary solid solutions with ABO3 lattice structure attract special attention in virtue of their large strain response when applying external loading. Furthermore, existence of morphological phase boundary (MPB) on their phase diagrams shed light on tuning material compositions to improve ferroelectric properties as well. Essentially, polarization domain properties play the key role in ferroelectric property enhancement, which need further investigations.

This thesis primarily focuses on the computational study of microstructure-property relation in representative ferroelectric material: Pb(Zr1-xTix)O3 (PZT). For its single crystal, domain engineering and ferroelectric nucleation mechanisms are studied. And for its polycrystal, grain texture development during sintering, grain shape effect, and twophase composites are investigated to exploit their effects on domain evolution and further property enhancement.

Phase field modeling is developed to simulate domain evolution in PZT single crystal and polycrystal. Extensive simulations show that wisely selecting electric field could design domain patterns, while purposely choosing operation temperature and electric field magnitude could realize domain size control. In addition, theoretical study shows that ferroelectric nucleation presents a correlated manner which is different from traditional isolated nucleation. For polycrystal studies, the model for templated grain growth (TGG) to generate texture is developed. To validate the model, the simulations are compared to the experiment with good agreement. As accompanied issues, grain shape anisotropy, texture-property relation and second-phase effects are studied with phase field modeling. It is revealed that grain shape plays the minor effect on ferroelectric properties as compared with grain texture, and competition between texture and second-phase results in an optimal volume fraction for template seeds involvement.

Further incorporation of domain microstructures potentially contributes to extraordinary X-ray diffraction peaks, especially when domain sizes shrink to nano-scale. As the candidate for the material who possesses the similar structural feature, layeredstructure lithium ion battery materials present nano-scale structural domain variants with stacking faults. Investigations on the structure of lithium ion battery not only facilitate the understanding of X-ray diffractions related to nano-domain, but also supply the novel methodology to quantitatively study microstructure-property relation. DIFFaX modeling is adopted to reveal its atomic level stacking structure information. And a new hierarchical algorithm is developed to quantitatively obtain the distribution of stacking fault probability which serves as potential evidence to explain that the best performance of battery cathode happens at certain composition. Additionally, instead of focusing on transition layer only, models to deal with possible oxygen faulting and voids are proposed as well to extend the capability of studies for more scientific problems concerning with particular microstructures.

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