bluuebunny/crossref_metadata_2025_split huggingface dataset:
A Unified Theory for the Glass Transition Dynamics and its Singularities
Authors: Odagaki T. , Matsui J. , Fujisaki M. , Higuchi M. 
Published: April 2011

ABSTRACTVitrification is a gradual freezing process of supercooled liquids, during which a slow process is separated from the fast diffusive and microscopic motions. The slow process is identified as a non-trapped jump motion and can be characterized by the waiting time distribution (WTD) of the elementary relaxation process. We first show that the WTD can be expressed as a power law function in the long time limit in general with modest assumptions. Defining the glass transition temperature by vanishing diffusivity or the divergence of the mean waiting time, we relate the exponent to the Adam-Gibbs parameter Tsc(T) where T is the temperature and sc(T) is the excess entropy. We also show that the divergence of the fluctuation of WTD leads to a cross over in the non-Gaussianity and present a unified view of the dynamics in the vitrification process.
Glass Transition and Ultrasonic Relaxation in Polystyrene
Authors: Sahnoune A. , Piché L. 
Published: April 2011

ABSTRACTWe present measurements of the glass transition and the ultrasonic relaxation modulus in a series of monodisperse polystyrenes. The temperature dependence of the modulus was analyzed using Havriliak-Negami relaxation model (HN) and Vogel-Tammann-Fulcher equation (VTF) for the relaxation time. The results allowed us to determine the fragility index, m, which decreases with increasing molecular weight, Mn. Furthermore, the relaxation time was found to saturate at high molecular weights and varies as Mnp, in the low molecular weight region. The exponent is p≈2 at high temperatures and p ≈ 7 at low temperatures close to Tg.
Time and Ensemble Averaged Dynamic Light Scattering in Orthoterphenyl Above and Below the Glass Transition
Authors: Sidebottom D. L. , Sorensen C. M. 
Published: April 2011

ABSTRACTWhile traditional dynamic light scattering is useful for following structural relaxation in the liquid, in the glassy domain the technique is limited by the ultimate patience of the experimentalist; i.e., the structural relaxation can not be measured when the experimental time scale is less than the structural relaxation time. Nevertheless, we show how useful information regarding structural relaxation can be accessed from light scattering in the glass using a novel ensemble-averaged technique. Dynamic light scattering (DLS) measurements performed on glass forming orthoterphenyl show an inequality between time and ensemble average correlation functions near and below the calorimetrie glass transition temperature, Tg, and hence demonstrate ergodicity breaking. Our ensemble averaged measurements provide a measure of the so-called non-ergodicity parameter, fq, below Tg. Our DLS results for orthoterphenyl indicate that the functional form for fq is consistent with Mode Coupling theory predictions, but occurs at the glass transition temperature, Tg≈243K, rather than at TC≈290K as observed in neutron scattering studies.
Molecular Dynamics Simulation of Alkali Borate Glass Using Coordination Dependent Potential
Authors: Park Byeongwon , Cormack Alastair N. 
Published: April 2011

ABSTRACTThe structure of sodium borate glass was investigated by molecular dynamics simulation using coordination dependent potential model. The simulated alkali borate glass consists of basic units, BO3, triangle, BO4 tetrahedra and structural groups such as boroxol ring and triborate units. The coordination of boron is converted from 3 to 4 by adding alkali oxide.
Molecular Dynamics Simulations of Fracture in Amorphous Silica
Authors: Wang Jinghan , Omeltchenko Andrey , Kalia Rajiv K. , Vashishta Priya 
Published: April 2011

ABSTRACTFracture in amorphous silica is studied using million-atom molecular dynamics simulations. The dynamics of crack propagation, internal stress fields, and the morphology of fracture surfaces are examined as a function of temperature and strain rate. At 300K and 600K we observe brittle fracture: internal stress increases to a critical value (typically 2 – 3 GPa) and then turns over when the crack reaches a terminal speed on the order of half the Rayleigh wave speed. At 900K crack propagation slows down dramatically due to plastic deformation and the material becomes ductile.
Anomalies of the Fast Relaxation Dynamics at Tg In Strong Glass Formers
Authors: Brodin A. , Torell L. M. 
Published: April 2011

ABSTRACTStructural dynamics of two network forming glasses, B2O3 and GeO2, has been investigated by Raman scattering over a wide temperature range from ∼10 K to above the respective glass transition temperatures (Tg = 526 K for B2O3 and 800 K for GeO2). The spectra are analyzed in terms of two distinct contributions, related to vibrational and fast relaxational dynamics, respectively, and conventionally referred to as the boson peak (BP) and quasielastic scattering (QS). A quantity proportional to the fast relaxation strength may be deduced from the integral intensity of QS relative to BP of the spectra. It turns out, that for T < Tg the so-obtained QS intensity of the two glasses is similar and smoothly temperature dependent, and can qualitatively be described by e.g. the defect model or the soft potential model. As Tg is passed, there is a pronounced change in behavior and dramatic differences between the two systems are observed. Thus, the fast relaxational dynamics is obviously affected by Tg, a finding which is in contrast to the predictions of the mode coupling theory (MCT) of a single crossover temperature Tc > Tg. Moreover, the experimentally obtained value of the MCT exponent a, describing the shape of the fast dynamics, is by far exceeding the limiting value (a ≈ 0.395) of the theory, the deviation increasing with the strength of the system (a ≈ 0.7 for B2O3 and ≈ 0.9 for GeO2). The observed difference between the two glasses is discussed in terms of the fragility of the system manifested in jumps in the specific heat temperature dependences.
Strong Liquid Behavior of Zr-Ti-Cu-Ni-Be Bulk Metallic Glass Forming Alloys
Authors: Busch Ralf , Masuhr Andreas , Bakke Eric , Johnson William L. 
Published: April 2011

ABSTRACTThe viscosities of the Zr46.75Ti8.25Cu7.5Ni10Be27.5 and the Zr41.2Ti13.8Cu12.5Ni10Be22.5 bulk metallic glass forming liquids was determined from the melting point down to the glass transition in the entire temperature range of the supercooled liquid. The temperature dependence of the viscosity in the supercooled liquid obeys the Vogel-Fulcher-Tammann (VFT) relation. The fragility index D is about 20 for both alloys and the ratio between glass transition temperature and VFT temperature is found to be 1.5. A comparison with other glass forming systems shows that these bulk metallic glass formers are strong liquids comparable to sodium silicate glass. Furthermore, they are the strongest among metallic glass forming liquids. This behavior is a main contributing factor to the glass forming ability since it implicates a higher viscosity from the melting point down to the glass transition compared to other metallic liquids. Thus, the kinetics in the supercooled liquid is sluggish and yields a low critical cooling rate for glass formation. The relaxation behavior in the glass transition region of the alloys is consistent with their strong glassy nature as reflected by a stretching exponent that is close to 0.8. The microscopic origin of the strong liquid behavior of bulk metallic glass formers is discussed.
Structural Studies of Rare-Earth Doped Phosphate Glasses
Authors: Matic A. , Börjesson L. , Wannberg A. , McGreevy R. L. 
Published: April 2011

ABSTRACTWe have performed neutron scattering experiments on rare-earth (La, Pr, Ho) doped phosphate glasses around the metaphosphate composition R(PO3)3. Combining the diffraction experiment with Reverse Monte Carlo simulations we obtain a 3-D model of the structure. Our models propose a rare-earth ion environment primarily consisting of oxygens with the average rare earth-oxygen distances; 2.56, 2.51 and 2.40 Å for the La, Pr and Ho samples respectively. We also observe that the rare earth ions are not uniformly distributed. The first R-R shell is on avergae about 3.3 Å to be compared with a value of 7 Å for a uniform distribution of R ions in the structure. From the models we also conclude that a chain like structure of the phosphate network is in agreement with the experiment.
Atomic Force Probe of Mesoscopic Dielectric and Viscoelastic Fluctuations Near the Glass Transition
Authors: Walther L. E. , Israeloff N. E. 
Published: April 2011

ABSTRACTWe report a new experimental approach to study the glass transition and glassy dynamics on a mesoscopic scale. Non contact atomic force microscopy is employed to measure dielectric fluctuations of glass forming polymers such as PVAc. Force modulation techniques, performed with the same instrument, allow us to study viscoelastic properties. A custom-built variable temperature UHV AFM with exceptional thermal stability utilizing piezoresistive cantilevers was used. First results on PVAc include large fluctuations of the viscoelastic properties as a function of applied stress below the glass transition.
Nitridation of Bioresorbable Phosphate Glass
Authors: Jiang H. , Lacourse W. C. 
Published: April 2011

ABSTRACTThe bioresorbable 10CaO·35Na2O·55P2O5 glass was nitrided by melting the glass under anhydrous ammonia. The nitrided glasses were fiberized at about 720 °C in air. The dynamic and the equilibrium pH value of the glass increases with the increase of nitrogen content. The incorporation of nitrogen not only increases the glass transition temperature, but also improves the chemical durability and makes it easier to fiberize. Further more, the nitrided glass is more resistant to devitrification.
Thermochemistry and Electrical Contact Behavior of Electrode-Thermistor Interfaces
Authors: Cann David P. , Randall Clive A. 
Published: April 2011

ABSTRACTThe electronic structure of electrode-thermistor interfaces will be related to the thermochemical properties of the interface. Sessile drop wetting experiments of metallic electrodes on commercial BaTiO3 PTCR ceramic devices in combination with measurements of the electrical contact properties of the interface through impedance spectroscopy measurements will be used to establish a fundamental perspective of the electrode-ceramic interface. It will be shown that the thermodynamic work of adhesion (Wad), which is the sum of the strengths of chemical interactions present at the interface, can be manipulated by the addition of chemically active elements to the electrode metal which can segregate to the interface and enhance adhesion. This same procedure will be used to modify the important electrical interfacial properties such as the contact resistance and capacitance.
Fiber-Matrix Interfaces in Ceramic Composites
Authors: Besmann T. M. , Stinton D. P. , Kupp E. R. , Shanmugham S. , Liaw P. K. 
Published: April 2011

ABSTRACTThe mechanical properties of ceramic matrix composites (CMCs) are governed by the relationships between the matrix, the interface material, and the fibers. In non-oxide matrix systems the use of compliant pyrolytic carbon or BN have been demonstrated to be effective interface materials, allowing for absorption of mismatch stresses between fiber and matrix and offering a poorly bonded interface for crack deflection. The resulting materials have demonstrated remarkable strain/damage tolerance together with high strength. Carbon or BN, however, suffer from oxidative loss in many service environments, and thus there is a major search for oxidation resistant alternatives. This paper will review the issues related to developing a stable and effective interface material for non-oxide matrix CMCs.
Energetics of Ideal Grain Boundary Fracture in Iron and the Thermodynamic Criterion of Impurity Embrittlement
Authors: Krasko Genrich L. 
Published: April 2011

ABSTRACTModeling of grain boundary (GB) relaxation during ideal fracture, and the fracture energetics of a Σ3 (111) GB in Fe was performed using the modified Finnis-Sinclair semi-empirical method, and utilizing the so-called “environment-sensitive embedding energies” of impurity atoms, introduced earlier by the author. The calculations were done for both the clean GB, and GB with the following impurity atoms: H, B, C, N, O, P and S. The ideal fracture was modeled by separating the two halves of crystal normal to the GB, step-wise, minimizing the total crystal energy at every step. The interplanar distances were varied, while the Fe interatomic spacing within the hexagonal planes was held fixed. When the distance between the two crystal halves: one with the impurity and another without, exceeded the interatomic interaction cut-off radius (3.6 Å), two different free surfaces - with and without the impurity - emerged. The GB and surface energies were found both for the pure Fe, and that with impurity atoms at the GB or free surface. Both the (111) GB energy and the (111) surface energy of pure Fe agree well with experimental data and results of previous semi-empirical modeling. In general, the correlation between the embrittling/ cohesion enhancing effect of impurities in GB and the difference between the GB and free surface energies agrees with the thermodynamic criterion of embrittlement.
Compositional Effects on Grain Boundary Dislocation Stability in Pure Aluminum and Aluminum Alloys
Authors: Song S. G. , Vetrano J. S. , Bruemmer S. M. 
Published: April 2011

ABSTRACTThe dissociation of extrinsic grain boundary dislocations in Al, Al-Mg and Al-Mg-Sn alloys was studied at various temperatures to examine the compositional effect on the dissociation process. It was found that both alloying elements (Mg and Sn) hinder the dissociation, however the effect of Sn is more significant even at a very low concentration due in part to grain boundary segregation.
Intergranular Fracture in Neutron Irradiated Vanadium-20 Wt.% Titanium Alloys Undoped and Doped with Phosphorus
Authors: Kameda J. , Bloomer T. E. , Lyu D. Y. 
Published: April 2011

ABSTRACTThis paper presents the effect of neutron irradiation (9.8 × 1024 n/m2 at 438 °C) on the mechanical properties in V-20 wt.% Ti alloys undoped and doped with P using a small punch testing method. The same amount of neutron irradiation-induced hardening, that is almost temperature independent, was observed in undoped and P doped alloys. Neutron irradiation facilitated heterogeneous formation of grain boundary microcracks, not leading to specimen failure, in the undoped alloy. An irradiated undoped alloy showed ductility loss, that is not as much as expected from the easy microcrack formation due to a mixed mode of intergranular and transgranular cracking. Conversely, in the P doped alloy, intergranular microcracking was suppressed and low temperature ductility was improved by the irradiation. The intergranular fracture behavior controlling the ductility change is discussed in terms of the grain boundary composition and yield strength affected by the neutron irradiation.
Formation Process of Ti3Al in Ti/Al2O3 System
Authors: Maruyama M. , Nakamura S. , Suenaga S. , Nakahashi M. 
Published: April 2011

ABSTRACTIt has been reported that Ti reduces Al2O3 forming Ti3Al at the interface. From the viewpoint that the structural change of the Ti3Al phase influences the metal-ceramic joining strength, the Ti3Al formation process was analyzed by XPS, XRD, TEM and RBS. Titanium films were deposited on the (1102) surface of Al2O3 substrates and annealed. XRD analysis shows that Ti3Al formation starts at 1073 K. Initially, the (1120) and (2020) Ti3Al planes are oriented parallel to the surface. After 1173 K-300 s heat treatment, XRD shows only the (2020) Ti3Al peak; After 1173 K-600 s heat treatment, HREM observation shows that the lattices of the Ti3Al (0220) plane match those of the A12O3 (1210) plane at the interface. It is suggested that the (2020) oriented grains grow preferentially on the (1102) Al2O3 plane.The quantity of formed Al increases with heating time. After 420 s, the rate of Al formation falls off. The rate of the Al2O3 reduction is in good agreement with the slightly modified Johnson-Mehl equation. The Ti2O/Ti3Al(O)/Al2O3 layer sequence and morphology can be explained by the pure Ti decrease.
The Effect of Protective Organic Thin Film Coatings on BaTiO3 Powders With Respect to Aqueous Processing
Authors: Lee Donghun , Condrate Robert A. 
Published: April 2011

ABSTRACTSurface properties of BaTiO3 which contain different Ba/Ti ratios were examined by FTIR spectroscopy. Most of the carbonates on the surfaces of these powders were removed by heat treatment at 1200°C. However, it was more difficult to remove the carbonates from the powder with a higher ratio of Ba/Ti. Analysis of the heat treated, aged powders in humid air showed that the barium-excess powder recovered carbonates within several hours. In contrast, titanium-excess powders took a longer time, indicating that barium ion concentration is a reaction-control parameter. It was found that oleic and stearic acids were effective in retarding the degradation of the BaTiO3 powders. They also made the dissolution rate of the powders in water considerably slower.
Acoustic Signature of Defects in SiC/Porous SiC Laminated Ceramics
Authors: Esquivel-Sirvent R. , Noguez C. 
Published: April 2011

ABSTRACTThe sensitivity of acoustic techniques to topological and morphological variations in SiC/porous SiC laminated ceramics is studied using a transfer matrix formalism. To implement this transfer matrix technique, the mechanical properties of the SiC porous layers are characterized using the effective medium approximation of Kuster and Toksoz. We show that topological defects have a stronger acoustic signature than morphological defects. Also, we observe that there are particular frequencies at which the defects do not present any acoustic signature.
Analysis of the Interface Between Plasma-Sprayed Calcium Phosphate Coating and Ti-6Al-4V
Authors: Park Eunsung , Hoelzer David T. , Condrate Robert A. 
Published: April 2011

ABSTRACTPlasma sprayed calcium phosphate coatings on Ti(alloy) have been considered advantageous over the uncoated Ti as dental implants or orthopedic prostheses due to their abilities to decrease healing time, attach firmer to the bone, and inhibit ion release from the Ti substrate. However, the coating was found not to adhere well to the Ti substrate, presumably because there is no or little chemical bonding between the calcium phosphate coating and the Ti substrate. The interfacial bond strength relies almost entirely on the mechanical locking of calcium phosphate splats onto the roughened Ti surface. In this study, the interfacial area between the calcium phosphate coating and the Ti-6A1–4V substrate was characterized using SEM and TEM. The results revealed the presence of amorphous calcium phosphate layer at the interface, which is believed to be responsible for the low bond strength. Also small particles were observed which were embedded in the amorphous phase near the interface. The presence of the amorphous phases is very important since they are more easily attacked by the physiological solution than crystalline phases are.
Oxide Laminates with High Strength and Work-of-Fracture
Authors: Kuo D. H. , Kriven W. M. 
Published: April 2011

ABSTRACTSix types of oxide laminates consisting of combinations of xenotime (YPO4) with zirconia (ZrO2), monazite (LaPO4) with ZrO2, and aluminum orthophosphate (AlPO4) with alumina (Al2O3) were studied. They were fabricated by repeatedly stacking two or three kinds of tape-cast layers, lamination, organic burnout and consolidation by hot-pressing. Two of the YPO4-containing ZrO2 laminates were stacked in a YPO4/yttria-stabilized ZrO2 (Y-ZrO2)/30 vol% Y-ZrO2-70 vol% Al2O3(YZ3-A7)/Y-ZrO2 sequence and in a YPO4/Y-ZrO2 sequence. High strength (∼360 MPa) and apparent work-of-fracture (WOF = ∼ 8.2 kJ/m2) were measured in the first laminate. This oxide laminate demonstrates high damage-tolerance without loss of strength. Both properties were comparable with those of non-oxide laminates. There was an approximately 200-fold increase in WOF, as compared with pure Al2O3. A toughening mechanism by means of the residual, interlaminar shear stress-enhanced, interface delamination is proposed for these good results. Two of the LaP04-containing ZrO2 laminates were fabricated in a LaPO4/70 vol% doped ZrO2-30 vol% Al2O3 stacking sequence and in a LaPO4/Y-ZrO2 sequence. Another two of the AlPO4-containing Al2O3 laminates are fabricated in an AlPO4/Al2O3 and in a (50 vol% AlPO4-50 vol% Al2O3)/Al2O3 stacking sequence. The fracture behavior of these multilayered laminates was also studied. The different results among the three kinds of laminates are discussed.
Porous Silicon Organic Vapor and Humidity Sensor
Authors: Poon M. C. , Sin J.K.O. , Wong H. , Han P. G. , Kwok W. H. , Bow Y. C. 
Published: April 2011

ABSTRACTThis paper presents new organic vapor sensitive device using anodized porous silicon (PS). The sensor has aluminum (Al)/PS/p-Si/Al Schottky diode structure and sensitivity at room temperature in 2600 ppm acetone, methanol, 2-propanol and ethanol is about 4, 5, 10 and 40 times respectively. The sensitivity in 800–2600 ppm ethanol vapor is 2 to 40 times. The diode sensor can be converted into an Al/PS/Al resistor sensor by switching the electrical contacts, and the sensitivity is about 500 times for a humidity change of 43–75%. All sensors have response time of about 0.5 min. The sensitivity is stable with time and the PS sensor can be integrated into VLSI Si devices to form novel microelectronic systems.
Optical Fibers with Patterned ZnO/Electrode Coatings for Flexural Actuators
Authors: Trolier-McKinstry S. , Fox G. R. , Kholkin A. , Muller C. A. P. , Setter N. 
Published: April 2011

ABSTRACTPiezoelectric ZnO coatings were used in this work to develop a flexural actuator for an optical fiber. The basic device geometry was as follows: inner Cr/Au electrodes were evaporated onto a cleaned optical fiber; a thick ZnO coating was then grown by sputtering; finally a set of 2mm ring top electrodes were deposited through a shadow mask. Flexural actuators were made by photolithographically patterning either the inner or outer Cr/Au drive electrodes so that it was split down the length of the fiber. This enables each half of the fiber to be actuated independently. The result is that the optical fiber is forced to flex.A processing scheme by which 30 μm gaps could be patterned into the electrodes was developed using standard clean room techniques. Such flexural actuators are attractive for scanning near field optical microscopes and in fiber alignment devices.
Surface Relaxation in Ferroelectric Perovskites: An Atomistic Study
Authors: Dorfman Simon , Heifets Eugene , Fuks David , Kotomin Eugene , Felsteiner Joshua 
Published: April 2011

ABSTRACTThe effect of the [001] surface relaxation on the polarization of the paraelectric BaTiO3 is simulated in the framework of the shell model. Our atomistic simulations show a large polarization of ions in the first several layers nearby the surface and confirm the possibility of co-existence of Ti-and Ba-terminated [001] BaTiO3 surfaces which have very close surface energies.