1,720,952 research outputs found
Evolution of local structure and stress development during thermal treatment of sol-gel-derived PZT-based thin layers
No full textSignificant progress has been made in recent years on the deposition of ferroelectric thin layers by sol-gel processing. However, to sustain further improvements in the technique necessary for widespread applications, a systematic approach to the study of physical, chemical and structural changes that occur during transformation from the as-deposited state to the desired perovskite phase must be undertaken. In view of the need for a fundamental understanding of structure-processing relationships in these systems, this thesis investigates variations in local structure and network development for sol-gel derived precursors in the lead zirconate titanate (PZT) system as a function of heat treatment conditions.Structural studies were based on extended x-ray absorption fine structure (EXAFS) analysis of gels and thin layers. Consolidation of the thin layer network was monitored by in situ ellipsometry and thermal analysis techniques. The resulting constrained shrinkage for the deposited layers produced large stresses (up to 180 MPa), which were determined by wafer bending measurements.EXAFS measurements for partially heat-treated PZT gels are reported. After gels were dried and pyrolyzed, the amorphous structure was determined from results obtained from the titanium and zirconium K-edges and the lead L\rm\sb{III}-edge. For lead titanate (PT) and PZT53/47 gels, the results indicated the formation of separate TiO\sb6 and ZrO\sb6 units linked via corner-sharing oxygen atoms, with Pb in random positions. For lead zirconate (PZ) gels, both Zr-O-Pb and Zr-O-Zr linkages were possible. These findings indicate heterogeneity at the molecular level and nanoscale.Partially heat-treated thin layers of lead titanate deposited on polycrystalline alumina substrates were heat treated under various conditions to examine the evolution of the crystalline phase. Structural ordering was initiated by a progressive enhancement in the Pb-O coordination number and increased occupancy of Pb in the second shell of Ti, with a corresponding breakdown in the Ti-Ti second neighbor ordering. However, crystallization preceded complete development of the short-range order characteristic of the tetragonal perovskite unit.Densification of PZT thin layers spin-coated on silicon was monitored by shrinkage and optical measurements. With increasing Zr content, the net consolidation was greater and occurred over a wider temperature range. These differences were related to differences in the structure of the as-hydrolyzed precursors. Most of the total shrinkage (e.g., 40-45% linear shrinkage) on heating to 500\sp\circC occurred during drying and pyrolysis, which resulted in large tensile stress (150MPa). Subsequent stress behavior was primarily governed by the thermal expansion mismatch between the substrate and the coating.Stress development for multideposited PT coatings was determined by the structure of the layer on which the coating was being deposited and heat treated. Progressive crystallization of the layer induced a change in the thermal expansion coefficient, thereby initiating a change in the stress state from tensile to compressive. The observed behavior is discussed in terms of nucleation mechanisms at the multilayer interfaces and within the coating as a whole.This study has demonstrated the importance of identifying structural pathways and developing a basic understanding of the densification behavior in sol-gel derived materials as a function of thermal processing conditions. The findings of this research work should aid in developing suitable experimental procedures for future processing of gel-derived thin layers.Made available in DSpace on 2011-05-07T13:23:41Z (GMT). No. of bitstreams: 2
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Evolution of local structure and stress development during thermal treatment of sol-gel-derived PZT-based thin layers
No full textSignificant progress has been made in recent years on the deposition of ferroelectric thin layers by sol-gel processing. However, to sustain further improvements in the technique necessary for widespread applications, a systematic approach to the study of physical, chemical and structural changes that occur during transformation from the as-deposited state to the desired perovskite phase must be undertaken. In view of the need for a fundamental understanding of structure-processing relationships in these systems, this thesis investigates variations in local structure and network development for sol-gel derived precursors in the lead zirconate titanate (PZT) system as a function of heat treatment conditions.Structural studies were based on extended x-ray absorption fine structure (EXAFS) analysis of gels and thin layers. Consolidation of the thin layer network was monitored by in situ ellipsometry and thermal analysis techniques. The resulting constrained shrinkage for the deposited layers produced large stresses (up to 180 MPa), which were determined by wafer bending measurements.EXAFS measurements for partially heat-treated PZT gels are reported. After gels were dried and pyrolyzed, the amorphous structure was determined from results obtained from the titanium and zirconium K-edges and the lead L\rm\sb{III}-edge. For lead titanate (PT) and PZT53/47 gels, the results indicated the formation of separate TiO\sb6 and ZrO\sb6 units linked via corner-sharing oxygen atoms, with Pb in random positions. For lead zirconate (PZ) gels, both Zr-O-Pb and Zr-O-Zr linkages were possible. These findings indicate heterogeneity at the molecular level and nanoscale.Partially heat-treated thin layers of lead titanate deposited on polycrystalline alumina substrates were heat treated under various conditions to examine the evolution of the crystalline phase. Structural ordering was initiated by a progressive enhancement in the Pb-O coordination number and increased occupancy of Pb in the second shell of Ti, with a corresponding breakdown in the Ti-Ti second neighbor ordering. However, crystallization preceded complete development of the short-range order characteristic of the tetragonal perovskite unit.Densification of PZT thin layers spin-coated on silicon was monitored by shrinkage and optical measurements. With increasing Zr content, the net consolidation was greater and occurred over a wider temperature range. These differences were related to differences in the structure of the as-hydrolyzed precursors. Most of the total shrinkage (e.g., 40-45% linear shrinkage) on heating to 500\sp\circC occurred during drying and pyrolysis, which resulted in large tensile stress (150MPa). Subsequent stress behavior was primarily governed by the thermal expansion mismatch between the substrate and the coating.Stress development for multideposited PT coatings was determined by the structure of the layer on which the coating was being deposited and heat treated. Progressive crystallization of the layer induced a change in the thermal expansion coefficient, thereby initiating a change in the stress state from tensile to compressive. The observed behavior is discussed in terms of nucleation mechanisms at the multilayer interfaces and within the coating as a whole.This study has demonstrated the importance of identifying structural pathways and developing a basic understanding of the densification behavior in sol-gel derived materials as a function of thermal processing conditions. The findings of this research work should aid in developing suitable experimental procedures for future processing of gel-derived thin layers.U of I OnlyETDs are only available to UIUC Users without author permissio
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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