bluuebunny/crossref_metadata_2025 huggingface dataset:
Structural Evolution of Simplified Nuclear Glasses Under β-Irradiation: A Raman Spectroscopy Study
Authors: Boizot B. , Petite G. , Ghaleb D. , Reynard B. , Calas G.
Published: April 2011

The ageing processes of simplified nuclear glasses under β-irradiation have been investigated on zirconium-bearing aluminoborosilicate glasses by micro Raman spectroscopy. No dose rate effect has been detected between 2.103 and 2.104 Gy/s for a 3.107 Gy integrated β dose. Important structural differences appear between the volume and the surface, with an increase of the polymerisation and a better defined danburite-like ring structure in the bulk relative to the surface. Molecular 02 is created during glass ageing, mostly close to the sample surface. Both processes indicate an important reorganisation of the glassy matrix during β-irradiation.
The Effect of Low Dose Rate Radiation on the Microchemistry of 304 Stainless Steel
Authors: Allen T. R. , Cole J. I. , Kenik E. A.
Published: April 2011

As part of the shutdown of the EBR-II reactor, structural materials were retrieved to analyze the effect of long term, low dose rate irradiation. In this work, the effect of low dose rate (10 to 10−9 dpa/s) irradiation on grain boundary and void surface chemistry is analyzed. These dose rates are comparable to those in light water reactor structural components. The components were irradiated at 375-379°C, temperatures near the highest temperatures experienced in pressurized water reactors. Radiation-induced segregation (RIS) was measured on samples taken from 304 stainless steel hex ducts irradiated to doses between 10 and 12 dpa. Radiation-induced segregation is shown to vary with dose rate, with measured grain boundary chromium concentrations reaching as low as 5 at. % and nickel concentrations reaching as high as 33 at. %. For some radiation conditions, significant grain boundary precipitation occurs, possibly leaving components susceptible to environmental attack.
Redistribution of Alloying Elements in Electron-Irradiated Iron-Based Fcc Alloys Studied by Hydrogen-Probe Mechanical Spectroscopy
Authors: Smuk S. , Häninen H. , Jagodzinski Y. , Tarasenko O.
Published: April 2011

Effect of electron irradiation on substitutional ordering was studied in Fe-36.7 wt.% Ni invartype alloy and Fe-25.2 wt.% Cr-20.2 wt.% Ni austenitic stainless steel. It was shown that the fine structure of the hydrogen Snoek-type peak in invar changes after irradiation to a fluence of 1019 e−.cm−2 with electrons with an energy of 3 MeV as compared to the solution treated condition. Irradiation affects the temperature behavior of the shear modulus of invar. No significant effect of irradiation on hydrogen Snoek-type peaks was detected in stainless steel.
Mixing and Demixing of Cu-Mo
Authors: Wei L. C. , Averback R. S.
Published: April 2011

Ion beam mixing of Cu/Mo multilayer samples and demixing of Cu-Mo alloy samples were examined as functions of temperature and ion mass. Even at liquid nitrogen temperature, the mixing of one component in other was very small under 1.0 MeV Kr irradiation. The maximum solubility was about 10%. Irradiation of homogeneous Cu-Mo alloys under the same conditions, moreover, led to phase separation. These conclusions were deduced from bulk X-ray diffraction measurements and corroborated by EXAFS examination. The maximum solubility obtained by irradiating multilayer samples occurred at about 600 K. At lower or higher temperature, the solubility of Cu in Mo-rich phase was lower. A model based on the ballistic difflusion explains these results.
Kinetic Lattice Monte Carlo Simulations of Cascade Aging in Iron and Dilute Iron-Copper Alloys
Authors: Wirth B. D. , Odette G. R.
Published: April 2011

Neutron hardening and embrittlement of pressure vessel steels is due to a high density of nm scale features, including copper-manganese-nickel rich precipitates and what are generally believed to be defect cluster-solute complexes. It has been postulated that the sub nanometer defect cluster-solute complexes form directly in displacement cascades. Cluster-complexes that are thermally unstable mediate the effect of flux on embrittlement kinetics. Larger cluster-complexes, that are relatively thermally stable for irradiation times up to 1 Gs, cause embrittlement in low copper steels. Robust characterization of these two types of so-called matrix defects has been an elusive goal. In this work, Kinetic Lattice Monte Carlo (KLMC) simulations of the long term evolution of the vacancy-rich cascade core regions were carried out for both pure iron and dilute iron-copper alloys at the nominal irradiation temperature of 563°K up to times when the vacancy clusters completely dissolve. Energetics were based on lattice embedded atom method potentials. Special time scaling and pulse annealing techniques were used to deal with the enormous range of inherent time scales involved, viz., rapid free vacancy jumps to slow emission from large complexes. Three-dimensional clusters rapidly form, containing a wide range of vacancies, as well as copper atoms in alloys. Small complexes are very mobile and growth takes place primarily by coalescence. The vacancy clusters ultimately dissolve at times from less than 0.1 to more than 100 MS. These simulations support the hypotheses that cascade cluster- complexes constitute both thermally stable and unstable matrix defect features.
Defect Generation by Proton Irradiation of Semi-Insulating Lec GaAs
Authors: Castaldin A. , Cavallini A. , Polenta L. , Canali C. , Nava F. , Puentee E. De La , Alvarez A. , Jimenez J.
Published: April 2011

High energy and high fluence proton irradiated semi-insulating GaAs has been studied by EBIC, PL mapping, C-V, NTSC, PICTS and p-DLTS. The main defects generated by the irradiation were analyzed. An EL2-like defect was found to be dominant. The generation of this defect annihilates the typical cellular distribution of EL2 in as-grown material. The generated EL2 defects present a different photoquenching behavior than the as-grown EL2 defects.
Amorphization Mechanism of Si/Ge Superlattices Upon Ion Implantation
Authors: Sobolev N.A. , Kaiser U. , Khodos I.I. , Presting H. , König U.
Published: April 2011

The damage production in the Si9Ge6 superlattices (SLs) upon implantation of 150 keV Ar+ ions at 300 K was studied my means of the cross-sectional transmission electron microscopy (XTEM) and electron microdiffraction. It was found that the amorphization occurs in a narrow dose range of (1 – 2) × 1014 cm-2 via accumulation of point defects. The conclusion drawn earlier (Mater. Sci. Forum 248-249, 289 (1997)) on the coherent amorphization of the Si and Ge layers in the SLs was confirmed. Possible mechanisms of the layer interaction leading to the observed behavior are discussed.
Characterization of the Electron Density in Si+-Implanted InP by Means of Raman Scattering by Lo-Plasma Coupled Modes
Authors: Ibáñez J. , Cuscó R. , Blánco N. , González-Díaz G. , Jiménez J. , Artús L.
Published: April 2011

We have studied by means of Raman spectroscopy the electron density in two different n-type InP samples with similar doping densities, obtained, respectively, by ion-beam implantation of 150 keV Si+ and by uniform Sn doping during LEC growth. The Raman spectra recorded at 80 K display in both cases the L+ and L– phonon-plasmon coupled modes. For the homogeneously doped InP:Sn sample, a simultaneous fit to the L+ and L– peaks of a line shape model based on the Lindhard-Mermin dielectric function yields accurate values of the charge density. In the implanted sample, the nonuniformity of the charge distribution substantially broadens the L+ modes, but the line shape fit to the L– mode still yields an average value of the electron density in the region probed by the laser beam.
Freeform Fabrication of Components with Designed Cellular Structure
Authors: Zimbeck W. R. , Rice R. W.
Published: April 2011

One of the more intriguing freeform fabrication application areas is the fabrication of bodies with designed microstmctures. While design of reinforced composite microstructures has received much attention, construction of designed porous or cellular structures may have greater technical feasibility and offers attractive practical benefits. Freeform fabrication advantages compared to existing foam and honeycomb fabrication techniques are discussed with emphasis on control over pore size, shape, orientation and distribution including hierarchical and functionally graded pore structures, all in combination with the ability to fabricate near net shape objects of complex geometry. Potential applications include the use of designed surface and bulk porosity to enhance both short and long term fixation of structural metal implants to bone, and lightweighting of aerospace components to approach optimized mass efficiency based on predicted stress distributions within a part. Progress using a stereo/photolithographic fabrication technique to construct designed pore structures in stainless steel bodies is presented. Various techniques used to fabricate fine porosity (size less than a layer thickness), coarse porosity (size greater than a layer thickness), and truss, open cell and honeycomb structures with characteristically high cell volume fraction (i.e., greater than 50 percent) are described.
Single Crystal Growth and Thermoelectric Properties of Ce5Cu19P12
Authors: Proctor K. J. , DiSalvo F. J.
Published: April 2011

Single crystals of the known ternary cerium intermetallic Ce5Cu19P12were grown by Sn flux and I2transport methods. The long axis of the black hexagonal needles was confirmed to be the c-axis by single crystal X-ray diffraction. Electrical resistivity of both single crystals and a pressed pellet was measured from 4 - 300 K; the room temperature resistivity is about 400 μΩ-cm for the needle axis of the crystals and about 5 mΩ-cm for the pressed pellet. The thermopower of the pressed pellet was found to be 34 μV/K at room temperature.
Substitutional Effects on the Thermoelectric Properties of Transition Metal Pentatellurides
Authors: Littleton R. T. , Kolis J. W. , Feger C. R. , Tritt Terry M.
Published: April 2011

The thermoelectric properties (resistivity and thermopower) of single crystals of the low-dimensional pentatelluride materials, Hffe5 and ZrTe5, have been measured as a function of temperature from 10K < T < 320K. Both parent materials exhibit a resistive transition peak, Tp ≈ 80K for HfTe5 and Tp ≈ 145K for ZrTe5. Each display a large positive (p-type) thermopower (α ≥ +125μV/K) around room temperature, which undergoes a change to a large negative (n-type) thermopower (α≤-125μV/K) below the peak temperature. The magnitude of this resistive anomaly is typically 3–7 times the room temperature value of ≈ 1 mΩ•cm. Through isoelectronic substitution of Zr for Hf (Hf1-xZrxTe5), a systematic shift is observed in Tp as the Zr concentration increases. Small Ti substitution for Hf and Zr affects the electronic properties strongly, producing a substantial reduction in Tp for either parent compound. However, the large values of thermopower and the magnitude of the resistive peak remain essentially unchanged. Substitutions of Se or Sb on the Te sites greatly affects the electronic behavior of the parent materials. Se doping increases the thermopower values by ≈20% while decreasing the resistivity by as much as 25%. These effects double the power factor, α2σT, of the parent materials. Small Sb substitutions appear to completely suppress the resistive anomaly. These features in the resistivity and thermopower signal a large degree of tunability in the temperature range of operation. The potential of these materials as candidates for low temperature thermoelectric applications will be discussed.
Semiconductor Clathrates: A pgec System with Potential for Thermoelectric Applications
Authors: Nolas G. S.
Published: April 2011

An investigation into the structural, chemical, electronic, and thermal properties of polycrystalline semiconductor clathrate compounds with different “guest” ions in the voids of these structures is presently underway by the author and his colleges. Despite the well-defined crystalline structure of these semiconductor materials, the thermal conductivity shows a magnitude and temperature dependence more typical of amorphous materials than crystalline materials. The localized low frequency vibrations of these “guest” ions is believed to interact with the acoustic phonons of the host lattice resulting in a very low thermal conductivity. Indeed in the case of Ge-clathrates a “glass-like” thermal conductivity was observed. The markedly low thermal conductivity displayed by these semiconductor materials, along with the high power factors, demonstrates the potential of this material system for thermoelectric applications.
Investigation of the Mechanism of the Enhanced Z3DT in PbTe Based Superlattices
Authors: Koga T. , Harman T. C. , Sun X. , Cronin S. B. , Dresselhaus M. S.
Published: April 2011

Various possible mechanisms for the recently discovered enhanced Seebeck coefficient S in PbTe/Te superlattices relative to the corresponding PbTe bulk are investigated. Among the various mechanisms which can account for the enhanced S, the energy dependent τ model (τ ∼ ɛr) seems the most plausible. Here the effective scattering parameter r is preferably increased due to the extra scattering by the periodic Te layers introduced in the superlattice. Other transport properties including the longitudinal magnetoresistance are also discussed.
Reliability of Thermal Conductivity Measured by Harman Method
Authors: Shinohara Y. , Imai Y. , Isoda Y. , Nishida I. A.
Published: April 2011

The Harman method was applied to measure thermal conductivity κ of thermoelectric materials, and the reliability of the measured κ was investigated. The quantitative κ requires a highly sensitive technique to measure minute Peltier heat. Temperature difference by Peltier heat pumping was successfully measured by developing the DC method of resistance measurement. κ ofn-type Bi2Te3sintered compact andn-type PbTe boules was measured at 295K by the Harman method. Static comparative method was also applied to obtain the standard value of κ. In the case of Bi2Te3, the κ by the Harman method agreed well with the standard value. In the case of PbTe in the electron concentrationnerange <5 × 1024/m3, the κ almost agreed with the standard value. However, PbTe in thenerange ≥1 × 1025/m3showed a larger κ than the standard value. The Harman method has an error to give the larger κ for the material with a large carrier component κ, of κ This error is due to the fast conduction of Peltier heat by the carrier. The reliable κ can be measured for the material with a small κ,.
Growth of Bismuth Telluride Thin Films by Hot Wall Epitaxy, Thermoelectric Properties
Authors: Tedenac J. C. , Corso S. Dal , Haidoux A. , Charar S. , Liautard B.
Published: April 2011

It is well known that bismuth telluride (Bi2Te3), its isomorphs (Bi2Se3 and Sb2Te3) and their alloys have the optimum bandgap (0.13 eV to 0.21 eV) for efficient solid state cooling applications around 300 K. Recently interesting work argued that the use of quantum well structures can enhance the figure of merit ZT as a result of the improvement of carrier charge density of state and the reduction of the thermal conductivity. However, for the production of such structures it is necessary to establish the optimum growth conditions and the doping levels of thin films based on Bi2Te3 and its isomorphs.

In this paper we report on the growth characteristics of Bi2Te3 ternary alloys (even quaternary) thin films elaborated by the Hot Wall Epitaxy (HWE) technique. Ternary alloys based on bismuth telluride have been deposited as thin films on silicon and silica substrates. Hot Wall Epitaxy have been demonstrated to be a suitable technique in chalcogenides growth. These films are formed in a closed chamber, that make possible to keep substrates at relatively high temperature Ts without selective loss of individual components from condensate. Experimental procedures, such as substrate and source materials preparations, have been described in our previous publications. Thin films obtained are well oriented (001) and have block single-crystal structure. These films were studied by microstructural investigations and electrical measurements (electrical conductivity σ, Hall coefficient RH and Hall mobility μn) in the temperature range from liquid nitrogen to 570 K.
Thermoelectric Properties of PbTe/Pb1−x. Eux Te Quantum Wells
Authors: Scherrer H. , Dashevsky Z. , Kantser V. , Casian A. , Sur I. , Sandu A.
Published: April 2011

The electrical conductivity, Seebeck coefficient, and thermoelectric power factor of PbTe/Pb1−xEuxTe quantum well structures are investigated theoretically. The variational method is employed. The anisotropy of effective masses, the multivalley character of the bulk semiconductors and also the dependence of effective masses in dimensional quantization subbands on the well width are taken into account. The carrier scattering both on optical and acoustical phonons is considered for structures with (111) and (100) crystallographic orientation. It is found that the power factor is larger in (100) oriented quantum wells. The results of recent experiments are discussed.
Conformal Electroless Copper and Nickel Deposition on Mems Structures
Authors: Neves Hercules P. , Kudrle Thomas D. , Chen Jia-Ming , Adams Scott G. , Maharbiz Michel , Lopatin Sergey , MacDonald N. C.
Published: April 2011

We propose electroless metallization as a method for conformal metal deposition microelectromechanical systems (MEMS). The intrinsically conformal nature of electroless deposition makes it ideal for coating high aspect ratio (greater than 50:1) structures frequently fabricated with micromachining techniques We take advantage of the selective nature of the deposition to obtain self-aligned electrical isolation. We minimize the metal film roughness for potential applications in RF and optics. Given the specific MEMS metallization requirements, we determined the ideal concentrations of additives and surfactants in order to provide good electrical isolation, low roughness and high film reliability. Our depositions were done using seed layers as well as through direct chemical activation of the silicon surface. Characteristics such as resistivity [ 1 ], morphology [ 1 ], microstructure [ 2 ], and electrochemical behavior [ 3 ] have already been reported in the literature; our paper is focused on the specific requirements for MEMS applications.
Circuit Pattern cu Deposition on Polyimide Surface Using ArF Excimer Laser
Authors: Tomita M. , Murahara M.
Published: April 2011

Circuit patterned nucleation of copper atoms onto polyimide surface was demonstrated by using ArF excimer laser (λ =193nm) and copper sulfate aqueous solution at an atmospheric pressure. Photo-excited C-H bonds of the polyimide surface were effectively dehydrated with hydrogen atoms which were photodissociated from the water. The dangling bonds of the dehydrated hydrogen atoms were combined with the oxygen and the copper atoms which were photodissociated by copper-sulfate aqueous solution. Thus, C-O-Cu bonds were formed on the surface. After this copper substitution, it was carried out onto the nucleated parts by usual electroless plating at 70°C. In this process, the conductive circuit pattern Cu thin film was deposited on polyimide surface.
A Novel Range of Noble Metal Organometallic Fluorides for use in the Fabrication of Submicron Metal Features by E-Beam or UV Irradiation
Authors: Thomson J. , Fzea A. H. , Lobban J. , McGivern P. , Cairns J. A. , Fitzgerald A. G. , Berry G. J. , Davidson M. R. , Fan Y. C.
Published: April 2011

The preparation a nd characterisationo f a novel organoplatinum fluoride is described. The physical vapour deposition (PVD) of the material was performed in the temperature range 160–170°C, and electron beam bombardment or uv irradiation, results in the degradation of the compound to give high quality metal features down to dimensions of ca 60 nm.
Sic Thin Film Characterization and Stress Measurements for High Temperature Sensors Applications
Authors: Gourbeyre C. , Aboughe-nze P. , Malhaire C. , Berre M. Le , Monteil Y. , Barbieri D.
Published: April 2011

In this work related to high temperature pressure sensors, a study was undertaken on the characterisation of β-SiC thin films through X-Ray Diffraction, AFM and stress measurements. 3C-SiC films were grown on (100) Si substrate in a vertical reactor by atmospheric-pressure chemical vapour deposition (APCVD). Silane and propane were used as precursor gas and hydrogen as carrier gas. Prior to the growth, Si surfaces were annealed at 1000°C for 5 minutes and carbonized with C3H8 at 1150°C during 10 minutes. At 1350°C, SiH4, C3H8 and H2 were introduced for the SiC deposition. The atomic ratio of Si/C in the gas phase was 0.3 and the growth rate was 3 μm/h. Only the process time was varying to obtain different SiC layer thicknesses varying from 3 to 9 μm as measured by FT-IR spectrometry. Stress measurements of thin β-SiC layers deposited on thick Si substrates were performed at room temperature using the bending plate method and the Stoney's equation. The stress for a 3 μm thick SiC layer is evaluated to be in the range of 400 MPa in tension. When increasing the SiC film thickness, this stress decreases due to the relaxation of the structure with bending. SiC/Si membranes were obtained by KOH etching and studied as a function of pressure in the [0-50 mbar] range. A residual stress in the membrane was deduced from the load-deflection measurement technique reaching 105 MPa in tension.
Synthesis, Structure and Dielectric Properties of Na2SnTeO6
Authors: Park J.-H. , Woodward P.M. , Parise J.B. , Lubomirsky I. , Stafsudd O.
Published: April 2011

A new perovskite was recovered from the high pressure-high temperature treatment of the α-TlSbO3 form of Na2SnTeO6 at 7 GPa and 950 °C for 30 minutes. Synchrotron x-ray powder diffraction data show the space group is P21/n with a=5.40361 (5), b=5.46152(5), c=7.69288(7) Å and ß=90.034(3)°. Using disk samples of both polymorphs, the dielectric properties were measured as a function of temperature. At ambient conditions, the perovskite form has a more than 1.5 fold enhancement in dielectric constant compared to the α-TlSbO3 form while the molar volume and the molecular polarizability decrease.
New Substituted Pyrochlore-Type Manganates with Magnetoresistive Properties
Authors: Cheikh-Rouhou W. , Senis R. , Chaillout C. , Strobel P. , Martinez B. , Obradors X.
Published: April 2011

Substitutions in the pyrochlore-type oxide Tl2Mn2O7 have been carried out on both the Mn and the TI site, using high pressure synthesis at 4-6 GPa. We show that a continuous solid solution exists between Tl2Mn2O7, and Tl2Ru2O7, and that the replacement of a fraction of Mn by Ru dramatically changes the transport properties from metallic to semiconducting and induces magnetoresistance (MR) in this system. MRs up to 95% (vs. RO) have been observed. The Tl site, already known to accept In or Sc, can also be substituted by the larger cation Bi3+, which also induces a metal-insulator transition at low substitution level.
New Synthetic Pathways to Mesostructured Thiogermanates
Authors: Oberender N. , Fröba M.
Published: April 2011

The synthesis and characterisation of several mesostructured thiogermanates are shown. In particular the first supramolecular templated synthesis of mesostructured binary metal chalcogenides in a microwave is presented. The obtained products are characterised by x-ray powder diffraction, transmission electron microscopy, thermal analysis and x-ray absorption spectroscopy.
A New Type of Coordination Polymer: Hydrothermal Synthesis, Crystal Structure, and Magnetic Properties of [(C10H8N2)2CuBr]Cu3Br4
Authors: Cabrera Brenda R. , Wang Ru-Ji , Li Jing , Yuen Tan
Published: April 2011

Growth of [(C10H8N2)2CuBr]Cu3Br4(I) crystals was achieved using the hydrothermal synthesis. Single crystal X-ray diffraction analysis shows that this compound crystallizes in monoclinic system, space group P21/c (no. 14) with four formula units in the unit cell. The cell dimensions are the following: a = 16.769(2) Å, b = 23.873(6) Å, c = 6.523(2) Å, β = 98.37(3)°, V = 2584(1) Å3. The title compound represents a new structure type. It consists of one-dimensional ribbons of 1[(Cu3Br4)] extending along the c-axis and discrete [(C10H8N2)2CuBr]+ complexes. The magnetic susceptibility study indicates a paramagnetic behavior due to the Cu(II) in the complex cations. The effective paramagnetic moment was calculated to be 2.20 μB from fitting the χ(T) data.
Synthesis and Al K-Edge Xanes Investigation of Mesostructured Aluminophosphates
Authors: Twemann M. , Fröba M. , Wong J.
Published: April 2011

We report on the synthesis of lamellar mesostructured aluminophosphate composites which contain variable relative amounts of aluminium oxide species in the core regions of the lamellae; this is investigated quantitatively by Al K-edge XANES spectroscopy. Templating is achieved by the utilisation of monododecyl phosphate surfactant. If no phosphorous source (such as H3PO4) is used for the synthesis, the phosphate head groups of the surfactant become incorporated into the inorganic network to form similar lamellar aluminophosphate structures. Thus, the surfactant serves as both template and reactant.
Processing and Properties of Amorphous Manganese Dioxide Formed by Sol-Gel Procedures
Authors: Xu Jun John , Passerini Stefano , Owens Boone B. , Smyrl William H.
Published: April 2011

Sol-gel derived amorphous manganese dioxide (a-MnO2) showed extremely high reversible lithium intercalation capacity. The composition and structure of the material were modified by heating at different temperatures. Cycling performance of the modified samples suggests that lowering the water content in the material is beneficial, while introducing crystallinity is detrimental, to its cyclability. A novel double-solvent-exchange process was tried for the processing of the material. Preliminary results indicated significant improvement in the reversibility of the insertion/release cycles.
π-Stacking in Conjugated Polymers and Oligomers: A Structural and Spectroscopic Study
Authors: Curtis M. David , Blanda Wendy , Politis Jeffrey K. , Francis Anthony H. , Lee Jihoon , Kampf Jeff W. , Gonzalez-Ronda Lebzylisbeth , Martin David C.
Published: April 2011

Regioregular, alkyl-substituted poly(heteroaromatics) tend to crystallize in π-stacked structures as opposed to the herringbone pattern characteristic of non-substituted, planar aromatic molecules, e.g. sexithiophene. π-Stacking, favored by the crystallization of the sidechains, induces planarity in the conjugated backbone. The increased planarity causes a large (50-100 nm) shift in λmax (abs.) compared to the solution phase in which the backbone is twisted out of coplanarity, π-Stacking is a form of ground state aggregation that causes “fine structure” on the absorption peak. Excitation into the aggregate states rapidly leads to the formation of excimers as shown by the excitation spectra. In -stacked polymers, photoluminescence is almost entirely from the excimer states.
Low Cost Filled Thermostable Ionomer Membrane for P.E.M.F.C.
Authors: Poinsignon C. , Amodio I. , Foscallo D. , Sanchez J.Y.
Published: April 2011

A filled ionomeric membrane was achieved by dispersing phosphatoantimonic acid H3Sb3P2014, ×H20 (H3) in a Sulfonated PolySulfone (SPS) solution [1]. Water up-take is higher for filled than unfilled membrane as well as Protonic conductivity which is larger than that expected from the overall calculated concentration in charge carriers : a conductivity value of 0.135 S.cm−1 was gained at 50°C under 1003% Relative Humidity (HR) for a 1.6 meq.g−1 cationic exchange capacity (cec) SPS filled with 8% in H3 against 0.06S.cm−1 for an unfilled one. Mechanical measurements on the wet membrane shows the plasticizing effect of sulfonation, water and of the filler content which simultanously reinforced the cohesion of the membrane.
How Unique are the Microstructure and the Electrical Properties of Nanocrystalline Ceramics?
Authors: Knauth P. , Tuller H. L.
Published: April 2011

A literature overview on microstructural and electrical properties of nanocrystalline ceramics is given. Space charge effects in nanosystems, especially thin-films and colloidal particles, are discussed from a theoretical point of view. Some common features of nanocrystalline ceramics are pointed out: nanoparticles present few extended lattice imperfections and the densification process begins at distinctly lower temperatures than that of coarse-grained ceramics. A significant decrease of grain boundary resistance occurs due to grain-size dependent dopant segregation, which leads also to an important increase of the apparent solubility of dopants in nanocrystalline materials. A number of studies confirm the theoretically expected reduction of the point defect formation enthalpy at interface sites, giving rise to significantly larger nonstoichiometry and electronic conductivity of nanocrystalline materials. Increased ionic conductivity has been found only in a limited number of cases, some of which remain controversial.
Mechanism of Cation Doping by the Soed 2 Method
Authors: Kamada K. , Matsumoto Y.
Published: April 2011

Electrochemical cation doping into the YBCO ceramics has been carried out using SOED 2 method (electro-bi-injection). The SOED 2 method consists of the Anode/M-β”-A1203/Ceramics/YSZ/Cathode electrolysis system, where the metal cation M and oxygen anion are simultaneously injected into the oxide ceramics so that electrical neutrality is maintained in the ceramics. YBa2Cu3Oy superconductor was used as the ceramics to be doped. In general, graded doping occurred at a relatively high temperature, because the migration rate of the oxygen anion is close to that of the metal cation in the grain boundaries of the ceramics at high temperature. As a result, the metal cation was graded on the anode side of the YBCO ceramics. The doping situation depended on the electrolysis temperature, the valence of the doped cation. The mechanism of the electro-bi-injection is discussed.
Oxygen Ion Conductivities of Rhombohedral Phases in the Ba-Sr-Bi Oxide System
Authors: Gökcen O.A. , Kim S. , Meen J.K. , Elthon D. , Jacobson A.J.
Published: April 2011

The rhombohedral phase of the Ba-Bi-O system is known to be a good oxygen ion conductor. Previous studies on conductivity of that system have shown that there is a sudden increase in conductivity at the β2-β1 polymorphic transition. Therefore, the high temperature β2 phase is a very good anionic conductor with values up to 10−1-100 S/cm. In the Ba-Sr-Bi-O system, the rhombohedral phase that contains Ba and Sr coexists with BaBiO3. Several specimens of the rhombohedral phase with different [Ba]-[Sr] ratios were synthesized. Electron microprobe analysis was used to determine the chemical composition of each specimen and to ensure that it consisted of a monophasic assemblage. Results of X-ray powder diffraction experiments confirmed that each sample has a rhombohedral unit cell. Oxygen ion conductivities of these materials were measured using the 2-probe AC Impedance technique over the 320-730°C temperature range. In each case, a sudden increase in conductivity indicates temperature range of the polymorphic transition. Exchange of the smaller cation Sr for Ba makes the transition temperature increase almost in a linear manner. Conductivities of all β2 polymorphs at a given temperature are very similar to conductivities of Ba-Bi-O and Sr-Bi-O β2 polymorphs. Conductivities of all β1 polymorphs are also similar. Apparently, the nature of the alkaline earth present has only slight influence on conductivities of these phases.
Hydrothermal Synthesis and Properties of Ce1−xMxO2-δ(M = La, Bi, Sm, Pr, Tb) Solid Solutions
Authors: Greenblatt M. , Shuk P. , Huang W. , Dikmen S. , Croft M.
Published: April 2011

A systematic study of hydrothermally prepared Ce1−x,MxO2−δ, (M= Sm, Bi, Pr, Tb; x= 0-0.30) solid solutions, promising materials for application in solid oxide fuel cells and oxygen membranes is presented. Ultrafine particles of uniform crystallite dimension, ∼ 20 nm can be formed in 30 min. under hydrothermal conditions (260°C, 10 MPa). The small particle size (20-50 nm) of the hydrothermally prepared materials allows sintering of the samples into highly dense ceramics at 900-1350°C, significantly lower temperatures than 1600-1650°C required for samples prepared by solid state techniques. The solubility limit of Bi2O3, in CeO2, was determined to be around 20 mol. %. The maximum conductivity, σ600°C ∼ 4.4 × 10−3 S/cm with Ea = 1.01 eV, and σ600°C = 5.7 × 10−3 S/cm with Ea ≈ 0.9 eV was found at x= 0.20 and x= 0.17 for Bi and Sm, respectively. In the Ce-Pr/Tb oxide systems, in addition to the high oxide ion conductivity, electronic conductivity occurs through the hopping of small polarons by a thermally activated mechanism (electron hopping from the Pr3+/Tb3+ to a neighboring Pr4+/Tb4+ ion).
Development of Mixed-Counducting Ceramics For Gas Separation Applications
Authors: Balachandran U. , Ma B. , Maiya P.S. , Dusek J.T. , Picciolo J.J. , Guan J. , Dorris S.E. , Liu M.
Published: April 2011

Mixed-conducting oxides are used in many applications, including fuel cells, gas separation membranes, sesors, and electrocatalysis. This paper describes mixed-conducting ceramic membranes that are being developed to selectively remove oxygen and hydrogen from gas streams in a nongalvanic mode of operation (i.e., with no electrodes or external power supply). Because of its high combined electronic/ionic conductivity and significant oxygen permeability, the mixed-coducting Sr-Fe-Co oxide (SFC) has been developed for high-purity oxygen separation and/or partial oxidation of methane to synthesis gas, i.e., syngas, a mixture of carbon monoxide and hydorgen. The electronic and ionic conductivities of SFC were found to be comparable in magnitude are presented as a function of temperature. The oxygen flux through dense SFC tubes during separation of oxygen from air is compared with the oxygen flux during methane conversion.

Unlike SFC, in which the ionic and electronic conductivities are nearly equivalent, BaCe0.80Y0.20O3 (BCY) exhibits protonic conductivity that is significantly higher that its electronic coductivity. To enhance the electronic conductivity and increase hydrogen permeation, metal powder was combined with the BCY to form a cermet membrane. Nongalvanic permeation of hydrogen through the cermet memebrane was demonstrated and characterized as a function of membrane thickness. A sintering aid was developed to avoid interconnected porosity in and improve the mechanical properties of the cermet membrane.
Surface Oxygen Exchange Kinetics and Oxygen Diffusion Rates in Ysz Single Crystals
Authors: Joos N.I. , van der Heide P.A.W. , Liu J.R. , Christoffersen R. , Chu W.K. , Mims C.A.
Published: April 2011

Isotope exchange with C18O2 followed by depth profiling analysis was used to study surface exchange and bulk diffusion of oxygen in single crystal ((100) surface orientation) yttria-stabilized zirconia (YSZ) in the temperature range 250°C - 350°C. The depth profiles, which were obtained using 18O(ρ,α)15N nuclear reaction analysis (NRA) and secondary ion mass spectrometry (SIMS), reveal both the bulk oxygen diffusion coefficients (D) and surface exchange coefficients (k). Bulk oxygen diffusion coefficients are consistent with an extrapolation to lower temperature of previously published results with an activation energy of 114 kJ/mol (1.2 eV). The surface exchange rates, however, depend strongly on the gas exchange species. Much higher exchange rates are observed with C18O2 than with 18O2 (over four orders of magnitude when compared to an extrapolation to lower temperatures of previously published results) with a measured activation energy of 152 kJ/mol (1.6 eV). This faster surface exchange rate enabled measurable 18O tracer profiles to be generated at lower temperatures than previously reported, further contributing to the understanding of YSZ material properties and bringing to light a possible order/disorder transition similar to that previously observed at 650°C.
Commercial Graphites for Li-Ion Battery Applications
Authors: Siapkas D.I. , Hatzikraniotis E. , Mitsas C.L. , Terzidis D. , Zorba T. , Moumouzias G. , Papadopoulos I.
Published: April 2011

In this work we have examined different types of synthetic graphites (SFG and KS types) that have different morphology and particle sizes. In our analysis we examined the incremental capacity (dC/dV), which shows a series of peaks that correspond to potential plateaus. This approach enable us to identify the processes involved (formation of SEI, Li+ intercalation or de-intercalation, etc.). Our analysis was mainly concentrated on the first lithiation, in an attempt to specify the origin of the capacity loss related to each type of synthetic graphite.
Novel Design and Fabrication of Thermal Battery Cathodes Using Thermal Spray
Authors: Ye Hui , Strock Chris , Xiao T. Danny , Strutt Peter R. , Reisner David E. , Guidotti Ronald A. , Reinhardt Frederick W.
Published: April 2011

Li-Alloy/FeS2 thermal batteries are the predominant thermal battery chemistry today. Conventional electrodes are fabricated by cold pressing of powders. A better means of providing thin electrodes would dramatically increase volumetric and gravimetric energy densities and cost efficiency of thermal batteries. In this study, experiments were conducted on fabricating the cathode via high-velocity oxygen-fuel (HVOF) and dc-arc plasma thermal spray technique. The deposited films were characterized by cross-section examination using Scanning Electron Microscopy (SEM) and X-ray Diffraction. The thermal decomposition of pyrite was suppressed by a proprietary additive. The electrochemical test results showed that pyrite cathodes prepared by dc-arc plasma spraying with additives demonstrated better performance compared traditional pressed-powder electrodes.
Molybdenum and Vanadium Oxide Polycrystalline Films: Properties and Application to Lithium Microbatteries
Authors: Yebka B. , El-Farh L. , Julien C. , Nazri G.A.
Published: April 2011

We report on the growth of molybdenum and vanadium oxide films, i.e., MOO3, V205, and V6013, and their application as positive electrodes in lithium microbatteries. We have characterized various polycrystalline samples and studied how their structural and electrical properties are affected by the different preparation conditions. The highest quality films were grown on silicon substrate maintained at 250°C and annealed at 300°C. It is shown that the growth conditions play an important role in the electrochemical properties of the film. Both thermodynamic and kinetic parameters are strongly dependent on film morphology and stoichiometry. Microbatteries fabricated with cathodes formed at moderate temperature have shown a volumetric capacity about 80 μAh/μm/cm2. The cells exhibit a monotonous discharge profile indicating that the cathode materials remain single phase even for a large degree of intercalation.
Propylene Combustion on Lanthanum Perovskites
Authors: Zenteno R. , Vicente L. , Viveros T.
Published: April 2011

The catalytic activity of lantane perovskytes in the combustion of propylene was studied. The catalysts were LaFeO3, LaNiC3, LaCoO3, La2-xSrxNiO4and La1-xSrxCoO3where x is the amount of Sr substitution. Below 400°C the only products are CO2and H2O, and above 400°C besides the total oxidation products, acroleine, acetaldehyde acetone and other partial oxidation products were obtained. The substitution of La by Sr improves the catalytic behaviour.
Preparing Monodispersed Hydrogel Microspheres and Microcapsules
Authors: Senuma Y. , Lowe Ch. , Zweifel Y. , Hilborn J. G. , Marison I.
Published: April 2011

Our spinning disk atomization (SDA) can, relative to other existing techniques, produce micronsized particles of very narrow size distribution. The aim of this work is to present this technology for the production of alginate microspheres. We have atomized and gelled aqueous alginate solutions into very narrowly dispersed microspheres with sizes ranging from 300 to 600 μm. Here the interest is to design particles of a given size with a narrow size distribution and to show a new method of encapsulation using the SDA. The viscosity and flow rate contributions in the drop formation is qualitatively analyzed to show how it affects the droplet size. In addition, a technique for high degree of encapsulation will be presented. As an example, yeast has been used as a model system. The production of yeast loaded microspheres will show the potential of the technique for biotechnology applications. Such alginate beads could potentially serve as carriers for acitive substances or cells in large scale bioreactors.
Ultrasound -Triggered Drug Delivery with Contrast Imaging: Effect of Microencapsulation Method
Authors: Wheatley M.A. , El-Sherif D. , Basude R. , Shimp R. , Narayan P.
Published: April 2011

A method for preparation of hollow, biodegradable polymeric microcapsules for use as contrast agents is described, and strategies for their use in concomitant imaging and drug delivery are outlined. Compared with X-ray or magnetic resonance imaging, diagnostic ultrasound is a safe, relatively inexpensive imaging technique, which allows the physician to view real-time images. Contrast agents are being developed which will greatly enhance the contrast of the received image, when injected into the patients blood stream. We have developed hollow polymeric CA based upon the ability to microencapsulate a solid core of ammonium carbonate which is then removed by decomposition and freeze-drying. The polymer poly D,L(lactide-co-glycolide) (PLGA) was chosen for it's FDA approval, and because it has the most rapid in vivo degradation of the α-hydroxy acid series. Spray dried and solvent extraction samples were used to test the concept of concomitant drug delivery and imaging. The method of fabrication had an important effect on the drug loading by adsorption, and on the amount of drug that was released when the capsules were insonated with ultrasound in the medical imaging range. Both were greater for spray dried samples. Both frequency and pressure of insonation also influenced release. The most dramatic increase in release was after 5 minutes for the 10 Mhz low (1.25 MPa) pressure insonation, which showed 316% greater release than control, a total of 1.89 mg.
Fiber Based Tissue Engineered Scaffolds for Musculoskeletal Applications:in VitroCellular Response
Authors: Laurencin Cato T. , Ko Frank K. , Borden Mark D. , Cooper James A. , Li Wan-Ju , Attawia Mohamed A.
Published: April 2011

The architecture of an engineered scaffold is an important consideration in the design of a synthetic tissue replacement. We have begun to explore the use of heirarchical fiber scale design ranging from microscale nonwoven to 3-D integrated fiber bundles in orthopaedic tissue engineering applications. The use of heirarchical fiber and design includes the following advantages: 1) the ability to tailor a broad spectrum of substrates with a wide range of mechanical properties, and 2) the ability to create structures capable of supporting cell proliferation as well as the micro-diffusion of nutrients throughout the structure. Using the bioresorbable copolymer, poly(D,L-lactide-co-glycolide) [PLAGA], we have fabricated two matrices based on fiber technology: 1) a microfiber non-woven mesh composed of 50:50 PLAGA and 2) a 3-dimensional braided structure composed of 5:95 PLAGA. These structures were examined by scanning electron microscopy [SEM] in anin vitrocell culture environment. Matrices were seeded with two types of cells (osteoblasts from neonatal rat calvaria and fibroblasts from the BALB/C cell line) to determine the effect of matrix architecture on cellular morphology and proliferation. SEM analysis of the microfiber matrix indicated a highly porous, structure resulting from the random arrangement of the microfibers. PLAGA fibers appear to have a range in diameter from approximately 2-7 μm. The 3-D braided matrix was shown to have a organized fibrous structure resulting from the 3-D braiding process. Examination of the attachment and proliferation of cells on the matrices revealed that cell morphology and proliferation patterns were dependent on cell type and matrix geometry. SEM analysis also indicated that cells responded dynamically to changes in structure due to the onset of degradation.
Putting Cells on Biomaterials to Engineer Cell Behavior and Tissue Repair, Taste, Touch and Force
Authors: Curtis A.S.G. , Wilkinson C.D.W.
Published: April 2011

Cells react to topography on the micro and nanoscale with a variety of consequences. These reactions can be used to advantage in controlling cell behavior on the surfaces of prostheses. This short paper examines two of the possible causes of these reactions, namely diffusion effects caused by the shape of the substratum and stretch reception by the cells.
Application of Conductive Polymers in Bone Regeneration
Authors: Shastri V.P. , Rahman N. , Martin I. , Langer R.
Published: April 2011

The role of electromagnetism in the physiology of the human body and in the healing process is well accepted. Electroactive polymers, such as electrically conducting polymers, by virtue of their susceptibility to either electrical, mechanical, optical or thermal phenomena, could be utilized as an interface between the external world and the physiological environment1. In this study we have evaluated the utility of polypyrrole (PPy)-a conductive polymer, as an interactive substrate for inducing differentiation in bovine bone marrow stromal cells (BMSC). It was observed, the PPy is an excellent substrate for BMSC attachment, proliferation and differentiation. Furthermore, an application of an electrical stimulus (ES) to BMSC via PPy substrate was found to enhance the osteogenic commitment of these cells.
Synthesis and Swelling Behavior of Hydrogels Based on Grafted Chitosan
Authors: Yazdani-Pedram M. , Retuert J.
Published: April 2011

The grafting of poly (acrylic acid) and /or acrylamide onto biopolymer chitosan were carried in order to obtain hydrogel materials- The grafting reactions were carried out in a homogeneous aqueous phase by using potassium persulfate in combination with ferrous ammonium sulfate as redox initiator system in the case of acrylic acid and potassium persulfate alone in the case of acrylamide The percentage of grafting was found to depend on the relative amount of monomer to chitosan, initiator and ferrous ion concentration, volume of the aqueous phase as well as reaction time and reaction temperature. In the case of acrylic acid a maximum grafting of 1800% was obtained, whereas with acrylamide the optimum percentage of grafting attained was near 400%. Evidence of grafting was obtained from comparison of FTIR of the grafted and ungrafted chitosan as well as solubility characteristics and swelling behavior of the products. The swelling degree of the grafted chitosan samples was determined at two different pH values. The percentage of grafting influenced the degree of swelling of the grafted chitosan, in different manner depending on the nature of the grafted chains, where values as high as 40 was observed.
An Investigation of the Release Properties of a Cationic Drug From a Hydrophobic Polyanhydride Matrix as a Function of Dissolution Medium
Authors: Ginsburg E. J. , Stultz T. D. , Stephens D. A. , Robinson D. , Tian Y. , LIU R. M. , Gao X. , Li L. C. , Quick J. E. , Chang H.-C.
Published: April 2011

The dissolution of a drug delivery system consisting of gentamicin sulfate in a hydrophobic polyanhydride matrix has been examined. The in vitro release of gentamicin is a function of the composition of the dissolution medium, with slower release in pH 7.4 buffer than in unbuffered water. This is consistent with an anion exchange taking place under conditions in which carboxylate polymer chain-ends form a poorly soluble salt with gentamicin, and sulfate is released into solution. Results of additional experiments probing this model are digeussed.