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Chiral Mesogen-Free Liquid Crystalline Polyethers With Sulfonylated Side Chains And Patchy Brush Nanoparticles, Caleb A. Bohannon

Doctoral Dissertations

Ferroelectric liquid crystalline polymers (LCPs) hold promise for various applications driven by low electric fields, e.g., electrocaloric materials, because of the higher molecular motion in the liquid crystalline (LC) state. However, traditional chiral smectic C (SmC*) LCPs exhibit small spontaneous polarizations due to the bulky aromatic mesogens and weak polar groups. This dissertation research is focused on the design of mesogen-free sulfonylated LCPs with a goal of seeking the ferroelectric SmC* phase. Such LCPs are expected to exhibit high polarizations owing to the sulfonyl’s large dipole moment. A series of poly(oxypropylene)s (POPs), with chirality being introduced into either the backbone …

Chemico-Physical Interactions In Metal Halide Perovskites, Yongtao Liu

Doctoral Dissertations

Metal halide perovskite (MHP) has attracted tremendous attention due to its success in optoelectronics, largely due to outstanding photovoltaic performance. A wide variety of characterization approaches have been used to explore the fundamentals behind the outstanding optoelectronic properties of MHP, which has yet to be unambiguously established despite considerable efforts to do so. Given the high ionic mobility in MHP, when physical phenomena are coupled with chemical changes, all behaviors will become very complex due to the strong ion migration. Therefore, chemico-physical interactions in MHP can no longer be ignored, which will be the focus of the researches in this …

Synthesis And Modeling Of Ferroelectric Nanocomposites, Yomery Espinal

Doctoral Dissertations

Nanocomposites consisting of a ferroelectric oxide embedded within a non-ferroelectric matrix are a unique class of materials with potential to improve performance in next-generation electronics and non-volatile memory. Dielectric losses and breakdown due to processing and intrinsic properties of a monolithic ferroelectric point to low figures of merit. Therefore, it is necessary to develop composite materials with an active ferroelectric that is physically confined within a low-loss dielectric matrix while maintaining significant dielectric and pyroelectric properties inherent to ferroelectrics. The purpose of this work is to explore the behavior of ferroelectric nanocomposites as a function of dimensionality, and composition. The …

Combined Intrinsic Caloric Effects In Ferroelectrics, Hamidreza Khassaf

Doctoral Dissertations

There exist multiple driving forces in solid–state materials that can be utilized for entropy changes and hence stronger caloric response. In multiferroic materials, adiabatic temperature changes (ΔT_ad) can be obtained via combined application of electric, stress, and magnetic fields. These external stimuli provide additional channels of entropy variations resulting in a multi–caloric response. In ferroelectric (FE) materials, caloric responses can be obtained with the application of electric and mechanical fields. Here, we compute the intrinsic electrocaloric and elastocaloric of prototypical FE materials using Landau–Devonshire theory of phase transformations with appropriate electrical and electro–mechanical boundary conditions. Also, the …

Properties And Manipulation Of Ionic Liquid-Solid Interfaces In Complex Oxide Materials, Anthony Thomas Wong

Doctoral Dissertations

Ionic liquids are liquid salts that are bringing rapid changes to the field of solid electronic materials. The implementation of ionic liquids in conjunction with these solid materials produces interfacial effects, especially when a bias is applied across the ionic liquid, forming an electric double layer. Electric double layers in ionic liquids are unique in their formation and the interfacial charges that are orders of magnitude higher than conventional techniques they can impart, providing new techniques for device design and implementation. In chapter 1, the fundamentals of the solid state electronic and magnetic materials are introduced, along with ionic liquids, …

Ferroelectric Switching And D33 Mapping Of Micro-Patterned Piezoelectrics By Piezo Force Microscopy, Linghan Ye

Doctoral Dissertations

The domain configurations and piezoelectric coefficient of ferroelectric materials such as PZT and PMN-PT thin films can have a significant effect on the optimization of future electronic devices. Piezo Force Microscopy (PFM) is an ideal tool based on Atomic Force Microscopy that allows unique investigations of such nanoscale effects, and can further be implemented to monitor domain switching dynamics. Utilizing PFM, the domain orientations as well as switching dynamics can be tracked in-situ. As the lateral dimension plays an important role in ferroelectric properties since it influences in-plane strain, both normal and lateral domain orientations are uniquely mapped simultaneously. Leveraging …

Study Of Ferroelectric Oxides And Field Effect In Complex Oxides Heterostructures, Lu Jiang

Doctoral Dissertations

With the rapid development of technology, the need for novel materials and state-of-theart devices is growing fast. Complex oxides which have strongly correlated electrons are favorable candidates for materials industry, due to their rich phase diagrams and multiple functions. Especially, ferroelectric oxides is very promising materials in the industry for storage, due to their bistable polarization states triggered by external electrical field. This thesis is centered on ferroelectric oxides, analyzing their lattice structures and investigating the interface of ferroelectrics and other complex oxides to examine the potential of the heteostructures in the application in electronic devices.

The most notable feature …