Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2001. / Includes bibliographical references (p. 99-102). / We present an extensive First Principles study of structure, defects and proton insertion in Mn02. It is shown that the paramagnetic extrapolations of spin-polarized results are essential to correctly reproduce pyrolusite as the ground state of Mn02. While many other structures are found to be near degenerate in energy with pyrolusite, no thermal disorder exists in the system up to several thousand degrees as the strong correlation of the Mn-vacancy order along the lines of face sharing octahedra removes any low-energy excitations from the system. Mn-vacancies compensated by protons, ubiquitously present in commercial Mn02 have a dramatic effect on phase stability and induce the formation of ramsdellite Mn02 and twinning defects. We believe these proton compensated Mn vacancies to be the source of the structural complexity of synthetic Mn02 produced either electrochemically or chemically. It is shown that protons are always covalently bonded to an oxygen atom in Mn02. In ramsdeHite, the proton prefers the pyramidal oxygen to the planar coordinated oxygen atom. In both pyrolusite and manganite, the protons may appear to be at an octahedral center in experiments as the activation barrier for hopping between the two stable sites on each side of the octahedral position is only about 25 meV. Introduction of die Wolff disorder and twinning defects is found to have a large adverse effect on the diffusivity of protons in [gamma]-Mn02. Protonation also increase barriers to proton migration due to Jahn-Teller distortion and H-H interactions. Results indicate that direct H-H interactions are not that significant compared to oxygen mediated indirect interactions, observed in manganite. Experimental and calculated ramsdellite discharge curves deviate significantly at the early stages of the reduction process. We believe that a significant source of this discrepancy is the presence of proton compensated Mn vacancies in real Mn02, which create local sites with higher discharge potential. Calculations also suggest that the ordered phase, observed in experiments at mid-reduction (groutellite, MnOOHo.5), may be due to lattice remaining coherent during intercalation. / by Dinesh Balachandran. / S.M.

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Materials Science and Engineering, 2015. / This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections. / Cataloged from student-submitted PDF version of thesis. / Includes bibliographical references (pages 126-130). / Recycling provides a key strategy to move towards a more sustainable society by partially mitigating the impact of fast-growing material consumption. Recent advances in reprocessing technologies enable recyclers to incorporate low-quality secondary materials into higher quality finished products. Despite technological development, the use of these materials in the re-melting stage to produce final alloys is still limited. This thesis addresses this issue by raising the following question: given the complexity of the reprocessing operational environment, what is the most effective way to manage two-stage recycling operations to maximize the usage of low-quality secondary materials? This thesis answers this question for two systems: when outputs from the reprocessing stage can be delivered (1) as sows and (2) as liquid metals to the re-melting stage. In the first system, the main barrier to use of these materials is the highly variable quality of raw materials. This study suggests the use of data mining as a strategy to manage raw materials with uncertain quality using existing data from the recycling industry. A clustering analysis provides criteria for grouping raw materials by recognizing the pattern of varied compositions. This grouping (binning) strategy using the clustering analysis increases the homogeneity and distinctiveness of uncertain raw materials, allowing recyclers to increase their usage while maintaining minimum information about them. In the second system, significant energy cost can be saved by immediately incorporating reprocessed secondary raw materials as liquid metal into final alloy production. In this case, the coordination between the reprocessing stage and the re-melting stage is critical. This study suggests integrated production planning for two stages. The mathematical pooling problem is used to model two-stage recycling operations. Integrated planning across the two operations can adjust batch plans and design intermediate products by reflecting demand information of final products. This approach maximizes the use of intermediate products as liquid in the remelting stage and, therefore, lowers energy cost significantly. Both strategies are applied to industrial cases of aluminum recycling to explore the benefits and limitations. The results indicate the potential opportunity to significantly reduce material costs and to increase the use of undervalued secondary raw materials. / by Jiyoun Christina Chang. / Ph. D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2011. / This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections. / Cataloged from PDF version of thesis. / Includes bibliographical references (p. 117-125). / Grain boundaries and their networks have a profound influence on the functional and structural properties of every class of polycrystalline materials and play a critical role in structural evolution and phase transformations. Recent experimental advances enable a full crystallographic characterization, including the boundary misorientation and inclination parameters, of grain boundaries. Despite these advances, a lack of appropriate analytical tools severely undermines our ability to analyze and exploit the full potential of the vast amounts of experimental data available to materials scientists. This is because the topology of the grain boundary space is unknown and even a well-studied part of the complete grain boundary space, the misorientation space, is relatively poorly understood. This thesis summarizes efforts to improve the representation of misorientation information and to understand the topology of the complete grain boundary space. First, the topology of the space of misorientations is discussed with a focus on the effect of symmetries on the minimum embedding dimensions in Euclidean space. This opens the door to a new method of representation of misorientation information in which grain boundaries can be uniquely colored by their misorientations. Second, conditions under which the topology of the grain boundary space has been resolved are presented. Resolving the topology of the complete grain boundary space not only facilitates statistical analysis of grain boundaries, but can also help describe the structure-property relationships of these interfaces. / by Srikanth Patala. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2006. / This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections. / Includes bibliographical references (p. 183-194). / Solid oxide fuel cells are a potential electrical power source that is silent, efficient, modular, and capable of operating on a wide variety of fuels. Unfortunately, current technologies are severely limited in that they provide sufficient power output only at very high temperatures (>800°C). One reason for this is because the electrodes have very poor (and poorly understood) kinetics. The work described in this dissertation involves the microfabrication of model systems with triple phase boundary lengths that varied over an order of magnitude to systematically quantify and ultimately improve the kinetics of platinum electrodes on the surface of yttria stabilized zirconia electrolytes. Platinum electrodes with well controlled geometry were sputtered onto the surface of bulk YSZ and onto sputtered YSZ thin films. An unexpected result was found whereby YSZ films of composition Y0.09Zr0.91O2-x had an ionic conductivity remarkably enhanced by a factor of 20-30. This is attributed to the films exhibiting nanometric grain sizes and thereby stabilizing the cubic morphology at considerably lower yttrium levels than is normally needed. This metastable cubic phase is suspected of having reduced defect ordering. / (cont.) Grain boundary resistance, which in YSZ is normally due to impurities that segregate and block ionic transfer, was found to also be significantly reduced in YSZ films. The films had a specific grain boundary conductivity enhanced by a factor of 30-100 compared to the bulk polycrystalline sample. This was believed to be due to the very low impurity content of the film grain boundaries. Concerning the electrode polarization resistance, it was found that the electrodes placed on bulk standards and films deposited at high temperatures were on par with the best electrode conductance values from the literature. However, when the electrolyte surface was a film deposited at reduced temperature, the resistance decreased further by a factor of 300-500. The cause of this was revealed to be silicon contamination on the surfaces of the poorer-performing electrolytes. Triple phase boundary length-specific resistances as low as 3.7·104 O·cm at 378°C and 4.0·107 O·cm at 215°C were measured; these appear to be the lowest ever recorded. The measurements are possibly the first electrochemical characterization of nearly silicon-free YSZ surfaces. This study emphasizes the key role of chemical purity at the electrode-electrolyte interface. / (cont.) Photolithography alone is unlikely to give technologically useful triple phase boundary lengths. In an attempt to achieve the triple phase boundary lengths needed for a practical device, reactive co-sputtering was used to produce composite Pt-YSZ thin films with a bi-continuous network morphology and grain sizes on the order of 30 nm. Such intimate mixing of the electronic and ionic conducting phases created an effective mixed ionic-electronic conductor with the entire surface of the film electrochemically active to the electrode reaction. The best processing conditions resulted in electrodes with an area specific polarization resistance less than 500 O·cm2 at 400°C and, by extrapolation, 10 O·cm2 at 511°C and 1 O·cm2 at 608°C. These films may enable operation of a micro-solid oxide fuel cell at intermediate temperatures (400-500°C), and perhaps even lower temperatures with further microstructural optimization. / by Joshua L. Hertz. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2007. / Includes bibliographical references (p. 133-140). / Manipulation of the distribution of phonons inM a solid is important for both basic science and applications ranging from heat management to reduction of noise in electronic circuits and creating materials with superior acoustic and acousto-optical properties. This thesis explores hypersonic phononic crystals as means to achieve control over high frequency acoustic phonons. An integrated approach to fabrication, measurement and analysis of hypersonic phononic crystals with band gaps in the GHz range is presented. First, the phonon dispersion relation for one dimensional polymeric phononic crystals fabricated by coextrusion of a large number of poly(methylmethacrylate)/poly(carbonate) and poly(methylmethacrylate)/poly(ethylene terephthalate) bilayer pairs is investigated as a function of a lattice constant and composition using Brillouin light scattering and numerical simulations. This set of relatively simple multilayer structures represents an excellent platform to gain a basic understanding of phononic band gap phenomena. In addition, their in-plane phonon dispersion is used to extract information about the elastic constants and glass transition temperatures of individual nanolayers in a periodic multilayer arrangement. Next, two dimensional epoxy/air phononic crystals fabricated in a photoresist using interference lithography are studied. These structures are 2D single crystalline, enabling direction-resolved measurements of their phonon dispersion relation. As a result, the complete experimental phononic band diagram is obtained and correlated with numerical simulations. Finally, phononic properties of three dimensional elastomeric poly(dimethylsiloxane) crystals are investigated and the mechanical tunability of their dispersion relation is demonstrated. / (cont.) This set of structures forms the basis for understanding how to design and fabricate acoustic and acousto-optical devices with performance characteristics that can be adjusted dynamically during operation. The investigations described in this thesis demonstrate both theoretically and experimentally that 1D, 2D and 3D periodic submicron structures have complex phonon dispersion relations at GHz frequencies. As a result, these crystals can be used to manipulate the flow of random thermal phonons as well as externally generated acoustic waves resulting in novel acoustic and thermal properties. / by Taras Gorishnyy. / Ph.D.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2011. / Cataloged from PDF version of thesis. / Includes bibliographical references (p. 90-92). / In order to satisfy the growing demand for renewable resources as a supply of electricity, much effort is being placed toward the development of battery energy storage systems that can effectively interface these new sources with today's electric grid. To be competitive with the prices dictated by the sources currently in use, namely fossil fuels, these new systems must be able to deliver energy at a cost of about $100/kWh for the active materials. Several battery systems have been developed and that target has been slowly coming into focus. The liquid metal battery attempts to redefine the typical storage system by maintaining components in a molten state and seeks to do so using cheap, widely available materials. One of the biggest problems facing the future of the LMB is that of resource scarcity. There are several candidate materials that can satisfy the operating needs of an LMB, but not all are available in large enough quantities to meet the new LMB demand without significant impact to the supply/demand equilibrium and, ultimately, price. A detailed model was built to investigate the use of various metals in this new technology and measure the impact expected as a result of large-scale LMB adoption. The report explains why antimony is the most likely candidate for the positive electrode due to its large, mature market and the relatively high energy output compared to other candidates. Alkali and alkaline earth materials make excellent candidates for the negative electrode and the vast quantities available will be more than enough to support the LMB market many times over. The analysis has also revealed a substantial concern that is often overlooked in battery development: electrolyte costs. The current use of ultra-pure, anhydrous salts cannot be sustained if the LMB is to be profitable and competitive. Large savings can be anticipated from purchasing tonnage-quantity salts, but the only way to bring these costs down to reasonable levels is through the use of lower-purity materials. This study shows that a reasonable LMB can be built with an active materials cost of less than $62/kWh and total system cost of around $1,000/kWh for a 1 MW facility. In the most optimistic case, assuming electrolyte costs on par with those of current battery technologies, the total sytem cost can be reduced to under $300/kWh, much cheaper than many of the most recent technologies. / by Michael C. Parent. / S.M.

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Materials Science and Engineering, 2015. / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 179-185). / Introduction: The motivation of this work is to create a platform that leverages the large area and low cost of Silicon wafers with the high performance of Ill-V materials. Ill-V semiconductor materials have enabled a host of electronic devices from record setting solar cells, high efficiency light emitting diodes, power amplifiers and high-mobility electron transistors. The last 60 years of research and development by the Si microelectronics industry has made the use of Si for microelectronics, power electronics and photovoltaics (PV) ubiquitous and low cost. The low cost of silicon technology is due to a mature and well developed supply chain infrastructure built from the microelectronics industry. While there has also been decades of research into III-V materials and electronic devices, widespread utilization has been limited due to the high cost of Ill-V substrates. Consequently Ill-V technologies have been limited to applications of high value added devices. Integration of high quality Ill-V materials on Si would open new dimensions of design space for electronic devices with high performance and at low cost. Potential applications could be the integration of light emitters, power amplifiers, RF radios and CMOS all on one large area low cost substrate. However, integration of these materials in non-trivial. Considerable challenges related to lattice mismatch, coefficient of thermal expansion mismatch, polarity mismatch and chemical incompatibility can degrade material quality and negate the potential benefits of Ill-V integration. This research specifically focuses on how to overcome these integration challenges to enable a high-efficiency, low-cost Ill-V/Si tandem solar cell. While the project motivation is solar, integration of Ill-V on Si in amenable for many semiconductor applications and the processes developed here can be generalized for other device structures. This research investigates the effect of growth processing parameters on the microstructure, electronic and optical properties of GaAsxP1 x alloys grown on Si substrates. From the knowledge gained in those studies, we demonstrate world class GaAsxP1 x single junction solar cells grown on Si substrates. This body of work serves as a demonstration of the potential of GaAsxP1 x solar cells integrated with Si solar cells and provides a tool kit for further optimization of cell design, processing and implementation. / by Timothy John Milakovich. / Ph. D.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2004. / Includes bibliographical references (p. 95-100). / (cont.) and filtration experiments, as well as other characterization techniques. Surface analysis is accomplished via x-ray photoelectron spectroscopy (XPS). Membrane samples are cleaned (in hydrogen peroxide or chromic-sulfuric acid (Chromerge)) and/or annealed (in 90⁰C deionized water), and their elemental surface composition and specific carbon binding environments are determined by XPS. Filtration experiments are done by alternating feed solutions of deionized water and a foulant (either bovine serum albumin or an oil/water emulsion). The flux of the feed solution is measured before fouling, during fouling, and after fouling, to determine the extent of fouling recovery. Also, the compositions of the permeates are analyzed via ultraviolet-visible spectroscopy to determine the rejection coefficient of the membrane. The data presented in this thesis show that PVDF blend membranes containing P(MMA-r-POEM) are capable of generating a fresh surface layer of PEO multiple times, even after extended cleaning sessions using concentrated acid. Membranes of varying thickness are shown to exhibit PEO-regenerative abilities, but it appears that thick membranes have better fouling recovery than thinner, filtration-series membranes. Also, it is found that a blend membrane stripped of all of its surface PEO (by a 24-hour-long exposure to Chromerge) is able to restore PEO to its surface with roughly 24 hours of annealing ... / Freshwater shortages are a tremendous problem for certain areas of the world, and given projected world population increases, they will pose a problem for a rising number of people in the future. A variety of technologies are currently used to extract usable water from wastewater, including water filtration membranes. Membrane technologies are promising because they require little energy and are scalable. However, many membrane materials tend to foul quickly when exposed to the organic species in wastewater feed streams. Approaches to preventing membrane fouling include surface grafting of hydrophilic polymers onto membranes and the use of hydrophilic polymers as the bulk material. The former approach works moderately well, but it requires an increased number of fabrication steps, and the surface treatments tend to lose their effectiveness over time. The use of hydrophilic bulk materials leads to loss of membrane strength and resistance to wastewater elements such as chlorine. Neither option provides membranes that can maintain fouling resistance for extended periods of time. This thesis investigates an alternative method of fouling prevention, first described by Hester et al. This approach involves the fabrication of blend membranes containing poly(vinylidene fluoride) (PVDF) and roughly 10 wt% of a comb polymer additive, poly(methyl methacrylate-r-poly(oxyethylene methacrylate)) (P(MMA-r-POEM)). The additive self-segregates to the membrane surface during fabrication and imparts long-term fouling resistance to the membrane. Even after harsh cleaning, which degrades the PEO chains present at the surface, membrane performance can be partially restored with a simple 18-hour anneal in a 90⁰C water bath. Membranes are subjected to both surface / by Caitlin Albright Devereaux. / S.M.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2007. / Includes bibliographical references. / The utility of incorporating continuous, nanoscale vanadium oxide phases within preferred domains of self-organizing copolymers was investigated towards the fabrication of composite, nanoarchitectured electrode materials for solid-state rechargeable batteries. In situ growth of cathodic phases within ion-conducting copolymer domains was explored as a means to control morphology and to increase the surface-area-to-volume ratio, thereby increasing the specific electrode area for faradaic reactions and decreasing ion diffusion distances within the electrode-active material. Copolymers of microphase-separating rubbery block and graft copolymers, previously developed as solid electrolytes, provide a matrix for directing the synthesis of an inorganic battery-active phase. The copolymers include poly[(oxyethylene)9 methacrylate]-block-poly(butyl methacrylate) (POEM-b-PBMA) with a domain periodicity of -35 nm made by atom transfer radical polymerization, and poly[(oxyethylene)9 methacrylate]-graft-poly(dimethyl siloxane) (POEM-g-PDMS) with a domain periodicity of-17 nm made by free radical polymerization. The resulting microphase-separated polymer is a structure of alternating hydrophilic (Li-ion conducting) and hydrophobic regions. / (cont.) Sol-gel chemistry involving a vanadium alkoxide precursor enabled the in situ growth of cathode-active vanadium oxide within the continuous ion-conducting POEM domains of the microphase-separated copolymers. Resulting films, termed POEM-b-PBMA/VOx and POEM-g-PDMS/VOx, were freestanding and mechanically flexible. Small angle x-ray scattering and transmission electron microscopy revealed the nanoscale morphology of the composite and confirmed the spatially-selective incorporation of up to 34 wt% VO, in POEM-b-PBMA and 31 wt% in POEM-g-PDMS. Electronically conductive components, necessary for wiring of the lithium-active vanadium oxide domains to the external circuit, were added through a variety of methods. Dispersions of acid-treated and cryo-ground carbon black within POEM-b-PBMA/VOx enabled the cycling of this material as a cathode. Reversible capacities of-~ 40 mAh/g were measured for batteries fitted with a polymer electrolyte doped with LiCF3SO3 and a lithium foil anode. Electrolyte thickness studies indicated battery performance was limited by the ionic conductivity of the solid electrolyte. / (cont.) Using liquid electrolyte resulted in improved capacity (at higher currents) over conventional composite cathodes made from sol-gel derived vanadium oxide without the polymer matrix. The vanadium oxide nanoarchitecture was preserved upon removal of the polymer by heat treatment. The resulting templated vanadium oxide, when repotted with carbon black and binder, exhibited improved capacity at high current over non-templated vanadium oxide cathodes. / by Elsa A. Olivetti. / Ph.D.

Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2001. / Includes bibliographical references (leaves 227-238). / The focus of this thesis was to investigate and characterize GaSb, GaInAsSb, and AlGaAsSb epilayers grown by organometallic vapor phase epitaxy (OMVPE). These epilayers were principally characterized using in situ spectral reflectance and ex situ transmission electron microscopy (TEM). An in situ spectral (380-1100 nm) reflectance monitoring system was designed and fitted to the OMVPE reactor. It was determined that longer wavelengths are more useful for quantitative growth rate analysis, while shorter wavelengths are more sensitive to the GaSb substrate oxide desorption process. It was also determined that the GaInAsSb and AlGaAsSb alloy compositions could be determined accurately using in situ reflectance ratios. Use of the in situ reflectance monitor to efficiently perform necessary reactor/growth calibrations was also demonstrated. Analytic functions were used to model the refractive indices of GaSb, AlGaAsSb, and GaInAsSb. Specifically, Adachi's Model Dielectric Function [1, 2] was curve-fit to data for GaSb between 400 and 1000 nm, and fourth-order polynomials were fit to data for GaSb and GaInAsSb between 1 and 3 gnm. A linear interpolation of binary functions was used to generate a refractive index model for AlGaAsSb between 1 and 3 m as a function of Al fraction. These models were helpful in interpreting in situ reflectance data, and also in designing distributed Bragg reflectors. Phase separation in GaInAsSb was studied using TEM. A wide range of microstructures was observed, from nearly homogeneous to strongly phase separated. / (cont.) It was seen that in phase separated samples, the composition modulations typically created and coupled to morphological perturbations in the surface. One interesting manifestation of the phase separation was the spontaneous formation of a natural superlattice (period typically 10-30 nm) throughout the epilayer. This superlattice had two variants: one parallel to the growth surface, and one tilted with respect to the growth surface. It was discovered that the tilted superlattice was coupled to surface to relieve surface strain associated with the superlattice ... / by Christopher J. Vineis. / Ph.D.