bluuebunny/crossref_metadata_2025 huggingface dataset:
Solid Freeform Fabrication of Composites by Direct Deposition and by In Situ Mineralization
Authors: Calvert Paul , Peng Jiong , Souvignier Chad
Published: April 2011

Freeform fabrication methods build materials by the repetitive addition of thin layers. This approach can be applied to build parts from epoxy resin which is modified with a gelling agent to solidify the material until curing occurs. High strength and stiffness parts can be obtained through fiber reinforcement but the fiber content is limited by packing effects. We have found that a combination of two types of fibers can be used to achieve higher strength and stiffness than can be obtained from a single fiber type.

An alternative route to reinforcement is to form the reinforcing phase after the material is deposited by an in situ reaction. This approach has been applied to the use of freeform fabrication to make bars of mineralized gel and of methacrylate-silica hybrids. Good mechanical properties can be attained in each case, with up to 50 vol.% inorganic phase and bend strengths in the range from 50-100 MPa.
Investigation on Morphology and Microstructure of the SALD SiC
Authors: Sun Lianchao , Crocker James E. , Shaw Leon L. , Marcus Harris L.
Published: April 2011

In this work, the deposition of silicon carbide lines using a tetramethylsilane (TMS) precursor was investigated. Effects of target temperatures on the morphology and crystal structure of the deposits were examined. It was found that the morphology of the SALD SiC depends strongly on the target temperature. The contour of the cross section of the SiC deposits changes from a triangle to trapezoid to volcano shape and the surface morphology of the deposited lines changes from smooth to rough to porous as the target temperature increases. A critical target temperature was found to be about 700°C to initiate deposition of SiC under the current experimental configurations. X-ray diffraction analyses show that the SALD SiC formed at 1000°C contains both crystalline and amorphous phases. The results are briefly discussed.
Modification of Thermoelectric Properties Using Insertion Techniques
Authors: Hatzikraniotis E. , Kyratsi Th. , Chrissafis K. , Paraskevopoulos K. M.
Published: April 2011

In this work is presented the application insertion techniques for the modification of the performance of thermoelectric materials. The results indicate that in cases as in Bi2Se3 compounds where insertion of foreign species in the lattice is possible due to its particular crystal structure, the insertion technique could be proved a valuable easy to apply and cost effective, alternative to doping technique. The techniques can produce homogeneous materials with electronic and thermoelectric properties finely tuned.
Iron Disilicide as a Base for New Improved Thermoelectrics Creation
Authors: Fedorov M. I. , Ivanov Yu. V. , Vedernikov M. V. , Zaitsev V. K.
Published: April 2011

It is well known that the temperature dependence of Seebeck coefficient of β-iron disilicide has unusual shape that cannot be described by an ordinary theory. A theory describing such a shape is suggested. It is shown this shape can be explained by optical phonon drag effect. Very high value of ZT could be achieved in some material on the base of this effect.
Thermoelectric Transport Properties of ReSi1.75 Thin Films
Authors: Kleint C. A. , Heinrich A. , Griessmann H. , Hofmann D. , Vinzelberg H. , Schumann J. , Schlaefer D. , Behr G. , Ivanenko L
Published: April 2011

Epitaxial ReSi1.75 thin films of variable thickness between 15nm and 150nm have been prepared in an one step process by Facing Target Sputtering (FTS) onto heated (100) and (111)Si and SOS wafers. The epitaxial relations and film structure have been investigated by Xray diffraction and transmission electron microscopy. Epitaxial growth was found at a substrate temperature of 1070K. Thermoelectric properties were measured between 100K and 450K and compared to the transport behavior of bulk ReSi1.75 and polycrystalline films. A distinct dependence of both the conductivity and thermopower was found on the film thickness, on unintentional doping and on the film structure. The results show that epitaxial ReSi1.75 films prepared by FTS can be a basis for further investigations of thermoelectric silicide/silicon multilayers.
Thermoelectric and Structural Properties of Bi1-xTe1+x Thin Films on CdTe(111)
Authors: Kim Yunki , Cho Sunglae , DiVenere Antonio , Wong George K. , Meyer Jerry R. , Ketterson John B.
Published: April 2011

Thin films of the hexagonal phase of Bi1-xTe1+x have been grown on CdTe(111) substrates using molecular beam epitaxy (MBE). Analysis of X-ray diffraction patterns (θ-2θ scans and rocking curves) of the films shows that their crystallinity depends upon the compositional deviation from stoichiometric BiTe. Measurements of the temperature-dependent thermoelectric power (TEP) of the films reveals that compositional changes cause the TEP to vary from electron dominant (n-type) to hole dominant (p-type), implying their possible application as a thermoelectric cooler or power generator. Measurements of the temperature-dependent resistivity of the films were conducted, and the analysis shows semimetallic behavior. These results demonstrate that Bi1-xTe1+xis an appropriate model system to study the dependencies of thermoelectric and structural properties on binary composition.
Mbe Growth and Thermoelectric Properties OF Bi2Te3 Thin Films
Authors: Cho Sunglae , Kim Yunki , DiVenere Antonio , Wong George K. L. , Meyer Jerry R. , Ketterson John B.
Published: April 2011

We have grown high quality Bi2Te3 thin films on CdTe(111)B substrates using MBE. Structural properties have been investigated using in-situ reflection high-energy electron diffraction (RHEED) and θ-2θ X-ray diffraction analysis. They show that Bi2Te3films on CdTe(111) grow along the (00.l) in the hexagonal cell with a layer-by-layer growth mode, resulting in a smooth surface, and an X-ray Bragg peak FWHM of 0.2°. The thermopower and electrical conductivity of the stoichiometric Bi2Te3 films were ∼200 μV/K and 103(Ωcm)−1, respectively, comparable to the single crystal bulk values. We have observed the antisite defect effect in Te-rich Bi2Te3films: excess Te occupies Bi lattice sites and behaves as an n-type dopant. Crystallinity and transport properties are strongly affected by non-stoichiometry.
Thermal Conductivity of Fe-Doped Cosb3 Skutterudites
Authors: Stokes Kevin L. , Ehrlich A. C. , Nolas G. S.
Published: April 2011

We investigate the effect of Fe substitution for Co on the lattice thermal conductivity of CoSb3 skutterudites. The polycrystalline materials are formed from uniaxially hot-pressed powders. Three alloys were prepared with 0, 3% and 10% Fe, respectively. Thermal conductivity measurements were made between 80 K to 450 K. The lattice thermal conductivity of 10%Fe:CoSb3 is approximately two times smaller than the lattice thermal conductivity of CoSb3 over the entire temperature range. This effect cannot be accounted for by the phenomenlogical theory considering only the mass difference and strain field due to the alloying (Fe) atom. Other phonon scattering mechanisms are discussed. Comparison is made with the partially-filled skutterudite alloy, La0.65Fe2.8Co1.1Sb12.
Approaches Toward Chemically Prepared Multiple Quantum Well Structures
Authors: Cronin S. B. , Koga T. , Sun X. , Ding Z. , Huang S.-C. , Kaner R. B. , Dresselhaus M. S.
Published: April 2011

An enhanced thermoelectric figure of merit, ZT, has been predicted for Bi2Te3 in the form of 2-dimensional quantum wells. A new approach to making multiple quantum well (MQW) structures for thermoelectric applications utilizing a chemical intercalation technique is proposed and investigated. It is proposed that by starting from Li intercalated Bi2Te3 and Bi2Se3, the layers of these materials can be separated by chemical means. The layers of Bi2Te3 or Bi2 Se3 can then be restacked, by self-assembly, forming a non-periodic array of quantum wells. These chemically prepared MQWs are characterized by X-ray diffraction, SEM (scanning electron microscopy) and TEM (transmission electron microscopy) at various stages in the sample preparation to assess the degree to which the actual samples match the proposal. Experimental measurements of the Seebeck coefficient (S) and the electrical conductivity (σ) were performed over a range of temperatures for the initial bulk materials. It is found that some of the steps in the proposed fabrication have been achieved but still much improvement is needed before any practical thermoelectric 2D-system can be provided.
Thermoelectric Properties of the Half-Heusler Compound (Zr,Hf)(Ni,Pd)Sn
Authors: Browning V. M. , Poon S. J. , Tritt T. M. , Pope A. L , Bhattacharya S. , Volkov P. , Song J. G. , Ponnambalam V. , Ehrlicha A. C.
Published: April 2011

Recent measurements of the thermoelectric transport properties of a series of the half- Heusler compound ZrNiSn are presented. These materials are known to be bandgap intermetallic compounds with relatively large Seebeck coefficients and semimetallic to semiconducting transport properties. This makes them attractive for study as potential candidates for thermoelectric applications. In this study, trends in the thermoelectric power, electrical conductivity and thermal conductivity are examined as a function of chemical substitution on the various fcc sub-lattices that comprise the half-Heusler crystal structure. These results suggest that the lattice contribution to the thermal conductivity may be reduced by increasing the phonon scattering via chemical substitution. The effects of these substitutions on the overall power factor and figure-of-merit will also be discussed.
LnPdSb and Ln3Au3Sb4: New Thermoelectric Materials
Authors: Mastronardi K. , Young D. , Wang C.-C. , Ramirez A. P. , Khalifah P. , Cava R. J.
Published: April 2011

The thermoelectric properties near ambient temperature of half-Heusler alloys based on HoPdSb, DyPdSb, and ErPdSb are reported. The Seebeck coefficients are between 60 and 250 μV/K. The resistivities range between 0.6 and 20 mΩcm, and the majority carriers are p-type. Thermal conductivities are smallest in intentionally disordered materials. The highest ambient temperature ZT obtained is 0.06. Band structure calculations are presented, and are compared to those for ZrNiSn. It is suggested that half-Heusler alloys with 18 electrons per formula unit may represent a large class of thermoelectric materials. The thermoelectric properties of another family of cubic symmetry antimonides, based on Ho3Au3Sb4 and Sm3Au3Sb4, are also reported.
Diamond and Polycrystalline Diamond for MEMS Applications: Simulations and Experiments
Authors: Çağin Tahir , Che Jianwei , Gardos Michael N. , Goddard William A.
Published: April 2011

To date most of the MEMS devices are been based on Silicon. This is due to the technological know-how accumulated on manipulating, machining, manufacturing of Silicon. However, only very few devices involve moving parts. This is because of the rapid wear arising from high friction in these Silicon based systems. Recent tribometric experiments carried out by Gardos on Silicon and polycrystalline diamond show that this rapid wear is caused by a variety of factors, related both to surface chemistry and cohesive energy density of these likely MEMS bearing materials. Therefore, theoretical and tribological characterization of Si and PCD surfaces is essential prior to device fabrication to assure reliable MEMS operation unded various atmospheric environments, especially at elevated temperatures.

In this paper, we summarize tribological experiments and theoretical studies of friction and wear processes on diamond surfaces. We studied the atomic friction of diamond (100)-surface employing an extended bond-order-dependent potential for hydrocarbon systems in MD simulations.
Micro-Tensile and Fatigue Testing of Copper Thin Films on Substrates
Authors: Hommel M. , Kraft O. , Baker S. P. , Arzt E.
Published: April 2011

A special micro-tensile tester was used to carry out tensile tests of thin copper films on substrates. The elastic strain in the film was measured in-situ using x-ray diffraction and the total strain with an external strain gage. From the elastic strains the stresses in the films were calculated and stress-strain curves were obtained. It was observed that the flow stress increases with decreasing film thickness. The method was also applied to investigate the mechanical behavior of films under cyclic loading.
Surface Dipoles Influence the Wettability of Terminally Fluorinated Organic Films
Authors: Colorado Ramon , Graupe Michael , Takenaga Mitsuru , Koini Thomas , Lee T. Randall
Published: April 2011

The correlation of differences in the wettabilities of partially fluorinated self-assembled monolayers (SAMs) to changes in the chemical structure and composition of the films was explored by contact angle goniometry and polarization modulation infrared reflection absorption spectroscopy (PM-IRRAS). SAMs of simple alkanethiols (CH3(CH2)nSH with n = 9-15) and their CF3-terminated analogs (CF3(CH2)nSH with n = 9-15) were prepared by adsorption from solution onto evaporated gold. Advancing contact angles of hexadecane were measured on both the terminally fluorinated surfaces and the hydrocarbon surfaces. These data were compared to those obtained using a series of polar aprotic contacting liquids. As expected, the contact angles of hexadecane were higher on the CF3-terminated SAMs than on the CH3-terminated SAMs. The contact angles of the polar aprotic solvents, however, were measurably lower on the CF3- terminated SAMs than on the CH3-terminated SAMs. These observations were rationalized on the basis that the introduction of the CF3 terminal groups yields oriented surface dipoles that interact with the dipoles of the polar contacting liquids. Further support for this model was provided by the observation of an inverse parity (“odd-even”) effect in the wettabilities of the polar aprotic solvents on the CF3-terminated surfaces. Analysis by PM-IRRAS revealed that both types of films consist of predominately trans-extended alkyl chains with relatively few gauche defects in a densely packed arrangement. The high degree of order is consistent with the detection of the parity effect, where small changes in the orientation of the tail groups can be sensed by contact angle measurements only in highly ordered organic thin films. The significance of the dipole-oriented dipole interaction in describing interfacial wettabilities is discussed.
Determining the High-temperature Properties of Thin Films Using Bilayered Cantilevers
Authors: Tada H. , Nieva P. , Zavracky P. , Miaoulis I.N. , Wong P.Y.
Published: April 2011

High-temperature applications of microelectromechanical systems (MEMS), especially in new temperature sensor designs, require an accurate knowledge of the temperature-dependent thermophysical properties of the materials. Although the measurement of the mechanical properties of materials at room temperature has been widely conducted, the same techniques often cannot be used for high-temperature property measurements. In this study, a new technique was developed to find the thermal expansion coefficient of thin films at high temperatures. Bilayered cantilever beams undergo thermally induced deflection at high temperatures, which can be measured and correlated to material properties. An imaging system was developed for the experimental measurement of the beam curvature for temperatures up to 1000°C. To find the high-temperature property of thin films, a bilayered beam, consisting of polycrystalline silicon and silicon dioxide, was designed such that the change in the property of SiO2 had little effect on the curvature of the beam. Furthermore, numerical analysis showed that the Young's modulus of Si also had negligible effect on the curvature. Therefore, the analytical model for beam curvature was simplified to be only a function of the thermal expansion coefficient of Si layer. Using this model, the thermal expansion coefficient of polycrystalline Si film was determined for temperature range between room temperature and 1000°C. The method can be easily modified to find the Young's modulus of Si, as well as properties of SiO2.
Thin Film Stress Measurement with a Tunneling Sensor
Authors: Zhang P. , Vinci R. P. , Bravman J. C. , Kenny T. W.
Published: April 2011

A new technique of measuring thin film stress with a tunneling sensor is presented. Basic measurement concepts, preliminary results on thin film stress measurement, and fabrication processes for the tunneling stress measurement sensor are described. The feasibility of implementing this technique for in-situ stress monitoring during thin film deposition demonstrated.
Etch Selectivity of Novel Epitaxial Layers for Bulk Micromachining
Authors: Borenstein J. T. , Gerrish N. D. , Currie M. T. , Fitzgerald E. A.
Published: April 2011

The present work demonstrates very high etch selectivity for a novel epitaxial layer in several standard bulk micromachining etchants. High selectivities have previously been achieved using high-concentration boron diffusions, resulting in a wide array of high performance micromechanical sensors. However, doping gradients, precipitates and dislocation arrays generated from the high boron concentrations can have deleterious effects on device performance. In this work, we report on the performance of a novel epitaxial structure composed of a silicon-germanium alloy device layer over a graded buffer layer. Chemical and microstructural analysis of the epitaxial layers reveal high purity and minimal defect densities. The selectivities of this layer and of boron-diffused layers are determined for a variety of etching conditions. High selectivity against low-doped silicon substrates is demonstrated in both ethylenediamine pyrocatechol and potassium hydroxide. Micromachined structures built using the SiGe epitaxial layer show smooth surfaces and precise build dimensions.
Silicon Electromachining Processes in Aqueous Solutions
Authors: Kovler M. , Starosvetsky D. , Nemirovsky Y. , Yahalom J.
Published: April 2011

High rate of etching of silicon was obtained by non conventional cathodic polarization in alkaline solutions. When the process was carried out at potentials more negative than −10 V it caused electropolishing of the etched surface. Shifting the potential in the cathodic direction increases the etch-rate parabolically and enhances the effect of polishing. The etch-rate increased by more than two orders of magnitude over the potential range from −10 to −40 V, and reached the value of about 250 micron/hour at 60 °C. Additionally, the etch-rate of n-Si was found to be markedly enhanced by illumination.
Microfabricated Silicon Carbide Microengine Structures
Authors: Lohner Kevin A. , Chen Kuo-Shen , Ayon Arturo A. , Spearing S. Mark
Published: April 2011

A research and development program is underway to develop technology for a MEMS-based microgas turbine engine. The thermodynamic requirements of power-generating turbomachinery drive the design towards high rotational speeds and high temperatures. To achieve the specified performance requires materials with high specific strength and creep resistance at elevated temperatures. The thermal and mechanical properties of silicon carbide make it an attractive candidate for such an application. Silicon carbide as well as silicon-silicon carbide hybrid structures are being designed and fabricated utilizing chemical vapor deposition of relatively thick silicon carbide layers (10–100 μm) over time multiplexed deep etched silicon molds. The silicon can be selectively dissolved away to yield high aspect ratio silicon carbide structures with features that are hundreds of microns tall.

Research has been performed to characterize the capabilities of this process. Specimens obtained to date show very good conformality and step coverage with a fine (≈0.1 μm dia.) columnar microstructure. Surface roughness (Rq) of the films is on the order of 100 nm, becoming rougher with thicker deposition. Residual stress limits the achievable thickness, as the strain energy contained within the compressive film increases its susceptibility to cracking. Room temperature biaxial mechanical testing of CVD silicon carbide exhibits a reference strength of 724 MPa with a Weibull modulus, m =16.0.
Investigation of Temperature and Composition Dependence of Relaxor Ferroelectric (1-x)PZN :xPT Using Micro-Raman Spectroscopy
Authors: Gupta S. , Katiyar R.S. , Bhalla A. S.
Published: April 2011

Micro-Raman spectra of relaxor ferroelectric (RFE) in the (1-x)Pb(Zn1/3Nb2/3)O3 :xTiO3 solid solution series have been measured as a function of temperature (70-580K) and composition (x = 0.02, 0.085, and 0.11). Micro-Raman spectra have been recorded in frequency range of 30-1000cm-1 and have been analyzed for all the Raman modes observed in terms of integrated intensity, phonon width and phonon frequency position. No soft mode like behavior is observed in the measured frequency range. We do observe two multiple phase transitions at 67°C (340K) and 147°C (420K) for the composition ≤ 0.91PZN:09PT, but both the transitions are slightly diffused in nature.
Lithium-Iodine Intercalation in The Ferroelectric Layered Compound Bi4Ti3O12-x
Authors: Kijima T. , Kimura S. , Kawahara Y. , Ohe K. , Yada M. , Machida M.
Published: April 2011

The reaction of Bi4Ti3O12-x with lithium iodide under an atmosphere of iodine at 400°C was found to afford a novel intercalation compound Lil3Bi4Ti3O11. The brownish red bismuth titanate is monoclinic with the lattice parameters of a=5.7417(2), b=5.4016(2), c=36.787(1) Å and ß=88.93(1) deg. The pathway to the new intercalation compound is proposed on the basis of X-ray, XPS, SEM and compositional observations.
An Tiferro Magnetic-Ferromagnetic Cu-O-Cu Coupljng Change in Copper Oxides: Se1-xTexCuO3 Perovskites
Authors: Subramanian M. A. , Ramirez A. P.
Published: April 2011

Se1-xTeCuO3 (O≤x<1) phases crystallizing in perovskite structure with divalent copper at the octahedral sites have been characterized by x-ray diffraction, magnetization measurements and specific heat. The perovskites are unusual for possessing an extremely small A-site cation (Se4+, Te4+) with Cu-O-Cu bond angles in the range 120-130°. A continuous evolution in both structural and bulk properties is observed between the ferromagnetic (FM) ground state for x = 0 and an antiferromagnetic (AF) state for x = 1. The correlation of structural and magnetic properties allows the first determination of the Cu-O-Cu bond angle where the superexchange interaction sign changes, providing a quantitative realization of the Anderson-Goodenough-Kanemori rules for copper-oxide compounds.
Vapour Phase Growth of Layered MoO3: A New Kinetic Approach for Volatile Metal Oxides
Authors: Zeng H.C.
Published: April 2011

A simple yet versatile growth kinetic method (and device) has been developed in conjunction with present vapour phase preparation of layered MoO3 (orthorhombic). Using purified air at atmospheric pressure a sufficient amount of oxygen is warranted to ensure stoichiometry of grown metal oxide. The empirical vapour condensation rate of MoO3 is RE = 1.20×10-3ΔP2.07 over 642 to 660°C, where ΔP is the partial pressure difference of MoO3 between the source and condensed crystals. Based on observed crystal morphology and XRD result, a more precise MoO3 condensation kinetic model has been developed to explain the layer-by-layer growth of the layered structure. The driving force of the condensation growth is investigated with respect to the experimental set-up. On the basis of this work, it is suggested that the new kinetic approach is suitable for other volatile metal oxides or inorganic crystalline materials when an appropriate preparative atmosphere is selected.
Structural Studies and Order-Disorder Phenomenon in a Series of New Quaternary Tellurates of the Type A2+M4+Te6+O6
Authors: Woodward P.M. , Sleight A.W. , Duw L.-S. , Grey C.P.
Published: April 2011

Five new compounds in the AxMTeO6 family were prepared and structurally characterized: Li2GeTeO6, Na2TiTeO6, Na2SnTeO6, and two forms of Na2GeTeO6. All compounds are layered structures based on various stacking arrangements of MTeO62- layers. Structural characterizations were carried out using a variety of tools, including Rietveld refinements of x-ray and neutron powder diffraction data, solid state MAS NMR and Raman spectroscopy. With the exception of Na2TiTeO6, the MTeO62-layers show a high degree of M4+/Te6+ order, but various degrees of disorder are present in the stacking of these layers. Disorder in the layer stacking favors the ilmenite structure, where both M4+ and Te6+ centered octahedra share faces with the AO6 octahedra. Coherent layer stacking favors an ordered variation of the α-TlSbO3 structure, where the AO6 octahedra preferentially share faces with either the MO6 or the TeO6 octahedra.
Influence of The Preparation Conditions on the Structure of Hydrotalcite Layered Double Hydroxides
Authors: Lukashin A.V. , Kalinin S.V. , Nikiforov M.P , Zhirov A.I , Kheifets L.I. , Privalov V.I , Vertegel A.A.
Published: April 2011

Influence of the precipitation conditions on the structure of Mg – Al layered double hydroxides (LDH) was investigated. XRD measurements demonstrate that species with hydrotalcite structure forms at high pH of reaction mixture (pH = 9 - 11), while at lower pH values (pH = 7 - 8) species with meixnerite structure arise. At the same time 27Al NMR studies of samples obtained at pH > 10 reveal the presence of tetrahedrally coordinated aluminum. XRD, NMR and IR data suggest that partial substitution of CO32- for Al(OH)4- in the interlayer space with subsequent formation of oxoaluminate bridges takes place at high pH. The optimal conditions for the preparation of intercalation-active materials were proposed.
In-Situ Neutron Diffraction Studies of Mixed Conducting Sr-Fe-Co-O Materials
Authors: Mitchell B.J. , Richardson J.W. , Ma B. , Hodges J.P.
Published: April 2011

SrFeCo0.5Oy has been identified as a potential dense ceramic membrane material used for gas separation at elevated temperatures. Neutrons play an important role in the study of such materials, particularly due to the favorable scattering lengths of Fe, Co and O. In-situ neutron diffraction experiments allow these materials to be studied under a wide range of temperatures and oxygen partial pressures. Results indicate very complex behavior of individual phases during synthesis and under operational membrane conditions.
Preparation and Magnetoresistance of Lanthanum Manganites and Silver Chalcogenide Thin Films
Authors: Dahmen Klaus-H. , Chuprakov Ilya S. , Gillman Ed S. , Li M. Ming
Published: April 2011

The effect of texture and orientation on the resistance (0T and 6T) and magnetoresistance (MR) of Lal-xCaxMnO3 (LCMO) and Ag2Te thin films on various substrates has been investigated. Similar features were found in the MR dependence of thin films of these compounds despite the fact that they belong to different types of MR materials. Epitaxial or strongly oriented films exhibit a peaked MR behavior while for polycrystalline films this curve does not have sharp features. Sign reversal effect of MR was found also in thin films of Ag2Te. MR changes from positive at transverse field-,current orientation to negative at parallel orientation.
Nitrogen/Oxygen Substitution within PO4 Tetrahedra: A Right Answer to the Poor Chemical Durability of Phosphate Glasses
Authors: Le Sauze A. , Montagne L. , Palavit G. , Marchand R.
Published: April 2011

By using both alumina addition and nitrogen/oxygen substitution within PO4 tetrahedra, it is possible to prepare durable phosphate glasses without affecting their specific properties such as low melting temperatures and high thermal expansion coefficients. In particular, “LiKMgAlPON” nitrogen-rich glass compositions have a chemical durability on the same order as soda lime window glass, associated with a glass processing temperature as low as 800°C.
Synthesis of Aluminum Nitride Whiskers Via a Vapor-Liquid-Solid Process
Authors: Dai Ying , Nan Ce-Wen
Published: April 2011

Aluminum nitride whiskers were synthesized by nitridation of commercial aluminum powder at 1623K in a nitrogen atmosphere. The starting materials consisted of aluminum and carbon black. The carbon acted as a barrier between aluminum powders during nitridation and was removed by heating in air at 923K. The whiskers were about 0.5-1μm in diameter and 10-20μm in length. The droplets at the whisker tips showed that the whiskers grew via a vapor-liquid-solid mechanism. The morphologies of the whiskers were studied by means of SEM and TEM. The formation of the whiskers depended on the processing conditions.
New Quaternary Selenoantimonates AHgSbSe3 (A = Rb, Cs): Synthesis, Structures and Optical Properties
Authors: Chen Zhen , Wang Ru-Ji , Li Jing
Published: April 2011

Solvothermal reactions in ethylenediamine have resulted in two quaternary mercury containing selenoantimonates: RbHgSbSe3 (I) and CsHgSbSe3 (II). Compound I crystallizes in monoclinic system, space group P2l/c (no. 14) with a = 7.758(2)Å, b = 11.234(2)Å, c = 8.849(2) Å, β = 106.60(3)°, V = 739.1(3)Å3, Z = 4. Compound II crystallizes in orthorhombic system, space group Cmcm (no. 63) with a = 4.444(1)Å, b = 15.514(6)Å, c = 11.261(7) Å, V = 776.4(6) Å3, Z = 4. Both compounds are layered materials and their crystal structures are closely related. Both contain layers of 2[HgSbSe3-] separated by alkali-metal cations A+ (Rb, Cs). Diffuse reflectance experiments show that both compounds are semiconductors with estimated band gaps of 1.7 eV for I and 1.6 eV for II, respectively.
Rationalization of Electrical Properties of The NiS2-xSex System
Authors: Honig J.M.
Published: April 2011

The electrical and optical properties of the NiS2-xSex system are interpreted in terms of a band structure diagram that places a Mott-Hubbard, correlation-split Ni 3deg and the S 3pσ* band in the vicinity of the Fermi level. A variety of seemingly problematic experimental findings are resolved by adoption of this hypothesis.
Synthesis of (Si2Ge)Cx and Related Ge1-xCx Phases in The Si-Ge-C System
Authors: Nesting David , McMurran Jeff , Kouvetakis John
Published: April 2011

The synthesis and characterization of binary and ternary semiconductor alloys and ordered phases based on C, Si and Ge are described. Thin films of these materials were synthesized using molecular precursors such as (SiH3)4C and (GeH3)4C in which the Si4C and Ge4C tetrahedra are incorporated as building blocks during deposition. Materials systems prepared include a new ordered structure (Si2Ge)1-xCx (x=5%), and Ge1-xCx hybrids of Ge and C-diamond. The (Si2Ge)Cx phase has a P 3ml structure formed by ordering of the [111] lattice planes in a Ge-Si-Si sequence. The Ge-C materials display unusual morphologies ranging from coherent heterostructures to carbide nanorods and quantum dots which are formed by CVD reactions utilizing a new family of (GeH3)4-xCHx (x=0-2) precursors. The morphology and microstructure in the samples is dependent upon the molecular design of the precursor and the carbon concentration.
Growth of Antimony Thin Films Using Perbenzylated Organometallic Precursors
Authors: Remington Michael P. , Kamepalli Smuruthi , Boudjouk Philip , Jarabek Bryan R. , Grier Dean G. , Winburn Ryan S. , Very Brian E. , McCarthy Gregory J.
Published: April 2011

The low temperature (ca. 300°C) deposition of antimony films by low-pressure chemical vapor deposition (LPCVD) on glass substrates from tribenzylantimony, Bn3Sb, is described. The facile elimination of the benzyl ligands results in preferentially oriented antimony films with low carbon content. The pyrolysis, decomposition mechanism and precursor design strategies are discussed. In addition, the deposition of bismuth from tribenzylbismuth, Bn3Bi, is presented. The potential for alloy growth using these precursors is discussed. Resulting films were characterized by XRD, SEM, and AFM.
Novel Organically Templated Mixed-Valent Titanium Phosphates with Open Framework Structures: Hydrothermal Synthesis and Characterization
Authors: Ekambaram S. , Sevov Slavi C.
Published: April 2011

We have hydrothermally synthesized the first reduced titanium phosphates with open-framework structures. The synthetic approach is quite unusual since elemental titanium is used. The full structural, thermal, magnetic, and spectroscopic characterization of a 1,3-diaminopropanetemplated compound, TiIIITiIV(PO4)(HPO4)2(H2O)2·(NH2CH2CH2CH2NH2)0.5, is presented. The frame of the compound is of the octahedral/tetrahedral type with octahedrally coordinated TiIII and TiIV atoms. The template of 1,3-diaminopropane occupies channels with dimensions that are comparable to those of many zeolites. Magnetic measurements are consistent with one d-electron per formula unit. TGA/DTA and IR data will be reported as well. This compound is most likely the first member of a larger class of reduced titanium phosphates. Some preliminary data suggests that similar reduced titanium phosphates with different templates and structures exist as well. All compounds are blue-purple due to Ti(III).
Processing and Performance of V205 Xerogel, Aerogel, and Aerogellike Materials as Lithium Intercalation Hosts
Authors: Manhart Leland H. , Xu Jun John , Coustier Fabrice , Passerini Stefano , Owens Boone B. , Smyrl William H.
Published: April 2011

Various forms of vanadium pentoxide, including xerogel, aerogel, and aerogel-like forms, were prepared by sol-gel synthesis and processed by novel procedures following synthesis. It was demonstrated that the intrinsic thermodynamics of lithium intercalation of the ARG and ARG-like materials prepared by solvent exchange processes involving methyl formate (MF/ARG and MF/ARG-xslike) are identical, while they are drastically different from those of the parent XRG, which gives rise to significantly increased specific energies for the MF/ARG or MF/ARG-like as lithium intercalation hosts. All three forms are capable of reversibly intercalating up to four moles of Li+ ions per mole of V205 electrochemically and can be cathode candidates for rechargeable lithium batteries. Various processing methods for fabricating composite electrodes with the XRG led to specific capacity in the range of 300 to 350 mAh/g at C4Li/ 20 rate, and good cyclability.
Preparation of Niobium Oxides Cathodes by Chimie Douce and Some Electrochemical Properties
Authors: Hernandez A. , Sanchez E. , Torres-Gonzalez L. C. , Fuentes A. F. , Torres-Martinez L. M.
Published: April 2011

Sol gel chemistry has been a useful technique to achieve hard-to-prepare metastable materials. Niobium oxide, for instance has a thermodynamic preference to crystallize on monocyclic lattice. Here, we were able to achieve synthesis of orthorhombic motif with a careful sol-gel preparation and tailored thermal treatment. Furthermore, formation of lithium inserted Nb205 phases were studied by electrochemical methods. When lithium is inserted, several single phases LixNb205 were observed in the range of 0 ≤ x ≤ 3.3 between 3.0 and 0.75 V. Even though the reaction is only reversible for x ≤ 1.8. Also, T-Nb205 polymorph showed improved intercalation characteristics.
New Iron Oxide Positive Active Material for Lithium Secondary Batteries
Authors: Amine K. , Yasuda H. , Yamachi M.
Published: April 2011

Beta-iron oxy-hydroxide, which exhibits a (2×2) tunnel-type structure similar to that of (α-MnO2, was found to intercalate reversibly lithium in the tunnels. This material exhibits three voltage plateaus at 2.3, 1.5 and 0.7 V and has an over all discharge capacity of 1100 mAh/g. When cycling in the 2–V region, the material exhibits high capacity of 275 mAh/g and very good cyclic reversibility. X-ray photoelectron spectroscopy (XPS) of the discharged material showed that iron is reduced to the divalent state, and the lithium incorporated in the tunnels is purely ionic. This result explains the good reversibility of this electrode material. When discharged to 0.5 V, however, the structure of the material collapsed, and metallic iron was detected in the X-ray diffraction pattern.
Host-Guest Systems in Microporous Carbons
Authors: Enoki Toshiaki , Takai Kazuyuki , Shibayama Yoshiyuki , Kobayashi Norikazu , Nakayama Atsuko , Sato Hirohiko , Yoshida Naohiko , Touhara Hidekazu
Published: April 2011

Microporous activated carbon fibers (ACF) having huge specific surface areas are characterized as a three-dimensional network of nano-sized graphite domains. We investigate ACF-hosting host-guest systems aiming at novel phenomena produced by the host-guest interface interactions. An extraordinarily large amount of helium is condensed in the ACF micropores, suggesting the presence of ultra-micropores and the enhancement in the helium- nano-graphite interaction. Chemisorbed oxygen molecules are stabilized in the singlet states caused by the interaction with nano-graphite and it makes the micorpore volume swell. Iodine forms an intercalation system with nano-graphites through charge transfer process, in contrast with the behavior of bulk graphite that does not accept iodine as an acceptor-type intercalate. Fluorine reacting with nano-graphite generates dangling bond spins by breaking graphite π- bonds, where the fluorine-induced defect is found to have a widely extended electronic structure.
Performance Characteristics of Gel Polymer Electrolyte Separators in Rechargeable Lithium Ion Cells
Authors: Huang Weiwei , Akridge James R.
Published: April 2011

The swelling behavior of poly(vinylidene fluoride-hexafluoropropylene), noted as P(VdF- HFP), was under various conditions. Increasing the HFP unit content in P(VdF-HFP) and temperature increased the swelling degree of the polymers considerably. The amount of the electrolyte solution absorbed by P(VdF-HFP) at room temperature showed the following trend: DMC>EC/DMC>DEC≈EC/DEC. The presence of LiPF6 in carbonate solvents did not affect on the swelling degree of PVdF and P(VdF-8%IIFP) in all solutions studied but lowered the swelling degree of P(VdF-15%HFP) in DMC, EC/DEC and EC/DMC/DEC solution at room temperature or prevented it from dissolution in the them at 55°C. A variable search experiment indicated that changing the pre-conditioning temperature from 21 to 55°C is more effective than other changes considered in the experiment for increasing high rate discharge capability. Some coins cells using the composite GPE separators had higher discharge capability than those using microporous polyethylene separators.
Rietveld Neutron Powder Profile Analysis and Electrical Conductivity of the Fast Silver-Ion Conductor (LaO)AgS
Authors: Wilmer Dirk , Wuensch Bernhardt J. , Jorgensen James D.
Published: April 2011

Lanthanum silver oxysulfide, (LaO)AgS, exhibits a predominantly ionic conductivity of 10−3 to 10−1 S/cm between 300 K and 770 K. The tetragonal structure consists of alternating (LaO) and (AgS) sheets, their sequence being O-La-S-Ag-S-La-O. The structure suggests that ionic transport arises from migration of silver ions within the AgS layers analogous to sodium ion transport in Na-β-alumina.

Neutron powder diffraction data measured at five temperatures between 300 K and 770 K are analysed using the Rietveld method to determine the distribution and thermal vibration parameters of the mobile silver ions. The structural investigation is accompanied by measurements of the total conductivity in the same temperature range in order to resolve severe discrepancies in the literature data.
Phase Transformations of Superionic PbSnF4 Above Ambient Temperature: X-Ray Diffraction Versus Temperature
Authors: DÉNÈS Georges , Milova Galina , Antonov Boris D.
Published: April 2011

PbSnF4 is the highest performance fluoride ion conductor. A fast amperometric response oxygen sensor based on PbSnF4 has been constructed and tested. A long life device with time independent response and reliable performance requires the materials used for its construction be stable over the life time of the device in the operating conditions. Since ionic conductivity is thermally activated, possible use at high temperature can be envisaged. Therefore, it is of prime importance to know in details the behavior of the material versus time in the expected temperature range of use and of storage. PbSnF4 can be prepared by many methods that we have investigated, and each method gives a material that is different from the others in one way or another (symmetry, strain, particle rendomization, particle dimensions, temperature range of stability). In addition, we have shown that several phase transitions take place versus temperature or when some other treatments are applied. Many of these transitions are very sluggish, and therefore give a false impression of stability, when the phases are actually metastable, and thus changes take place slowly over time. We have studied the stability of tetragonal α-PbSnF4 and o-PbSnF4 by use of X-ray diffraction, in the most probable conditions of use (ambient temperature to 200°C in air). Changes were found to take place, which should be taken into account in the design of devices and when establishing their optimum temperature of use and storage.
Oxygen Transport Kinetics in La0.5Sro0.5Fe0.8Ga0.2O3−δ Membranes Under Both Small and Large Oxygen Partial Pressure Gradients
Authors: Kim Sangtae , Jacobson Allan J. , Abeles Benjamin
Published: April 2011

Oxygen permeation through a new perovskite La0.5Sr0.5Fe0.8Ga0.2O3−δ membrane has been measured both under small (air/He) and large (air/CO, CO2) oxygen partial pressure gradients. In both cases oxygen transport is close to surface limited. By modeling the pressure dependence of the oxygen flow rate under small pressure gradient an ambipolar diffusion coefficient 9.65 × 10−7cm2/s and a surface exchange coefficient 7.15 × 10−6 cm/s at 974 °C were determined. With air/CO, CO2 on the permeate side, the permeability increases linearly with the partial pressure of CO. The observed increase is greater than the maximum enhancement predicted by our model.
Mechanisms and Kinetics of Electrochemical Intercalation of Oxygen into Nd2NiO4+δ
Authors: Fritze H. , Tuller H. L. , Berthold J. , Schultrich B.
Published: April 2011

Overstoichiometric insertion of oxygen into thin films of Nd2NiO4+δwas performed electrochemically at room temperature (RT) in order to obtain an in-situ compositional analysis of the process. Thin Nd2NiO4+δlayers were deposited onto resonators of a Quartz Crystal Microbalance (QCM) by Pulsed Laser Deposition (PLD). Cyclic voltammograms showed oxidation and reduction peaks typical for these oxides. The change in oxygen stoichiometry was determined by in-situ QCM measurements during potential step experiments. The resulting maximum mass change was on the order of 50 ng and corresponded to a maximum excess oxygen content of δ = 0.12 in Nd2NiO4+δ. The time dependence of the mass change was described by a transport model which leads to oxygen diffusion coefficients in the range from 2.10−12 to 10−11 cm2/s depending on δ and the direction of the reaction.
The Applications of Neutron Scattering Methods to the Study of High-Temperature Protonic Conductors
Authors: Udovic T. J. , Yildirim T. , Karmonik C. , Huang Q.
Published: April 2011

Perovskite-based high-temperature protonic conductors have generated increased interest because of their potential use in such areas as solid-oxide fuel-cell technology. In this paper, we outline the utility of neutron scattering methods in conjunction with first-principles total-energy calculations for characterizing the proton dynamics in these materials.
Cerium Containing Chalcogenides with Chromatic Properties
Authors: Gauthier G. , Jobic S. , Macaujdiere P. , Brec R.
Published: April 2011

λ–Ce2S3, like many other cerium containing chalcogenides, presents a strong absorption in the visible spectra in relation with the CeIII-4fl → CeIII-5d1 electronic transition taking place at around 1.9 eV. This transition energy, that induces a red hue for the phase, can be increased by changing the nature of the Ce-S bonding, in particular through an enhancement of its ionicity. This can be made by inserting/substituting some alkali metal ions in the structure of λ-Ce2S3. The sodium-doped λ-Na3/8Ce15/2S3 phase for instance undergoes a CeIII-4f1 → Cemi-5d1 transition energy increase of 0.12 eV. This shift is sufficient to modify substantially the pigment properties of the material and it has been mainly related to the narrowing of the electronic bands. In CePS4, Ce2SiS5, Ce4Si3S12and Ce6Si4S17, strong covalent bondings enhance the ionic Ce-S bond through inductive effect, leading to a CeIII-4f1 → CeIII-5d1 electronic transition in the blue (Eg - 2.5 eV) hence the yellow hue of these materials. Within the Ce-Si-S family, small differences may be attributed to difference in the [CeSx] and [SiS4] polyhedra bonding. The Ce3(TS4 )2X family (X = Cl, Br, I, T = Si, Ge) does not show pigment properties because of the Ce-X bond inducing a more Ce-S ionic character (in particular when X = Br, I) and thus a higher gap that is found in the near ultraviolet. On the other hand, the phases present an important room temperature blue fluorescence.
Intercalate Aggregation and Nlo Properties of Intercalated Lamellar Chalcogeno Phosphate Lattices
Authors: Coradin T. , Clement R. , Amoual E. , Holt J. , Francis A.
Published: April 2011

Intercalation compounds of CdPS3 with 4-[4-(dimethylamino)-α-styryl]- 1-methylpyridine cation (DAMS+) exhibit high-efficiency optical second harmonic generation (SHG). This is unexpected since the native CdPS3 host crystallizes in a centrosymmetric lattice. It is believed that the SHG results from the aggregation of the intercalate within the interlamellar spaces of the host lattice. For efficient SHG the spatial organization must have a characteristic length scale on the order of the second harmonic wavelength, or about 1 micron. We have studied the temperature dependence of the fluorescence of CdPS3:DAMS intercalation compounds and have demonstrated the presence of DAMS aggregates.
The Surface Structure of Manganese Cation and MnTMPyP Intercalated Potassium Niobate
Authors: Lee D. H. , Kim Y. , Sato O. , Fujishima A. , Hashimoto K.
Published: April 2011

K4Nb6O173H2O has a cation exchange ability in K+ ion existing in the interlayer and a property of photocatalyst host. As a preliminary step in the preparation of this catalyst, the cation exchange plays an important role. In this study, we prepared potassium niobate intercalated with Wn2+ and Mn(III)TMPyP7+ (Mn(III)5,10,15,20-tetra(4-pyridyl)-porphyrin) ions and observed the evidence of cation exchange in the interlayer by means of atomic force microscopy. AFM images showed that the Mn2+ ion and MnTMPy7+ cations regularly occupied the potassium sites. This indicates that the metallic oxide reduction center was formed in the interlayer by the cation exchanged species prior to redox treatment and not on the surface of the potassium niobate.
Preparing Titania Fibers and Their Photocatalytic Activity
Authors: Koike H. , Oki Y. , Takeuchi Y.
Published: April 2011

Continuous titania fibers were prepared by a polytitanoxane precursor method. Polytitanoxane was synthesized through hydrolysis and polymerization reaction between partially chelated titanium isopropoxide and water without acid catalyst. Polytitanoxane, which was precipitated from an isopropanol solution by adding adequate amount of water to titanium isopropoxide, was then dried and dissolved in tetrahydrofuran. The concentrated viscous solution of polytitanoxane was considerably stable to further self-condensation and had good spinnability. The precursor fiber which was obtained by spinning the solution was calcined to form titania fibers.

Two types of titania fibers were obtained under different calcination conditions from the same precursor fiber; Dense fiber with high tensile strength of higher than 1 GPa, and porous fiber with high surface area of more than 10 m2/g.

Photocatalytic activity of those fibers was studied using the phenol mineralization reaction in water. The phenol degradation ability of high-surface-area titania fiber was almost the same as that of commercial titania powder for photocatalyst.