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Materials, Volume 5, Issue 6 (June 2012) – 9 articles , Pages 1005-1175

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5265 KiB  
Review
Transition Metal Compounds Towards Holography
by Volker Dieckmann, Sebastian Eicke, Kristin Springfeld and Mirco Imlau
Materials 2012, 5(6), 1155-1175; https://doi.org/10.3390/ma5061155 - 20 Jun 2012
Cited by 20 | Viewed by 7665
Abstract
We have successfully proposed the application of transition metal compounds in holographic recording media. Such compounds feature an ultra-fast light-induced linkage isomerization of the transition-metal–ligand bond with switching times in the sub-picosecond regime and lifetimes from microseconds up to hours at room temperature. [...] Read more.
We have successfully proposed the application of transition metal compounds in holographic recording media. Such compounds feature an ultra-fast light-induced linkage isomerization of the transition-metal–ligand bond with switching times in the sub-picosecond regime and lifetimes from microseconds up to hours at room temperature. This article highlights the photofunctionality of two of the most promising transition metal compounds and the photophysical mechanisms that are underlying the hologram recording. We present the latest progress with respect to the key measures of holographic media assembled from transition metal compounds, the molecular embedding in a dielectric matrix and their impressive potential for modern holographic applications. Full article
(This article belongs to the Special Issue Advanced Materials for Modern Holographic Applications)
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807 KiB  
Review
Two Decades of Negative Thermal Expansion Research: Where Do We Stand?
by Cora Lind
Materials 2012, 5(6), 1125-1154; https://doi.org/10.3390/ma5061125 - 20 Jun 2012
Cited by 279 | Viewed by 14073
Abstract
Negative thermal expansion (NTE) materials have become a rapidly growing area of research over the past two decades. The initial discovery of materials displaying NTE over a large temperature range, combined with elucidation of the mechanism behind this unusual property, was followed by [...] Read more.
Negative thermal expansion (NTE) materials have become a rapidly growing area of research over the past two decades. The initial discovery of materials displaying NTE over a large temperature range, combined with elucidation of the mechanism behind this unusual property, was followed by predictions that these materials will find use in various applications through controlled thermal expansion composites. While some patents have been filed and devices built, a number of obstacles have prevented the widespread implementation of NTE materials to date. This paper reviews NTE materials that contract due to transverse atomic vibrations, their potential for use in controlled thermal expansion composites, and known problems that could interfere with such applications. Full article
(This article belongs to the Special Issue Negative Thermal Expansion Materials)
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381 KiB  
Review
Strain Measurements within Fiber Boards. Part I: Inhomogeneous Strain Distribution within Medium Density Fiberboards (MDF) Loaded Perpendicularly to the Plane of the Board
by Jörn Rathke, Gerhard Sinn, Johannes Konnerth and Ulrich Müller
Materials 2012, 5(6), 1115-1124; https://doi.org/10.3390/ma5061115 - 19 Jun 2012
Cited by 11 | Viewed by 6130
Abstract
Internal bond strength testing is a widely used approach for testing quality traits of wood based panels. Generally, failure of internal bond specimens is due to adhesion and/or wood failure in the specimen. It has been reported that a composite product with a [...] Read more.
Internal bond strength testing is a widely used approach for testing quality traits of wood based panels. Generally, failure of internal bond specimens is due to adhesion and/or wood failure in the specimen. It has been reported that a composite product with a large variation in the vertical density profile fails in the center part of the board which is either the middle of the core layer or the transition zone between core layer and face layer. The density in the failure zone is typically 50% lower than the maximum density in the face layers. The aim of this study was to analyze the strain distribution in a specimen under tension perpendicular to the panel plane. The results showed that a high variety of strain magnitude occurred in the specimen. The strain is either aligned with the tension direction or a tension zone is built in one of the edge zones leading to failure. Vector graphics of the specimen show the problematic test setup of internal bond strength measurement. Strain spots in the edges lead to the assumption of an uneven stress distribution due to the momentum which results from non-perfect alignment or irregularities in the test setup. Full article
(This article belongs to the Special Issue Creep and Fracture of Engineering Materials and Structures)
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31 KiB  
Correction
Correction: Dense CO2 as a Solute, Co-solute or Co-solvent in Particle Formation Processes: A Review. Materials 2011, 4, 2017-2041.
by Ana V.M. Nunes and Catarina M.M. Duarte
Materials 2012, 5(6), 1114; https://doi.org/10.3390/ma5061114 - 18 Jun 2012
Viewed by 4046
Abstract
Due to a lapse the Acknowledgements section was missed from the original article version. [...] Full article
6162 KiB  
Article
Glass Fiber Reinforced Polypropylene Mechanical Properties Enhancement by Adhesion Improvement
by Mariana Etcheverry and Silvia E. Barbosa
Materials 2012, 5(6), 1084-1113; https://doi.org/10.3390/ma5061084 - 18 Jun 2012
Cited by 170 | Viewed by 23488
Abstract
Glass fibers (GF) are the reinforcement agent most used in polypropylene (PP) based composites, as they have good balance between properties and costs. However, their final properties are mainly determined by the strength and stability of the polymer-fiber interphase. Fibers do not act [...] Read more.
Glass fibers (GF) are the reinforcement agent most used in polypropylene (PP) based composites, as they have good balance between properties and costs. However, their final properties are mainly determined by the strength and stability of the polymer-fiber interphase. Fibers do not act as an effective reinforcing material when the adhesion is weak. Also, the adhesion between phases can be easily degraded in aggressive environmental conditions such as high temperatures and/or elevated moisture, and by the stress fields to which the material may be exposed. Many efforts have been done to improve polymer-glass fiber adhesion by compatibility enhancement. The most used techniques include modifications in glass surface, polymer matrix and/or both. However, the results obtained do not show a good costs/properties improvement relationship. The aim of this work is to perform an accurate analysis regarding methods for GF/PP adhesion improvement and to propose a new route based on PP in-situ polymerization onto fibers. This route involves the modification of fibers with an aluminum alkyl and hydroxy-α-olefin and from there to enable the growth of the PP chains using direct metallocenic copolymerization. The adhesion improvements were further proved by fragmentation test, as well as by mechanical properties measurements. The strength and toughness increases three times and the interfacial strength duplicates in PP/GF composites prepared with in-situ polymerized fibers. Full article
(This article belongs to the Special Issue Fibre-Reinforced Composites)
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948 KiB  
Review
Formation of Degenerate Band Gaps in Layered Systems
by Anton I. Ignatov, Alexander M. Merzlikin, Miguel Levy and Alexey P. Vinogradov
Materials 2012, 5(6), 1055-1083; https://doi.org/10.3390/ma5061055 - 07 Jun 2012
Cited by 9 | Viewed by 6318
Abstract
In the review, peculiarities of spectra of one-dimensional photonic crystals made of anisotropic and/or magnetooptic materials are considered. The attention is focused on band gaps of a special type—the so called degenerate band gaps which are degenerate with respect to polarization. Mechanisms of [...] Read more.
In the review, peculiarities of spectra of one-dimensional photonic crystals made of anisotropic and/or magnetooptic materials are considered. The attention is focused on band gaps of a special type—the so called degenerate band gaps which are degenerate with respect to polarization. Mechanisms of formation and properties of these band gaps are analyzed. Peculiarities of spectra of photonic crystals that arise due to the linkage between band gaps are discussed. Particularly, it is shown that formation of a frozen mode is caused by linkage between Brillouin and degenerate band gaps. Also, existence of the optical Borrmann effect at the boundaries of degenerate band gaps and optical Tamm states at the frequencies of degenerate band gaps are analyzed. Full article
(This article belongs to the Special Issue Photonic Materials and Applications)
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534 KiB  
Article
Atomistic Modeling of the Negative Thermal Expansion in δ- Plutonium Based on the Two-State Description
by Tongsik Lee, Michael I. Baskes, A. C. Lawson, Shao Ping Chen and Steven M. Valone
Materials 2012, 5(6), 1040-1054; https://doi.org/10.3390/ma5061040 - 07 Jun 2012
Cited by 6 | Viewed by 7425
Abstract
The δ phase of plutonium with the fcc structure exhibits an unusual negative thermal expansion (NTE) over its narrow temperature range of stability, 593–736 K. An accurate description of the anomalous high-temperature volume effect of plutonium goes beyond the current capability of electronic-structure [...] Read more.
The δ phase of plutonium with the fcc structure exhibits an unusual negative thermal expansion (NTE) over its narrow temperature range of stability, 593–736 K. An accurate description of the anomalous high-temperature volume effect of plutonium goes beyond the current capability of electronic-structure calculations. We propose an atomistic scheme to model the thermodynamic properties of δ-Pu based on the two-state model of Weiss for the Invar alloys, inspired by the simple free-energy analysis previously conducted by Lawson et al. The two-state mechanism is incorporated into the atomistic description of a many-body interacting system. Two modified embedded atom method potentials are employed to represent the binding energies of two competing electronic states in δ-Pu. We demonstrate how the NTE takes place in δ-Pu by means of Monte Carlo simulations implemented with the two-state mechanism. Full article
(This article belongs to the Special Issue Negative Thermal Expansion Materials)
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112 KiB  
Article
Influences of Sample Preparation on Nanoindentation Behavior of a Zr-Based Bulk Metallic Glass
by Hu Huang, Hongwei Zhao, Zhiyu Zhang, Zhaojun Yang and Zhichao Ma
Materials 2012, 5(6), 1033-1039; https://doi.org/10.3390/ma5061033 - 01 Jun 2012
Cited by 21 | Viewed by 6834
Abstract
Influences of two different sample preparation methods, mechanical polishing and plunge cutting, on nanoindentation behavior of a Zr-based bulk metallic glass were studied. Mechanical polishing suppresses the serrated flow but promotes the creep. In contrast, plunge cutting promotes the serrated flow but suppresses [...] Read more.
Influences of two different sample preparation methods, mechanical polishing and plunge cutting, on nanoindentation behavior of a Zr-based bulk metallic glass were studied. Mechanical polishing suppresses the serrated flow but promotes the creep. In contrast, plunge cutting promotes the serrated flow but suppresses the creep. However, hardness and elastic modulus obtained from these two methods are nearly the same. Full article
(This article belongs to the Special Issue Creep and Fracture of Engineering Materials and Structures)
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717 KiB  
Review
Extrinsic and Intrinsic Frequency Dispersion of High-k Materials in Capacitance-Voltage Measurements
by J. Tao, C. Z. Zhao, C. Zhao, P. Taechakumput, M. Werner, S. Taylor and P. R. Chalker
Materials 2012, 5(6), 1005-1032; https://doi.org/10.3390/ma5061005 - 01 Jun 2012
Cited by 62 | Viewed by 11398
Abstract
In capacitance-voltage (C-V) measurements, frequency dispersion in high-k dielectrics is often observed. The frequency dependence of the dielectric constant (k-value), that is the intrinsic frequency dispersion, could not be assessed before suppressing the effects of extrinsic frequency dispersion, such as [...] Read more.
In capacitance-voltage (C-V) measurements, frequency dispersion in high-k dielectrics is often observed. The frequency dependence of the dielectric constant (k-value), that is the intrinsic frequency dispersion, could not be assessed before suppressing the effects of extrinsic frequency dispersion, such as the effects of the lossy interfacial layer (between the high-k thin film and silicon substrate) and the parasitic effects. The effect of the lossy interfacial layer on frequency dispersion was investigated and modeled based on a dual frequency technique. The significance of parasitic effects (including series resistance and the back metal contact of the metal-oxide-semiconductor (MOS) capacitor) on frequency dispersion was also studied. The effect of surface roughness on frequency dispersion is also discussed. After taking extrinsic frequency dispersion into account, the relaxation behavior can be modeled using the Curie-von Schweidler (CS) law, the Kohlrausch-Williams-Watts (KWW) relationship and the Havriliak-Negami (HN) relationship. Dielectric relaxation mechanisms are also discussed. Full article
(This article belongs to the Special Issue High-k Materials and Devices)
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