<p>Functional oxide-based thin films have attracted much attention owing to their broad applications in modern society. The multifunction tuning in oxide thin films is critical for obtaining enhanced properties. In this dissertation, four new nanocomposite thin film systems with highly textured growth have been fabricated by pulsed laser deposition technique. The functionalities including ferromagnetism, ferroelectricity, multiferroism, magnetoelectric coupling, low-field magnetoresistance, transmittance, optical bandgap and dielectric constants have been demonstrated. Besides, the tunability of the functionalities have been studied via different approaches.</p> <p>First, varies deposition frequencies have been used in vertically aligned nanocomposite BaTiO₃:YMnO₃ (BTO:YMO) and BaTiO₃:La_0.7Sr_0.3Mn₃(BTO:LSMO) thin films. In both systems, the strain coupling effect between the phases are affected by the density of grain boundaries. Increasing deposition frequency generates thinner columns in BTO:YMO thin films, which enhances the anisotropic ferromagnetic response in the thin films. In contrast, the columns in BTO:LSMO thin films become discontinuous as the deposition frequency increases, leading to the diminished anisotropic ferromagnetic response. Coupling with the ferroelectricity in BTO, the room temperature multiferroic properties have been obtained in these two systems.</p> <p> Second, the impact of the film composition has been demonstrated in La_0.7Ca_0.3MnO₃ (LCMO):CeO₂thin film system, which has an insulating CeO₂in ferromagnetic conducting LCMO matrix structure. As the atomic percentage of the CeO₂increases, enhanced low-field magnetoresistance and increased metal-to-insulator transition temperature are observed. The thin films also show enhanced anisotropic ferromagnetic response comparing with the pure LCMO film.</p> <p> Third, the transition metal element in Bi₃MoM_TO₉(M_T, transition metals of Mn, Fe, Co and Ni) thin films have been varied. The thin films have a multilayered structure with M_T-rich pillar-like domains embedded in Mo-rich matrix structure. The anisotropic magnetic easy axis and optical properties have been demonstrated. By the element variation, the optical bandgaps, dielectric constants as well as anisotropic ferromagnetic properties have been achieved. </p> <p> The studies in this dissertation demonstrate several examples of tuning the multifunctionalities in oxide-based nanocomposite thin films. These enhanced properties can broaden the applications of functional oxides for advanced nanoscale devices.</p><br>

<div>Despite the advances of analytical and numerical methods for composite materials, it is still challenging to predict the onset and evolution of their different failure mechanisms. Because most failure mechanisms are irreversible processes in thermodynamics, it is beneficial to model them within a unified thermodynamic framework. Noting the advantages of so-called generalized standard models (GSMs) in this regard, the objective of this work is to formulate constitutive models for several main failure mechanisms: brittle fracture, interlaminar delamination, and fatigue behavior for both continuum damage and delamination, in a generalized standard manner.</div><div><br></div><div>For brittle fracture, the numerical difficulties caused by damage and strain localization in traditional finite element analysis will be addressed and overcome. A nonlocal damage model utilizing an integral-type regularization technique will be derived based on a recently developed ``local'' continuum damage model. The objective is to make this model not only rigorously handle brittle fracture, but also incorporate common damage behavior such as damage anisotropy, distinct tensile and compressive damage behavior, and damage deactivation. A fully explicit integration scheme for the present model will be developed and implemented.</div><div><br></div><div>For fatigue continuum damage, a viscodamage model, which can handle frequently observed brittle damage phenomena, is developed to produce stress-dependent fatigue damage evolution. The governing equation for damage evolution is derived using an incremental method. A class of closed-form incremental constitutive relations is derived. </div><div><br></div><div>For interlaminar delamination, a cohesive zone model (CZM) will be proposed. Focus is placed on making the associated cohesive elements capable of displaying experimental critical energy release rate--mode mixture ratio relationships. To achieve this goal, each cohesive element is idealized as a deformable string exhibiting path dependent damage behavior. A damage model having a path dependence function will be developed, which will be constructed such that each cohesive element can exhibit designated, possibly sophisticated mixed-mode behavior. The rate form of the cohesive law will be subsequently derived.</div><div><br></div><div>Finally, a CZM for interlaminar fatigue, capable of handling brittle damage behavior, is developed to produce realistic interlaminar crack propagation under high-cycle fatigue. An implicit integration scheme, which can handle complex separation paths and mixed-mode delamination, is developed. Many numerical examples will be utilized to clearly demonstrate the capabilities of the proposed nonlocal damage model, continuum fatigue damage model, and CZMs for quasi-static and fatigue delamination.</div>

The thesis addresses two related problems. It is argued that the materiality of physical artifacts serves the purpose of expressing abstract information. In contrast, the intangibility of IT is of such a kind that it poses different conditions for expressing abstract information. The background problem concerns conditions and possibilities of designing information visualization artifacts that retain the experiential qualities typically associated with physical artifacts. Massification design is introduced as a design ideal that aims towards a design of visualization artifacts that cater to the need of intersubjective understanding of abstract and intangible information. Massification design is further articulated as an ideal where the designed artifact as such bears witness of its own meaning. This ideal is put in contrast to design that depends on arbitrary, interpretative conventions for people's understanding of visualization artifacts. It is argued that design striving towards this ideal should be theoretically informed. The main problem of the thesis concerns to what extent the theory of embodied realism can serve as an informing theory for massification design. In order to investigate embodied realism as a candidate for informing massification design, two design projects are presented. Based on the design projects and associated evaluations, it is suggested that an embodied realist foundation for massification has the capacity to constrain and suggest form for expressions of abstract information. Suggestively, embodied realism may also inform design in such a way that it affects the experience of using the artifacts. The evaluations also suggest that design that draws on embodied meaning may come in conflict with conventional ways of expressing information. To further investigate a foundation for massification it is there is a need to investigate foundations that stays sensitive to conventional expressions. Additionally, it is suggested that massification design can be understood as striving towards authentic experiences of IT.

<div>Accelerating the development of novel materials is one of the central goals of the Materials Genome Initiative and improving the predictive power of computational</div><div>material science methods is critical to attain this goal. Molecular dynamics (MD) is one such computational technique that has been used to study a wide range of materials since its invention in the 1950s. In this work we explore some examples of using and increasing the predictive power of MD simulations to understand materials phenomena and provide guidelines to design tailored materials. We first demonstrate the use of MD simulations as a tool to explore the design space of shape memory alloys, using simple interatomic models to identify characteristics of an integrated coherent second phase that will modify the transformation characteristics of the base shape memory alloy to our desire. Our approach provides guidelines to identify potential coherent phases that will achieve tailored transformation temperatures and hysteresis. </div><div><br></div><div>We subsequently explore ideas to enhance the length and time scales accessible via MD simulations. We first discuss the use of kinetic Monte Carlo methods in MD simulations to predict the microstructure evolution of carbon fibers. We ?find our approach to accurately predict the transverse microstructures of carbon fibers, additionally predicting the transverse modulus of these fibers, a quantity difficult to measure via experiments. Another avenue to increase length and time scales accessible via MD simulations is to explore novel implementations of algorithms involved in machine-learned interatomic models to extract performance portability. Our approach here results in significant speedups and an efficient utilization of increasingly common CPU-GPU hybrid architectures.</div><div><br></div><div>We finally explore the use of machine learning methods in molecular dynamics, specifically developing machine learning methods to discover interpretable laws directly from data. As examples, we demonstrate the discovery of integration schemes for MD simulations, and the discovery of melting laws for perovskites and single elements. Overall, this work attempts to illustrate how improving the predictive capabilities of molecular dynamics simulations and incorporating machine learning ideas can help us design novel materials, in line with the goals of the Materials Genome Initiative.</div>

<p dir="ltr">Conducting polymers have garnered enormous attention due to their unique properties, including tunable chemical structure, high flexibility, solution processability, and biocompatibility. They hold promising applications in flexible electronics, renewable energies, sensing, and healthcare. Despite notable progress in conducting polymers over the past few decades, most of them still suffer from complicated synthesis routes, limited processability, low electrical conductivity, and poor ambient stability compared to their inorganic counterparts. Additionally, the susceptibility of conducting polymers to high temperatures makes them not applicable in real-life electronics. To address the challenges of developing high-performance and stable conducting polymers, we present two key approaches: dopant innovation for polymer-dopant interaction engineering and the discovery of new conjugated polymer hosts. From the perspective of dopant design, we first utilize cross-linkable chlorosilanes (C-Si) to design thermally and chemically stable conductive polymer composites. C-Si can form robust siloxane networks and simultaneously<i> </i>dope the host conjugated polymers. Besides, we have introduced a new class of dopants, namely aromatic ionic dopants (AIDs). The use of AIDs allows for the separation of doping and charge compensation, two processes involved in molecular doping, and therefore leads to highly efficient doping and thermally stable doped systems. We then provide insights into the design of novel conjugated polymer hosts. Remarkably, we have developed the first thermodynamically stable n-type conducting polymer, n-doped Poly (3,7-dihydrobenzo[1,2-b:4,5-b′]difuran-2,6-dione) (n-PBDF). n-PBDF is synthesized from a simple and scalable route, involving oxidative polymerization and reductive doping in one pot in the air. The n-PBDF ink is solution processable with excellent ink stability and the n-PBDF thin film is highly conductive, transparent, patternable, and robust. In addition, precise control over the doping levels of n-PBDF has been achieved through chemical doping and dedoping. By tuning the n-PBDF thin films between highly doped and dedoped states, the system shows controllable conductivity, optical properties, and energetics, thereby offering potential applications in a variety of organic electronics. Overall, this research advances the fundamental understanding of molecular doping and offers insights for the development of high-conductivity, stable conducting polymers with tunable properties for next-generation electronics.</p>

<p>The Materials Genome Initiative (MGI) has established guidelines to accelerate the discovery, development, and implementation of advanced materials in order to address current and future challenges. A key area of interest is the pressing need for more efficient energy storage systems to support technologies such as electric vehicles and renewable energies. In this work, we present an Integrated Computational Materials Engineering approach for the development of novel solid-state electrolyte materials. In particular, we embark on a quest to unravel the potential of ceramic garnet lithium lanthanum zirconium oxide (LLZO) for next-generation battery technologies.</p> <p>Our exploration begins with an overview of the current state of the Materials Innovation Infrastructure (MII) and our rationale behind choosing LLZO. Through the use of machine learning techniques and molecular dynamics simulations, we aim for efficient material optimization. Our findings are reinforced through experiments by using these materials as inorganic fillers in composite polymer electrolytes. Our findings demonstrate that the combined use of these complementary techniques facilitates the discovery of potential alternative solid-state electrolytes. Finally, we propose future research directions in materials science for the design of advanced materials using these integrated approaches. </p>

<p>Modern structural materials utilize tailored microstructures to retain peak performance within the most volatile operating conditions. Features such as grain size, grain boundary (GB) character and morphology and secondary phases are just a few of the tunable parameters. By tailoring these types of microstructural features, the deformation behavior of the material is also altered. The localization of plastic strain directly correlated to material failure. Thus, a systematic approach was utilized to understand the effect of microstructural features on the localization of plastic deformation utilizing digital image correlation (DIC). First, at the macroscopic scale, strain accumulation is known to form parallel to the plane of maximum shear stress. The local deviations in the deformation pathways at the meso-scale are investigated relative to the plane of maximum shear stress. The deviations in the deformation pathways are observed to be a function of the accumulated local plastic strain magnitude and the grain size. Next, strains characterized via DIC were used to calculate a value of incremental slip on the active slip systems and identify cases of slip transmission. The incremental slip was calculated based on a Taylor-Bishop-Hill algorithm, which determined a qualitative assessment of deformation on a given slip system, by satisfying compatibility and identifying the stress state by the principle of virtual work. Inter-connected slip bands, between neighboring grains, were shown to accumulate more incremental slip (and associated strain) relative to slip bands confined to a single grain, where slip transmission did not occur. These results rationalize the role of grain clusters which lead to intense strain accumulation and thus serve as potential sites for fatigue crack initiation. Lastly, at GB interfaces, the effect of GB morphology (planar or serrated) on the cavitation behavior was studied during elevated temperature dwell-fatigue at 700 °C. The resulting γ′ precipitate structures were characterized near GBs and within grains. Along serrated GBs coarsened and elongated <a>γ′ </a>precipitates formed and consequently created adjacent regions that were denuded of γ′ precipitates. Dwell-fatigue experiments were performed at low and high stress amplitudes which varied the amount of imparted strain on the specimens.<a> Additionally, the regions denuded of the γ′ precipitates were observed to localize strain and to be initial sites of cavitation.</a> <a>These results present a quantitative strain analysis between two GB morphologies, which provided the micromechanical rationale for the increased proclivity for serrated GBs to form cavities.</a></p>

<div>The global demand for energy of mankind, the ever-increasing cost of energy, and the expected depletion of fossil energy carriers within the next centuries urge the exploration of alternative and more sustainable ways to provide energy. The current quest for energy-efficient technologies for the replacement of existing cooling devices has made the magnetocaloric effect a field of current scientific interest. Cooling technologies based on magnetic refrigerants are expected to have a better environmental impact compared with those based on the gas compression-expansion cycle. This technology provides an alternative for refrigeration applications with advantages, such as high energy efficiency, environmental friendliness, and low power consumption. In search of promising magnetocaloric materials, several rare earth-depleted transition metal-based materials were designed and investigated.</div><div>In this work, RCrxAl2-x and RZnAl (R = Gd, Tb, Dy, Ho) belonging to the ternary rare-earth transition-metal Laves phases, were chosen as the starting point to establish the effect of valence electron concentration (VEC) on the magnetic behavior and magnetocaloric effect. Our result and the results from the previously studied RTAl phases (T = Cu, Ni, Co, Fe, Mn) shows that the perturbation of the valence electron concentration at the Fermi level is found to be the driving force that dictates the crystal structure, magnetocaloric and magnetic properties of these systems. Most notably, the decrease in the valence electron concentration at the Fermi level leads to an increase in the curie temperature.</div><div>In addition, we have further extended this theory to GdNiAl2 systems. GdNiAl2 is a known magnetocaloric material which exhibits an isothermal magnetic entropy change of ΔSM = 16.0 Jkg-1K-1 at TC = 28K under a magnetic field change from 0-5T. However, the low TC limits its application as a room temperature refrigerant. We, therefore, substituted Co for (Ni/Al) in the structure of GdNiAl2, intending to substantially perturb the position of the Fermi level of Ni since that will lead to a decrease in the VEC and hence elevate the TC. The study was also extended to another Icosagenides (Ga,), which saw the substitution of Ga for Al in GdNiAl2 and its Co substituted analogs. The Ga analogs exhibit complex magnetic behavior with a cascade (multiple) of magnetic transitions, as opposed to the rather simple magnetism of their Al congeners.</div>

<p></p><p>Global demand for high performance, low cost, and eco-friendly electronics is ever increasing. Ion/charge transport ability and mechanical adaptability constitute two critical performance metrics of battery and semiconductor materials, which are fundamentally correlated with their structural dynamics under various operating conditions. It is imperative to reach the mechanistic understanding of the structure-property relationships of electronic materials to develop principles of materials design. Nevertheless, the intricate atomic structure and elusive phase behaviors in the operation of devices challenge direct experimental observations. Herein, we employ a spectrum of modeling methods, including quantum chemistry, ab-initio modeling, and molecular dynamics simulation, to systematically study the phase dynamics and physico-mechanical behaviors of multiple electronic materials, ranging from transition-metal cathodes, polymer derived ceramics anodes, to organic semiconductor crystals. The multiscale atomistic modeling enriches the fundamental understanding of the electro-chemo-mechanical behaviors of battery materials, which provides insight on designing state-of-the-art energy materials with high capacity and high structural stability. By leveraging the genetic-algorithm refined molecular modeling and phase transformation theory, we unveil the molecular mechanisms of thermo-, super- and ferroelastic transition in organic semiconductor crystals, thus promoting new avenues of adaptive organic electronics by molecular design. Furthermore, the proposed computational methodologies and theoretical frameworks throughout the thesis can find use in exploring the phase dynamics in a variety of environmentally responsive electronics.</p><p></p>

Over the last decade, a confluence of strategic and security concerns has threatened the European Union’s survival both within and beyond its political dimension. As a result, security and defence have risen to the top of the EU’s political agenda, culminating in the approval of the EU Global Strategy (EUGS) in 2016. The EUGS represented a watershed moment in the EU’s Common Security and Defence Policy: the EU agreed on ambitious levels of security and defence. The new policy is based on supporting capacity building among member states through instruments such as PESCO. Nonetheless, these instruments have caused variations in patterns of member state behaviour that have enhanced defense integration. This research aims to understand what was the PESCO institutional effect on Member States' preferences and how it has affected the European security and defense goals. The research highlights the role of European agencies and how they contributed to solve collective action problem through a ‘forum effect' on participants, using pro-actively the task of assessing co-operative projects proposals. As a result, PESCO’s institutional effect led to cooperative outcomes between nations that allowed them to overcome coordination dilemmas, namely uncertainty about the willingness to contribute to a common project, which is typical of defense cooperation. Here, we used Rational Choice Institutionalism theory to investigate the PESCO project structure and its interaction with the European Defence policy. Cooperation between participating member states is presented within a cooperative game action, as part of a theoretical approach to game theory. It explains formally how PESCO entails elements to overcome collective action problem among participating member states, while emphasising the institutional design that promoted the European interests, and how this has led to more Europeanised security and defence. Findings are interpreted under the Differentiated integration concept.