This thesis focuses on materials whose properties are directly linked with the dimensionality of their structures. We utilise diffraction techniques to characterise three systems. The first of these is an organic crystal, 2,3,6,7,10,11-hexahydroxytriphenylene tetrahydrate that contains one-dimensional water channels. These channels are polar and net polarity is achieved at low temperatures. The structure undergoes a phase transition to a non-polar state at higher temperatures. Mapping this finding onto an Ising model is undertaken in this thesis. We also investigate the possibility of transforming the same crystals to an organic metal with oxidation. Furthermore, this work characterises two-dimensional layered structures silver(I) tricyanomethanide and nickel(II) cyanide. We show that the former possesses the unprecedented property of negative area compressibility and the latter shows ordinary compressibility behaviour. Both these structures exhibit area negative thermal expansion. Finally, we investigate copper(II) and cobalt(II) doping into the structure of nickel(II) cyanide and demonstrate that the latter leads to a 10-fold increase in area negative thermal expansion.

<p>Phase change materials (PCMs) has emerged as advanced functional materials for efficient thermal energy storage and release. Compared to other organic and inorganic PCMs, oxide-based PCMs have attracted growing interest because of small volume expansion, minor leakage issue, and moderate latent heat. In this dissertation, two special cases of oxide-based PCMs is discussed, i.e., vanadium dioxide (VO₂), and Bi-based perovskite/supercell structures. Specifically, VO₂ emerges as a focus of research because of its well-known semiconductor-to-metal transition (SMT) upon heating close to 68 °C. The intrinsic coupling of SMT and R-M1 structural change makes VO₂ a favorite material both scientifically interesting and technologically important for potential sensor and memory device applications. On the other hand, BFMO supercell structure originates from the double-perovskites, while the substrate-induced epitaxial strain induces the stacking and commensurate modulations of Fe/Mn double layers. The significantly enhanced multiferroic response is attributed to its non-centrosymmetric structure.</p> <p>In this dissertation, a comprehensive study on the FM integration and novel approaches to achieve broad range transition temperature (<em>T</em>_<em>c</em>) tuning is explored in VO₂ thin films. Specifically, three novel metal/VO₂ nanocomposite designs are discussed, i.e., Pt/VO₂, Ni/VO₂ and Li/VO₂, with different morphology and Tc tuning mechanisms. First, by reconstructing the energy band structure at the metal/VO₂ interface, bidirectional <em>T</em>_<em>c</em> tuning in Pt/VO₂ nanocomposites can be achieved owing to the size dependent work function of Pt NPs. Next, by engineering the morphology by lattice matching, diffusion kinetics, and interfacial mixing, the exploration on Ni/VO₂ nanocomposites achieve the combined goals of Tc tuning and magnetic incorporation/magneto-optical (MO) coupling. Finally, by varying Li concentration during the metal-ion intercalation, <em>T</em>_<em>c</em> of both VO₂(B) and VO₂(M1) thin films can be systematically tailored because of structural deformation and the change in charge carrier density. The demonstration of metal/VO₂ nanocomposite thin films reveals a promising approach to fulfill various working environments for VO₂-based novel electronics, photonics, and spintronics. Furthermore, the microstructure evolution of the ultrathin BFMO supercell structure as well as its physical properties is first studied. The robust ferromagnetic and ferroelectric response is preserved in the ultrathin structure less than 10 nm, making it an attractive candidate for next-generation spintronics based on 2D materials.</p>

The thesis entitled “Towards the Design of Functional Materials: Evaluation based on Crystal Structure, Photocatalysis and Conductivity Measurements” consist of six chapters. A short introductory note outlines the basis of designing functional materials, different synthetic procedures, characterization techniques and properties such as photocatalysis and ionic conductivity. Chapter 1 describes the effect of Ti doping on photocatalytic activity in orthorhombic perovskite type LnVO3. All the compounds were synthesized by solid state method. Rietveld refinement with high resolution PXRD reveals that the substituent Ti occupies V site rather than Ln Site. Ti substituted compound showed higher photocatalytic activity than the unsubstituted compound and is comparable with that of commercial catalyst. These classes of compounds showed specific degradation towards chlorinated compounds. Chapter 2 discusses the solution combustion synthesis of γ(L)-Bi2MoO6 and its photocatalytic activity under solar radiation. The particle sizes were in the range 300–500 nm with a band gap of 2.51 eV. The degradation of wide variety of cationic and anionic dyes was investigated under solar radiation. Despite the low surface area (<1 m2/g), γ(L)-Bi2MoO6 showed higher photocatalytic activity under solar radiation due to its electronic and morphological properties. Chapter 3 presents a series of visible light photocatalyst M2Ce2O7, synthesized via solution combustion method and characterized by powder X-ray diffraction, solid-state UV-Visible diffuse reflectance spectra, SEM and TEM. The structure of Bi2Ce2O7 has been determined using laboratory as well as synchrotron PXRD. It crystallizes in a disordered F-type structure. The particle sizes are in the range 5–6 nm, band gaps lie within the range 1.7 to 3.2 eV. Bi2Ce2O7 shows high photocatalytic activity, comparable to the commercial Degussa P-25 TiO2 under solar radiation. Chapter 4 examines the effect of Bismuth substitution on crystal chemistry, photocatalysis and conductivity in Sr3V2O8, a variant of palmierite class. These compounds were synthesized by ceramic method and powder X-ray data reveals the limit of the Bi substitution in Sr3-xBi2x/3V2O8 is x=0.4. Single crystal study followed by careful difference Fourier analysis shows that Bi occupies a unique 18h position which is different than Sr1 and Sr2 position. The experimental band gap for Sr3V2O8 was calculated to be 3.45 eV and upon substitution band gap of the material decreases and reaches a value 3.15 eV for the composition x=0.4. Compound exhibits photocatalytic activity specifically towards anionic dyes. However, Bi Substitution leads to lower photocatalytic activity. Chapter 5 describes synthesis, structure, phase transition and ionic conductivity in scheelite type Li0.5Ce0.5MoO4. The compound was synthesized by ceramic method and single crystal study reveals that it crystallizes in the space group I41/a and exhibits conductivity of ~10-3 Ohm-1cm-1 at elevated temperature( 700 °C). It undergoes a first order phase transition around 510 °C. The nature of this transition has been evaluated by laboratory and synchrotron PXRD, DSC, dielectric spectroscopy and variable temperature Raman spectroscopy. The phase transition is shown to be characterized by an iso-structural phase transition which is first example in literature for temperature induced Cowley’s “Type Zero” phase transition. Chapter 6 discusses a new methodology for generating functional materials for fast ion conductors. Several varients of hydrated sodium cadmium bisulfate, Na2Cd2(SO4)3⋅3H2O, Na2Cd(SO4)2⋅2H2O and Na2Cd(SO4)2⋅4H2O have been synthesized and their thermal properties followed by phase transitions have been invesigated. Na2Cd2(SO4)3⋅3H2O (space group P3c). Na2Cd2(SO4)3⋅3H2O loses water completely when heated to 250 °C and transforms to a dehydrated phase (I⎯43d ) whose structure has been established using abinitio powder diffration techniques. Na2Cd(SO4)2⋅2H2O (P21/c) transforms to α−Na2Cd(SO4)2 (space group C2/c) on heating to 150 °C which is a known high ionic conductor. However, when α−Na2Cd(SO4)2 is heated to 570 °C followed by sudden quenching in liquid nitrogen, β−Na2Cd(SO4)2 (P21/c) is formed. β−Na2Cd(SO4)2 takes up water from the atmosphere and gets converted completely to the Kröhnkite type mineral. Further, β−Na2Cd(SO4)2 has a conductivity behavior comparable to α form up to 280 °C, the temperature required for the transformation of β to α form.

<p>Cladophora cellulose polypyrrole composites are recognized as potential biomaterials with future applications in hemodialysis. In this project conductive Cladophora cellulose-polypyrrole (clad-ppy) composites were prepared using two different oxidizing agents: iron (III) chloride and phosphomolybdic acid (PMo). Cyclic voltammetry, conductivity and Specific surface area measurements were done to characterize the synthesized composites. Furthermore in vitro blood compatibility studies were performed. Whole blood was incubated with clad-ppy membranes and then blood was analyzed for platelet number reduction and complement activation products (C3a and sC5b-9). Clad-ppy with Iron (III) chloride membranes were found to be superior in terms of conductivity and surface area while Clad-ppy with PMo membranes were found to provoke less blood activation. The results indicated that each oxidizing agent gave distinct properties to the composite material.</p>

<p>New smart drugs demand new smart drug delivery systems and also new smart analysis methods for the drug delivery process and material characterization. This thesis contributes to the field by introducing a new electrodynamic approach for studying the drug diffusion proc-esses as well as the formation of a new type of drug delivery systems, the so called mesoporous nano excipients.</p><p>Drug diffusion processes from different pharmaceutical materials were examined. The transport of charged drug substances was investigated by electrodynamic methods; either as a release process governed by diffusion using the alternating ionic current method or by applying a voltage, sinusoidal or dc, to force the drug ions to move in an electric field.</p><p>Temperature-dependent drug release from microcrystalline cellulose tablets was examined in order to extract information about the diffu-sion process. Percolation theory was also employed to binary mixtures of an insoluble and electrically insulating matrix material together with a soluble and ionic conducting drug. Further, dielectric spectros-copy was proven to be a powerful method for examining the state of vesicle formation of drug and surfactant molecules in a carbopol gel. Finally, a new potential class of pharmaceutical materials were exam-ined, namely the AMS-n mesoporous materials, showing that the al-ternating ionic current method is powerful both in the study of the synthesis of and in the release process from these. </p>

Cladophora cellulose polypyrrole composites are recognized as potential biomaterials with future applications in hemodialysis. In this project conductive Cladophora cellulose-polypyrrole (clad-ppy) composites were prepared using two different oxidizing agents: iron (III) chloride and phosphomolybdic acid (PMo). Cyclic voltammetry, conductivity and Specific surface area measurements were done to characterize the synthesized composites. Furthermore in vitro blood compatibility studies were performed. Whole blood was incubated with clad-ppy membranes and then blood was analyzed for platelet number reduction and complement activation products (C3a and sC5b-9). Clad-ppy with Iron (III) chloride membranes were found to be superior in terms of conductivity and surface area while Clad-ppy with PMo membranes were found to provoke less blood activation. The results indicated that each oxidizing agent gave distinct properties to the composite material.

New smart drugs demand new smart drug delivery systems and also new smart analysis methods for the drug delivery process and material characterization. This thesis contributes to the field by introducing a new electrodynamic approach for studying the drug diffusion proc-esses as well as the formation of a new type of drug delivery systems, the so called mesoporous nano excipients. Drug diffusion processes from different pharmaceutical materials were examined. The transport of charged drug substances was investigated by electrodynamic methods; either as a release process governed by diffusion using the alternating ionic current method or by applying a voltage, sinusoidal or dc, to force the drug ions to move in an electric field. Temperature-dependent drug release from microcrystalline cellulose tablets was examined in order to extract information about the diffu-sion process. Percolation theory was also employed to binary mixtures of an insoluble and electrically insulating matrix material together with a soluble and ionic conducting drug. Further, dielectric spectros-copy was proven to be a powerful method for examining the state of vesicle formation of drug and surfactant molecules in a carbopol gel. Finally, a new potential class of pharmaceutical materials were exam-ined, namely the AMS-n mesoporous materials, showing that the al-ternating ionic current method is powerful both in the study of the synthesis of and in the release process from these.

abstract: ABSTRACT Along with the fast development of science and technology, the studied materials are becoming more complicated and smaller. All these achievements have advanced with the fast development of powerful tools currently, such as Scanning electron microscopy (SEM), Focused Ion Beam (FIB), Transmission electron microscopy (TEM), Energy dispersive X-ray spectroscopy (EDX), Electron energy loss spectroscopy (EELS) and so on. SiTiO3 thin film, which is grown on Si (100) single crystals, attracts a lot of interest in its structural and electronic properties close to its interface. Valence EELS is used to investigate the Plasmon excitations of the ultrathin SrTiO3 thin film which is sandwiched between amorphous Si and crystalline Si layers. On the other hand, theoretical simulations based on dielectric functions have been done to interpret the experimental results. Our findings demonstrate the value of valence electron energy-loss spectroscopy in detecting a local change in the effective electron mass. Recently it is reported that ZnO-LiYbO2 hybrid phosphor is an efficient UV-infrared convertor for silicon solar cell but the mechanism is still not very clear. The microstructure of Li and Yb co-doped ZnO has been studied by SEM and EDX, and our results suggest that a reaction (or diffusion) zone is very likely to exist between LiYbO2 and ZnO. Such diffusion regions may be responsible for the enhanced infrared emission in the Yb and Li co-doped ZnO. Furthermore, to help us study the diffusion zone under TEM in future, the radiation damage on synthesized LiYbO2 has been studied at first, and then the electronic structure of the synthesized LiYbO2 is compared with Yb2O3 experimentally and theoretically, by EELS and FEFF8 respectively. / Dissertation/Thesis / Ph.D. Materials Science and Engineering 2013

<div>Multifunctional characteristics of Bismuth-based oxides offer great opportunities to design a variety of devices exploiting either a single functionality or the synergistic multifunctionalities. In the past decades, strain engineering of thin films arose as a solution for fabrication of novel structures with highly desired properties. In this thesis, strain engineering has been applied to Bismuth-based oxides to explore the strain effect on thin film structures and functionalities.</div><div>BiFeO₃ (BFO) servers as the first study platform, because of its strain-induced phase transition and the corresponding diverse polarization properties. The strain effect of SrRuO₃ (SRO)-buffered substrates on ferroelectric and optical properties of BFO thin films has been investigated. A wide range of strain states have been achieved in BFO films. The ferroelectricity and bandgap have been effectively tuned even with partial strain relaxation. However, pure BFO suffers from high leakage current and large coercive field. To overcome these limitations, Sm-doped BFO (BSFO) systems emerged and has been used in controlling the microstructure and properties of BFO. Our detailed structure analysis proves the Sm doping amount in BSFO thin films can be tuned effectively via deposition temperature. Consequently, the Sm dopant influences phase formation of BSFO and the macroscopic ferroelectric properties. </div><div>Another member in Bismuth-based oxide family, Bi₂WO₆ (BWO), has been selected as the base material for the design of the two-phase nanocomposites, because of its unique layered structure and ferroelectric property. To introduce ferromagnetic component into BWO, two methods have been explored. The first method incorporates Mn cations into the BWO matrix (BWMO), and the second method couples CoFe2O4 (CFO) as secondary phase with BWO to form a vertically aligned nanocomposite (VAN) system. Both systems exhibit robust ferromagnetic and ferroelectric response at room temperature and demonstrate their promise as room temperature multiferroics for future spintronics and memory applications. </div><div>The studies in this dissertation demonstrate the great structure flexibility and tunable functionalities of BFO and BWO systems. It shows the potential structure modification and property control of other Bi-based oxides. In the last chapter, new experimental plans and directions are proposed. The connections between the strain engineering and the tunable material properties are being built for various applications. </div><div><br></div>

<p>Architected materials are a class of materials with novel properties that consist of numerous periodic unit cells. <a>In past investigations, researchers have demonstrated how architected materials can achieve these novel properties by </a><a>tailoring the features of the unit cells without changing the bulk materials</a>. <a>Here, a group of architected materials called Phase Transforming Cellular Materials (PXCMs) are investigated with the goal of mimicking the novel properties of shape-memory alloys.</a> <a>A general methodology is developed for creating 1D PXCMs that exhibit temperature-induced reverse phase transformations (i.e., shape memory effect) after undergoing large deformations. During this process, the PXCMs dissipate energy but remain elastic (i.e., superelasticity). </a>Next, inspired by the hydration-induced shape recovery of feathers, a PXCM-spring system is developed that uses the superelasticity of PXCMs to achieve shape recovery. Following these successes, the use of PXCMs to resist simulated seismic demands is evaluated. To study how they behave in a dynamic environment and how well their response can be estimated in such an environment, a single degree of freedom-PXCM system is subjected to a series of simulated ground motions. Lastly, the concept of PXCMs is extended into two dimensions by creating PXCMs that achieve superelasticity in two or more directions. Overall, the findings of this investigation indicate that PXCMs<a>: 1) can achieve shape memory and recovery effects through temperature changes, 2) offer a novel alternative to traditional building materials for resisting seismic demands, and 3) can be expanded into two dimensions while still exhibiting superelasticity. </a></p> <p> </p>