Strong electron-electron correlations and lattice frustration are two physical interactions that pose serious challenges to condensed matter physics. A variety of exotic physical phenomena, for example, charge ordering, spin liquid, and unconventional superconductivity, are believed to arise from the interplay of the two interactions. In this dissertation, I examine two families of systems which exhibit both electron-electron correlations and lattice frustration – charge transfer solids and layered cobaltates. The half-filled band Hubbard model on the triangular lattice has been proposed by mean-field theories as the minimal model for the superconductivity in the charge transfer solids. In the first part of this dissertation, by using exact calculations, I prove the absence of superconductivity in this model. This result calls for a new theoretical approach to describe the rich physics in charge transfer solids. In the second part of this dissertation, I study charge transfer solids by focusing on its real bandfilling ¼. I show that a new kind of insulating phase, paired electron crystal, emerges from antiferromagnetism as the frustration is increased. The paired electron crystal state can explain the various insulating states adjacent to the superconducting state, thus provides a new avenue towards the understanding of the unconventional superconductivity in charge transfer solids and other ¼ filled systems. In the third part of this dissertation, I investigate the carrier concentration-dependent electronic behavior in layered cobaltates. I provide a natural yet simple explanation for this behavior. I show that it can be described within correlated-electron Hamiltonians with finite on-site and significant nearest neighbor hole-hole Coulomb repulsions. I also point out the similarities between organic charge transfer solids and layered cobaltates, which may involve superconductivity.

The dissertation consists of a critical preface and a novel. The preface analyzes what it terms “polyvocal” novels, or novels employing multiple points of view, as well as “layered storytelling,” or layers of textuality within novels, such as stories within stories. Specifically, the first part of the preface discusses polyvocality in twenty-first century American novels, while the second part explores layered storytelling in novels responding to World War II or the terrorist attacks of 9/11. The preface analyzes the advantages and difficulties connected to these techniques, as well as their aptitude for reflecting the fractured, disconnected, and subjective nature of the narratives we construct to interpret traumatic experiences. It also acknowledges the necessity—despite its inherent limitations—of using language to engage with this fragmentation and cope with its challenges. The preface uses numerous novels as examples and case studies, and it also explores these concepts and techniques in relation to the process of writing the novel After the Planes. After the Planes depicts multiple generations of a family who utilize storytelling as a means to work through grief, hurt, misunderstanding, and loss—whether from interpersonal conflicts or from war. Against her father’s wishes, a young woman moves in with her nearly-unknown grandfather, struggling to understand the rifts in her family and how they have shaped her own identity. She reads a book sent to her by her father, which turns out to be his story of growing up in the years following World War II. The book was intercepted and emended by her grandfather, who inserts his own commentary throughout, complicating her father’s hopes of reconciliation. The novel moves between two main narratives, one set primarily in 1951 and the other in the days and weeks immediately prior to September 11, 2001.

The primary aim of this thesis is to explore the immunostimulatory properties of a family of layered, crystalline, inorganic materials known as layered double hydroxides (LDHs). <strong>Chapter One</strong> provides an introduction to relevant aspects of the immune system, and the context for investigating the immunostimulatory properties of inorganic materials in terms of vaccine/adjuvant formulations. The possible mechanisms of action of commercial adjuvant materials are also reviewed, and the structure, synthesis methods and applications of LDHs are discussed. <strong>Chapter Two</strong> details the controlled synthesis and characterisation of LDHs in specific particle sizes. A series of MgAl-CO3 LDHs with precisely controlled particle sizes ranging from 20 to 10000 nm were successfully synthesised, then the techniques used were extended to other compositions to create a panel of LDHs for use in subsequent Chapters. In <strong>Chapter Three</strong>, the responses of monocyte-derived dendritic cells (Mo-DC) to the LDH particle sizes discussed in Chapter Two are assessed in terms of viability, surface molecule expression, and cytokine secretion. A statistical modelling approach using the physicochemical properties of the LDHs as explanatory variables for immune responses was employed to evaluate the validity of the model formulated in the previous work, and to establish if particle size could be used to improve its predictive ability. It was found that strong relationships between LDH particle size and certain Mo-DC responses exist, and that these responses could be predicted with a high degree of accuracy. <strong>Chapter Four</strong> is concerned with the investigation of T cell responses to LDH-stimulated allogeneic Mo-DC. Various methods were used for assessing T cell division and proliferation, and a protocol for intracellular cytokine staining was developed to probe T cell polarisation. Five LDHs, which have elicited potentially interesting T cell responses in previous work, were selected for investigation. However, using the assays described, no discernible improvement in proliferation or polarisation was observed with any of the LDHs tested. <strong>Chapter Five</strong> presents an initial exploration of the interactions between LDH particles and cells. Experiments have shown that LDH particles both adhere to and are internalised by Mo-DC. Variations in the extent of internalisation with both particle size and composition were highlighted by confocal microscopy studies. Through investigations into interactions between LDH particles and the plasma membrane using protease enzymes, it was revealed that adhesion of LDH particles is partly protein-dependent. Further studies have also demonstrated a pH-dependent element to particle association with Mo-DC. Details of the experimental procedures employed are included in <strong>Chapter Six</strong>. Supplementary information referred to in the main thesis may be found in the <strong>Appendices</strong>.

Topochemical strategies, techniques that allow one to effectively manipulate the structures of nonmolecular solids once a crystal lattice is established, are effective in the low temperature (< 500 °C) modification of solid state structures, allowing the preparation of nonmolecular compounds not accessible by standard synthetic routes. Some of the techniques, ion exchange, intercalation/deintercalation, have proven to be excellent synthetic methods for preserving specific frameworks. The combination of these techniques can allow one to create a multistep approach that can be used to design new compounds with interesting properties. As an expansion to the field of topotactic reactions, a multistep approach was developed towards the synthesis of the new compounds (A xM0.5Cly)LaNb2O7 (where A = Rb, Cs; M = Fe, Ni; x ≈ 1.5;y ≈ 1) at temperatures below 400oC. The first reaction step involved the ion exchange of the host materials (ALaNb2O7, A = Rb, Cs) to form the products M0.5LaNb2O7 (where M = Fe, Ni), a structure open to further chemistry. The next step involved reductive intercalation with Rb or Cs metal to form the air sensitive mixed-valence products with the nominal compositions, A1.5M0.5LaNb2O7. The last step involved the oxidative intercalation of chlorine using chlorine gas to obtain the final compounds. This multistep approach is a design to form mix-metal halide layers, specifically those with divalent cations, within layered perovskites, opening the doors to compounds that can have interesting properties. This reaction series was also applied to the tantalate layered oxides, leading to the formation of the new compound Ni 0.5LaTa2O7 through ion exchange. The further multistep topochemical manipulation of this new compound was not successful and was indicative of the difference in chemical behavior of the tantalates versus the niobates. We have also investigated the oxidative intercalation of halogens into a series of Ruddlesden-Popper (R-P) ruthenate oxides with the formula Ae n+1RunO3n+1 (Ae = Ca, Sr; n = 1, 2, 3) using several sources of fluorine, chlorine, and bromine. A new method was developed to intercalate chlorine into layered systems; this new approach avoids the use of chlorine gas which is highly toxic. The new phase Sr3Ru2O7Cl0.7 was synthesized by the new method and further topotactic manipulations were explored. The chemistry was not limited to the n = 2 phase but was also applied to the n = 3 phase, Sr4Ru3O10.

Layered perovskites can be classified in three major groups: Dion-Jacobson AA′n-1BnO3n+1, Ruddlesden-Popper A2A′n-1BnO3n+1,and Aurivillius phase (Bi2O2)A′n-1BnO3n+1. (A: Alkali metal, Alkali-earth metal; A′: Lanthanides and Bi; B: Ti, Nb, Ta; n: thickness of slabs). For more than two decades researchers have shown much interest in this series because of their magnetic and electrical properties. Tuning synthesis parameters such as temperature, time, and host structure can be used to direct such properties. Low temperature synthetic methods (topochemical methods) allow the preparation of compounds not accessible by traditional high temperature reactions. This dissertation mainly considers the topochemical methods of ion exchange and reductive and oxidative intercalation to build new low temperature or metastable layered perovskites. The two-dimensional Dion-Jacobson ALaNb2O7 layered perovskites were intercalated reductively to produce A2LaNb2O7 andthen oxidized with water or hydro-chalcogenides (H2Ch, Ch: S, Se) to produce the novel alkali metal hydroxide, (A2OH)LaNb2O7, and alkali metal hydro-chalcogenides, (A2ChH)LaNb2O7, respectively. The synthesis and characterization of these compounds are presented in Chapters 2 and 3. In another set of studies, high temperature ceramic methods lead to the new host APrNb2O7. When this reaction is followed by ion exchange, (CuCl)PrNb2O7 can be prepared. The structural refinement, magnetic properties, and thermal stability of new phases have been studied in Chapter 4. The utility of praseodymium niobates for the formation of other metal oxyhalides was also developed; the series (MX)PrNb2O7 (M: Mn, Fe, Co, Cu and X: F, Cl) were prepared by the ion exchange of LiPrNb2O7 and the obtained phases characterized (Chapter 5). Further, to expand the library of materials and because of interesting properties of lanthanides (Ln: La, Pr, Nd, Sm), lanthanide tantalates have been explored for the preparation of oxyhalides and resulted in the compounds (CuCl)LnTa2O7 (Ln: Pr, Nd) (Chapter 6). Manipulation of Dion-Jacobson layered perovskites are not limited to lanthanides, other hosts with interesting properties have been examined (e.g. ABiNb2O7) (A: alkali metal, CuCl) and their crystal structures characterized along with thermal stability and magnetic response.

MSc (Med),Dept of Pharmacy and Pharmacology, Faculty of Health Sciences, University of the Witwatersrand / Pain is the net effect of multidimensional mechanisms that engage most parts of the central nervous system (CNS) and the treatment of pain is one of the key challenges in clinical medicine (Le Bars et al., 2001; Miranda et al., 2008). Polypharmacy is seen as a barrier to analgesic treatment compliance, signifying the necessity for the development of fixed dose combinations (FDCs), which allow the number of tablets administered to be reduced, with no associated loss in efficacy or increase in the prevalence of side effects (Torres Morera, 2004). FDCs of analgesic drugs with differing mechanisms of nociceptive modulation offer benefits including synergistic analgesic effects, where the individual agents act in a greater than additive manner, and a reduced occurrence of side-effects (Raffa, 2001; Camu, 2002). This study aimed at producing a novel, rate-modulated, fixed-dose analgesic formulation for the treatment of mild to moderate pain. The fixed-dose combination (FDC) rationale of paracetamol (PC), tramadol hydrochloride (TM) and diclofenac potassium (DC) takes advantage of previously reported analgesic synergy of PC and TM as well as extending the analgesic paradigm with the addition of the anti-inflammatory component, DC. The study involved the development of a triple-layered tablet delivery system with the desired release characteristics of approximately 60% of the PC and TM being made available within 2 hours to provide an initial pain relief effect and then sustained zero-order release of DC over a period of 24 hours to combat the on-going effects of any underlying inflammatory conditions. The triple-layered tablet delivery system would thus provide both rapid onset of pain relief as well as potentially address an underlying inflammatory cause. The design of a novel triple-layered tablet allowed for the desired release characteristics to be attained. During initial development work on the polymeric matrix it was discovered that only when combined with the optimized ratio of the release retarding polymer polyethylene oxide (PEO) in combination with electrolytic-crosslinking activity, provided by the biopolymer sodium alginate and zinc gluconate, could the 24 hour zero-order release of DC be attained. It was also necessary for this polymeric matrix to be bordered on both sides by the cellulosic polymers containing PC and TM. Thus the application of multi-layered tableting technology in the form of a triple-layered tablet were capable of attaining the rate-modulated release objectives set out in the study. The induced barriers provided by the three layers also served to physically separate TM and DC, reducing the likelihood of the bioavailability-diminishing interaction noted in United States Patent 6,558,701 and detected in the DSC analysis performed as part of this study. The designed system provided significant flexibility in modulation of release kinetics for drugs of varying solubility. The suitability of the designed triple-layered tablet delivery system was confirmed by a Design of Experiments (DoE) statistical evaluation, which revealed that Formulation F4 related closest to the desired more immediate release for PC and TM and the zero-order kinetics for DC. The results were confirmed by comparing Formulation F4 to typical release kinetic mechanisms described by Noyes-Whitney, Higuchi, Power Law, Pappas-Sahlin and Hopfenberg. Using f1 and f2 fit factors Formulation F4 compared favourably to each of the criteria defined for these kinetic models. The Ultra Performance Liquid Chromatographic (UPLC) assay method developed displayed superior resolution of the active pharmaceutical ingredient (API) combinations and the linearity plots produced indicated that the method was sufficiently sensitive to detect the concentrations of each API over the concentration ranges studied. The method was successfully validated and hence appropriate to simultaneously detect the three APIs as well as 4-aminophenol, the degradation product related to PC. Textural profile analysis in the form of swelling as well as matrix hardness analysis revealed that an increase in the penetration distance was associated with an increase in hydration time of the tablet and also an increase in gel layer thickness. The swelling complexities observed in the delivery system in terms of both the PEO, crosslinking sodium alginate and both cellulose polymers as well as the actuality of the three layers of the tablet swelling simultaneously suggests further intricacies involved in the release kinetics of the three drugs from this tablet configuration. Modified release dosage forms, such as the one developed in this study, have gained widespread importance in recent years and offer many advantages including flexible release kinetics and improved therapy and patient compliance.

Os materiais híbridos orgânico-inorgânicos constituem uma classe especial compostos, obtidos pela combinação adequada entre duas ou mais fases (orgânica e inorgânica), que têm recebido muita atenção nos últimos anos. Quando combinados em escala molecular, os nanocompósitos formados promovem o sinergismo entre as propriedades destas fases podendo produzir materiais com características e propriedades únicas e inusitadas que não são encontradas nas partes individuais. As particularidades dos novos materiais podem resultar em aplicações como melhoria de propriedades mecânicas, da estabilidade térmica, permeabilidade de gases, retardadores de chama, polímeros eletrólitos, dentre outras. As siliconas aniônicas são materiais poliméricos utilizados como agentes dispersantes, espumantes, emulsificantes e complexantes promovendo a compatibilidade entre a silicona e outros polímeros, permitindo a formulação de géis estáveis e limpos com aplicações principalmente na indústria de cosméticos. Hidróxidos Duplos Lamelares (HDL) são materiais cuja estrutura lamelar é constituída de camadas de um hidróxido duplo carregadas positivamente, com ânions hidratados no domínio interlamelar. A esfoliação de HDL é um processo que permite a separação em escala nanométrica das contrapartes inorgânica (do hidróxido duplo) do ânion interlamelar (que pode ser orgânico ou não). O foco do presente trabalho é a preparação e a caracterização de materiais híbridos orgânico-inorgânicos através da utilização de siliconas aniônicas funcionalizadas com os grupos fosfato, sulfato, ftalato e succinato como matriz orgânica e as lamelas esfoliadas de um HDL do sistema Zn-Al como aditivo inorgânico. Novos compósitos foram preparados, em blocos e na forma de filmes, a partir da interação entre as siliconas aniônicas e diferentes cargas do HDL esfoliado utilizado como aditivo. Os compósitos apresentaram modificações em suas características como aumento da estabilidade térmica, resistência mecânica e maleabilidade comparada às siliconas puras. Tais características podem ser aproveitadas para aplicações até então inexploradas por estes materiais. / Hybrid composites are a class of materials obtained by the appropriate combination of two or more phases (organic and inorganic), which have nowadays received a lot of attention. When these composites are combined at the molecular scale, the resulting nanocomposites resulting promote the synergism among the properties of the lonely phases and can then produce materials with unique and unusual characteristics and properties not found in individual species. The particularities of the new materials can result in applications such as the improvement of mechanical properties, thermal stability, permeability of gases, flame retarder, polymeric electrolytes, etc. Anionic silicones are polymeric materials used as dispersant, foaming, emulsifiant and complexant agents capable of promoting compatibility among the silicone and the other polymers, thus allowing the formulation of stable and clean gels for applications mainly in the cosmetic industry. Layered double hydroxides (LDH) are lamellar materials constituted of positively charged layers of a double hydroxide, with hydrated anions in the interlayer domain. The exfoliation of LDH is a process that allows to separate the inorganic sheets (of the double hydroxide) from the interlayer anion (which can be organic or not) at nanometric scale. The present work focus on the preparation and the characterization of organic-inorganic hybrid materials by using anionic silicones functionalized with the phosphate, sulfate, ftalato and succinate groups (organic matrix) and the layer of the exfoliated LDH of the Zn-Al system as the inorganic additive. New composites in block and films forms were prepared, starting from the interaction between the anionic silicones and different loads of LDH exfoliated as additive. The composites presented modifications in their characteristics such as the increase of thermal stability, mechanical resistance and malleability compared to pure silicones. Such characteristics can be used for applications in unexplored areas of these materials.

Praguicidas são substancias capazes de prevenir, destruir, repelir ou mitigar uma praga e por isso desempenham um papel de grande importância na agricultura moderna. A elevada utilização destes compostos visa atender à crescente demanda de produção de alimentos, e para isso pesquisas vem sendo realizadas para o desenvolvimento de novas formulações. Entretanto a utilização descontrolada destes compostos pode levar à contaminação de alimentos, solo, águas superficiais e subterrâneas. Os Hidróxidos Duplos Lamelares (HDL) ou argilas aniônicas apresentam estrutura lamelar na qual uma variedade de ânions podem ser intercalados entre as lamelas através de interações eletrostáticas, incluindo praguicidas ácidos. Estes materiais apresentam propriedades interessantes como blindagem das moléculas intercaladas e capacidade de liberação lenta das mesmas. Assim, os principais objetivos deste trabalho foram: estudar a intercalação dos herbicidas ácidos Triclopir, Fluroxipir e Quinclorac, utilizados na agricultura nacional, em HDL de dois sistemas diferentes; estudar a liberação dos herbicidas intercalados em soluções aquosas e em suspensões solo/água; estudar o comportamento dos materiais obtidos quanto à lixiviação em colunas de solo; e comparar a eficácia herbicida dos híbridos com os herbicidas livres através de bioensaios com plantas. Os resultados obtidos demonstraram que os herbicidas ácidos foram intercalados nos HDL dos sistemas Mg/Al e Zn/Al, resultando em sólidos lamelares com boa organização estrutural ainda desconhecidos da literatura. Os híbridos liberaram os herbicidas de forma lenta e contínua para a solução aquosa, diferentemente do observado para o caso dos herbicidas livres, que apresentaram liberação praticamente instantânea para a solução. O tipo de solo também não interferiu na liberação dos princípios ativos. Os estudos de lixiviação em colunas de solo demonstraram que os HDL são bons suportes para a liberação dos herbicidas, pois apresentam liberação lenta do ingrediente ativo, atrasando sua passagem através do solo e diminuindo as concentrações obtidas nos lixiviados. Os híbridos apresentaram a mesma eficácia herbicida que os princípios ativos em forma livre, regulando o crescimento das plantas de agrião nos testes de bioensaios, utilizando as doses de aplicação recomendadas no campo. / Pesticides are substances that prevent, destroy, repel, or mitigate a plague; hence, they play a crucial role in modern agriculture. The widespread use of these compounds aims to meet the growing demand for food production, and this research has focused on the development of new pesticides formulations. However, the uncontrolled use of these compounds can lead to food, soil, surface, and groundwater contamination. Layered Double Hydroxides (LDH) or anionic clays present a lamellar structure in which a variety of anions can intercalate via electrostatic interactions, including acid pesticides. These materials offer interesting properties such as shielding and slow release of intercalated molecules. In this contest, the main objectives of this work were: to study the intercalation of the acid herbicides Triclopyr, Fluroxypyr, and Quinclorac, employed in the Brazilian agriculture, into LDH of two different systems; to study the release of these herbicides into aqueous solutions and soil/water suspensions; to study the behavior of the obtained materials as to their leaching in soil columns; and to compare the herbicidal efficacy of the hybrids with free herbicides through bioassays with plants. Our results showed that acidic herbicides intercalated into the Mg/Al and Zn/Al LDH systems, to yield in lamellar solids with good structural organization, which are yet unknown in the literature. The hybrids released the herbicides slowly and continuously into the aqueous solution, in contrast with free herbicides, which presented virtually instantaneous release into the solution. The soil type did not interfere in the release of active ingredients. Leaching studies in soil columns showed that the LDH are good carriers for herbicides release - they feature slow release of the active ingredient, delaying its passage through the soil and decreasing the concentrations obtained in the leachate. The hybrids displayed the same herbicide effectiveness as the active ingredients in the free form; they regulated the growth of plants in bioassays, when the doses recommended for field use were applied.

Hidróxidos duplos lamelares (HDL) ou compostos lamelares do tipo da hidrotalcita, são materiais com estrutura formada pelo empilhamento de camadas de hidróxidos mistos de cátions divalentes e trivalentes contendo ânions hidratados nos espaços entre essas camadas. Os HDL apresentam uma grande diversidade de aplicações podendo ser utilizados como catalisadores ou suporte para catalisadores, trocadores iônicos, antiácidos, adsorventes. A adsorção de tensoativos em interfaces sólido/líquido é um fenômeno amplamente estudado devido à sua relação direta com estabilidade de colóides. A adsorção de tensoativo em superfícies de óxidos minerais é um processo importante no estudo de detergência, flotação de minerais, dispersão/floculação, crescimento de partículas em suspensão, melhoria na recuperação de óleos, lubrificação, cromatografia, entre outros processos. Mesmo sendo a adsorção um processo muito estudado em sólidos como carvão mineral, resinas poliméricas, polímeros, fibras naturais e sintéticas e em óxidos minerais, os trabalhos que tratam da adsorção de tensoativos em HDLs são escassos. Este projeto teve como principais objetivos a síntese e caracterização de HDL de magnésio e alumínio intercalado com ânion carbonato e o estudo das propriedades de adsorção de tensoativos aniônicos sulfonados, dodecilbenzenosulfonato e octilbenzenosulfonato, na superfície deste HDL, investigando o efeito da temperatura, do pH e da força iônica do meio e a influência do tamanho da cadeia hidrofóbica, no processo de adsorção. Para a síntese do HDL foi utilizado o método de coprecipitação a pH variável seguido de tratamento hidrotérmico. O material obtido foi caracterizado através das técnicas de difração de raios-X no pó, espectroscopia no infravermelho, análise termogravimétrica, análise térmica diferencial, adsorção de nitrogênio, análise elementar, e espalhamento de luz. A adsorção foi realizada pelo método de batelada, com o controle dos parâmetros envolvidos. Os resultados de adsorção mostraram que para ambos os tensoativos, as variáveis afetam a adsorção de maneira semelhante. Uma diminuição na quantidade de tensoativo adsorvida é observada em maiores temperaturas e em maiores valores de pH. Quando a adsorção é realizada em maior força iônica, uma maior quantidade adsorvida é observada para ambos os tensoativos estudados, exceto para o caso da adsorção de SDBS em concentrações acima da CMC. Uma competição entre a formação de micelas e a adsorção explica estes resultados. / Layered double hydroxides (LDH) or the hydrotalcite-like compounds are a class of material with structure formed by the stacking of positively charged layers of mixed divalent and trivalent cations hydroxides, containing in the interlayer spaces solvated anions. According to their chemical composition, crystallinity, thermal stability and other physical-chemical properties, the LDH can be used in a wide variety of application areas as catalysts or catalysts support, as antacid, as anionic exchanger, as adsorbents. The adsorption of surfactants at the solid/liquid interfaces has been extensively studied due to its direct relationship with colloids stability. The surfactant adsorption on mineral oxides is an important process in the study of detergency, mineral flotation, dispersion/flocculation, particles growth in suspension, oil recovery enhanced, lubrication and chromatography, among others. Even though this is an extensively studied process, few reports concerning to the adsorption of surfactants on LDH are available in the literature. The aim of this project was the synthesis and characterization of HDL of magnesium and aluminum containing carbonate as the intercalated anions and the adsorption study of sulfonated anionic surfactants, dodecylbenzenesulfonate and octylbenzenesulfonate, on this HDL, investigating the influence of the temperature, of the pH, of the ionic strength media and of the hydrophobic chain length on the adsorption process. The adsorbent was synthesized by the co precipitation method and characterized by PXRD analysis, infrared spectroscopy, TG/DT analysis, specific surface area, zeta potential measurements, and elemental chemical analysis. The adsorption was carried out by the batch method, with the control of the involved parameters. The results of the adsorptions showed that for both surfactants the variables affect the adsorption in a similar way. A decrease in the amount of adsorbed surfactant is observed at higher temperature and higher pH values. At higher ionic strength medium, the amount of adsorption increase for both surfactants, except for SDBS at equilibrium concentration higher than CMC. A competition between the micelle formation and adsorption can explain these results.

Perovskite-like layered structured (PLS) compounds display a range of interesting physical and chemical properties, including photocatalysis, photoluminescence, ion conductivity, electrochemical stability, magnetic properties, ferroelectricity and piezoelectricity. There are mainly three homologous series of PLS compounds distinguished by their different BO6 octahedra orientation: the Dion-Jacobson phase (A'An-1BnO3n+1); the AnBnO3n+2 phase; and the hexagonal phase (AnBn-1O3n). Some of the 4-layer AnBnO3n+2 compounds, like La2Ti2O7 and Sr2Nb2O7, have been reported to be ferroelectrics with super high Curie point (above 1300 °C), but no ferroelectric properties have been reported for the 2-layer and 3-layer AnBnO3n+2 compounds, and also there are few reports on the ferroelectric properties of compounds with Dion-Jacobson structure and hexagonal structure. Consequently, in this work, the crystallographic structures, microstructures, dielectric, ferroelectric and piezoelectric properties of (AxLa1-x)Ti2O7 (A = Sm and Eu) solid solutions with 4-layer AnBnO3n+2 structure, Pr3Ti2TaO11 with 3-layer AnBnO3n+2 structure, LaTaO4 with 2-layer AnBnO3n+2 structure, ABiNb2O7 (A = Rb and Cs) with Dion-Jacobson structure and Sr6TiNb4O18 with hexagonal structure were studied. Spark plasma sintering (SPS) was used to sinter ceramics with high density and preferred orientation. X-ray diffraction refinement (XRD) and transmission electron microscopy (TEM) were used to study the crystallographic structures and microstructures of the layer structured compounds. The ferroelectricity was studied using the current-electric field and polarization-electric field hysteresis loops. The Curie point and phase transitions were studied using the temperature dependence of the dielectric constant and loss. Piezoresponse force microscopy (PFM) was also used to study the ferroelectric domain structure of some layer structured compounds. In the first part of this work, the piezoelectric constant of La2Ti2O7 was improved by doping Sm. The crystallographic structure of (Eu1-xLax) 2Ti2O7 and (Sm1-xLax) 2Ti2O7 solid solutions were well studied. (AxLa1-x)Ti2O7 solid solutions were isomorphous with La2Ti2O7 when x was less than 0.5 for (EuxLa1-x)Ti2O7 and 0.8 for (SmxLa1-x)Ti2O7. When x was above their solubility limit, a biphase was observed. The XRD and Raman data suggested that the biphase consisted of (AxLa1-x)2Ti2O7 perovskite-like layered structure and pure Sm2Ti2O7 pyrochlore structure. Ferroelectric domain switching was observed in the I-E and P-E hysteresis loops for textured (SmxLa1-x)Ti2O7 (x < 0.2). The highest d33 was 2.8 pC/N for (Sm0.1La0.9)Ti2O7. In the second part, The Pr3Ti2TaO11 compound was demonstrated to have a 3-layer type II AnBnO3n+2 PLS structure belonging to space group Pmc21 with unit cell parameters a = 3.8689(3) Å, b = 20.389(2) Å, c = 5.5046(5) Å, and its ferroelectric properties were investigated. Analysis of the XRD and TEM results showed that Pr3Ti2TaO11 ceramics have an n = 3 (type II) heteroblock structure consisting of alternating n = 2 and n = 4 octahedral oxide layers. High resolution electron microscopy revealed the layered structure to be highly disordered, with faulting of the heteroblock structure and the coexistence of a n = 4 phase on a fine scale (nm), which was evident as a broadening of the XRD peaks of the ceramics. Pr3Ti2TaO11 ceramic exhibits a super-high Curie point (1415±5 °C). A small, but measurable piezoelectric constant d33 between 0.1 and 0.2 pC/N was detected for the samples poled above 900 °C under an electric field of 100~200 V/cm. Pure LaTaO4 powders with orthorhombic phase were be prepared by co-precipitation method. The orthorhombic LaTaO4 powders have a 2-layer perovskite-like layered structure with space group A21am, which was refined using Rietveld method. The single phase O-LaTaO4 ceramic was prepared using SPS with a slow cooling rate (20 °C/min). A d33 of 0.3 pC/N was obtained from the electric field induced orthorhombic phase. In the second part of this work, the ferroelectricity and piezoelectricity of CsBiNb2O7 with Dion-Jacobson type PLS structure was successfully demonstrated for the first time. The ferroelectricity and piezoelectricity of RbBiNb2O7, which have similar structure with CsBiNb2O7, were also fully studied. Highly textured 2-layer Dion-Jacobson ceramics ABiNb2O7 (A = Rb and Cs) were prepared by one-step SPS. High resolution TEM showed well ordered (0 0 1) lattice planes. Striped ferroelectric domains were observed using PFM. The ferroelectricity and piezoelectricity of CsBiNb2O7 has been demonstrated for the first time. The Tc of RbBiNb2O7 and CsBiNb2O7 are 1098±5 and 1033±5 °C, respectively. The piezoelectric constant of RbBiNb2O7 and CsBiNb2O7 were approximately 5 and 8 pC/N. Thermal depoling studies confirmed the Curie point and the stability of the piezoelectricity. Sr6Nb4TiO18 ceramics with non-centrosymmetric structure were successfully prepared, but no obvious evidence was found to prove its ferroelectricity. The untextured and textured 6-layer Hexagonal compound Sr6Nb4TiO18 was prepared by solid state reaction and spark plasma sintering. Its Curie point was found to be greater than 1500 °C. No ferroelectric properties were observed by studying of I-E and P-E loops, and no d33 was observed after poling.