Chemistry - Theses, Dissertations, and other Required Graduate Degree Essays

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Crystal chemistry and properties of bismuth-modified complex oxide perovskites

Date created: 
2017-08-23
Abstract: 

There is a great interest in developing new high-performance piezo-/ferroelectric materials that are lead-reduced or lead-free. This work focuses on using bismuth as a lead alternative, and studies solid solutions based on the end-member Bi(Zn2/3Nb1/3)O3 (BZN). First, ceramics of the (1-x)PbTiO3-xBi(Zn2/3Nb1/3)O3 [(1-x)PT-xBZN] solid solution were synthesized. The tetragonality (c/a ratio) and A-site displacement increase with increasing BZN content, as revealed by X-ray diffraction analysis. Dielectric measurements show that the Curie temperature TC increases with increasing BZN up to a maximum of 520 °C for the composition of x = 0.20. These results indicate the structural origin of the enhanced tetragonality and properties that arise from the increased anisotropy in the Bi-bonding environment with the increased substitution of Bi3+, with its 6s2 stereochemically active lone electron pair. Synchrotron X-ray pair distribution functions (PDFs) reveal that the tetragonal distortions are preserved down to the local scale, suggesting that studies of the average structure provide reasonable insight into the structure-property relationships in this system. These results provide guidance for designing new materials with high TC. Single crystals of (1-x)PT-xBZN were then successfully grown using the high-temperature solution growth (HTSG) method. The dielectric measurements indicate the ferroelectric-paraelectric phase transition at an average TC of 436 °C. Polarized light microscopy reveals the domain structure of tetragonal symmetry, with domain walls oriented along the <100>cub directions, and birefringence measurements as a function of temperature confirmed the first order phase transition. HTSG allows for a higher BZN content to be incorporated into the crystals in comparison to their ceramic counterpart. Moving toward lead-free materials, ceramics of a novel solid solution, (1−x)BaTiO3 xBi(Zn2/3Nb1/3)O3 (BT-BZN) were synthesized. With increasing BZN content, the materials show a decrease in tetragonality and undergo a transition to pseudocubic symmetry, which is accompanied by a crossover from normal ferroelectric to relaxor behaviour. This crossover is explained by increased cationic disorder that disrupts the ferroelectric order. Synchrotron X-ray PDF analysis reveals that all the compositions show local tetragonal distortions that decrease at larger scales to reach the average structure, demonstrating the striking difference between the local and long-range structures.

Document type: 
Thesis
File(s): 
Senior supervisor: 
Zuo-Guang Ye
Department: 
Science: Department of Chemistry
Thesis type: 
(Thesis) Ph.D.

Design and Synthesis of Novel, Lead-reduced Piezo-/Ferroelectric Materials

Author: 
Date created: 
2017-08-24
Abstract: 

Relaxor-based piezo-/ferroelectric materials of complex perovskite structure, represented by (1-x)Pb(Mg1/3Nb2/3)O3-xPbTiO3 (PMN-PT), have demonstrated excellent piezoelectric performance. However, they also exhibit some inherent drawbacks, such as a low Curie temperature, an even lower de-poling temperature due to the presence of a morphotropic phase boundary (MPB) region, a weak coercive field and a high content of lead, which make them unsuitable for high-temperature and high-field (power) applications and raise environmental concerns. Bismuth-based complex perovskites, such as Bi(Zn1/2Ti1/2)O3 (BZT) seem to be an interesting candidate for the replacement of lead-based compounds because, like Pb2+ ion, Bi3+ also contains the 6s2 lone electron pair which is considered to be essential for the high piezo-/ferroelectric performance in lead-based perovskite. In addition, the solid solution between BZT and PT indeed exhibits larger structural distortion resulting in a higher Curie temperature than PT. However, its coercive field is too large for the material to be poled in order to make its potentially high piezo-/ferroelectric properties useful. Faced with those issues and challenges, outcomes of this thesis are two-fold: Firstly, addition of a non-stereochemically active ion and related complex compound, namely La(Zn1/2Ti1/2)O3 (LZT), as an end-member "softens" the structures, chemical bonding and electric properties of "hard" ferroelectric materials, to achieve improved electric properties, such as giant dielectric constant, smaller coercive field and switching polarization and excellent piezoelectricity and ferroelectricity.Secondly, addition of BZT as the third component "hardens" the structures, chemical bonding and electric properties of PMN-PT binary system in order to increase its coercive field and to improve its piezo-/ferroelectricity. In particular, special efforts have been made to grow the single crystals of the PMN-PT-BZT ternary system. The studies of the single crystals provide invaluable information on the phase symmetry, domain structures, phase transitions and electric properties and allow to gain a better understanding of the relationship between crystal formation, chemical composition, phase symmetry and macroscopic properties.

Document type: 
Thesis
File(s): 
Senior supervisor: 
Zuo-Guang Ye
Department: 
Science: Department of Chemistry
Thesis type: 
(Thesis) Ph.D.

Design and Synthesis of Novel, Lead-reduced Piezo-/Ferroelectric Materials

Author: 
Date created: 
2017-08-24
Abstract: 

Relaxor-based piezo-/ferroelectric materials of complex perovskite structure, represented by (1-x)Pb(Mg1/3Nb2/3)O3-xPbTiO3 (PMN-PT), have demonstrated excellent piezoelectric performance. However, they also exhibit some inherent drawbacks, such as a low Curie temperature, an even lower de-poling temperature due to the presence of a morphotropic phase boundary (MPB) region, a weak coercive field and a high content of lead, which make them unsuitable for high-temperature and high-field (power) applications and raise environmental concerns. Bismuth-based complex perovskites, such as Bi(Zn1/2Ti1/2)O3 (BZT) seem to be an interesting candidate for the replacement of lead-based compounds because, like Pb2+ ion, Bi3+ also contains the 6s2 lone electron pair which is considered to be essential for the high piezo-/ferroelectric performance in lead-based perovskite. In addition, the solid solution between BZT and PT indeed exhibits larger structural distortion resulting in a higher Curie temperature than PT. However, its coercive field is too large for the material to be poled in order to make its potentially high piezo-/ferroelectric properties useful. Faced with those issues and challenges, outcomes of this thesis are two-fold: Firstly, addition of a non-stereochemically active ion and related complex compound, namely La(Zn1/2Ti1/2)O3 (LZT), as an end-member "softens" the structures, chemical bonding and electric properties of "hard" ferroelectric materials, to achieve improved electric properties, such as giant dielectric constant, smaller coercive field and switching polarization and excellent piezoelectricity and ferroelectricity.Secondly, addition of BZT as the third component "hardens" the structures, chemical bonding and electric properties of PMN-PT binary system in order to increase its coercive field and to improve its piezo-/ferroelectricity. In particular, special efforts have been made to grow the single crystals of the PMN-PT-BZT ternary system. The studies of the single crystals provide invaluable information on the phase symmetry, domain structures, phase transitions and electric properties and allow to gain a better understanding of the relationship between crystal formation, chemical composition, phase symmetry and macroscopic properties.

Document type: 
Thesis
File(s): 
Senior supervisor: 
Zuo-Guang Ye
Department: 
Science: Department of Chemistry
Thesis type: 
(Thesis) Ph.D.

Design and Synthesis of Novel, Lead-reduced Piezo-/Ferroelectric Materials

Author: 
Date created: 
2017-08-24
Abstract: 

Relaxor-based piezo-/ferroelectric materials of complex perovskite structure, represented by (1-x)Pb(Mg1/3Nb2/3)O3-xPbTiO3 (PMN-PT), have demonstrated excellent piezoelectric performance. However, they also exhibit some inherent drawbacks, such as a low Curie temperature, an even lower de-poling temperature due to the presence of a morphotropic phase boundary (MPB) region, a weak coercive field and a high content of lead, which make them unsuitable for high-temperature and high-field (power) applications and raise environmental concerns. Bismuth-based complex perovskites, such as Bi(Zn1/2Ti1/2)O3 (BZT) seem to be an interesting candidate for the replacement of lead-based compounds because, like Pb2+ ion, Bi3+ also contains the 6s2 lone electron pair which is considered to be essential for the high piezo-/ferroelectric performance in lead-based perovskite. In addition, the solid solution between BZT and PT indeed exhibits larger structural distortion resulting in a higher Curie temperature than PT. However, its coercive field is too large for the material to be poled in order to make its potentially high piezo-/ferroelectric properties useful. Faced with those issues and challenges, outcomes of this thesis are two-fold: Firstly, addition of a non-stereochemically active ion and related complex compound, namely La(Zn1/2Ti1/2)O3 (LZT), as an end-member "softens" the structures, chemical bonding and electric properties of "hard" ferroelectric materials, to achieve improved electric properties, such as giant dielectric constant, smaller coercive field and switching polarization and excellent piezoelectricity and ferroelectricity.Secondly, addition of BZT as the third component "hardens" the structures, chemical bonding and electric properties of PMN-PT binary system in order to increase its coercive field and to improve its piezo-/ferroelectricity. In particular, special efforts have been made to grow the single crystals of the PMN-PT-BZT ternary system. The studies of the single crystals provide invaluable information on the phase symmetry, domain structures, phase transitions and electric properties and allow to gain a better understanding of the relationship between crystal formation, chemical composition, phase symmetry and macroscopic properties.

Document type: 
Thesis
File(s): 
Senior supervisor: 
Zuo-Guang Ye
Department: 
Science: Department of Chemistry
Thesis type: 
(Thesis) Ph.D.

Design and Synthesis of Novel, Lead-reduced Piezo-/Ferroelectric Materials

Author: 
Date created: 
2017-08-24
Abstract: 

Relaxor-based piezo-/ferroelectric materials of complex perovskite structure, represented by (1-x)Pb(Mg1/3Nb2/3)O3-xPbTiO3 (PMN-PT), have demonstrated excellent piezoelectric performance. However, they also exhibit some inherent drawbacks, such as a low Curie temperature, an even lower de-poling temperature due to the presence of a morphotropic phase boundary (MPB) region, a weak coercive field and a high content of lead, which make them unsuitable for high-temperature and high-field (power) applications and raise environmental concerns. Bismuth-based complex perovskites, such as Bi(Zn1/2Ti1/2)O3 (BZT) seem to be an interesting candidate for the replacement of lead-based compounds because, like Pb2+ ion, Bi3+ also contains the 6s2 lone electron pair which is considered to be essential for the high piezo-/ferroelectric performance in lead-based perovskite. In addition, the solid solution between BZT and PT indeed exhibits larger structural distortion resulting in a higher Curie temperature than PT. However, its coercive field is too large for the material to be poled in order to make its potentially high piezo-/ferroelectric properties useful. Faced with those issues and challenges, outcomes of this thesis are two-fold: Firstly, addition of a non-stereochemically active ion and related complex compound, namely La(Zn1/2Ti1/2)O3 (LZT), as an end-member "softens" the structures, chemical bonding and electric properties of "hard" ferroelectric materials, to achieve improved electric properties, such as giant dielectric constant, smaller coercive field and switching polarization and excellent piezoelectricity and ferroelectricity.Secondly, addition of BZT as the third component "hardens" the structures, chemical bonding and electric properties of PMN-PT binary system in order to increase its coercive field and to improve its piezo-/ferroelectricity. In particular, special efforts have been made to grow the single crystals of the PMN-PT-BZT ternary system. The studies of the single crystals provide invaluable information on the phase symmetry, domain structures, phase transitions and electric properties and allow to gain a better understanding of the relationship between crystal formation, chemical composition, phase symmetry and macroscopic properties.

Document type: 
Thesis
File(s): 
Senior supervisor: 
Zuo-Guang Ye
Department: 
Science: Department of Chemistry
Thesis type: 
(Thesis) Ph.D.

Design and Synthesis of Novel, Lead-reduced Piezo-/Ferroelectric Materials

Author: 
Date created: 
2017-08-24
Abstract: 

Relaxor-based piezo-/ferroelectric materials of complex perovskite structure, represented by (1-x)Pb(Mg1/3Nb2/3)O3-xPbTiO3 (PMN-PT), have demonstrated excellent piezoelectric performance. However, they also exhibit some inherent drawbacks, such as a low Curie temperature, an even lower de-poling temperature due to the presence of a morphotropic phase boundary (MPB) region, a weak coercive field and a high content of lead, which make them unsuitable for high-temperature and high-field (power) applications and raise environmental concerns. Bismuth-based complex perovskites, such as Bi(Zn1/2Ti1/2)O3 (BZT) seem to be an interesting candidate for the replacement of lead-based compounds because, like Pb2+ ion, Bi3+ also contains the 6s2 lone electron pair which is considered to be essential for the high piezo-/ferroelectric performance in lead-based perovskite. In addition, the solid solution between BZT and PT indeed exhibits larger structural distortion resulting in a higher Curie temperature than PT. However, its coercive field is too large for the material to be poled in order to make its potentially high piezo-/ferroelectric properties useful. Faced with those issues and challenges, outcomes of this thesis are two-fold: Firstly, addition of a non-stereochemically active ion and related complex compound, namely La(Zn1/2Ti1/2)O3 (LZT), as an end-member "softens" the structures, chemical bonding and electric properties of "hard" ferroelectric materials, to achieve improved electric properties, such as giant dielectric constant, smaller coercive field and switching polarization and excellent piezoelectricity and ferroelectricity.Secondly, addition of BZT as the third component "hardens" the structures, chemical bonding and electric properties of PMN-PT binary system in order to increase its coercive field and to improve its piezo-/ferroelectricity. In particular, special efforts have been made to grow the single crystals of the PMN-PT-BZT ternary system. The studies of the single crystals provide invaluable information on the phase symmetry, domain structures, phase transitions and electric properties and allow to gain a better understanding of the relationship between crystal formation, chemical composition, phase symmetry and macroscopic properties.

Document type: 
Thesis
File(s): 
Senior supervisor: 
Zuo-Guang Ye
Department: 
Science: Department of Chemistry
Thesis type: 
(Thesis) Ph.D.

Surface Modification of Indium Tin Oxide

Author: 
Date created: 
2017-07-26
Abstract: 

Indium tin oxide serve a critical function in many organic devices, such as organic light emitting diodes and organic photovoltaics. To optimize the performances of these devices, it is desirable to tune the interface between the indium tin oxide and the next functional layer of these devices. A common surface modification of transparent conductive oxides is through the use of self-assembled monolayers. This methodology enables a simultaneously tuning of the properties and performance of this interface, including the surface energy, work function and durability of the transparent conductive oxide. Phosphonic acid and silane based monolayers have been extensively studied and used in devices for their ability to tune the interfacial properties of transparent conductive oxide. Herein, alcohol based monolayers are first demonstrated on transparent conductive oxide surfaces. The electrochemical and chemical stabilities of alcohol based monolayers, as well as changes in the optical properties of the Indium tin oxide as a function of their stability were evaluated in comparison to more traditional routes of surface modification, such as through the use of silanes and phosphonic acid based monolayers. The tunability of both work function and surface energy of the modified Indium tin oxide were also determined for assessing their electronic properties.

Document type: 
Thesis
File(s): 
Senior supervisor: 
Byron Gates
Department: 
Science: Department of Chemistry
Thesis type: 
(Thesis) M.Sc.

An improved synthesis of gold nanorods with tunable dimensions and localized surface plasmon resonance properties

Author: 
Date created: 
2018-04-19
Abstract: 

Gold nanorods have been pursued due to their unique optoelectronic properties, which have led to potential uses in multiple applications. We sought to prepare gold nanorods that would potentially be used in biomedical applications, such as bio-imaging, photothermal therapies, and drug delivery systems. Typically in biomedical applications, gold nanorods with a localized surface plasmon resonance band that lies in the near infrared window between 650 to 1350 nm is highly desirable to obtain better images and an efficient photothermal effect over a range of depths within biological tissues. In addition, the dimensions of gold nanorods also play an important role in terms of cellular uptake and retention, as well as controlling the ratio between their absorbance and scattering properties. Thus, a primary goal of our study was to regulate dimensions and localized surface plasmon resonance of the gold nanorods to improve their potential utility in applications requiring both cellular uptake and photothermal triggered processes through the use of localized surface plasmon resonance bands in the near infrared “window”. We have modified the seed-mediated method by sequentially varying concentrations of hydrochloric acid and chloroauric acid to tune the dimensions, and thus the properties of the gold nanorods. The average dimensions of the gold nanorods were tuned from 24±4 nm in length and 7±1 nm in width, to 47±10 nm in length and 11±2 nm in width from these adjustments in the concentration of hydrochloric acid and chloroauric acid in the growth solution.

Document type: 
Thesis
File(s): 
Senior supervisor: 
Byron D. Gates
Department: 
Science: Department of Chemistry
Thesis type: 
(Thesis) M.Sc.

Photocatalytic fluorination of benzylic C-H bonds and studies towards the synthesis of salinosporamide C

Author: 
Date created: 
2018-04-18
Abstract: 

Fluorinated pharmaceuticals comprise nearly a quarter of the total pharmaceutical market. However, current fluorination methods and reagents lack a certain range particularly in the fluorination of C-H bonds. The first part of this thesis describes the fluorination of benzylic C-H bonds utilizing the hydrogen abstracting ability of a classic photocatalyst and a bench stable fluorine atom transfer reagent. The simple and straightforward reaction demonstrates a wide range of tolerance to functionalities and provides access to fluorinated compounds in moderate to good yield. The second part of this thesis consists of research towards the synthesis of a marine natural product, salinosporamide C, which was discovered in 2002 and has yet to be synthesized. The true activity of the compound is unknown, however its biogenetically related counterpart salinosporamide A is considered a potent 20S proteasome inhibitor. Though the total synthesis of salinosporamide C was not accomplished, an advanced intermediate was successfully synthesized and the groundwork for a successful synthesis of this natural product was completed.

Document type: 
Thesis
File(s): 
Senior supervisor: 
Dr. Robert A. Britton
Department: 
Science: Department of Chemistry
Thesis type: 
(Thesis) M.Sc.

Mechanistic applications of volume profiles for chemical and biochemical processes

Date created: 
2018-04-16
Abstract: 

Pressure has a profound effect on both the speed and direction of chemical reactions; an effect which is inextricably linked to the change in volume of the system. Experimentally, this effect is described by the activation and reaction volumes, defined as the pressure derivatives of rate constants and equilibrium constants respectively. These quantities provide information about the relationships between the partial molar volumes of the reactant, product and transition state (TS). However, mechanistic interpretation of these volumes has posed a challenge due to the lack of an accurate computational technique for relating the geometrical structure of a reaction system to its volume. We have formulated a theoretical methodology that can be used to describe and predict the effects of pressure on reaction systems using the concept of a volume profile. These profiles, which detail how the partial molar volume of a system changes over the course of a reaction, can be calculated using the recently developed Archimedean displacement model of molecular volume. We explore two mechanistic applications of these profiles. The first is the calculation of Gibbs energy profiles at elevated pressures, allowing for the prediction of interesting and potentially useful chemical transformations that can occur with pressure. This technique was used to investigate high pressure structural transformations for a radical hydrogen transfer reaction, and also to examine the feasibility of pressure-driven molecular machines. The second application is the elucidation of TS structures from a comparison of the theoretical volume profile with the experimentally-determined activation volume. This technique is especially useful for systems with a high degree of conformational flexibility whose TSs are not readily identified using standard computational methods. We used this method to identify the TS ensemble for a flexible model chain, and for conformational changes in a cyclophane system. To apply this method to larger, more complex systems such as the unfolding of proteins, a reaction coordinate for the process is required. A proper definition for such a coordinate was investigated and some preliminary results are presented for biological systems.

Document type: 
Thesis
File(s): 
Senior supervisor: 
Michael H. Eikerling
Noham Weinberg
Department: 
Science: Department of Chemistry
Thesis type: 
(Thesis) Ph.D.