No description available.

No description available.

No description available.

No description available.

No description available.

No description available.

In the process of developing my thesis, I wanted to let go of the contemporary way of thinking about the relationship between architecture and sustainability, which lately tends to be through a lens of applied technology and a baseline understanding of building code that assumes the structure will be designed around an HVAC system that runs 24/7/365 and windows that will never open. I found it difficult to shed that habit, as the first sketches I produced showed massive amounts of insulation in the walls (which again, assumes that the interior air is mechanically conditioned). I thought about how long air conditioning has been a factor in culture today. Just one generation ago, young people were growing up in homes that didn't have air conditioning, or if they did, it was space-based, cooling whatever room happened to be occupied. Certainly, the generation before the previous did not live in a culture where air conditioning was an assumed part of building design. We're now spending more time huddled in our air conditioned homes, which is harmful to our health, distorting the way in which our bodies naturally acclimatize to changing weather. Air conditioning was once considered a luxury expense, and now is practically, or actually, illegal to be without. In addition to the relationship between architecture and air, I also thought about water. Where do we get our potable water from and how? Is the way we currently collect, filter, distribute, receive, use, and dispose of water the best practice for keeping our rivers and aquifers healthy and clean? What about the way we heat our buildings? Every apartment I've lived in the city of Richmond, VA has had at least one fireplace, and they are all bricked up. My current apartment has two chimneys, one in the living room and one in the bedroom, both of which have been long forgotten when the building was hooked up to gas heat. I look around the skyline of my neighborhood and see hundreds of unused chimneys. Is that progress? Is the technology we have now to heat homes more efficient, able to provide more comfort, or better for our environment that what we had used for staying warm in the winter for thousands of years? Lastly, I thought about the relationship between architecture and landscape, especially in regard to plants and animals with which we share our habitat. Not just the native plants and animals that happen to be around us, but also the plants and animals we choose to cultivate and raise. I also think architecture also has a place in the reconsideration of our culture's relationship with food, which is to say, our relationship with the earth, our source of food. I was adamant that the site I chose, and the way in which I created architecture on it, would have a positive impact on both the people who visit, and the local ecosystem. In order to stay focused on my concept of what sustainability is for the future of architecture, rather than what society tells me sustainability should be, I framed my argument around the four elements: air, water, fire and earth. As I dove into developing a program and designing structure and landscape, I used these elements as a framework, my own baseline for what good, comfortable, and environmentally responsible architecture should be. / Master of Architecture / How can I redefine conservation through site and architectural design? I’m going to test a new way to think about environmentally responsible design by designing an off-grid habitat and systems sensitive artists’ retreat in a place that not only has personal meaning to me, a popular getaway spot for Richmond, VA locals, but is currently under threat of 85,000 acres of groundwater-contaminating natural gas fracking in adjacent counties, a thousand acre nearby bald eagle habitat-destroying golf resort development, and irresponsible but difficult to change agricultural practices allowing rampant overgrowth of algae and bacteria severely undermining the health of the river’s ecosystem. The program I chose to investigate also has personal meaning to me, and is usually considered an unsustainable practice: ceramic art. I began learning ceramics my first semester of graduate school and quickly became hooked. However, I noticed many fossil fuel dependent energy and water-intensive practices that were considered quite normal at the studios I worked in at the time. However, the longer I was exposed to ceramics and the more studios I visited, I found more people that approached their making methodology through a conservational lens. They were able to teach me their methods and over time I learned how to properly reclaim clay and use limited and recycled water in the process of making pots and cleaning up the studio. There are still many more aspects of the art to study and perfect, some of which I begin to tackle in my thesis design. Merging the retreat nature of the site and its needs for an intervention to achieve a greater potential for human and environmental health, preserving and protecting the river for its beauty, health, retreat and recreational purposes, and my growing interest in the usually wasteful and environmentally irresponsible art form of ceramics-making launched a thesis level investigation into how to both live in a community that satisfies our basic needs as humans and make this type of art I’ve been drawn to recently in a responsible way.

Yes / The paper attempts to explain the chronological gap between middle Neolithic and Early Bronze Age ceramics and examines the processes by which the latter could have developed from the former despite an 800 year hiatus.

In recent years bismuth-based, layer-structured perovskites such as SrBi2Nb2O9 (SBN) and SrBi2Ta2O9 (SBT) have been investigated extensively, because of their potential use in ferroelectric random access memories (FeRAMs). In comparison with non-layered perovskite ferroelectrics such as Pb(Zr,Ti)O3 (PZT), these offer several advantages such as fatigue free, lead free, low operating voltages and most importantly their ferroelectric properties are independent of film thickness in the 90 to 500 nm range. For FeRAM device applications, large remnant polarization (Pr), low coercive field (Ec) accompanied by high Curie temperature (Tc) are required for better performance and reliable operation. Much effort has been made to improve the ferroelectric properties of SBN and SBT ceramics by doping on A or B sites. It was known in the literature that partial substitution of Sr2+ by Bi3+ ions in SBN and SBT would increase the Curie temperature and improve the dielectric properties. The focus of the investigations that were taken up was to improve the electrical, dielectric and ferroelectric characteristics of SrBi2Nb2O9 ceramics. It was reported that the ferroelectric and nonlinear optical properties of LiNbO3 and LiTaO3 could be improved when vanadium, the lightest element in group V of the periodic table is substituted for Nb or Ta along with Li and three oxygens. It is with this background the investigations have been taken up to see whether one can extend the same argument to the Aurivillius family of oxides. Therefore, the central theme of the present investigations aimed at substituting Nb5+ by a smaller cation V5+ in SBN and study its influence on the formation temperature, sinterability, structural and microstructural characteristics apart from its physical properties. Recently the optical properties of this material have been recognized to be important from the optical device point of view. Unfortunately single crystal growth of vanadium doped SBN was hampered because of the bismuth and vanadium loss (high volatility) observed in the process of growth. One of the routes that attracted our attention has been the glass-ceramic. It would be interesting to visualize the behavior of crystallites of nano/micrometer size embedded in a glass matrix as these crystals were known to give rise to exotic properties. One of the crucial steps in the process of fabrication of a glass nanocrystalcomposite system in which crystalline phases have symmetries that would eventually give rise to basic non - centrosymmetric properties such as piezoelectric, pyroelectric and Pockels effects, has been to choose a compatible matrix material associated with easy glass forming capability and the ability to evenly disperse dipolar defects within itself. Recent investigations into strontium borate SrB4O7 (SBO), lithium borate Li2B4O7 (LBO) glasses indicated that LBO by virtue of its favorable structure, thermal and optical properties would form a suitable host glass matrix for dispersing layer structured ferroelectric oxides belonging to the Aurivillius family of oxides. Since lithium borate has wide transmission window, it was worth making an attempt to fabricate optical composite of Li2B4O7 (LBO) and vanadium doped SrBi2Nb2O9 (SBVN) and to study its structural, dielectric, pyroelectric, ferroelectric and optical properties. Therefore the present thesis reports detailed investigations into the effect of vanadium doping on the structural and various physical properties of an n = 2 member of the Aurivillius family of oxides in the polycrystalline form and novel glass composites comprising nano/microcrystallites of this phase. Chapter 1 comprises a brief introduction to the dielectric, pyroelectric, ferroelectric and nonlinear optical properties of materials. In addition to the principles and phenomena, the material aspects of these important branches of physics are discussed. It also forms a preamble to the glasses, criteria for glass formation, glass – ceramics and subsequently ferroelectric and nonlinear optical effects that were observed in glasses and glass - ceramics. Chapter 2 describes the material fabrication techniques adopted to prepare polycrystalline and grain – oriented ceramics, glasses and glass nanocrystalcomposites. The details of various structural, dielectric, pyroelectric, ferroelectric and optical measurement techniques employed to characterize these materials are also included. Chapter 3 discloses the fabrication of strontium bismuth niobate ceramics and their characterization for dielectric and impedance properties. The dielectric properties of strontium bismuth niobate ceramics have been modeled based on Jonscher’s Universal formalism. The coefficients of the Jonscher’s expression, exponent n(T) undergoes a minimum and A(T) exhibits a peak at the Curie temperature, Tc (723K). A strong low frequency dielectric dispersion (LFDD) associated with an impedance relaxation has been found to exist in these ceramics in the temperature range 573 - 823K. The Z′′ of the AC complex impedance showed two distinct slopes in the frequency range 100Hz-1MHz suggesting the existence of two dispersion mechanisms. The exponents m and n were obtained from the curve fitting. The exponent n was found to exhibit a minimum at the Curie temperature, Tc (723K) whereas the m was temperature independent. Chapter 4 deals with the fabrication of vanadium doped SrBi2Nb2O9 ceramics and their characterization for microstructural, dielectric, pyroelectric and ferroelectric properties. The average grain size of the SrBi2Nb2O9 (SBN) ceramic containing V2O5 was found to increase with increase in V2O5 content. The dielectric constant (εr) as well as the dielectric loss (D) increased with increase in grain size (6µm-17µm). The pyroelectric coefficient was found to be positive at 300K and showed an increasing trend with increasing grain size. Interestingly, the SrBi2(Nb0.7V0.3)2O9-δ ceramics consisting of 17µm sized grains showed higher remnant polarization (Pr) and lower coercive field (Ec) than those with grains of 7µm. Chapter 5 deals with the dielectric properties which were studied in detail in the 100Hz to 1MHz frequency range at various temperatures (300 – 823 K) for undoped and vanadium (10 mol%) doped SrBi2Nb2O9 (SBVN10) ferroelectric ceramics. A strong low frequency dielectric dispersion was encountered in these ceramics in the 573 – 823 K temperature range. The dielectric constants measured in the wide frequency and temperature ranges for both the samples were found to fit well to the Jonscher’s dielectric dispersion relations. The dielectric behavior of SBN and SBVN10 ceramics was rationalized using the impedance and modulus data. The electrical conductivity studies of layered SrBi2(Nb1-xVx)2O9-δ ceramics with x lying in the range 0 to 0.3 (30 mol%) were centered in the 573 – 823K temperature range as the Curie temperature lies in this range. The concentration of mobile charge carriers (n), the diffusion constant (D0) and the mean free path (a) were calculated using Rice and Roth formalism. The conductivity parameters such as ion hopping rate (ωp) and the charge carrier concentration (K′) term have been calculated using Almond and West formalism. The afore mentioned microscopic parameters were found to be V2O5 content dependent in SrBi2(Nb1-xVx)2O9-δceramics. Chapter 6 describes the fabrication of partially grain – oriented SrBi2(Nb1-xVx)2O9-δ (0 ≤x≤3.0 in molar ratio) ceramics and characterization for their structural, microstructural, dielectric, pyroelectric and ferroelectric properties. The grain – orientation factor and the microstructural features were studied by XRD and scanning electron microscopy as a fuction of sintering temperature and V2O5 content. The dielectric constant measured along the direction parallel and perpendicular to the pressing axis has shown a significant anisotropy. The pyroelectric and ferroelectric properties were superior in the direction perpendicular to the pressing axis (polar) to that in the parallel direction. The fabrication and characterization details of (100 – x) (Li2B4O7) – x (SrO - Bi2O3 - 0.7 Nb2O5 – 0.3 V2O5) (10 ≤ x ≤ 60, in molar ratio) glasses and glass nanocrystal composites are dealt within Chapter 7. The nanocrystallization of strontium bismuth niobate doped with vanadium (SrBi2(Nb0.7V0.3)2O9-δ(SBVN)) has been demonstrated in Li2B4O7 glasses. The glassy nature of the as – quenched samples was established by differential thermal analyses (DTA). The amorphous nature of the as – quenched glasses and crystallinity of glass nanocrystal composites were confirmed by X – ray powder diffraction studies. High resolution transmission electron microscopy (HRTEM) of the glass nanocrystal composites (heat – treated at 783K/6h) confirm the presence of nano rods of SBVN embedded in Li2B4O7 glass matrix. Chapter 8 presents the physical properties of the glasses and glass nanocrystal composites. Dielectric constant of both the as – quenched and glass nanocrystal composites was found to increase with increase in the composition, whereas the loss was observed to decrease with increasing SBVN composition. Different dielectric mixture formulae were employed to analyze the dielectric properties of the glass nanocrystal composite. The electrical behaviour of the glasses and glass nanocrystal composites was rationalized using impedance spectroscopy. The observed pyroelectric response and ferroelectric hysteresis of these composites confirmed the polar nature. Various optical parameters such as optical band gap (Eopt), Urbach energy (∆E), refractive index (n), optical dielectric constant (ε′∞) and ratio of carrier concentration to the effective mass (N/m*) were determined. The effects of composition of the glasses and glass nanocrystal composites on these parameters were studied. Transparent glasses embedded with nanocrystallites of SBVN exhibited intense second harmonic signals in transmission mode when exposed to IR laser light at λ = 1064 nm. The thesis ends with a summary of the important findings and conclusions.

No description available.