bluuebunny/crossref_metadata_2025 huggingface dataset:
Stability of Ionic Tin(II) in a Chloride Fluoride Matrix: the Unexpected Ba1−xSrxCl1+yF1−y Solid Solution Crystallizing in the Bacif Structure
Authors: Denes Georges , Bratigny Julie , Le Roux David , Muntasar Abdualhafeed
Published: April 2011

We have prepared a wide Ba1−xSrxCl1+yF1−y solid solution (0<x<0.25, −0.20<y<0.20) that has the BaClF structure without any sign of lattice distortion or ordering of the cations or of the anions other than that already present in BaClF. Furthermore, 119Sn Mossbauer spectroscopy shows that tin(ll) is present in this material in the form of Sn2+ ions instead of being covalently bonded Sn(ll) with a stereoactive lone pair of electrons, which is nearly always the case when the anions are small and strongly electronegative, like for F and Cl. The tin situation is similar to that observed in SnCl2.
Synthesis and Structure of Novel Ternary Manganese Tellurides: MMnTe2 (M = Li, Na), Na3Mn4Te6, and Na3Mn4.7Te6
Authors: Wang Chwanchin , Kim Joonyeong , Hughbanks Timothy
Published: April 2011

The synthesis and structure of four ternary manganese tellurides are reported. All the title compounds form layered structures wherein MnTe4 tetrahedra are the fundamental building blocks. In two compounds MMnTe2 (M = Li, Na), MnTe4 tetrahedra share three corners in the formation of [MnTe3/3Te]1− layers, the fourth Te is bound to only one Mn and formally bears a negative charge. MnTe4 tetrahedra share both corners and edges in the formation of [Mn4Te6]3− and [Mn4.7Te6]3− layers in Na3Mn4Te6 and Na3Mn4.7Te6, respectively. Structural relationships between these ternary tellurides and oxides will be discussed.
Ln3Cu4P4O2: a New Lanthanide Transition Metal Pnictide Oxide Structure Type
Authors: Cava R. J. , Zandbergen H. W. , Krajewski J. J. , Siegrist T. , Hwang H. Y. , Ramirez A. P. , Batlogg B.
Published: April 2011

A new type of lanthanide transition metal pnictide-oxide, Ln3Cu4P4O2 (for Ln = La, Ce, and Nd), is reported. The crystal structure is made from Ln2O2 layers of the Pb2O2 type stacked with layers of Cu2P2 tetrahedra. The existence of a homologous series of compounds with similar chemistry connecting the BiCuOSe and ThCr2Si2 structure types is indicated. The resistivity of La3Cu4P4O2 is metallic, with no superconductivity observed above 2K. The Ce and Nd compounds have magnetic susceptibilities characteristic of the trivalent Lanthanides. The Ce compound orders magnetically at approximately 0.8 K.
Critical Transport and Magnetization of La0.67Ca0.3MnO3
Authors: Jeffrey Snyder G. , Hiskes R. , DiCarolis S. , Beasley M. R. , Geballe T. H.
Published: April 2011

The critical magnetic properties of bulk La0.67Ca0.3MnO3 and magnetoresistance of a thin film with the same Tc were measured and critical exponents determined. The magnetization data can be scaled with β = 0.3 and γ = 0.9, except above Tc which appears to be affected by a region where X3 (M = XH + X3H3) is positive. An M2 dependence of the magnetoconducitvity is observed above Tc. Below Tc, however, such a correspondence between the critical magnetic and transport behavior is not found.
The Ir3Ge7 (D8f) Structure: an Electron Phase Related to γ-Brass
Authors: Swenson D.
Published: April 2011

The crystallographic similarity between the Ir3Ge7 (D8f) and γ-brass (Cu5Zn8, D82) structures is discussed. By considering all phases known to possess the Ir3Ge7 structure, it is shown that phases of this structure type obey essentially the same electron concentration rules as does γ-brass, possessing on average 22 atoms/formula unit. Based on crystal-chemical considerations, it is further suggested that the Ir3Ge7 structure may be considered to be a structural derivative of γ-brass, in which 12 atoms have dropped out of the γ-brass lattice and the remaining atoms have undergone a certain amount of rearrangement in order to accommodate such a large concentration of vacancies. Finally, as further support of this idea, the phase NiGa4 is presented as an example of another γ-brass derived structure which contains crystallographic features of both γ-brass and the Ir3Ge7 structure.
On the Brass- and Silver-Colored Forms of PtGa2
Authors: Morosin B. , Swenson D.
Published: April 2011

PtGa2has previously been reported to exist as both a brass-colored, fluorite-structured phase and as a silver-colored alloy of unknown crystal structure. The crystal structure of the silver-colored form is reported here, along with a discussion of the stoichiometric factors responsible for the polymorphy of this phase. The silver-colored form belongs to the space group141/acd, with the lattice parametersa= 8.5544(4) andc= 21.574(17) Å, andZ= 32. The structure consists of layers of Pt and Ga stacked along the c axis, in which two crystallographically different Pt and Ga atoms have similar environments involving eight and nine nearest neighbors, respectively. This structural arrangement may be the prototype for a family of ternary platinum metal-Group B-based phases. The present investigation also necessitates changes in the currently accepted Ga-Pt phase diagram. Stoichiometric PtGa2undergoes a structural transformation upon cooling from a brass-colored fluorite structure to this silver-colored, tetragonal structure. However, the transformation is inhibited if the composition of the fluorite-structured phase is Ga-poor.
Modeling Phase Stability in a(B1/3B'2/3)O3 Perovskites
Authors: McCormack R. , Burton Benjamin P.
Published: April 2011

Order-disorder phenomena on the simple-cubic B-site sublattice in A(B1/3B'2/3)O3 perovskites is examined. A simple cubic groundstate analysis in the cube approximation reveals that this approximation is inadequate for A(B1/3B'2/3)O3 perovskites, because it cannot predict a common experimentally-observed [111] superstructure. A partial vertex enumeration technique is used to demonstrate that a 12 interaction subset of the cube + linear triplet approximation is sufficient. First-principles calculations were performed for Ba(Zn1/3Ta2/3)O3 (BZT) and Pb(Mg1/3Nb2/3)O3 (PMN), two technologically interesting materials, in an effort to construct generalized Ising model Hamiltonians to enable simulations of these materials. Both ionic model (SSCAD) and pseudopotential (PP) calculations were done, enumerating the relative energies of a series of B-site superstructures. Structural hierarchies are reasonble and predict the [111] groundstate for both BZT and PMN, despite the fact that it is not observed in the latter. The pseudopotential results also indicate the possibility of metal-insulator transitions in BZT as a function of B-site configuration.
Structural Modeling Based on the Oxygen Sublattice Features in the Perovskite Family
Authors: Depero L. E. , Sangaletti L. , Parmigiani F. , Giulotto E. , Rollandi L.
Published: April 2011

A new approach based on the study of distortion in the AO3 layer of ABO3 perovskites is proposed with the aim to discuss their ferroelectric properties. Rhombohedral distortions exist for either A-O average distances shorter than 2.7 A (space group Nr.161) or A-O distances larger than 3 Å (space group Nr.160). In the case of small distortions tetragonal or orthorhombic symmetries are preferred. Moreover, a relationship between the dimension of the B cation and the distortion in this type of structure has been established. Preliminary results show interesting correlations between distortions in the AO3 plane and the critical temperature of ferroelectric materials.
Influence of Li Addition on the Sintering and Dielectric Properties of PNN-PMW-PT Relaxor Ferroelectrics
Authors: Natarajan Raghu , Dougherty Joseph P.
Published: April 2011

Compositions in the PNN-PMW-PT system can be tailored to give high dielectric constant for MLC applications. Low temperature firing of MLC is always advantageous in using the less expensive electrode systems. Controlled addition of LiNO3 reduces the sintering temperature, increases the fired density and influences the microstructure of the ceramics. It also raises the peak dielectric constant and shifts the Curie temperature. The possible role of Li+ in modifying the characteristics of the ceramics is discussed.
Characterization of Cation-Ordering Induced Structures in Ba(Mg1/3Nb2/3)O3-BazrO3 Microwave Ceramics.
Authors: Akbas M. A. , Davies P. K.
Published: April 2011

Compositions in the Ba(Mg1/3Nb2/3)O3-BazrO3 (BMN-BZ) pseudo-binary system were prepared to evaluate the effect of BaZrO3 on the B-site cation ordering. While pure BMN adopts a 1:2 ordered structure, space group , 5 to 15 mole% additions of BZ stabilize a cubic 1:1 ordered phase with a doubled perovskite repeat. At higher levels of substitution (>25 mole% BZ), the B-site cations are disordered. Analytical TEM studies revealed that the 1:1 ordering is limited to nanometer-sized domains and the microstructure was found to strongly depend on the thermal history of the ceramics. For example, a cooling rate of 300°C/hr from a sintering temperature of 1640°C produced a partially ordered microstructure comprised of 4–5nm 1:1 domains dispersed in a disordered matrix. A completely ordered structure with 30–40 nm domains could be achieved when the cooling rate was reduced to 10°C/hr. The structure of the ordered 1:1 phases is interpreted using a “random layer” model in which one site is occupied exclusively by Nb, and the second contains a random distribution of all the remaining cations. Similar thermal annealing experiments were also conducted in an attempt to grow the 1:1 ordered domains in PMN-type (PbMg1/3Nb2/303) relaxor ferroelectric ceramics. Through experiments on PbZr03 (PZ)-doped PMT (PbMg1/3Ta2/3O3), the first observation of thermally induced domain growth in this class of relaxor ceramics are presented. These results cannot be explained by the widely accepted “space charge” model for relaxor ferroelectrics, but instead favor a charge-balanced random layer model for the 1:1 cation order.
Effect of Defects on Dielectric Properties in KTiOPO4, KTiOAsO4, RbTiOAsO4 and CsTiOAsO4 Single Crystals
Authors: Guo A. R. , Cheng Z. -Y. , Katiyar R. S. , Guo Ruyan , Bhalla A. S.
Published: April 2011

Dielectric measurements were carried out in single crystals of KTiOPO4, KTiOAsO4, RbTiOAsO4 and CsTiOAsO4. All of the materials exhibit a clear dielectric relaxation process in the low temperature range and a conductance mechanism in the high temperature range. The dielectric relaxation process can be well described by the Debye dielectric model with an activation energies of 0.8 eV, 0.5 eV and 0.4 eV respectively. The relaxation process is associated with the deviation of the alkali ions from its ideal lattice positions. The high temperature conductance is associated with the motion of the alkali ions from one lattice site to another. Therefore, both the low temperature relaxation process and the high temperature conductance originate from different features of defect behavior of alkali ions in the cage structure of these materials.
Electrical Conductivity and Structure of Nanocrystalline CeO2 Thin Films
Authors: Kosacki Igor , Anderson Harlan U.
Published: April 2011

The results of structural and electrical measurements of nanocrystalline CeO2 thin films are presented. A correlation between the electrical conductivity and microstructure has been observed and discussed. The electrical properties of nanocrystalline CeO2 thin films are attributed to a dominant role of grain boundary phase.
Rietveld X-ray Powder Profile Analysis and Electrical Conductivity of Fastion Conducting Gd2(Til-ySny)2O7 Solid Solutions
Authors: Eberman Kevin , Önnerud Per , Yu Tae-Hwan , Tuller Harry L. , Wuensch Bernhardt J.
Published: April 2011

The A3+2B4+2O7 pyrochlores have fast-ion conduction properties that make them attractive candidates for applications in fuel cells. Rietveld powder-profile analysis of x-ray diffraction data has been used to determine structural parameters for Gd2(Ti1-ySny)2O7 solid solutions (y = 0.20, 0.40, 0.60, and 0.80) for correlation with composition-dependence of the specimens' electrical conductivity. In accord with Vegard's law, the lattice constants increase linearly with y as the larger Sn ion replaces Ti4+. The structures in the system remain remarkably ordered in view of the fact that it had been suggested that increasing the average radius of the ions that occupy the B4+ site relative to A3+ drives the system toward a disordered defect-fluorite state. A small but significant increase in mixing of the occupancy of the cation sites was found with increasing y to a maximum of [GdB] = 0.05. We could detect no significant disorder in the anion array. The activation energy and pre-exponential term for oxygen ion conduction were found to increase linearly and exponentially with y, respectively, such that at a given temperature, the ionic conductivity changes by less than an order of magnitude across the system. The behavior is in marked contrast to other systems where the substitution of a larger cation in the B site increases conductivity by up to three orders of magnitude as a consequence of substantial disorder that is introduced in both the cation and anion arrays.
Phase Stability and Properties of Superionic PbSnF4 as a Function of the Method of Preparation
Authors: Calandrino Raimondo , Collin Anthony , Denes Georges , Cecilia Madamba M. , Parris Juanita M.
Published: April 2011

Superionic PbSnF4 can be prepared using a variety of different methods. It crystallizes in various different unit-cells. All structures are closely related to that of the fluorite type structure, with various degrees of order/disorder and different types of superstructures. Reaction of lead(ll) nitrate and stannous fluoride in water gives highly stressed and highly oriented tetragonal α-PbSnF4, however, in HF/H2O, it gives orthorhombic O-PbSnF4, which is also stressed but less. Reactions of solid α-PbF2 with an aqueous solution of SnF2, in excess SnF2, also gives stressed α-PbSnF4. Solid state reactions of SnF2 and PbF2 give unstressed and much less oriented α-PbSnF4 at 250°C, whereas tetragonal β-PbSnF4 is obtained above 270°C and is quenchable to ambient temperature. At 390°C, cubicy-PbSnF4 is obtained, however, this is not quenchable. Ball milling of o-PbSnF4 gives stressed α-PbSnF4, and ball milling of a- and β-PbSnF4 gives microcrystalline γ-PbSnF4. Annealing the latter gives unstressed and non oriented α-PbSnF4. Stirring a slurry of microcrystalline γ-PbSnF4 in water gives α-PbSnF4 except the one originating from o-PbSnF4, which gives back o-PbSnF4. The texture of these phases, and therefore the macroscopic properties related to it, can be drastically modified by modifying the method of preparation.
Sol-Gel Synthesis of the Strontium-Copper Oxycarbonate Superconductor Sr2CuO2(CO3)1−x(BO3)x
Authors: Babcock Audrey J. , Pico Alexander R. , Page Catherine J.
Published: April 2011

We have developed an ambient-pressure sol-gel synthetic route to superconducting borate-doped Sr2CuO2(CO3) using polyether alkoxide precursors. In our sol-gel preparation, the starting solutions contain strontium and copper alkoxide complexes in 2-(2-methoxy-ethoxy)ethanol. Boron is incorporated into the solution by using an aqueous boric acid solution for hydrolysis. Dried gels were examined by x-ray diffraction and thermal gravimetric analysis. By experimenting with various firing sequences and atmospheres we have established a successful route for reproducibly preparing relatively pure Sr2CuO2CO3 and boron-doped phases. Final products were characterized by x-ray diffraction, elemental analysis and magnetic susceptibility. Samples of nominal composition Sr2CuO2(CO3)0.85(BO2)0.15 are superconducting with a Tc(onset) of ∼25K. Subsequent treatment at 1100°C and 3 GPa for one hour increased Tc(onset) to ∼35K.
A Quantitative Tunneling/Desorption Model for the Exchange Current at the Porous Electrode/Beta"- Alumina/Alkali Metal Gas Three Phase Zone at 700–1300K
Authors: Williams R. M. , Ryan M. A. , Saipetch C. , LeDuc H. G.
Published: April 2011

The exchange current observed at porous metal electrodes on sodium or potassium beta"-alumina solid electrolytes in alkali metal vapor is quantitatively modeled with a multi-step process with good agreement with experimental results. No empirically adjusted parameters were used, although some physical parameters have poor precision. Steps include: (1) diffusion of Na+ ions to the reaction site; (2) stretching of the Na+ ionic bond with the β3"-alumina surface to reach a configuration suitable for accepting an electron to form a surface bound Na0 atom; (3) electron tunneling from the Mo electrode to the ions; and (4) desorption of Na0 atoms weakly bound at the reaction site on the β"-alumina surface; (5) electron tunneling between Na0 or Na+ on the defect block and (6) Na0 and/or Na+ mobility on the spinel block surface may extend the reaction area substantially.

The rate is increasingly dominated by the region close to the three-phase boundary as temperature increases and the rate near the three-phase boundary increases fastest, because desorption has a higher energy than reorganization. At high temperatures, surface diffusion of Na+ ions from the defect block edges to the spinel block edges is responsible for an increase in the total effective reaction zone area near the three-phase boundary.
Synchrotron X-Ray Diffraction Study of the Surface Layer in Poled Ceramic BaTiO3#
Authors: Balzar D. , Stephens P. W. , Ledbetter H. , Li J. , Dunn M. L.
Published: April 2011

Both unpoled and poled BaTiO3 were studied by laboratory and synchrotron x-ray sources. The shorter-wavelength synchrotron radiation was used to probe deeper below the specimen surface. Diffraction patterns revealed a distinctive surface layer of the same tetragonal structure as the main BaTiO3 fraction. A sin2 Ψ analysis of peak shift confirmed that no measurable change of elastic strain occurs upon poling. This indicates that poling may induce excessive strain that was relieved by microcracking or that a majority of domains reverse orientation. However, domain switching and possible microcracking may induce inhomogeneous strain (microstrain) and alter domain-size distribution. Line-broadening analysis showed large anisotropy of both coherently diffracting domain size and microstrain. The poled specimen shows a larger microstrain and smaller average domain size, which indicates possible effects of microcracking and additional defects created during poling.
CVD-Growth of Thin-Film Layered Se-Carbon Compounds
Authors: Grigorian L. , Fang S. , Sumanasekera G. , Rao A. M. , Schraderi L. , Eklund P. C.
Published: April 2011

Oriented films of layered Se-carbon compounds are grown on Ni substrates in evacuated sealed quartz tubes. Results of X-ray diffraction, Raman scattering and the c-axis electrical transport studies are reported. A discussion of possible models for the carbon -Se interaction is presented.
How does the Support Influence the Catalytic Activity of the Keggin Ion?
Authors: Smith Zakiyyah , Palmieri Michael , Buecheler Nancy , Jansen Susan A.
Published: April 2011

Heteropoly acids, HPA are well known solid acid and oxidation catalysts that find application in hetergeneous and homogeneous reactions. In the former, surface area and stability problems are diminshed by supporting the HPA. Typical supports include oxide substrates and porous carbon materials. The HPA's show some instability on these supports however. In this work, we demonstrate that HPA encapsulated in sol-gel silica matrices show enhanced catalytic performance without compromising the catalytic activity of the HPA. In addition, the specific role of the support in the catalytic process is described as well.
Enhanced Oxidation of Air Contaminants on an Ultra-Low Density UV-Accessible Aerogel Photocatalyst
Authors: Dreyer M. , Newman G. K. , Lobban L. , Kersey S. J. , Wang R. , Harwell J. H.
Published: April 2011

This research developed new forms of photocatalysts that could potentially move photocatalytic degradation of air contaminants into the main stream of industrially used remediation technologies. Tests of the photocatalytic activity of the TiO2 aerogel catalysts have been carried out using both acetone and methane as the air contaminant. For comparison, the same tests were carried out on a standard (non-aerogel) anatase powder. Despite having very low crystallinity, the aerogel decontaminates the air far more effectively than an equal volume of the anatase powder which indicates that a much larger fraction of the aerogel is activated by the UV light. Experimental data were used to determine adsorption equilibrium constants for acetone, and to determine reaction rate constants assuming a Langmuir-Hinshelwood type rate expression.
Aerogel Derived Catalysts
Authors: Reynolds John G. , Hair Lucy M. , Coronado Paul R. , Droege Michael W. , Wong Joe
Published: April 2011

Aerogels are a class of colloidal materials which have high surface areas and abundant mesoporous structure. SiO2 aerogels show unique physical, optical and structural properties. When catalytic metals are incorporated in the aerogel framework, the potential exists for new and very effective catalysts for industrial processes. Three applications of these metal-containing SiO2 aerogels as catalysts are briefly reviewed in this paper — NOx reduction, volatile organic compound destruction, and partial oxidation of methane.
Characterization Studies of Copper Supported on a Variety of Carbonaceous Substrates
Authors: Ma J. , Rodriguez N. M. , Vannice M. A. , Baker R. T. K.
Published: April 2011

Copper catalysts supported on different allotropie forms of carbon, such as activated carbon, graphite, pitch-based carbon fibers and diamond have been prepared and characterized using TPR, XRD, TPO, TEM and CAEM techniques. Preparation procedures were established for each support system and were dependent upon the oxidation characteristics of the particular carbonaceous solid. The ease of the reduction of copper oxide to metallic copper was found to be dependent upon the nature of the carbonaceous supports as well as the possible interactions between these two components. It was postulated that the epitaxial relationship that might exist between metallic copper and the diamond would make it easy for copper oxide to be reduced to its metallic state on this support. Attack of the graphite surface occurs in the presence of copper species in hydrogen at low temperatures. This behavior is rationalized according to the notion that dissociation of molecular hydrogen takes place on Cu2O and the active atomic species “spill-over” onto the graphite and undergo reaction with the π-electrons of the basal plane resulting in the creation of pits in the surface. In-situ electron diffraction highlighted the changes in the chemical state of copper species. Cu2O was found to be stabilized at certain stages of the reaction possibly due to its interaction with the carbonaceous supports. It is suggested that this type of copper species might exhibit some unique catalytic behavioral patterns.
Dynamical heterogeneities in glass-forming materials
Authors: Heuer A. , Kuebler S. C. , Tracht U. , Spiess H. W. , Okún K.
Published: April 2011

Cooperative dynamics around the glass transition leads to complex motional behavior of the individual molecules, resulting in non-exponential relaxation. The nature of this non-exponentiality is clarified theoretically as well as experimentally. The non-exponentiality may be due to heterogeneous relaxation (superposition of exponential processes with different rate constants) or homogeneous relaxation (identical intrinsically non-exponential processes). A precise definition of both limits is given. It is shown that the type of relaxation, i.e. to which degree heterogeneous and homogeneous contributions are present, reflects geometrical properties of the dynamics. The heterogeneous contribution can be further classified according to the timescale of fluctuations within the underlying distribution of relaxation rates, thereby introducing the concept of the rate memory. Determination of the type of relaxation and the rate memory essentially boils down to analysing the properties of multi-time correlation functions. Experimentally they are accessible by multidimensional NMR methods. Alternatively, they can be directly obtained from computer simulations. In order to clarify these concepts, the dynamics of polymers above the glass transition is analysed experimentally as well as numerically. The rotational dynamics of polymer segments turns out to be mainly heterogeneous with only small homogeneous contributions. Interestingly, the fluctuations within the heterogeneous distribution occur on the same timescale as the reorientation process itself.
Slow Dielectric Relaxation of Supercooled Liqutos Investigated by Nonresonant Spectral Hole Burning
Authors: Chamberlin R. V. , Schiener B. , Böhmer R.
Published: April 2011

When supercooled propylene carbonate and glycerol are subjected to a large-amplitude, low-frequency electric field, a spectral hole develops in their dielectric relaxation that is significantly narrower than their bulk response. This observation of nonresonant spectral hole burning establishes that the non-Debye response is due to a distribution of relaxation times. Refilling of the spectral hole occurs abruptly, indicative of a single recovery rate that corresponds to the peak in the distribution. The general shape of the spectral hole is preserved during recovery, indicating negligible interaction between the degrees of freedom that responded to the field. All relevant features in the behavior can be characterized by a model for independently relaxing domains that are selectively heated by the large oscillation, and which recover via connection to a common thermal bath, with no direct coupling between the domains.
Fluctuation Model for Structural Relaxation and the Glass Transition
Authors: Moynihan C. T. , Whang J.-H.
Published: April 2011

The fluctuation or independently relaxing nanoregion model attributes the distribution of structural relaxation times in a glassforming melt to a physical distribution of nanoregions which vary in their properties. A quantitative test of this model is described, in which parameters derived from relaxational data on B2O3 glass are shown to be capable of predicting the anomalous light scattering in the glass transition region. It is also shown that the local inhomogenieties which lead to the distribution of structural relaxation times make only a very minor contribution to the distribution of electrical relaxation times in ionically conducting glasses and melts.
Modeling DSC Annealing Peaks for Polyetherimide: Incorporation of Temperature Gradients
Authors: Simon Sindee L.
Published: April 2011

Enthalpy recovery of polyetherimide is measured during heating with differential scanning calorimetry (DSC) after cooling at various rates. The resulting annealing peaks are fit using the Moynihan-Tool-Narayanaswamy model of structural recovery. A self-consistent phenomenological equation is used to describe the experimentally observed structure and temperature dependence of the relaxation time in both glass and equilibrium regimes. Temperature gradients in the DSC sample are incorporated into the model calculations. When no thermal gradients are assumed, model parameters are found to vary with thermal history despite the use of the self-consistent equation for the relaxation time. Accounting for the presence of thermal gradients in the DSC sample is found to affect the values of the model parameters needed to fit the data. However, thermal gradients are unable to account for the thermal history dependence of the model parameters or for the discrepancy between the observed and calculated shapes of the DSC annealing peaks.
Reorientational Dynamics and Intermolecular Cooperativity of Reactive Systems
Authors: Mijovic Jovan
Published: April 2011

An investigation was conducted of the effects of the advancement of chemical reactions and the prepolymer molecular weight on the reorientational dynamics and intermolecular cooperativity in reactive epoxy-amine systems. Experimental results were obtained by dielectric spectroscopy over a wide range of frequency (1 mHz to 1 GHz) and temperature (−170 to +200 °C). A strong effect of the progress of reaction on reorientational dynamics was noted and, for the first time, an explanation was put forward within the framework of the coupling theory. It was proposed that the molecular-level characteristics of a reactive system that affect its intermolecular cooperativity can be classified into two categories: 1) molecular architecture - determined by molecular symmetry, rigidity and steric hindrance; and 2) dielectric architecture - determined by the type and concentration of all dielectrically active species.
Temperature Dependence of Spatial and Dynamic Heterogeneities above the Ising Spin Glass Transition
Authors: Glotzer S. C. , Poole P. H. , Coniglio A. , Jan N.
Published: April 2011

The temperature dependence of the microstructure and local dynamics in the paramagnetic phase of the d = 2 and d = 3 ± J Ising spin glass model is examined by comparing the equilibrium distributions of local flip-rates and local energies calculated in large-scale Monte Carlo simulations. The emergence in this model of fast processes as the glass transition is approached corresponds with recent experimental results.
Slow Dynamics and Glass-Like Behavior of Liquid Crystals Dispersed in Nanoporous Media
Authors: Aliev F. M. , Sinha G. P.
Published: April 2011

We have investigated the dynamic behavior of liquid crystals (LC), which are not glass formers when in bulk form, confined in porous matrices with randomly oriented, interconnected pores as well as in parallel cylindrical pores with different pore sizes by photon correlation (time range: 20 ns-103s) and dielectric spectroscopies (frequencies: 0.1 Hz-1.5GHz). We observed that in random pores (pore size is 10 nm and 100 nm) LC does not crystallize at temperatures about 25° C below bulk crystallization temperature and the non-Debye relaxational processes studied by both photon correlation and dielectric experiments were found not to be frozen. Slow relaxational process which does not exist in bulk LC and a broad spectrum of relaxation times (10−8− 10)s appear not only for LC in random pores but in cylindrical pores as well. However in matrices with random pores of 100 Å, glass-like behavior of slow mode (τ> 1ms) was observed. The relaxation time (determined in photon correlation experiment) of this slow process strongly increases when temperature decreases from 300 K up to 270 K varying from 0.2ms to 14 s and it's temperature dependence is described by the Vogel-Fulcher law.
Small Atom Diffusion and Breakdown on Stokes-Einstein Relation in the Supercooled Liquid State of Zr-Ti-Cu-Ni-Be Alloys
Authors: Geyer U. , Schneider S. , Qiu Y. , Macht M.-P. , Tombrello T. A. , Johnson W. L.
Published: April 2011

Be diffusivity data in the bulk metallic glass forming alloys Zr41.2Ti13.8Cu12.5Ni10Be22.5 and Zr46.7Ti8.3Cu7.5Ni10Be27.5 are reported for temperatures between 530K and 710K, extending up to 80K into the supercooled liquid states of the alloys. At the glass transition temperature, Tg, a change in temperature dependence of the data is observed in both alloys, and above Tg the diffusivity increases faster with temperature than below. The data in the supercooled liquid can be described by a modified Arrhenius expression containing the communal entropy of the supercooled liquid and based on a diffusion mechanism suggested earlier. The comparison with viscosity data in the supercooled liquid state of Zr46.7Ti8.3Cu7.5Ni10Be27.5 reveals a breakdown of the Stokes- Einstein relation, whereas D(T) and η(T) follow a relation close to van den Beu-kel's. The breakdown of the Stokes- Einstein relation indicates a cooperative diffusion mechanism in the supercooled liquid state of the ZrTiCuNiBe alloys.
Spac-Ttme-Correlations for Cation Motion in Alkali Silicates
Authors: Kieffer John
Published: April 2011

The motion of structural components in alkali silicates has been studied using molecular dynamic simulations. The relevant time correlation functions have been recorded over periods of up to 0.5 nanoseconds. The van Hove correlation functions reveal that alkali cation diffusion occurs by hopping between rather well defined sites, even at temperatures far above the melting point. The accessibility of such sites is controlled by the relaxation of the surrounding network, and constitutes the mechanism of coupling between the motion of network and modifier elements. The intermediate scattering functions exhibit a stretched exponential behavior, with a wavevector dependent stretching exponent. This is the result of a distribution of residence times at individual cation sites. When the diffusion process is examined on a coarser scale, at which Brownian motion is applicable, this distribution remains undetected. As an alternative to the Kohlrausch function, several mechanistic approaches for describing the relaxation behavior of these structures are discussed.
A Crystallographic Guide to the Structure of Borate Glasses
Authors: Wright Adrian C. , Vedishcheva Natalia M. , Shakhmatkin Boris A.
Published: April 2011

Borate glasses are an enigma in that there is now increasing evidence that their structures are dominated by superstructural units, which comprise well defined arrangements of the basic BO3 and BO4 structural units, with no internal degrees of freedom in the form of variable bond or torsion angles. In the present paper, it is shown that considerable insight into the structure of borate glasses can be gained from a study of the corresponding crystalline polymorphs. A simple, model is proposed to predict the fraction, x4, of 4-fold co-ordinated boron atoms in vitreous borate networks and the topological criteria for the formation of such networks are discussed, taking into account the degrees of freedom necessary for conventional glass formation.
Development of the Glassy State of Benzophenone and Effect of Heating Rate from the Glassy State on Solidification
Authors: Thoma Paul E. , Boehm John J.
Published: April 2011

Benzophenone supercools to a glass when cooled to −100°C. In fact, it is difficult to freeze benzophenone on cooling. In this investigation, the effect of cooling rate and the minimum cooling rate to obtain benzophenone as a glass is determined. From the glassy state, the influence of heating rate on the solidification temperature of benzophenone is determined. When heated at 3°C/min., solidification starts at about −29°C. Upon additional heating, melting usually starts at about +24°C, which is 23°C lower than the solid equilibrium structure melting temperature of 47°C. Occasionally the solid that forms at about −29°C undergoes a solid state phase transformation at about +22°C, when heated at 3°C/min. If this solid state phase transformation occurs, then the solid benzophenone starts to melt at 47°C. When solid benzophenone with the equilibrium structure is cooled to −100°C, no solid state phase transformation occurs. It appears that the structure that solidifies at −29°C is metastable.
The Effect of Iron and Oxygen Additions on the Properties of Zr-Al-Cu-Ni Bulk Metallic Glass Forming Alloys
Authors: Eckert J. , Mattern N. , Seidel M. , Schultz L.
Published: April 2011

The effect of iron and oxygen additions on the thermal stability of rapidly quenched amorphous Zr65Al7.5Cu17.5Ni10) was studied by x-ray diffraction and differential scanning calorimetry. With increasing Fe content the glass transition temperature Tg and the crystallization temperature Tx shift to higher temperatures. The increase is more significant for Tg than for Tx, resulting in a decrease of the supercooled liquid region with increasing Fe content. For oxygen additions Tx decreases with increasing oxygen content whereas Tg increases slightly, causing a decrease of the supercooled liquid region with increasing oxygen content. The results reveal that even minor iron or oxygen contaminations lead to drastic changes in the glass transition behavior and the crystallization mode. Large iron or oxygen contents lead to the formation of nanocrystalline microstructures instead of coarse-grained material.
Synthesis and Properties of Bulk Metallic Glasses in Pd-Ni-P and Pd-Cu-P Alloys
Authors: He Y. , Schwarz R. B.
Published: April 2011

Bulk amorphous Pd-Ni-P and Pd-Cu-P alloy rods with diameters ranging from 7 to 25 mm have been synthesized over a wide composition range using a fluxing technique. For most bulk amorphous Pd-Ni-P alloys, the difference ΔT = Tx - Tg between the crystallization temperature Tx and the glass transition temperature Tg is larger than 90 K, while for bulk amorphous Pd-Cu-P alloys, ΔT varies from 27 to 73 K. Pd40Ni40P20 has the highest glass formability, and 300-gram bulk amorphous cylinders, 25 mm in diameter and 50 mm in length, can be easily produced. This size, however, is not an upper limit. The paper presents the glass formation ranges for both ternary alloy systems and data on the thermal stability of the amorphous alloys, as well as their specific heat, density, and elastic properties.
Fast Dynamics in Glass Forming Systems: Vibrations vs Relaxation
Authors: Sokolov A. P.
Published: April 2011

Two contributions specific for the spectra of the fast dynamics in glass forming systems, a broad quasielastic scattering and the boson peak, are analyzed. It is shown that the vibrational contribution (the boson peak) decreases strongly in fragile systems. Some speculations about dependence of the degree of fragility (a la Angeli) on peculiarity of the spectrum of fast dynamics are presented. The existence of some intrinsic relation between the broad quasielastic contribution and the boson peak is demonstrated from analysis of the recent neutron and Raman scattering data. It is shown that this relation can be explained in framework of the model of damped oscillator. The model ascribes the quasielastic contribution to the scattering of light or neutrons on the vibrations around the boson peak, which are damped by some relaxation channel and have a quasielastic part in their response function. It is demonstrated that the model can explain many peculiar properties of the fast dynamics in the Raman, neutron and far-infrared absorption spectra.
Interfacial Composition Measurements in Complex Ni-Base Superalloys
Authors: Hall E. L. , Bentley J.
Published: April 2011

In this study, three different Ni-base superalloy / heat treatment combinations are studied in an attempt to assess the role of grain boundary morphology, composition, and phase distribution on mechanical properties, particularly time-dependent fatigue crack growth. The alloys chosen include one in which crack growth can be slowed by slow-cooling, and one in which crack growth is slow in the fast-cooled state. Both x-ray spectroscopy and energy-filtered imaging in the analytical electron microscope were used to measure grain boundary composition. The x-ray spectroscopy showed some enhancement of Cr, Mo, and W in the γ matrix at grain boundaries in the fast-cooled state, which was not present after slow cooling. Energy-filtered imaging showed no significant enhancement in alloying elements at interfaces in any of the samples studied. The results did show the tendency for the γ matrix to quickly equilibrate by second-phase precipitation, and a preference to avoid γ ‘- γ’ interfaces. The conclusions of this study are that time-dependent fatigue crack growth behavior in these alloys cannot be completely explained on the basis of grain boundary composition of major alloying elements.
Microstructure and Microchemistry of Interfaces in Structural Ceramic Composites
Authors: Alexander K. B. , Becher P. F. , Rice P. M. , Braski D. , Sun E. Y.
Published: April 2011

The performance of reinforced ceramics, particularly the toughness and creep resistance, is often determined by the nature of the interface between the reinforcement and the ceramic matrix. Specially-designed experiments to investigate the role of the interfacial characteristics on toughening mechanisms and crack propagation in reinforced (silicon carbide whisker reinforced alumina) and self-reinforced (silicon nitride) ceramic composites will be described. In the whisker-reinforced composites, the interfacial topography and chemistry were of primary importance, whereas in the silicon nitride materials the formation of interfacial phases and glassy-phase chemistry influenced the interfacial debonding process. The composite interfaces were characterized by high resolution electron microscopy and high spatial resolution microchemical analysis, including energy-dispersive X-ray and electron energy loss spectroscopy. Results from energy-filtered images from ceramic interfaces will also be shown.
Effect of Glass Composition on Mechanical Properties of Interfaces Between Alumina and Silicate Glass
Authors: Zagrebelny Andrey V. , Lilleodden Erica T. , Barry Carter C.
Published: April 2011

Interfaces between glass and crystalline grains have been examined using a thin-film geometry which allows the use of newly developed experimental methods for micromechanical testing of interfaces. In this approach, continuous films of thicknesses ranging 100–200 nm of anorthite (CaAl2Si2O8), celsian (BaAl2Si2O8), and monticellite (CaMgSiO4) are deposited onto single-crystal Al2O3 (α-structure) surfaces of different crystallographic orientations by pulsed-laser deposition (PLD).

Mechanical properties such as hardness, stiffness, and reduced Young's modulus were probed with a newly developed high-resolution depth-sensing indentation instrument. Emphasis has been placed on examining how changes in the glass composition will affect the mechanical properties of the single-crystal Al2O3/silicate-glass interfaces. The indentation data obtained from these experiments correlate directly to the morphology of the deformed regions imaged with atomic force microscopy (AFM). Nanomechanical tests combined with AFM imaging of the deformed regions allow force-displacement measurements and in-situ imaging of the same regions of the specimen before and immediately after indentation. This new technique eliminates the uncertainty of locating the indenter after unloading.
Atomistic Simulation of Grain Boundary Structure and Diffusion in B2 NiAl
Authors: Mishin Yuri , Farkas Diana
Published: April 2011

Using embedded atom potentials and molecular statics we calculate the structure and energy of [001] tilt grain boundaries in NiAl for 25 orientations with Σ values from 5 to 185. For three structures (stoichiometric, Ni-rich and Al-rich) of the Σ = 5 (210) boundary we simulate tracer self-diffusion by the vacancy mechanism both parallel and perpendicular to the tilt axis using the Monte Carlo technique. The effective activation energy calculated in a wide temperature range is compared with the spectrum of individual jump energies in the boundary core. The results are interpreted in terms of the grain boundary structure-diffusion relationship and the role of the jump correlation effect in grain boundary diffusion.
Grain Rotation and Grain Boundary Selection in Thin Films
Authors: Singh Varun , King Alexander H.
Published: April 2011

Computer simulations of the phenomenon of grain rotation in polycrystalline <111> textured films have been carried out. These simulations provide insight into the evolution of film microstructure due to grain rotation. It is found that grain rotation diminishes with annealing time and stops almost completely when a metastable equilibrium is obtained. The incidence of Σ1, Σ7 and Σ3 Coincident Site Lattice (CSL) boundaries increases with time while the other CSLs reduce in number. Sequential annealing experiments have been performed on thin films of gold. Grain rotation is found to take place with an average rotation rate of about 4°/hour at both 250°C and 350°C.
Diffusion Barrier Effect of Carbide Layer on Bonding Characteristics of Ti/Steel Clad
Authors: Morizono Y. , Nishida M. , Chiba A.
Published: April 2011

Bonding characteristics and interfacial microstructures in explosively welded Ti/stainless steel clad of the as-welded and annealed states were investigated. In case of Ti/SUS430 ferritic stainless steel combination, the average shear strength of an as-welded clad was 555 MPa, and metastable phases such as amorphous and fine crystalline phases were observed at the interface. These were considered to be the trace of melting and subsequently rapid solidification at the contact surface of both the parent materials. By annealing below 1173 K, the strength gradually decreased with increasing holding time. The average shear strength of the clad annealed at 1073 K for 360 ks was 242 MPa, while that of the clad annealed at 1273 K abruptly decreased down to 107 MPa with increasing holding time up to 360 ks. The reaction layer formed at the interface consisted only of TiC in the former. On the other hand, the coexistence of TiC, TiFe, TiFe2 and χ was observed at the interface in the latter. The TiC in the former was considered to serve as a barrier for diffusion of Ti, Fe and Cr across the interface and to suppress the formation of intermetallic compounds. As a result, the growth of reaction layer was inhibited and high bonding strength was preserved even after prolonged annealing. The results of the Combination of Ti and SUS304 austenitic stainless steel were also discussed.
Structure and Mechanical Properties of Titanium Nitride, Zirconium Nitride, and Chromium Nitride Films by Reactive Magnetron-Sputter Deposition
Authors: Soe W.-H. , Kitagaki T. , Ueda H. , Shima N. , Otsuka M. , Yamamoto R.
Published: April 2011

TiN, ZrN, and CrN films were grown by reactive magnetron sputtering on WC-Co sintered hard alloy substrates. Hardness and elastic modulus were measured by nano-indentation tester with low load on tip at 200 mgf. Hardness values were shown the higher value the thinner film thickness due to stress in the films.
Mechanisms of Oxygen and Water Diffusion Through Multilayer Inorganic/Organic Coatings
Authors: Tropsha Yelena G. , Harvey Noel G. , Graper Jane C.
Published: April 2011

Polyethyleneterephthalate substrates were coated with thin films of silicone oxide deposited by magnetically enhanced chemical vapor deposition. The rates of oxygen and water vapor transport through the coated and uncoated film systems were obtained as a function of temperature. Activated rate theory treatment of oxygen transmission rates revealed that silicone oxide coatings were imperfect; the apparent free energies of activation (ΔEp) for transport through film substrates which were coated on a single side were statistically identical to uncoated controls. However, multilayer coatings, consisting of two silicone oxide layers separated by an organic layer resulted in a dramatic increase in the ΔEp value. Similar effects were observed in polymer films coated on both sides with identical oxide layers. A simple empirical model for the change in transport mechanism is offered to explain this unanticipated results.

Activated rate theory treatment of water vapor transmission rates for these same film systems showed no obvious change in transport mechanism. However, ΔEp values obtained for water vapor permeation through silicone oxide coated polyethyleneterephthalate, polystyrene, polypropylene, and polycarbonate substrates were identical within experimental error, suggesting attractive interaction between the oxide layer(s) and water.
Links Between the Interface Plane Scheme and Grain Boundary Properties
Authors: Randle Valerie
Published: April 2011

This paper describes the current experimental knowledge base concerning the geometry and property relationships at the gram boundary plane. In order to analyse the data the interface-plane scheme is used, and its application is described here. The most important points to emerge from the data are that particular boundary properties - energy, mobility, segregation, precipitation and cracking - correlate with boundary plane types. Recent data illustrating the high occurrence of asymmetrical tilt grain boundaries and importance of low-index grain boundary planes are discussed in more detail.