bluuebunny/crossref_metadata_2025_split huggingface dataset:
An Infrared Study of Metal Isopropoxide Precursors for SrTiO3
Authors: Riman R. E. , Haaland D. M. , Northrup C.J.M. , Bowen H. K. , Bleier A. 
Published: March 2011

ABSTRACTA Sr/Ti bimetallic isopropoxide complex was synthesized by two methods. The complex served as a precursor to the production of homogeneous SrTiO3 powders via alkoxide hydrolysis. Infrared spectra were obtained for Sr(OPri)2, Ti(OPri)4, and the product of the syntheses. In addition, the IR spectra of the solutions of each of the alkoxides were followed as hydrolysis reactions proceeded. Detailed analysis of the spectral features support the existence of a 1:1 Sr/Ti bimetallic alkoxide. The new Sr/Ti compound exhibits characteristic absorption bands at (1017, 993, 972, 961 cm−1), (844, 838, 827 cm−1) and (620, 596, and 572 −1). A band at 819−1 might also be associated with the new Sr/Ti bimetallic alkoxide. The infrared spectra suggest that the isopropoxide ligands in the bimetallic alkoxide are in at least three separate local environments. This information offers insight into possible structures for the complex.
Physical-Chemical Variables in Processing Na2O - B2O3 - SiO2 Gel Monoliths
Authors: Orcel Gerard , Hench Larry L. 
Published: March 2011

ABSTRACTThe addition of a dryinq control chemical additive (DCCA) to the solvent allows short drying times for monolithic gel samples. The variables involved in the use of a DCCA in preparing gels from the Na2O-SiO2 -B2O3 system are described. Due to its higher reactivity, a DCCA influences the chemical behavior of the material at each step of the processing. The effects of formamide as a DCCA on the qelation process, surface charge, and surface area are presented. The variations of the physical properties of the gel, due to the addition of the DCCA, are related to the reactions of the formamide with the sol. Although the DCCA helps in producing monolithic dried gels, the problem of densification is not solved as yet.
The Role of Water in Densification of Gels
Authors: Gallo T. A. , Brinker C. J. , Klein L. C. , Scherer G. W. 
Published: March 2011

ABSTRACTThe densification behavior of a gel-derived borosilicate glass was studied. Surface area, thermal gravimetric and infrared measurements were used to calculate the surface hydroxyl coverage as a function of time at several temperatures. Application of a viscous sintering model to the isothermal shrinkage data showed viscosity to increase isothermally by almost two orders of magnitude at the lowest investigated temperature. Although most of this increase is attributable to increased crosslinking accompanying dehydroxylation, structural relaxation was also shown to significantly affect the densification kinetics.
X-RAY and Electron Diffraction Studies of AS-Deposited rf Sputtered Thin Films of lrO2
Authors: Penfold I. T. , Moss S. C. , Kulik J. , Kreider K. G. 
Published: March 2011

ABSTRACTIridium oxide films produced by reactive sputtering (SIROFs) have considerably higher densities than those made by other techniques such as the anodic reaction at metal surfaces which contain pores and Microvoids. It has been previously reported that SIROFs deposited with substrate temperatures of 300K are amorphous. Here we report x-ray and electron diffraction measurements on SIROFs deposited on Al2O3, Si, NaCI and MgO substrates at 40°C. The x-ray diffraction patterns, I(Q), show “diffuse” structure that extends to beyond Q(=4εsinθ/) =10Â−1. We show that it is possible to reproduce qualitatively the main features of the diffraction pattern by convolving the crystalline rutile powder pattern with a Lorentzian profile. The width of this profile is compatible with that determined from the Scherrer equation although significant peak shifts and texture are observed. This analysis reveals that as-deposited SIROFs are crystalline with particle sizes in the range 25À to 35Å rather than amorphous (for which no crystalline model would be appropriate). The electron microdiffraction data are also consistent with a crystallite size of a few nm and high resolution TEM reveals lattice fringes from crystallites few nm in size. The peak shifts, however, remain to be explained.
Determination Of Aluminum Coordination Environments In Amorphous AI2O3By Solid State Nmr Spectroscopy
Authors: Rees William S. , Chopin Lamy J. 
Published: March 2011

ABSTRACTIt previously has been difficult to probe the localized coordination environment of aluminum atoms in amorphous alumina samples by solid state NMR spectroscopy. Such anin situtechnique has benefits in probing the structure of the material and monitoring the evolution of the microstructural development during thermal processing. The recent developments of more sophisticated NMR techniques by Pines,et al., specifically devised for treatment of problems unique to the solid state spectroscopy of quadrupolar nuclei, have permitted a glimpse into these Materials. As a result of applying these experimental techniques to new materials systems, a better understanding of the solid state structure of amorphous aluminas derived from polymer pyrolysis has emerged. Correlations between the onset and completion of crystallization and the localized structure may now be possible.
Dynamics of Crystalline and Amorphous Polytetrafluoroethylene Studied by Multiple Quantum NMR
Authors: Lathrop David A. , Gleason Karen K. 
Published: March 2011

ABSTRACTWe report a new technique for probing polymer dynamics through the refocussing of multiple quantum (MQ) nuclear magnetic resonance (NMR) coherences. The MQ-NMR experiment follows the correlated behavior of multiple spin-1/2 nuclei interacting through dipolar couplings. Motion which modulates the dipolar coupling strengths on the same time scale as the experiment (∼1 to 20 kHz) alters the intensity of the observed coherences. Temperature dependent 19F data are presented on polytetrafluoroethylene samples of varying crystallinity. For the as-polymerized 98% crystalline PTFE sample, a sharp increase in MQ coherence refocussing occurs, centered at -298 K. The 64% crystalline melt-quenched sample shows a increase at the same temperature but which has a lower intensity. Thus, the ∼298 K peak is most associated with motion in the crystalline phase. This temperature is intermediate between the two first order transition at 293 and 303 K. Oscillations in the refocussed fractions are observed from 208 to 230 K for the 98% crystalline sample, while this ratio is constant over the same temperature range for the 64% crystalline sample. These oscillations may be associated with paracrystalline defects found only in the first sample. Thus, the MQ refocussing experiment is able to clearly differentiate between polymer samples which have different thermal histories. The sharpness of the MQ refocussing features and their variations in magnitude, shape, and sign with temperature are signatures of the molecular level details of the underlying dynamics which produce them.
Crystal to Glass Transition and Melting in Two Dimensions
Authors: Li M. , Johnson W. L. , Goddard W. A. 
Published: March 2011

ABSTRACTThermodynamic properties, structures, defects and their configurations of a two-dimensional Lennard-Jones (LJ) system are investigated close to crystal to glass transition (CGT) via molecular dynamics simulations. The CGT is achieved by saturating the LJ binary arrays below glass transition temperature with one type of the atoms which has different atomic size from that of the host atoms. It was found that for a given atomic size difference larger than a critical value, the CGT proceeds with increasing solute concentrations in three stages, each of which is characterized by distinct behaviors of translational and bond-orientational order correlation functions. An intermediate phase which has a quasi-long range orientational order but short range translational order has been found to exist prior to the formation of the amorphous phase. The destabilization of crystallinity is observed to be directly related to defects. We examine these results in the context of two dimensional (2D) melting theory. Finite size effects on these results, in particular on the intermediate phase formation, are discussed.
Visco-Elastic Relaxations in Alkali Borates and Alkali Silicates
Authors: Kieffer J. , Masnik J. E. , Reardon B. J. , Bass J. D. 
Published: March 2011

ABSTRACTThe Brillouin light scattering technique was used to study short time relaxations in glass forming oxide melts. The line shape analysis of Brillouin spectra yields a complex mechanical Modulus. The temperature dependence of this modulus provides insight into the structural disintegration above the glass transition, as well as the thermally activated mechanisms which facilitate the momentum transport in the process of viscous dissipation.A series of binary and ternary alkali borates and alkali silicates have been investigated. The results show fundamental differences in the way alkali cations affect the network structure in borates as compared to silicates. While these cations move relatively freely within the rigid silicate network, their motions are strongly coupled to the network relaxation in borates. The activation energies for cation motion are in good agreement with those found by other methods.
An Investigation of the Viscous Flow Problem Associated with the Heating of the Glass Preform During Optical Fiber Processing
Authors: Rosenberg Sara E. , Papamichael Haris , Miaoulis Ioannis N. 
Published: March 2011

ABSTRACTA thermal study of the optical fiber manufacturing process involves some of the most challenging, and in some cases, unsolved fundamental problems in heat transfer and fluid Mechanics. The heating stage of the process, where the glass cylinder (preform) is heated radiantly by the cylindrical muffle furnace, greatly influences the resultant quality of the fiber. During the process a neckdown region is formed that is characterized by the stretching of the glass. The two-dimensional transient equations of motion and Mass conservation, with viscosity dependent on temperature, were solved to obtain the velocity profiles in the glass and the shape of the neckdown region. Axial velocity contours and the neckdown profiles were examined for various drawing conditions. Differences between the new method presented here and existing one-dimensional method were examined. The analysis can be used for drawing of other materials such as metals and polymers, and the modeling is applicable to other viscous liquids.
Crystal Nucleation in Submicron Droplets of Pure Elements
Authors: Holzman Louis M. , Kelly Thomas F. , Hitchon W. N. G. 
Published: March 2011

ABSTRACTLiquid-to-crystal nucleation has been studied extensively through droplet experiments to locate examples of homogeneous nucleation. However, prior to this work very few examples have been found, which implies that the experiments have not been able to isolate heterogeneous nucleants in a small percentage of the droplets as is required. In this research, electrohydrodynamic atomization (EHD) is used to produce sub-Micron droplets of pure elements that are largely free of heterogeneous nucleants.Diffraction patterns of individual EHD-produced droplets are viewed to determine the fraction of crystalline droplets produced as a function of droplet radius. These results are compared to theories for surface and volume heterogeneous nucleation and for homophase nucleation. It is found that Si and Ge nucleate through either homogeneous nucleation or nucleation by homophase impurities. Nucleation results for vanadium and iron were not conclusive.
Plastic Deformation-Induced Nanocrystalline Aluminum in Al-Based Amorphous Alloys
Authors: Chen H. , He Y. , Shiflet G. J. , Poon S. J. 
Published: March 2011

ABSTRACTWe report the first direct observation of crystallization induced in the slipped planes of aluminum based amorphous alloys by bending the amorphous ribbons. Nanometer-sized crystalline precipitates are found exclusively within a thin layer (shear band) in the slipped planes extending across the deformed amorphous alloy ribbons. It is also found that the nanocrystalline aluminum can be produced by ball-Milling. It is likely that local atomic rearrangements within the shear bands create the nanocrystals which appear after plastic deformation.
Solid State Reactions In Binary Mixtures Of Nanometer-Sized Particles
Authors: Dickenscheid W. , Birringer R. 
Published: March 2011

ABSTRACTSolid state reactions in mixtures of nanometer-sized Cu and Zr as well as Ni and Zr crystallites -produced by inert-gas condensation followed by in situ compaction - have been investigated by x-ray diffraction and thermal analysis. The annealing behavior is compared to that of corresponding multilayer samples. The results are discussed with emphasis placed on the different parameters controlling solid state reactions.
The Kinetics of the Order-Disorder Transformation in the Pt1Co1−xNix Alloy System
Authors: Tu Huan , Ruiz Eduardo O. , Orehotsky J. 
Published: March 2011

ABSTRACTThe kinetics of atomic ordering in a series of alloys in the Pt1Co1−xNix ternary system where 0<x<0.5 were investigated by magnetic measurements. For all the alloys, the ordering kinetics as monitored by the saturation magnetization as a function of isothermal ordering time at a series of specified ordering temperatures, were found to be exponentially time dependent. The associated time constant was found to have an Arrhenius temperature dependence characterized by an activation energy that, with increasing nickel concentration, initially increased to maximum value at a nickel composition of x ∼.2 and then systematically decreased. This result for the activation energy as a function of nickel content was found to correlate roughly with the behavior of the saturation magnetization of the ordered alloys, suggesting that the kinetics of the transformation in this alloy system is sensitive to the magnetic properties of the ordered state.
Amortization And Dynamic Recovery Of A2BO4 Structure Types During 1.5 MeV Krypton Ion-Beam Irradiation
Authors: Wang L. M. , Gong W. L. , Ewing R. C. 
Published: March 2011

ABSTRACTThe temperature dependence of the critical amorphization dose, Dc, of four A2BO4 compositions, forsterite (Mg2SiO4), fayalite (Fe2SiO4), synthetic Mg2GeO4, and phenakite (Be2SiO4) was investigated by in situ TEM during 1.5 MeV Kr+ion beam irradiation at temperatures between 15 to 700 K. For the Mg- and Fe-compositions, the A-site is in octahedral coordination, and the structure is a derivative hep (Pbnm); for the Be-composition, the A- and B-sites are in tetrahedral coordination, forming corner-sharing hexagonal rings (R3). Although the Dc's were quite close at 15 K for all the four compositions (0.2–0.5 dpa), Dc increased with increasing irradiation temperature at different rates. The Dc-temperature curve is the result of competition between amorphization and dynamic recovery processes. The Dc rate of increase (highest to lowest) is: Be2SiO4, Mg2SiO4, Mg2GeO4, Fe2SiO4. At room temperature, Be2SiO4 amorphized at 1.55 dpa; Fe2SiO4, at only 0.22 dpa. Based on the Dc-temperature curves, the activation energy, Ea, of the dynamic recovery process and the critical temperature, Tc, above which complete amorphization does not occur are: 0.029, 0.047, 0.055 and 0.079 eV and 390, 550, 650 and 995 K for Be2SiO4, Mg2SiO4, Mg2GeO4 and Fe2SiO4, respectively. These results are explained in terms of the materials properties (e.g., bonding and thermodynamic stability) and cascade size which is a function of the density of the phases. Finally, we note the importance of increased amorphization cross-section, as a function of temperature (e.g., the low rate of increase of Dc with temperature for Fe2SiO4).
Defect Induced Amortization in Silicon: A Tight Binding Molecular Dynamics Simulation
Authors: Maric D. , Colombo L. 
Published: March 2011

ABSTRACTWe present an investigation on the amorphization process of crystalline silicon induced by ion beam bombardment by simulating the insertion of self-interstitials at different temperatures. The simulation is carried out by tight-binding molecular dynamics which allows for a detailed characterization of the chemical bonding and electronic properties of the irradiated samples. The irradiation process consists of two steps: (i) insertion of defects at a constant rate; (ii) annealing of the sample and observation of its structural properties. Thanks to the large size of the simulation cell (up to 276 atoms) we can characterize the amorphous network both on the short-range and Medium-range length scale. Electronic properties are investigated as well and their evolution is monitored during the insertion process. Finally, we present a thorough comparison of the structural properties of the irradiated sample with amorphous silicon as obtained by rapid quench from the Melt.
Photoinduced Amorphous ↔ Crystalline Transitions In Sbx Sc1−x Films
Authors: Stradins Paul , Balors Ojars , Gerbreder Vyatcheslav 
Published: March 2011

ABSTRACTWe present a study of laser pulse induced crystallization and amorphization in SbxSc1−x films. The time required to reach stable amorphous state after the pulse increases with exciting pulse length and becomes constant when stationary temperature field is approached by the end of the pulse. The time dependence of the excited spot's local temperature is deduced directly from amorphization threshold intensity dependence on the pulse length and is used to calculate the cooling times after the amorphizing pulse. Two photocrystallization regimes are distinguished depending on whether the melting starts before or after the end of crystallization, the condition depending on crystallization tendency for given composition x. The occurrence of melting limits the maximum optical contrast during photocrystallization. The results show that the crystallization tendency of SbxSei-x rises with x and has a local maximum between x = 0.5 and x = 0.7.
Questions And Answers On The Activation Strain
Authors: Aziz Michael J. 
Published: March 2011

ABSTRACTThe activation strain tensor describes the effect of nonhydrostatic stresses on atomic or interfacial Mobilities. It has been measured for solid phase epitaxial growth of crystalline Si (001) into amorphous Si. The activation strain concept is explained and some subtle points are discussed. Implications for proposed mechanisms of solid phase epitaxy are reviewed, and new implications for combined bulk and interfacial control are presented. Questions raised during the oral presentation are answered.
Strain Relaxation During Solid-Phase Epitaxial Crystallisation Of GexSi1−x Alloy Layers with Depth Dependent Ge Compositions
Authors: Wong Wah-Chung , Elliman Robert G. 
Published: March 2011

ABSTRACTSolid-phase epitaxial growth (SPEG) of amorphous GeSi alloy layers has been examined. It is shown that fully strained depth dependent GeSi alloy layers can be produced by multiple ion-implantation and SPEG for implant doses below critical values. For doses above these critical values strain relaxation is shown to occur during SPEG at a well defined depth, and to be correlated with a reduction in the SPEG velocity caused by roughening or faceting of the crystalline/amorphous interface. The velocity reduction is shown to be a reliable indicator of strain relaxation. Both the critical dose and the depth at which strain relaxation occurs are shown to be in excellent agreement with equilibrium critical thickness theory.
Small-Angle Scattering Investigations of Crystalline Blend Morphologies of Poly (E-Caprolactone) (PCL)/Polycarbonate (PC) Blends
Authors: Wilson Cheung Y. , Stein R. S. , Wignall G. D. , Lin J. S. 
Published: March 2011

ABSTRACTCrystalline Morphologies of poly (e-caprolactone) (PCL) and deuterated polycarbonate (PC) blends in both the semicrystalline/amorphous state and semicrystalline/semicrystalline state were probed by small-angle neutron and X-ray scattering (SANS and SAXS). Due to the different contrast between the phases for neutrons and X-rays, SANS exhibited a monotonie drop in intensity with increasing scattering angle while SAXS showed lamellar (peak) scattering.Crystal- and amorphous-phase thickness were determined from the correlation function calculated from SAXS. This correlation function analysis suggested a transition from interlamellar exclusion to interlamellar incorporation of amorphous PCL in the PC lamellae. A two-correlation length model provided an excellent fit for the SANS data over the entire composition range. This Model not only reproduced the shape but also the absolute magnitude of the scattering profiles. The long range correlation length (∼102 Å) and the short range correlation length (∼ 10 Å) derived from this model were inferred to be associated with the crystalline PC domains and the local clusters found in the amorphous phase, respectively.
Interdiffusion of Amorphous Si/Ge Multilayers Under Hydrostatic Pressure
Authors: Theiss Steven D. , Mitha S. , Spaepen F. , Aziz M. J. 
Published: March 2011

ABSTRACTWe report initial results of an x-ray diffraction study of the pressure-dependence of the interdiffusion rate in amorphous Si/Ge Multilayers. Anneals were performed in a diamond anvil cell at 700 K for various pressures and durations. Interdiffusion was measured by Monitoring the rate of decay of the artificial Bragg peaks associated with the multilayer periodicity. A consistent increase in diffusivity was seen with pressure, characterized by an activation volume of -25±11 percent of the atomic volume of Si. An atomistic mechanism that Might account for such behavior is discussed.
Crystallization Dynamics Of Ferroelectric Pzt (52/48) Thin Film Prepared By Reactive Cosputtering On Pt On Si(100)
Authors: Choo Woong Kil , Kim Hyo Jin , Kim Kwang Young , Kim Sung Tae 
Published: March 2011

ABSTRACTThe crystallization process and microstructural evolution of PZT (52/48) thin films deposited on Pt thin film electrode on Si (100) by reactive multitarget cosputtering technique have been studied as a function of post-annealing temperature and holding time. As annealing temperature increases, the Amorphous PZT films as-deposited at low substrate temperature of 200 °C crystallize into pyrochlore at 450 °C and ferroelectric perovskite phase with pseudo-cubic structure at 550 °C in sequence. X-ray diffraction data show crystallization into perovskite phase to be complete in 30 Minutes at 550 °C. Furthermore, the change of PZT/Pt/Ti/SiO2/Si interfacial TEM Morphology during heat-treatment has been closely scrutinized.
Characterisation of Ferroelectric Lithium Tantalate Thin Films Prepared by a Sol-Gel Process
Authors: Ye Chianping , Baude Paul , Polla Dennis L. 
Published: March 2011

ABSTRACTThin LiTaO3 films were prepared by spin coating of polymerized sol-gel precursor solution. Films have been deposited on single crystal silicon substrate, Ti/Pt or SiO2 coated silicon substrate. Films were characterized by x-ray diffraction, dielectric and pyroelectric Measurements. High Curie temperature (above 550 °C) was assumed for LiTaO3 thin films from the temperature dependence of dielectric constant. Replacing 35% of tantalum by titanium atoms in the LiTaO3 precursor solution has resulted the thin films with Curie temperature of 330 °C. The lower Curie temperature leads to the larger pyroelectric coefficient at room-temperature, which is more than double that of the undoped LiTaO3 thin films. The dielectric, pyroelectric, and ferroelectric properties have been compared to the single crystal LiTaO3 and ceramic Li0.91Ta0.73Ti0.36O3. LiTaO3 thin films are available by sol-gel process at low temperature, and their properties may possibly be controlled by varying the composition of the sol-gel precursor solution.
On Preparation of Crystalline MgO-Ceramics from Amorphous Precursors
Authors: Jost H. , Carius Ch. , Peplinski B. 
Published: March 2011

ABSTRACTAmorphous precursors are obtained as a result of the precipitation from magnesium acetate solutions with ammonia in the presence of citric acid. Compared with crystalline precursors they have a higher reactivity and a changed behaviour in calcination process as well as during sintering. Already at 1300 °C sintered pellets are achieved, whereas in technological process 1700 °C are needed.