bluuebunny/crossref_metadata_2025 huggingface dataset:
Possible Ferroelectricity in SnTiO3 by First-Principles Calculations
Authors: Konishi Yoshinori , Ohsawa Michio , Yonezawa Yoshiyuki , Tanimura Yoshiya , Chikyow Toyohiro , Wakisaka Toshiyuki , Koinuma H. , Miyamoto Akira , Kubo Momoji , Sasata Katsumi
Published: April 2011

The prospect of lattice structure and ferroelectricity of SnTiO3 have been studied by first-principles calculations within local density approximation. The results showed that the SnTiO3 has the minimum total energy within almost tetragonal perovskite structure of a=b=3.80 Å, c=4.09 Å. The calculated electronic structure of SnTiO3 resembles that of PbTiO3 because the Ti 3d states, Sn 5s and 5p states hybridize with the O 2p orbitals. The moment of spontaneous polarization of SnTiO3 was estimated as 73 μ C/cm2, which is as large as that of PbTiO3.
Simulation of Steady State Leakage Current in Thin Films
Authors: Schroeder Herbert , Schmitz Sam , Meuffel Paul
Published: April 2011

Numerical simulation studies were performed in order to shed light on the controlling mechanism for the steady state leakage current through metal/insulator/metal capacitors with high permittivity dielectric or ferroelectric materials such as SrTiO3, (Ba,Sr)TiO3 or Pb (Zr,Ti)O3. As a model we used an extension of the combined injection-diffusion model, i.e. we have solved the Poisson and continuity equations inside the dielectric assuming thin, low permittivity (“dead”) layers at the electrode interfaces. As “new” boundary conditions we used injection / recombination terms at both electrodes, also taking into account the barrier lowering due to the coulomb mirror potential.

The simulation data are presented in dependence on several extrinsic and intrinsic parameters (voltage, temperature, film thickness, barrier height, dead layer properties, etc.) for symmetrical electrodes together with first results on asymmetrical ones. The most important result is that for nearly all parameter sets the leakage current is (film) bulk-limited, mostly due to the low carrier mobilities in these insulating materials. Only for very special conditions the interface-limited current, e.g. thermionic injection at the cathode for electrons, is a good approximation. The numerical data are compared to experimental true leakage current results on STO and BST.
Investigations of Mesoscopic Ferroelectric Structures Prepared by Imprint Lithography
Authors: Harnagea C. , Alexe M. , Schilling J. , Wehrspohn R. B. , Hesse D. , Gösele U.
Published: April 2011

Arrays of mesoscopic ferroelectric PZT structures with lateral sizes from several micrometers down to below 300 nm were prepared applying nanoimprint lithography. The ferroelectric properties of the mesoscopic structures were investigated by scanning force microscopy in piezoresponse mode. The best chemical route to obtain ferroelectric structures was found to be the sol-gel method. Using Nb-doped SrTiO3 single crystals as bottom electrodes, the crystallization into the ferroelectric phase was uniform with grain sizes in the 35 nm range. The best ferroelectric properties of individual 300 nm structures were obtained if an intermediate, continuous ferroelectric layer was present on the bottom electrode.
Growth, Structure, and Properties of Uniformly a-Axis Oriented Ferroelectric Bi3.25La0.75Ti3O12 Thin Films on Si(100) Substrates
Authors: Hesse D. , Lee H. N. , Zakharov N. D. , Gösele U.
Published: April 2011

Uniformly a-axis-oriented, epitaxially twinned Bi3.25La0.75Ti3O12 (BLT) thin films having the major spontaneous polarization entirely along the film normal were grown by pulsed laser deposition on yttria-stabilized zirconia-buffered Si(100) substrates covered with very thin SrRuO3 bottom electrodes. Using SrRuO3 bottom electrodes of a specific low thickness in combination with a relatively high growth rate and a high oxygen pressure, the volume fraction of the BLT (100) orientation, which is competing with the BLT (118) orientation, was increased up to 99%. In this way the growth of fully a-axis-oriented BLT epitaxial films was achieved, attaining a remanent polarization of 32 mC/cm2. Initial fatigue experiments indicated hardly any fatigue after 109 switching cycles.
Fabrication of Sequential Nanostripes by Controlled Electrodeposition
Authors: Mikhaylova M. , Kim D. K. , Toprak M. , Muhammed M.
Published: April 2011

Au nanowires and sequential metal nanostripes were prepared by AC pulse electrodeposition in anodic alumina membrane (AAM). Due to the high toxicity of cyanide-based electrolytes, which commonly used for electrodeposition of noble metals, new types of Au electroplating solution has been introduced. Electroplating solutions of noble metals Au, Ag and Pt were alternately used for nanostripes fabrication. The AAM was prepared by a two-step electrochemical anodization process in oxalic acid. The pore size was controlled by varying anodizing voltage and current density. The AAM was investigated by SEM and AFM. The results show hexagonally ordered channels with a pore diameter 50 nm. The morphology and composition of nanowires and nanostripes were examined by TEM and optical microscopes, which show uniformly, ordered Au nanowires with a length about 250 nm and a diameter about 50 nm. Au-Ag-Au-Pt-Au sequential nanostripes have a length about 3.5 μm and diameter 50 nm has been successfully prepared.
Fabrication of Zirconia Coatings using Electrophoretic Deposition and Reactive Sintering
Authors: Yuan Ying , Wang Xin , Xiao Ping
Published: April 2011

Electrophoretic deposition (EPD) technique has been used to fabricate green YSZ/Al composite coatings with controlled thickness and morphology. Such green coating was transformed into the YSZ/Al2O3 composite coating during following thermal treatment in air at temperatures up to 1200°C. Suspension for EPD was prepared by attrition-milling a mixture of yttria -stabilised zirconia (YSZ) and aluminium (Al) in acetyl-acetone (ACAC). The attrition milling reduced the particle size of the powder mixture. A mechanical alloying behaviour is believed to control the agglomeration and the breaking of large Al particles. Attrition milling also reduced the YSZ crystallite size, which can be attributed to the chemical reaction between YSZ/Al particles and ACAC. Thermal analyses and dilatometry measurements of the green compact indicate the temperature range for oxidation of Al and its effect on sintering of the coating. The coating obtained from EPD in the suspension after a longer milling time was found to have more uniform in microstructure.
Effects of Irradiation by Low Energy Nitrogen Ions on Carbon Nitride Thin Films
Authors: Nasu Yuka , Aono Masami , Aizawa Shinichiro , Kitazawa Nobuaki , Watanabe Yoshihisa
Published: April 2011

Carbon nitride (CNx) thin films have been prepared by hot carbon filament chemical vapor deposition, and the nitrogen content in the films is approximately 0.05. The CNx films have been irradiated by 0.1 keV nitrogen ions to increase the nitrogen content after deposition. The nitrogen content in the CNx films was obtained with X-ray photoelectron spectroscopy. Scanning electron microscopy was employed to study microstructures of the films. The experimental results show that nitrogen ions are chemically combined with the CNx films and as a result the nitrogen content increases up to approximately 0.30. Furthermore, it is found that nitrogen ions change the film microstructures and sputter the surfaces of CNx films.
Effects of Laser Texturing on Technical Surfaces
Authors: Gerbig Y. , Dumitru G. , Romano V. , Spassov V. , Haefke H.
Published: April 2011

Different laser beam techniques were applied to AISI M3 steel samples in order to produce well-defined surface microtextures consisting of pores, which can act as lubricant pockets (reservoir) as well as traps for wear debris. Both effects contribute to improve the tribological performance of textured functional surfaces. The tribological performance of lasertetxures was studied as function of the pore depth and diameter in unidirectional sliding tests under starved lubrication. The lasertetxured surfaces tested under those conditions were produced by a well-established ns laser technique using a Q switched Nd:YAG laser. The topographical microstructures of these laser-induced textures were characterized by optical and scanning electron microscopy as well as replica technique. A significant change in friction behavior as compared to untextured tool surfaces was observed when using microtextured surfaces.

In another part of the study, the influence of new-developed fs laser technique of the tool steel was investigated. The fs laser texturing of the steel results in a change of the metallographic structure of the laser-affected zone, which is clearly detectable in cross-section samples. The structure of the material and chemical composition of the laser-affected, pore-near region was analyzed by transmission electron microscopy with combined EDX analysis. It could be shown that the laser-affected zone seems to consist of an amorphous or nanocrystalline material in opposite to the ‘macrocrystalline’ steel substrate. Nanoindentations revealed a two times higher hardness of the laser-affected zone than the steel bulk phase.
Bright plasma nitriding of ferritic steel with several alloying elements
Authors: Kamminga J.-D. , Kwakernaak C. , Janssen G. C. A. M.
Published: April 2011

Hot work tool steel was plasma nitrided in a PVD apparatus. Phases occurring and nitrogen depth profiles were assessed for the nitrided specimens. In all cases bright nitriding was achieved. Increasing the nitriding time from 15 to 120 min yielded a nitriding depth increasing from about 15 to 35 μm, whereas the nitrogen flux decreased from 8.0 to 5.5 × 10-7 kg s-1m-2. Results from an existing model, predicting nitrogen depth profiles due to plasma nitriding, did not accurately describe the experimental data. Therefore the existing model cannot be used straightforwardly to predict the formation of iron nitrides. The discrepancies of model results and experimental results are discussed in view of the assumptions underlying the model for plasma nitriding.
Micromechanical Properties of He-Implanted Ni
Authors: Knapp J. A. , Follstaedt D. M. , Myers S. M.
Published: April 2011

Detailed finite-element modeling of nanoindentation data is used to obtain the micromechanical properties of Ni implanted with ∼5 at.% He to a depth of 600–700 nm. Properties of He-containing metals have implications for studies of radiation damage and for fundamental issues of dislocation pinning. Cross-section TEM shows the implantation produces a highly damaged layer containing a fine dispersion of He bubbles with diameters of ∼1 nm or smaller, with some evidence for interconnection between bubbles. Nanoindentation of the Ni(He) layers gave a fairly hard, stiff response to depths of 100–120 nm, beyond which the layer failed. By modeling the layer as an isotropic, elastic-plastic solid with the Mises yield criterion, the Ni(He) is shown to have a hardness nearly 7 times that of untreated Ni. However, unlike other treatments that we have used to produce very hard Ni-based layers, the Ni(He) layer fails at relatively modest shear stress levels.
Effects of Inclusions and Porosity on the Indentation Response
Authors: Ege E. S. , Shen Y.-L.
Published: April 2011

A combined numerical and experimental study was undertaken to investigate the effect of microstructural heterogeneity on indentation response. Finite element analyses were carried out to simulate the stress-strain behavior and the indentation response of two model heterogeneous systems: one with hard particles embedded within a soft matrix and the other with a pore-containing ductile material. For the particle-containing system, the indentation response consistently overestimates the overall strength of the composite. This is largely due to the localized increase in particle concentration directly underneath the indent. For the porous system, the indentation response consistently underestimates the overall strength due to the pore-crushing effect. Experiments on metal-ceramic composites confirmed the non-correspondence between the indentation and stress-strain responses, even when the indent size is much greater than the microstructural feature size. Implications of the present findings in utilizing indentation to quantify surface mechanical properties are discussed.
Surface Modification of Silica with Ultrahighmolecular Weight Polyethylene (UHMWPE)
Authors: Debnath Subir , Ding Jiang , Wunder Stephanie L. , Baran George R.
Published: April 2011

UHMWPE (Ultrahighmolecular Weight Polyethylene) was attached to silica using a two step process, in which the first step involves silanating the silica surface with a 0.5–1.2 mole % vinyltrimethoxysilane-ethylene copolymer (PE-silane), and in which the UHMWPE (Mw = 3–6 × 106) is solution coated onto the silanated silica in the second step. Glass beads (3.6 μm diameter) were cleaned using distilled water or refluxed with 5% aqueous Na2S2O8, to remove metallic surface contaminants, were used for UHMWPE attachments. SEM and optical microscopy showed individual particles. TGA (thermogravimetric analysis) studies confirmed the attachments as well as their stability after attachment. The integrity of the coatings was examined by SEM following treatment with HF, which left thin “skins” of polymer remaining. Both washing methodologies for the glass beads provided similar UHMWPE coatings. Bend bars (10) prepared using UHMWPE coated beads show no adverse drop in moduli and strength.
Microstructure Development and the Mechanisms of Lubrication in Magnetron Sputtered HfC-Ag and SiC-Ag Composite Thin Films
Authors: Endrino Jose L. , Nainaparampil Jose J. , Krzanowski James E.
Published: April 2011

A soft thin coating on top of a hard substrate is a highly effective way to reduce friction of sliding mechanical components. However, soft coatings often have high wear and short lifetimes, and the restoring of solid lubricants can be remarkably uneconomical. In our recent work, composite TiC-Ag films were successfully deposited by the magnetron-sputtering pulsed laser deposition technique (MSPLD). Secondary electron (SE) images from the wear tracks revealed that silver migrates to the surface and smears along the sliding direction providing low friction, while the carbide phase provides adequate support and storage for the solid lubricant phase, all resulting in lower wear and longer lifetime. One proposed mechanism for lubrication is the friction-induced thermally activated migration of silver to the surface due to the insolubility of the carbide and silver phases which was corroborated by X-ray diffraction (XRD) analysis. The formation of incoherent interfaces between the two phases, observed by transmission electron microscopy (TEM), may influence the adhesive friction behavior of the soft metal. In this study, we investigate the structural properties and vacuum tribological behavior of SiC-Ag and HfC-Ag films.
Effects of Substrate Materials on Nanoindentation Tests of AlN Thin Films
Authors: Miyabe Shuichi , Aono Masami , Kitazawa Nobuaki , Watanabe Yoshihisa
Published: April 2011

Aluminum nitride (AlN) thin films with different thickness were synthesized by ion-beam assisted deposition on various substrates, Corning 7059 glass, fused silica, Si single crystal, and sapphire, which show the hardness ranging from 7 to 37 GPa. Effects of substrate materials on indentation-hardness of AlN films were studied by using a nanoindentation system equipped with a diamond Berkovich indenter. The maximum force applied to the films was kept at 3 mN. For the films on the Corning 7059 glass substrate, when the normalized penetration depth to the film thickness is 0.98, the film hardness is found to be about 7 GPa, which is close to the hardness of the substrate. While the normalized penetration depth is reduced to 0.11, the film hardness becomes to be about 16 GPa. On the other hand, for the films on the sapphire substrate, when the normalized penetration depth is 0.83, the film hardness is observed to be about 25 GPa, while the normalized penetration depth is reduced to 0.10, the film hardness is found to be about 15 GPa. These results reveal that when the normalized penetration depth to the film thickness is about 0.1, the hardness of the AlN film can be evaluated to be about 15 GPa without being affected by substrate materials.
Development of In-Situ Surface Observation System with an Atomic Resolution under Tensile Stress by Atomic Force Microscope
Authors: Matsumuro Akihito , Kayukawa Kimiharu , Fujimoto Youhei , Ando Taeko , Sato Kazuo
Published: April 2011

A new in-situ surface observation system under tensile stress with an atomic resolution has been developed for the purpose of the explanation of the deformation of the surface and the crack growth mechanism for thin films in the micro- and nano-mechanical systems. The mechanical properties such as Young's modulus can be determined at the same time. This observation system consists of the on-chip tensile testing system and a commercialized atomic force microscope (AFM). The on-chip testing system is characterized by a static loading mechanism with a flat spring and a test chip of single-crystal silicon of 15×15×0.5 mm. Particular attention has been paid to the suppression of the vibration which effects on images of the surface with an atomic resolution. Atomic images of the surface of mica can be observed under various tensile strains till the occurrence of the fracture. The growth of the cracks and Young's modulus for TiN thin film deposited on silicon (100) specimen can be also clarified.
Failure Mechanism Researches of Material Surface and Interface in Micro-Scratch Test
Authors: Wei Yueguang , Zhao Manhong , Tang Shan
Published: April 2011

In the present research, the adhesion properties and failure mechanisms for a ductile thin film on a silicon substrate (Ni/Si) are studied experimentally, and are simulated theoretically. In the experimental research, the relations of the horizontal driving force, vertical displacement and the frictional coefficients with horizontal displacement are measured. Furthermore, the variation of the total energy release rate and the frictional coefficient between contact surfaces are measured through obtaining a frictional effect law. The law displays that the frictional influences on the energy release rate of the total system weakly depend on the thin film thickness. This conclusion leads to that the frictional effect can be eliminated in the toughness ratio relation approximately. So that one can directly obtain the interfacial adhesion toughness from measurements in the micro-scratching test. In addition, the micro-scratching process for the ductile thin film/brittle substrate systems is simulated using the double cohesive zone model. Prediction results of the energy release rate are obtained, and are compared with the experimental results obtained in the present research.
Metrology Issues in Cu-Low-K Chemical Mechanical Planarization
Authors: Zantye Parshuram B. , Sikder Arun K. , Thagella Swetha , Gulati Nivedita , Kumar Ashok
Published: April 2011

Ultra low-k materials used in Cu damascene process are inherently soft and weak in nature; hence the evaluation of tribological properties of these materials is an issue of paramount importance in the field of semiconductor fabrication. Chemical Mechanical Polishing (CMP) of these films is a major challenge due to their reduced modulus and cohesive strength. The objective of this research is to develop a strong understanding of the tribological properties of Cu ultra low-k dielectric materials for successful implementation in the semiconductor devices. The Cu ultra low-k systems are polished at different conditions of load and platen rotation and their polishing behavior is compared with the standard Cu-SiO2 system. The polishing behavior of Cu and the barrier Ta material is studied in order to effectively detect the end point of the Cu CMP process. Delamination studies, post process surface characterization using scanning electron microscopy and the reliability issues of these materials also come within the scope of this study.
Fabrication And Application Of Zeolite Membranes
Authors: Kita Hidetoshi
Published: April 2011

Zeolite Membranes Were Prepared On A Porous Ceramic Support By Hydrothermal Synthesis Using Conventional Heating System And Microwave Heating. Naa And T Type Zeolite Membranes Were Highly Selective For Permeating Water Preferentially With The High Permeation Flux, While Silicalite Membranes Exhibited Preferential Organic Compound Permeation From Water Such As Ethanol/Water. Nay And Nax Zeolite Membranes Showed A High Alcohol Selectivity For Several Feed Mixtures With Methanol Or Ethanol And A High Benzene Selectivity For Benzene/Cyclohexane And Benzene/N-Hexane Separation. The Performance Of The Zeolite Membranes Was The Most Favorable One For Pervaporation Membranes Which Have Been Published So Far And A Tubular Type Module Using A Type Zeolite Membrane For Dehydration Of Organic Liquids Has Been Put Into Industrial Operation. The Tubular Type Pervaporation And Vapor Permeation Module Can Produce 99.8 Wt% Ethanol From 600 L/H, 90 Wt% Ethanol Feed At 120 °C. For The Mass Production Of Zeolite Membrane A New Synthetic Method Using A Microwave Heating Is Also Proposed.
Pervaporative Dehydration of an Industrial Ketonic Solvent Using Ceramic Silica Membranes
Authors: Urtiaga Ane M. , Casado Clara , Ortiz Inmaculada
Published: April 2011

In this work, the dehydration of an industrial ketonic solvent used in the chemical industry is investigated by means of pervaporation (PV) using commercially available silica membranes (from Sulzer Chemtech and Pervatech BV). The solvent used is an industrial acetone-water mixture, with minor quantities of other reaction products. The initial water content is 30wt.%. The removal of water by PV has been previously experimentally studied using a polymeric Symplex membrane (GKSS), with relative success though the selectivity was low. Recent developments in the inorganic membrane field have led to the commercial availability of silica microporous membrane materials, like those used in this study. The performance of these ceramic membranes is compared, regarding their fluxes and selectivities. A simplified mathematical model is applied in order to be able to predict the pervaporation flux through pervaporation membranes.
The Zeolite ZSM-5 membrane study; synthesis, permeation and modeling.
Authors: Oonkhanond Bovornlak , Mullins Michael E.
Published: April 2011

Zeolite particles formed in the synthesis solution assume a negative charge due to electrical double layer effects. The membranes synthesized via electrophoretic deposition produce a thin continuous zeolite ZSM-5 layer on the porous alumina substrates. The thickness of membranes can be controlled by varying the precursor concentration, applied potential, and synthesis time. The permeation for a variety of gases through the membranes is examined. The diffusion properties are measured at near ambient temperature and pressure. Selectivity of n-butane over iso-butane is observed on every membrane. The diffusion coefficient of gases on ZSM-5 is also evaluated by gas adsorption on zeolite powders. The results of these studies show an ability to predict the effective diffusion coefficients. The estimation of molar fluxes across the membranes using the Maxwell-Stefan approach predicts a higher flux for thinner membranes. However, the calculations also show that even minor defects in the membrane have a great effect on the permeation rates.
Selective Matrimid Membranes Containing Mesoporous Molecular Sieves
Authors: Balkus Kenneth J. , Cattanach Kyle , Musselman Inga H. , Ferraris John P.
Published: April 2011

We have employed mesoporous molecular sieves in polymer membranes in an effort to enhance the permselectivity. The principal advantage of these materials is that the polymer chains can penetrate the pores reducing the nonselective voids that are often observed with inorganic additives. In this study, we have prepared Matrimid® membranes with various loadings of the all silica molecular sieve DAM-1 (Dallas Amorphous Material) as well as DAM-1 functionalized with amines in the channel wall, to enhance the gas permeability characteristics of a high performance polymer. For all gases tested (N2, O2, CO2, CH4), the permeability increased in proportion to the wt % of the amine DAM-1 present in the membrane. The addition of the amine DAM-1 resulted in modest ideal O2/N2 permselectivity, while the ideal CO2/CH4 permselectivity values were >100, depending upon the moisture content of the feed. The ideal CO2/CH4 permselectivity values are among the highest for this type of composite membrane. Details of membrane fabrication as well as permeability and permselectivity results will be presented for a range of Matrimid®/molecular sieve composites.
Numerical Solution of the Coupled Nernst-Planck and Poisson Equations for Ion-Selective Membrane Potentials
Authors: Lingenfelter Peter , Sokalski Tomasz , Lewenstam Andrzej
Published: April 2011

A numerical model is presented for analyzing the propagation of ionic concentrations and electrical potential in space and time in the solution ion-exchanging membrane system. Diffusion and migration according to the Nernst-Planck (NP) flux equation govern the transport of ions, and the electrical interaction of the species is described by the Poisson (P) equation. These two equations and the continuity equation form a system of partial non-linear differential equations that is solved numerically. As a result of the physicochemical properties of the system, both the contact/boundary potential and the diffusion potential contribute to the overall membrane potential. It is shown that interpreting the electrical potential of ion-exchanging membranes exclusively in terms of boundary potential at steady-state is incorrect. The Nernst-Planck-Poisson (NPP) model is general and applies to ions of any charge in space and time domains.
Orientation Dependence of the Texture Evolution in Cold-Rolled Thin Foils of Ni3Al Single Crystals
Authors: Kishida Kyosuke , Yozo Suga Masahiko Demura. , Hirano Toshiyuki
Published: April 2011

Texture evolutions of cold-rolled thin foils of binary stoichiometric Ni3Al single crystals were examined as a function of the initial crystal orientation. In the cases of the initial rolling direction (RD) close to <001>, the rolling texture above 90% reduction is composed of two {110}<112> textures, which resulted from the formation of the banded structure with two types of differently oriented matrix bands. The macroscopic shape of these cold-rolled foils is straight and simply elongated along RD keeping their rectangular shape. In contrast, when the initial RD is close to <112>, the texture and the microstructure are rather uniform but the foils are curved, twisted, and eventually cracked from the side edge of the samples. Based on the analysis of the texture evolution and the microstructure observation, the operative slip systems were determined.
Investigation on Additional Hardening Mechanisms in Off-Stoichiometric Al-Rich Ni3Al Alloys in Terms of Anti-Site Defect Configuration
Authors: Miura Seiji , Takizawa Satoshi , Mishima Yoshinao , Mohri Tetsuo
Published: April 2011

One of the unsettled issues of the mechanical properties of L12-Ni3Al compound is the effect of off-stoichiometry on the 0.2% flow stress at low temperature region. 0.2% flow stress at 77 K increases as deviating from the stoichiometric composition to both Ni-rich and Al-rich sides, but in Al-rich side the increasing rate is higher. According to the XRD results for the binary Ni3Al alloys, however, the composition dependence of the lattice constant is the same in both sides of the stoichiometric composition, which implies that the magnitude of lattice strain induced at off-stoichiometric composition is symmetrical. And it is not rational to associate the strengthening mechanism to a sole effect of isotropic strain due to an atomic size difference. In this study, attempts are made to explain the additional strengthening in Al-rich alloys in terms of the tetragonal distortion hardening mechanism, which arises from anisotropic atomic configuration around an anti-site Al atom.
Transition Metal Alloying and Phase Stability in the Mo-Si-B System
Authors: Sakidja R. , Kim S. , Park J. S. , Perepezko J. H.
Published: April 2011

The effect of transition metal substitution for Mo on the phase stability and multi-phase microstructures in the Mo-Si-B ternary system has been examined. The metal-rich portion of the ternary Mo-Si-B system at equilibrium is comprised of thermally stable BCC Mo(ss) phase, a ternary-based Mo5SiB2 (T2 phase), binary-based metal-rich silicides (Mo3Si [the A15 phase] and Mo5Si3 [the T1 phase]) and borides (Mo2B and MoB phases). Systematic alloying with selected transition metals which are substitutional in both Mo(ss) and T2 phases such as Cr, V, Nb, W, Ti and Hf, has been performed to elucidate the roles of the substitution on the stability of the three phase fields of Mo(ss) + T2 + A15 and T2+ T1 + A15. The potential of the alloying effects on the microstructure design and control of the solidification pathways is further detailed.
Eutectoid Phase Transformations in Nb-Silicide In-Situ Composites
Authors: Bewlay B. P. , Sitzman S. D. , Brewer L. N. , Jackson M. R.
Published: April 2011

Nb-silicide based composites have excellent potential for future high-temperature structural applications. Nb-silicide composites possess Nb together with high-strength silicides, such as Nb5Si3 and Nb3Si. Alloying elements such as Ti and Hf, are added to obtain a balance of properties such as creep performance and oxidation resistance. In Nb-silicide composites generated from Nb-rich binary Nb-Si alloys, Nb3Si is unstable and experiences eutectoid decomposition to Nb and Nb5Si3. The present paper describes a low temperature eutectoid phase transformation during which (Nb)3Si decomposes into (Nb) and (Nb)5Si3, where the (Nb)5Si3 possesses the hP16 structure, as opposed to the tI32 structure observed in binary Nb5Si3.
Atomistic Studies of Dislocation Glide in γ-TiAl
Authors: Porizek R. , Znam S. , Nguyen-Manh D. , Vitek V. , Pettifor D. G.
Published: April 2011

Computer simulation of the core structure and glide of ordinary 1/2<110] dislocations and <101] superdislocations in L10 TiAl has been performed using the recently constructed BondOrder Potentials. This description of atomic interactions includes explicitly, within the tight-binding approximation, the most important aspects of the directional bonding, namely d-d, p-p and d-p bonds. The ordinary dislocation in the screw orientation was found to have a non-planar core and, therefore, high Peierls stress. The superdislocation was found to possess in the screw orientation either a planar (glissile) or a non-planar (sessile) core structure. However, the glissile core transforms into the sessile one for certain orientations of the applied stress. This implies a strong asymmetry of the yield stress and the break down of the Schmid law when the plastic flow is mediated by superdislocations. At the same time, this may explain the orientation dependence of the dislocation substructure observed in the single-phase γ-TiAl by electron microscopy.
Effect of Growth Rate on Microstructure and Mechanical Properties of the Directionally Solidified Nb-Si Eutectic Alloy
Authors: Sekido Nobuaki , Kimura Yoshisato , Mishima Yoshinao
Published: April 2011

The development of ultra-high temperature structural materials having superior mechanical properties to the nickel based superalloys has been pursued in the niobium silicide based composites. The unidirectional solidification technique was performed on the (Nb)/Nb3Si eutectic alloy in the Nb-Si binary system. A continuity of Nb phases in the eutectic microstructure increases with decreasing a growth rate, which yields the enhancement of fracture toughness as well as high temperature strength. The mechanisms of microstructural formation, toughening, and strengthening are briefly discussed.
On Mo-9Si-18B Alloys with T2-Moss eutectic microstructure: Mechanical Properties and Protective Silicide Coating
Authors: Kumagai Michiaki , Ito Kazuhiro , Yamaguchi Masaharu
Published: April 2011

Direct access to a T2-Moss eutectic microstructure with a nominal composition of Mo-9Si-18B (at.%) was obtained using an optical floating zone method at a growth rate of less than 5mm/h. The Mo-9Si-18B two-phase alloy has relatively high 0.2% proof stress at 1500°C of about 700 MPa and fracture toughness at room temperature (RT) of ∼11 MPaVm. The (Mo,Nb)-19.5Si-B alloys with (Mo,Nb)ss-T1-T2 three-phase eutectic microstructure have lower yield stress at 1500°C and fracture toughness at RT lower than the Mo-9Si-18B two-phase alloy. The dense short rod-type morphology of Moss in the Mo-9Si-18B alloy may be pulled out of T2 matrix and crack bridging may play a crucial role in toughening. Due to the limited ductility of Mo at RT, its morphology is more important rather than its volume fraction in improving the fracture toughness of multi-phase alloys.

Silicide coating on the Mo-9Si-18B alloys with the T2-Moss two-phase microstructure using a halide-activated pack cementation was also examined. The B-doped Mo5Si3 layer with the D8m structure was formed on the substrate after oxidation at 1500°C for 24 hours. The substrate is the source of B atoms. A steady-state weight gain was observed at 1300–1500°C and their steady-state constants are almost equal to those of MoSi2. The weight loss was saturated in 16–26 cycles at 1500°C. It was about -0.4mg/cm2, suggesting thermal stress resistance of the coated Mo-9Si-18B two-phase alloys is sufficient in the present condition.
Physical and Mechanical Properties of Mo5X3+α (X=Si, B, C) Single Crystals
Authors: Hayashi Taisuke , Ito Kazuhiro , Tanaka Katsushi , Yamaguchi Masaharu
Published: April 2011

Mo5X3+α (X=Si, B, C) intermetallic compounds such as Mo5SiB2 (D8l), Mo5Si3 (D8m) and Mo5Si3C (D88) have a great potential for ultra-high temperature applications. The present study was undertaken putting greater emphasis on clarifying how their physical and mechanical properties are similar or different in terms of a structure type. Some interesting features are summarized in this paper.

The resistivity of Mo5SiB2, Mo5Si3 and Mo5Si3C single crystals exhibited a negative curvature (d2ρ(T)/dT2<0), with a tendency towards saturation. In the Mo5Si3C with large ρ0 due to impurity carbon atoms, resistivity saturation is pronounced. In contrast, a much higher temperature is required to reach saturation in the Mo5SiB2. The anisotropy ratio of CTE (αc/αa) for the Mo5SiB2 is about 1.2–1.6 and is significantly reduced from about 2 of the Mo5Si3 and Mo5Si3C. On the other hand, the Young's modulus of the Mo5SiB2 is more anisotropic than those of the Mo5Si3 and Mo5Si3C. Plastic anisotropy was observed in the Mo5SiB2, because only slip on [001] {100} is operative at 1500°C. On the contrary, plastic deformation was observed at temperatures above 1300°C for the Mo5Si3C and Mo5Si3. Anisotropy of their plastic deformation was much less than that of the Mo5SiB2, presumably because more than two slip systems can be activated. Creep resistance of the Mo5SiB2 is much better than that of the Mo5Si3 as well as the most advanced materials such as MoSi2 and Si3N4 based structural ceramics.
Defect Properties and Magnetism in B2-type CoFe Alloys
Authors: Harada Keiichi , Ishibashi Hiroki , Kogachi Mineo
Published: April 2011

Point defect properties have been studied for B2-type Co1-cFec alloys (0.4 ≤ c ≤ 0.6 ) by X-ray diffraction and density measurements. The lattice constant increases with increase in composition c and indicates a distinct change in the slope beyond c = 0.5. Further, it shows a decrease with increase in quenching temperature. The obtained vacancy concentration is very low for any composition and temperature concerned. Thus, it can be concluded that defect type in B2 CoFe is an antisite atom. The change in the lattice constant with quenching temperature can be related to the long-range order (LRO): it is well approximated by a linear form with respect to square of the LRO parameter. CoFe alloys in both B2 and higher temperature A2 phase regions show ferromagnetism. Observed results are discussed taking a correlation between the defect structure and the magnetic behavior into account.
A Mechanism of Polycrystallization in Fully Lamellar Ti-48Al-8Nb Single Crystal Alloy Aged at Elevated Temperatures
Authors: Yamamoto Yukinori , Takeyama Masao , Matsuo Takashi
Published: April 2011

Polycrystallization mechanism of a fully lamellar microstructure during aging at 1473 and 1273 K has been examined using Ti-48Al-8Nb fully lamellar single crystal, which consists mostly of γ/γ interfaces (variant, perfect-twin and pseudo-twin boundaries). After a certain period of aging, a few γ grains are formed within the lamellae and the lamellar microstructure collapses rapidly to become a γ grained microstructure at both temperatures. An EBSP analysis for aged sample revealed that most of the grains follow the orientation of variant domains in the lamellar microstructure. A kinetic analysis of the grain growth during aging revealed that the activation enthalpy of the growth rate is estimated to be 390 kJ/mol, which is very close to that for volume diffusion coefficient of Al and Nb in γ-TiAl. Based on the results, it is concluded that the formation of the grains is attributed to coarsening of variant domains within the lamellar plates and coalescence of the same variant domains across the lamellae, leading to a γ grained microstructure following the orientation of variant domains. These reactions also make the number of the variant domains decrease during aging, which remains only two variant domains with perfect-twin relationship.
Phase Stability and Magnetic Properties of E21-(Co, Ni)3AlC Based Alloys
Authors: Kimura Yoshisato , Iida Kaoru , Mishima Yoshinao
Published: April 2011

Phase stability of E21 (Co, Ni)3AlC was investigated from the viewpoint of magnetic properties in the Co-Ni-Al-C quaternary system. Isotherms of the Co-Al-C and Ni-Al-C ternary systems at 1373 K were revised and evaluated by means of electron probe microanalysis. Magnetic properties measurement revealed that discontinuity appearing on the chemical concentration dependence of Curie temperature and saturation magnetization of E21 (Co,Ni)3AlC indicates the existence of two types of E21 phase in the Co-Ni-Al-C quaternary system.
Characteristics of Hydrogen Absorption-Desorption Reaction in R-M (R=Y, La, Ce; M=Co, Rh, Ir, Ni, Pd, Pt) Binary Systems
Authors: Mizutani H. , Hirano K. , Kadono J. , Nishiuchi S. , Yamamoto S. , Tanabe T. , Kawai J.
Published: April 2011

The amount of absorbed hydrogen, the absorption rate and the reversibility of hydrogen absorption-desorption reaction were measured for binary systems R-M (R= Y, La, Ce; M=Co, Rh, Ir, Ni, Pd, Pt). These experimental results were discussed by comparing the number of states unoccupied by electrons, the cohesive energy and the energy fluctuation, which were calculated by the extended Hückel method. The main results are as follows. (a) The more the number of unoccupied electronic states in the compounds, the more hydrogen is absorbed, (b) the critical concentrations of hydrogen in the R-M compounds where the energy fluctuation decreases remarkably correspond to the inflection or saturation points in the absorption curve, and (c) when the cohesive energy of a compound decreases linearly with hydrogen concentration, the compound easily desorbs hydrogen. On the other hand, when a sharp knickpoint is observed in the curve of cohesive energy - hydrogen concentration, the desorption reaction is hard to occur.
Crystal structure and thermoelectric properties of ReSi1.75 silicide
Authors: Gu J-J , Kuwabara K. , Tanaka K. , Inui H. , Yamaguchi M. , Yamamoto A. , Ohta T. , Obara H.
Published: April 2011

The crystal structure of the defect disilicide formed with Re (ReSi1.75) has been refined by transmission electron microscopy combined with first-principles calculation. The crystal structure is monoclinic with the space group Cm (mc44) due to an ordered arrangement of vacancies on Si sites in the underlying (parent) C11b lattice. The thermoelectric properties of ReSi1.75 are highly anisotropic. Its electrical conduction is of n-type when measure along [001] while it is of p-type when measured along [100]. Although the value of Seebeck coefficient along [100] is moderately high (150–200 μV/K), it is very high along [001] (250–300 μV/K). As a result, a very high value of dimensionless figure of merit (ZT) of 0.7 is achieved at 1073 K when measured along [001].
Solving the Structure of the Phases in the Al-Mg-Si Alloy System with the Help of Ab Initio Modelling
Authors: Froseth A. G. , Andersen S. J. , Marioara C. D. , Derlet P. M. , Hoier R.
Published: April 2011

The Al-Mg-Si (6xxx-series) alloy system is a precipitation hardened alloy gaining much of its strength from precipitate phases acting as pinning centers for dislocation movement. Five years ago, Zandbergen, Andersen and coworkers identified the crystallography of the so-called β″ phase, one of the main hardening phases, using solely electron microscopy techniques [1]. Later, several other phases have been identified using high resolution microscopy. To solve the crystallography of these phases and to get an increased understanding of the electronic structure and bonding, ab initio modeling has proven to be a valuable tool. We present results from calculations on two recently discovered phases and show how ab initio modeling can give insight into the bonding trends and electronic structure of the phases in this alloy system.
Pressure Induced Structural Transitions in Manganites with Orbital Ordering
Authors: Kaplan Michael D. , Zimmerman George O.
Published: April 2011

In order to explain magneto-elastic and pressure measurements in doped colossal magneto-resistance manganites, we postulate a doublet-triplet model and use it to predict the occurrence of the various phase transitions.
Optical Properties of Anatase, Rutile and Amorphous Phases of TiO2 Thin Films Grown at Room Temperature by RF Magnetron Sputtering
Authors: Naik V. M. , Haddad D. , Naik R. , Benci J. , Auner G. W.
Published: April 2011

Anatase (A), rutile (R) and amorphous phase TiO2 thin films have been prepared by RF magnetron sputtering on unheated glass substrates by controlling the total pressure of sputtering gases (Ar + O2) and the substrate bias. The crystal structures of the films were confirmed by x-ray diffraction and Raman scattering. The analysis of optical absorption data for A- TiO2 film shows an energy bandgap (Eg) of 3.2 eV (indirect extrapolation) and ∼ 3.5 eV (direct extrapolation). On the other hand, R-TiO2 film shows Eg ∼ 2.9 eV (indirect) and 3.2 eV (direct). The latter film also shows the presence of amorphous regions with Eg ∼ 3.0 eV (indirect) and 3.8 eV (direct). The bandgap of both the films, obtained using indirect extrapolation, has a value range consistent with the previous measurements.
Electrical and Dielectric properties of Bi6Mn2Ti3O18
Authors: Suryanarayana S.V , M.B Suresh , K Srinivas , E Venkata Ramana , G Swaminathan
Published: April 2011

Bismuth layer structured ferroelectrics show interesting physical property variations as a function of external parameters viz., temperature, frequency and magnetic field. In some of these materials, when a magnetic ion is incorporated in the lattice, they show simultaneous ferroelectricity and magnetism, thus exhibiting magnetoelectric output under the influence of an external magnetic field. This paper reports the synthesis and characterization of Bi6Mn2Ti3O18(BMT) which is isomorphous with Bi6Fe2Ti3O18(BFT). The material was prepared both by solid state and microwave sintering routes. The characterization includes X-ray, SEM, conductivity, dielectric constant and pyroelectric coefficient. The results are compared with Fe containing analogue.
Thermoelectric Properties of Magnetically c-axis Aligned Poly crystals in (Ca2ComOm+2δ)∼0.62Co02 (m=2 and 2) Systems
Authors: Horii S. , Matsubara I. , Sano M. , Funahashi R. , Shikano M. , Shimoyama J. , Kishio K.
Published: April 2011

We report preparation and thermoelectric properties of c-axis aligned and densified Ca3Co4O9 and [Ca2(Co0.65Cu0.35)2O4]0.624CoO2 polycrystals. The c-axis alignment and densification were accomplished by magnetic alignment and spark plasma sintering methods, respectively. The obtained samples showed high degrees of c-axis orientation and relative densities, which were close to those of single crystals, resulting in the highest values of power factors in Ca3Co4O9 and [Ca2(Co0.65Cu0.35)2O4]0.624CoO2 polycrystals.
Synthesis of a New Class of Hybrid Solids via Salt Inclusion
Authors: Huang Qun , Kartin Mutlu , Mo Xunhua , Hwu Shiou-Jyh
Published: April 2011

Via salt inclusion methods, we have recently isolated a new class of transitionmetal-containing hybrid solids that consist of a composite structure of covalent and ionic lattices. These new solids can be synthesized by conventional high-temperature, solid-state methods employing reactive molten alkali and alkaline-earth metal halide salts. Single crystal structure studies have revealed fascinating extended salt lattices that exhibit structural directing effects that give rise to a variety of nano-structured covalent oxide frameworks. Depending upon the composition of incorporated salt and the coordination environment of halide anions, resulting covalent lattices range from sheets, clusters, to porous structures. Due to the weak interaction between the two chemically dissimilar lattices, the salt lattice, in some cases, is removable showing reversible salt-intercalation at room temperature. In this report, we will demonstrate the utilities of salt-inclusion reactions in the formation of metal-oxide nanostructures in the selected compound families. We will also give some highlights on the recent discoveries of non-centrosymmetric solids via newly exploited salt-inclusion methods.
A Drastic Influence of Point Defects on Phase Stability in MnO2
Authors: Morgan Dane , Balachandran Dinesh , Ceder Gerbrand , van de Walle Axel
Published: April 2011

Despite its importance as a cathode material in primary alkaline batteries, the structure of γ-MnO2 is still not well determined. Different authors have suggested that a number of different polymorphs, as well as highly disordered phases, may be present in γ-MnO2. The origin of this structural complexity remains largely unexplained. In this paper we use first principles methods to explore the energetics of the MnO2 system. We find a number of low-energy polymorphs with similar energies, suggesting that relatively small changes in the energetics might influence the stable phases. Using nonzero-temperature models we demonstrate that thermal disorder is not the cause of structural disorder in these materials. However, we then show that point (Ruetschi) defects, even in surprisingly low concentrations, have a dramatic effect on the phase stability. We propose that Ruetschi defects may be the key to some of the structural complexity in γ-MnO2, and that any realistic structural study must take them into account.
Cation Site Mixing for Strain Relief in Three-Layer Aurivillius Ceramics
Authors: Haluska Michael S. , Misture Scott T.
Published: April 2011

Three-layer Aurivillius ceramics Bi2SrCaNb2TiO12, Bi2Sr1.5Ca.5Nb2TiO12, Bi2Sr2Nb2TiO12, Bi2Sr1.5Ba.5Nb2TiO12, Bi2SrBaNb2TiO12 were formed via solid-state synthesis and their structures characterized by Rietveld analysis of powder x-ray diffraction data. Site mixing was observed for all species with the largest amount of mixing occurring in Bi2SrBaNb2TiO12. Bond valence sum calculations (BVS) showed that the A-site BVS increased from underbonded in the Bi2SrCaNb2TiO12 composition to overbonded in Bi2SrBaNb2TiO12. The A-site BVS increased linearly with lattice parameter and average A-site cation radius. Bi-site position relaxation was observed as the average size of the alkaline earth cation on the Bi-site increased. Site mixing occurs in these compounds in order to relieve interlayer strain between the (Bi2O2)2+ layer and the perovskite blocks, between the Nb and Ti-layers of the perovskite blocks, and to reduce the BVS of the perovskite A-site.