Piezoelectric materials find applications in multitude of devices such as sensors, actuators and energy harvesters. However, most of these piezoelectric materials utilize lead-based systems which are becoming serious problem owing to the restrictions imposed by regulatory agencies across the globe. In the functional ceramics community, currently there is no problem more important than to find a replacement for lead-based piezoelectrics used for actuators. The electromechanical properties required for actuators (high piezoelectric constant, high coupling factor, low loss, and high transition temperatures) for known lead-free compositions are, however, far inferior to those of lead-based systems. There are three lines of research for addressing this fundamental problem "C (i) search for new systems through a combination of theory-based prediction followed by experimental effort (doping, solid solutions having a morphotropic (M) or polymorphic (P) phase boundary (PB), (iii) stabilization of metastable phases or finding the high temperature triclinic systems, and (iii) improving the properties of known compositions through microstructure optimization, domain engineering and multilayering. All these approaches are challenging and require innovation to make a significant impact on the current state-of-the-art. In this thesis, the later line of research was focused which is promising for near future applications, as it builds upon the known material systems with high depoling temperatures that have demonstrated the potential to be practical. In the first chapter, a novel method for the synthesis of lead-free (1-x)(Na0.5Bi0.5)TiO₃ "C xBaTiO3 piezoelectric ceramics was investigated. Initially, multiple compositions around morphotrpic phase boundary (MPB) were synthesized to identify the optimum composition 0.93Na0.5Bi0.5TiO3-0.07BaTiO3 (NBT-BT) for electromechanical effect. The new synthesis method starts with the synthesis of Na2Ti6O13 (NTO) whiskers which are then transformed into lead-free NBT-BT ceramics. Synthesis of NTO whiskers was performed using molten salt synthesis (MSS) method. Tape casting method was used to align the whiskers in base matrix powder and subjected to various processing temperatures to elucidate the microstructure and texture evolution. For this, scanning electron microscopy (SEM), high resolution transmission electron microscopy (HRTEM), atomic force microscopy (AFM) and energy dispersive spectroscopy (EDS) analysis were used as principal tools. The sintering process can be understood by dividing it into three stages, namely (i) transformation of monoclinic whiskers in to NBT-BT perovskite phase through topochemical reaction (<800°C), (ii) localized sintering confined on single whisker (800-1050°C), and (iii) liquid phase sintering as densification and grain growth occurs in the whole matrix (>1050°C). The concentric growth ledges observed on grain surfaces were found to be preferably confined on the corners of cubical grains indicating <111> growth direction. The Lotgering factor (f100) for the sintered matrix was found to decrease with increase in sintering temperature. The longitudinal piezoelectric constant (d33) of samples sintered for 20h at 1175°C, 1200°C and 1225°C was measured to be ~153 pC/N, ~216 pC/N and ~180 pC/N, respectively. Next, a novel method was developed for the synthesis of nanostructured lead-free ferroelectric NBT-BT whiskers with high aspect ratio using NTO as a host structure. High energy x-ray diffraction coupled with atomic pair distribution function (PDF) and Raman scattering analyses were used to confirm the average structure of lead-free NBT-BT whiskers as rhombohedral, i.e. a ferroelectricity enabling type. The HRTEM analysis revealed local monoclinic-type structural distortions indicating a modulated structure at the nanoscale in the MPB composition of lead-free NBT-BT whiskers. The structural rearrangement during the synthesis of lead-free NBT-BT whiskers was found to occur via translation of edge shared octahedra of NTO into a corner sharing coordination. The high temperature morphological changes depicting disintegration of isolated whiskers into individual grains due to higher grain boundary energy have been found to occur in a close analogy with Rayleigh-type instability. In lead-based ABO3 compounds, with B-site disorder, the origin of enhancement of piezoelectric properties near MPB has been associated with the presence of an intermediate monoclinic/orthorhombic state that bridges the adjacent ferroelectric rhombohedral and tetragonal phases. However, the origin of high piezoelectric response in lead-free ABO3 compounds with A-site disorder has not been conclusively established. In this thesis, a microscopic model derived from comparative analyses of HR-TEM and neutron diffraction was developed that explains the origin of high piezoelectric response in lead "C free MPB compositions of NBT-BT. Direct observation of nanotwins with monoclinic symmetry confirmed the presence of an intermediate bridging phase that facilitates a pathway for polarization reorientation. Monoclinic distortions of an average rhombohedral phase were attributed to localized displacements of atoms along the non-polar directions. These results provide new insight towards design of high performance lead "C free piezoelectric materials. Microstructure and domain structure play dominant role towards controlling the magnitude of piezoelectric coefficient and hysteretic losses in perovskites. Brick-wall like microstructure with large grain size and small domain size can provide significant enhancement in the magnitude of piezoelectric coefficient. A synthesis technique for lead-free piezoelectric NBT-BT system that can provide [001]pc/[012]Rh grain oriented ceramics with large grain size and an electrical poling technique that results in smaller domain size will have significant impact on the electromechanical response. In this research, a synthesis technique was developed and the processing variables that play deterministic role in achieving the large grain brick-wall like microstructure were explained. Interfaces in the microstructure were found to be coherent at the atomic scale facilitating the domain wall motion with applied electric field. The piezoelectric response was found to increase monotonously with the incease in the degree of texturing and optimized microstructure was found to provide 200% enhancement in the magnitude of piezoelectric coefficient as compared to its random form. In order to understand the mechanism of enhanced piezoelectric response in textured NBT-BT, in-situ neutron diffraction experiments revealed that characteristically different structural responses are induced in textured and randomly-oriented NBT-BT ceramics upon application of electric fields (E), which are likely related to the varying coherence lengths of polar nano regions and internal stresses induced by domain switching. In conjunction to focus on NBT-BT, new lead-free piezoelectric materials with enhanced piezoelectric response were synthesized. This study provides fundamental understanding of the enhanced piezoelectric instability in lead-free piezoelectric (1-x) BaTiO₃-xA(Cu1/3Nb2/3)O3₃ (A: Sr, Ba and Ca and x = 0.0-0.03) solid solutions. These compositions were found to exhibit large d33 of ~330 pC/N and electromechanical planar coupling constant (kp)~ 46% at room temperature. The piezoelectric instability in these compositions was found to increase with x despite monotonous decrease in the long range polar ordering. High energy X-ray diffraction coupled with PDFs indicated increase in local polarization. Raman scattering analysis revealed that substitutions on A and B-site both substantially perturbed the local octahedral dynamics and resulted in localized nano polar regions with lower symmetry. These localized polar distortions were found to persist much above the Curie temperature (Tc). Polarization "C electric field (P-E) hysteresis loop analysis indicated presence of the internal bias that was found to be correlated with the formation of polar defects. This defect structure was found to modulate the domain structure resulting in nano domains and broad domain walls with higher mobility as revealed through analysis from HR-TEM and piezoresponse force microscopy (PFM). The presence of nano domains and local structural distortions smears the Curie peak resulting in diffuse order-disorder type phase transitions. The electron paramagnetic resonance (EPR) investigations revealed that substitution of Cu²⁺ takes place on octahedral sites that are distorted due to Jahn-Teller effect. The A-sites were distorted by substitution of Sr and Ca on Ba-site possessing different ionic radii and electronegativity. The effect of these distortions on the variations in physical property was modeled and analyzed within the context of nanodomains and phase transitions. As an application, the solid solution with nominal composition of (1-x)BaTiO₃-xBa(Cu1/3Nb2/3)O₃ (BCN) (x = 0, 0.025) was synthesized by conventional mixed oxide route, followed by compositional modification with varying concentration of Sn, as given by the formulation: 0.975 BaTi1-ySnyO₃ "C 0.025 Ba(Cu1/3Nb2/3)O₃ (y = 0.05, 0.06, 0.075, 0.1). Room temperature XRD patterns showed decrease in tetragonality of BT after modifying with BCN (BT-BCN). Modifications with Sn lead to further decrement in tetragonality and the room temperature structure became cubic at 6.0 at% doping level. The decrement in tetragonality was accompanied by lowering of Tc.  BT-BCN doped with 6 and 7.5 at% Sn were found to exhibit diffuse phase transition accompanied by high dielectric constant "Ý 7000, low loss tangent "Ü 1% and grain size in the submicron regime ("Ü 1 "Ìm). These compositions were found to be promising for Y5V type multilayer ceramic capacitors (MLCCs). Lastly, the dielectric and ferroelectric responses of compositionally graded bilayer and trilayer composites consisting of BT and 0.975BaTiO₃-0.025Ba(Cu1/3Nb2/3)O₃ (BT-BCN) were investigated. Two types of graded bilayer samples were synthesized, one with same thickness of BT and BT-BCN while other with different layer thicknesses. The graded trilayer sample consisted of BT layer sandwiched between two BT-BCN layers of equal thickness. SEM and TEM images showed a sharp interface with needle-shape domains across the interface. The domain size on BT-side was found to be larger than that on BT-BCN-side. The temperature dependence of dielectric response for all composite systems was found to exhibit shifting of characteristic Curie peak compared to constituent material which was associated to coupling between layers. Moreover, the differences in grain size, tetragonality, domain mobility of each layer was found to perturb the electrical response of composite. The polarization mismatch between uncoupled BT and BT-BCN established internal electric field in composite specimen and defined new polarization states in each layer by perturbing free energy functional of the composite specimen. Dynamic hysteresis behaviors and power-law scaling relations of all specimens were determined from P"CE field hysteresis loop measurements as a function of frequency. All systems were found to exhibit similar dynamic scaling relationships. Hysteresis area, Pr and EC decreased with increasing frequency due to delayed response, but increased with increasing applied electric field due to enhancement of driving force. Trilayer system was found to exhibit strong internal-bias field and double hysteresis behavior. The coupling effect resulting due to polarization mismatch between layers had substantial influence on the dynamic hysteresis behavior and power-law scaling relations. / Ph. D.

Ligaments and tendons are rope-like structures in our body that possess time- and history-dependent material properties. Despite the many advances made in experimental and theoretical biomechanics, the material properties of these biological structures are still not fully characterized. This dissertation represents a step forward in the development of combined theoretical and experimental tools that capture the time- and history-dependent material properties of ligaments and tendons. The mechanical behavior of bundles of collagen fibers which form ligaments and tendons was investigated. Axial stress-stretch data and stress relaxation data at different axial stretches were collected by testing rat tail tendon fascicles. The experimental results demonstrated, for the first time, that the shape of the normalized axial stress relaxation curve depends on the axial stretch level thus suggesting that the fascicles are nonlinear viscoelastic. A constitutive model was then formulated within the nonlinear integral representation frame- work proposed by Pipkin and Rogers (1968). Unlike the well-known quasi-linear viscoelastic model, the proposed constitutive law was able to capture the observed nonlinearities in the stress relaxation response of rat tail tendon fascicles. By extending the constitutive model for collagen fiber bundles, a new nonlinear three- dimensional model for the stress relaxation of skeletal ligaments was formulated. The model accounts for the contribution of the collagen fibers and the group substance in which they are embedded. Published uniaxial experimental data on the stress relaxation of human medial collateral ligaments were used to determine the model parameters. The model predictions for simple shear in the fiber direction, simple shear transverse to the fiber direction, and equibiaxial extension were then examined and, for the case of simple shear in the fiber direction, such predictions were found to be in good agreement with published experimental data. The relationship between the mechanical response and structure of suspensory ligaments was examined by performing state-of-the-art small angle x-ray diffraction experiments in tandem with incremental stress relaxation tests. Specifically, small angle x-ray diffraction was used to measure changes in strain and orientation of collagen fibrils during the stress relaxation tests. Throughout the tests the collagen fibrils were found to gradually orient towards the loading direction. However, the collagen fibril strain did not change significantly suggesting that collagen fibers do not play a significant role in dissipating load during stress relaxation. / Ph. D.

No / Solvent influences on the crystallization of polymorph and hydrate forms of the nootropic drug piracetam (2-oxo-pyrrolidineacetamide) were investigated from water, methanol, 2-propanol, isobutanol, and nitromethane. Crystal growth profiles of piracetam polymorphs were constructed using time-resolved diffraction snapshots collected for each solvent system. Measurements were performed by in situ energy dispersive X-ray diffraction recorded in Station 16.4 at the synchrotron radiation source (SRS) at Daresbury Laboratory, CCLRC UK. Crystallizations from methanol, 2-propanol, isobutanol, and nitromethane progressed in a similar fashion with the initial formation of form I which then converted relatively quickly to form II with form III being generated upon further cooling. However, considerable differences were observed for the polymorphs lifetime and both the rate and temperature of conversion using the different solvents. The thermodynamically unstable form I was kinetically favored in isobutanol and nitromethane where traces of this polymorph were observed below 10°C. In contrast, the transformation of form II and subsequent growth of form III were inhibited in 2-propanol and nitromethane solutions. Aqueous solutions produced hydrate forms of piracetam which are different from the reported monohydrate; this crystallization evolved through successive generation of transient structures which transformed upon exchange of intramolecular water between the liquid and crystalline phases

No / Four new ternary crystalline molecular complexes have been synthesised from a common 3,5-dinitrobenzoic acid (3,5-dnda) and 4,4'-bipyridine (bipy) pairing with a series of amino-substituted aromatic compounds (4-aminobenzoic acid (4-aba), 4-(N,N-dimethylamino)benzoic acid (4-dmaba), 4-aminosalicylic acid (4-asa) and sulfanilamide (saa)). The ternary crystals were created through the application of complementary charge transfer and hydrogen-bonding interactions. For these systems a dimer was created through a charge-transfer interaction between two of the components, while hydrogen bonding between the third molecule and this dimer completed the construction of the ternary co-crystal. All resulting structures display the same acidpyridine interaction between 3,5-dnba and bipy. However, changing the third component causes the proton of this bond to shift from neutral OHN to a salt form, O(-) HN(+) , as the nature of the group hydrogen bonding to the carboxylic acid was changed. This highlights the role of the crystal environment on the level of proton transfer and the utility of ternary systems for the study of this process.

Yes / Spurred by the enormous interest in co-crystals from the pharmaceutical industry, many novel co-crystals of active pharmaceutical ingredients have been discovered in recent years and this has in turn led to an increasing number of reports on polymorphs of co-crystals. Hence, a thorough characterization and understanding of co-crystal polymorphs is a valuable step during drug development. The purpose of this study is to perform in situ structural analysis and to determine thermodynamic stability of a dimorphic co-crystal system, 1:1 caffeine-glutaric acid (CA-GA, Forms I and II). We performed thermal and structural characterizations by differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), hot-stage microscopy (HSM), slurry and in situ variable temperature X-ray diffraction (VTXRD). For completeness, we have also re-determined crystal structures of CA-GA Forms I and II at 180 K using single crystal X-ray diffraction. Our results revealed that Form II is stable and Form I is metastable at ambient conditions. Further, the results suggest that the dimorphs are enantiotropically related and the transition temperature is estimated to be 79 Celcius degrees. / This work was supported by Science and Engineering Research Council of A*STAR (Agency for Science, Technology and Research), Singapore.

Feldspars are one of the archetypical families of framework silicates. They not only comprise around 60% volumetrically of the Earth's crust, but are among some of the most structurally complicated minerals. Investigation into the structural behavior of various intermediate plagioclases at pressure has been undertaken with the intent of categorizing the elastic behavior with pressure across the solid solution series and establishing a conceptual model to characterize feldspar compression. Complex behavior has been observed in the Equation of State for plagioclase feldspars in excess of 3 GPa, including an anomalous softening of ordered albite in excess of 8.4 GPa (Benusa et al 2005: Am Min 90:1115-1120). This softening was not observed in the EoS for the more intermediate plagioclase compositions containing between 20 and 40 mol% of end-member anorthite. The calculated elastic compliance tensor sums at room pressure show a general stiffening with increasing anorthite component, small elastic changes at the C-1 to I-1 transition, and a dominantly first-order response at the P-1 to I-1 transition near end-member anorthite. The crystal structure of An37 plagioclase was determined by single-crystal X-ray diffraction. The compression mechanisms in An37 are similar to those in albite at lower pressures. The softening in albite at higher pressures is therefore attributed to the structural shearing in albite that is absent in An37 plagioclase up to 9.5 GPa. / Master of Science

The objective of this thesis is to improve understanding of the development of corrosion products (scales) that form on the inner walls of carbon steel pipelines in CO2-rich (sweet) oilfield environments. If well adherent to the carbon steel surface, such scales can significantly reduce the metal’s rate of corrosion. Typically, the open literature labels sweet corrosion scale as ferrous (II) carbonate (FeCO3) or siderite, although this may not always be the case. For example, Fe2(OH)2CO3 (chukanovite) and Fe3O4 (magnetite) are known to modify the protective character of a sweet corrosion product scale. Practical electrochemical methods for the assessment of substrate corrosion, and electron/photon-based characterisation techniques for investigating scale structure and composition, have revealed interesting aspects of the nature of sweet corrosion scale development on model high purity Fe and real-world pipeline steel surfaces. Concerning scale development on model Fe substrates immersed in CO2-saturated deionised water (buffered to pH = 6.8, T = 80°C, Ptotal = 1 bar), electrochemical data supplemented by grazing incidence x-ray diffraction (GIXRD) and scanning electron microscopy (SEM) show that a semi-protective mixed corrosion scale comprising siderite and chukanovite becomes a highly protective siderite scale with longer exposure time. The introduction of sodium chloride to the CO2-saturated solution (T = 80°C, pH = 6.8, Ptotal = 1 bar) impedes the rate of scale formation. Increasing [NaCl] from the start of experiment is suspected to limit the precipitation kinetics of sweet corrosion scale crystals, since chukanovite is no longer observed, and siderite formation is somewhat slowed as well. SEM imaging, using an electronic workfunction-sensitive detector (in lens), reveals nanoscale deposits on the corroded Fe surface in regions that are devoid of µm-scale crystals. With the Raman spectra from these regions considered, it is interpreted that the nanoscale deposits are likely amorphous iron carbonate, albeit oxidised to a significant extent. Moving to real-world carbon steel immersion in sweet solutions, a scale comprising predominantly chukanovite is observed (using GIXRD and SEM) on the 1% Ni weld zone (WZ) surface of a pipeline weld-joint, but not on adjacent, distinct regions (heat affected zones (HAZ) and base metal (BM)). This selective scaling is suggested to be due to some initial corrosion of the weld-joint, which generates sufficient [Fe2+(aq)], and a macro-galvanic effect across the weld, i.e. WZ is cathodic to HAZ and BM. Further, to gain mechanistic insight into compositional changes during sweet corrosion scale growth, an electrochemical cell for in situ GIXRD (named E-cell) has been developed and commissioned. Diffraction patterns acquired using synchrotron radiation, from a pipeline steel surface, reveal the formation and temporal evolution of a multicomponent corrosion scale. Accompanying electrochemical data suggest that the scale is quite protective.

No description available.

The objective of this research is to develop a water-based processing method for incorporating large filler loadings into nanocomposite systems. Specifically, cellulose nanocrystal/poly(vinyl alcohol) (CNC/PVA) nanocomposite aqueous suspensions and films were processed and characterized at CNC loadings up to 67 wt.% with respect to polymer concentration. Both aqueous suspended and freeze-dried CNCs were studied with this method. Two methods for incorporating the CNCs were investigated: solution processing and batch mixing of aqueous suspensions. The materials produced by these methods were characterized using rheology of aqueous suspensions and a method for understanding the morphology of these aqueous suspension through rheological characterization was developed. The CNC/PVA suspensions were dried and the structure of the film studied using x-ray diffraction, Fourier transform infrared spectroscopy, and differential scanning calorimetry. With regard to characterization of polymer structure by these methods, PVA crystallinity was seen to increase with increasing CNC loading. Finally, dynamic mechanical analysis and micro-tensile testing were conducted on consolidated films and CNCs were seen to increase modulus, yield stress but decrease strain at failure. Biodegradation studies were also conducted and CNCs were seen to increase the biodegradation characteristics of PVA. While the general trends in experimental data were the same, differences in properties between systems made with solution processing and batch mixing were observed, attributed to differences in the CNC dispersion. Overall, results indicated that this methodology is feasible for the industrially scalable production of highly loaded nanocomposites.

Analysis of the molecular speciation of organic compounds in solution is essential for the understanding of ionic complexation. The Raman spectroscopic technique was chosen for this purpose because it allows the identification of compounds in different states and it can give information about the molecular geometry from the analysis of the vibrational spectra. In this research the ionisation steps of relevant pharmaceutical material have been studied by means of potentiometry coupled with Raman spectroscopy; the protonation and deprotonation behaviour of the molecules were studied in different pH regions. The abundance of the different species in the Raman spectra of aqueous salicylic acid, paracetamol, citric acid and salicylaldoxime have been identified, characterised and confirmed by numerical treatment of the observed spectral data using a multiwavelength curve-fitting program. The non-destructive nature of the Raman spectroscopic technique and the success of the application of the multiwavelength curve-fitting program demonstrated in this work have offered a new dimension for the rapid identification and characterisation of pharmaceuticals in solution and have indicated the direction of further research. The work also covers the formation of novel cocrystal systems with pharmaceutically relevant materials. The existence of new cocrystals of salicylic acid-nicotinic acid, DLphenylalanine , 6-hydroxynicotinic acid, and 3,4-dihydroxybenzoic acid with oxalic acid have been identified from stoichiometric mixtures using combined techniques of Raman spectroscopy (dispersive and transmission TRS), X-ray powder diffraction and thermal analysis. Raman spectroscopy has been used to demonstrate a number of important aspects regarding the nature of the molecular interactions in the cocrystal. Cocrystals of salicylic acid - benzamide, citric acid-paracetamol and citric acid -benzamide have been identified with similar analytical approaches and structurally characterised in detail with single crystal X-ray diffraction. From these studies the high selectivity and direct micro sampling of Raman spectroscopy make it possible to identify spectral contributions from each chemical constituent by a peak wavenumber comparison of single-component spectra (API and guest individually) and the two- component sample material (API/guest), thus allowing a direct assessment of cocrystal formation to be made. Correlation of information from Raman spectra have been made to the X-ray diffraction and thermal analysis results. Transmission Raman Spectroscopy has been applied to the study cocrystals for the first time. Identification of new phases of analysis of the low wavenumber Raman bands is demonstrated to be a key advantage of the TRS technique.