bluuebunny/crossref_metadata_2025_split huggingface dataset:
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

ABSTRACTThe 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

ABSTRACTDirect 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

ABSTRACTMo5X3+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

ABSTRACTPoint 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

ABSTRACTPolycrystallization 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

ABSTRACTPhase 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

ABSTRACTThe 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

ABSTRACTThe 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

ABSTRACTThe 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.
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

ABSTRACTAnatase (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

ABSTRACTBismuth 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

ABSTRACTWe 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

ABSTRACTVia 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

ABSTRACTDespite 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

ABSTRACTThree-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.
Preparation and Properties of Li-Mn-O-F Compounds as Cathode in Li-Ion Batteries
Authors: Liu Hanxing , Hu Chen , Xia Junlei , Zhao Shixi , Ouyang Shixi 
Published: April 2011

ABSTRACTIn present study LiMn2O4-xFxwere prepared by the sol-gel method. X-ray diffraction (XRD) and scanning electron microscope (SEM ) were employed to detect the microstructure of the reaction products. It were found perfect crystal particles were obtained, and its' size were uniform in 1∼2 μ m. The specific capacity and cycleability were measured basing on battery program control test system. The results shown the substitution of F for O increased the specific capacity of the material at the cost of the cycleability due to more Mn3+and less Mn4+existed in the material. The exist of Mn3+would reduce cycleability of cathode material due to the Jahn-Teller effect which were caused by the deformation of the crystal structure.
Preparation and Characterization of Pb2SnF6, The First Lead(II)-TIN(II) Fluoride that is a Superstructure of A-PbF2
Authors: Calandrino Raimondo , Collin Anthony , Dénés Georges , Logiou Morgane , Cecilia Madamba M. 
Published: April 2011

ABSTRACTAll the known phases in the PbF2/SnF2 system have structures derived from the fluorite-type β-PbF2, and are either disordered, and therefore cubic, or ordered with lattice distortion and superstructures. In addition, they are the highest performance fluoride-ion conductors, with PbSnF4 being the very best. In this work, a new phase, Pb2SnF6 has been prepared and characterized. Contrary to the other lead(II) tin(II) fluorides known up to date, the structure of Pb2SnF6 is a superstructure of a-PbF2, instead of β-PbF2, with a large (4 × 4) bidimensional supercell. Pb2SnF6 is prepared by the reaction of a-PbF2 with an aqueous solution of SnF2.
Exploration of Cation Substitution in the Layered Compound CrWN2
Authors: Scott Weil K. , Kumta Prashant N. , Grins Jekabs 
Published: April 2011

ABSTRACTA series of derivative compounds based on the layered parent phase CrWN2 have been synthesized using a complexed precursor synthesis route. X-ray diffraction analyses demonstrate that both the chromium and tungsten display mutual substitution for one another and can also undergo considerable extensive replacement by a wide variety of cation species without significantly altering the original layered structure of the parent dinitride compound. The precursor approach employed here appears to offer a ready technique for exploring compositional phase space in layered nitrides of this type.
Epitaxial Stabilization in Thin Films of Oxides
Authors: Kaul A. , Gorbenko O. , Graboy I. , Novojilov M. , Bosak A. , Kamenev A. , Antonov S. , Nikulin I. , Mikhaylov A. , Kartavtzeva M. 
Published: April 2011

ABSTRACTThis paper is a survey of recent author's results obtained by the authors. It shows that many oxides can be obtained as thin epitaxial films in spite of their thermodynamic instability in bulk state at the film deposition conditions. This new synthetic approach, named epitaxial stabilization, is based on free energy gain due to structural coherence at the film/substrate interface. The epitaxial stabilization can be effectively used to enlarge the spectrum of new functional materials.
High Quality Erbium-Doped Bismuth Based Oxide Film for Planar Waveguide Amplifier Prepared by Sputtering
Authors: Suzuki S. , Kondo Y. , Nagashima T. , Sugimoto N. , Ebisawa J. , Ito S. 
Published: April 2011

ABSTRACTHigh quality Bi2O3 based Er-doped films for planar waveguide amplifier have been deposited by sputtering from sintered targets. It was found that both the amount of residual water and the Er concentration in films mainly affected a lifetime of the fluorescence at 1530nm. By optimizing these parameters, we have obtained films with a lifetime over 3msec, as the same as that of bulk glass prepared by the melting method.
Electrochemical Properties of Blockcopolymer Templated Mesoporous Silicates with Heteropolyacids clusters
Authors: Yun Hui Suk , Kuwabara Makoto , Zhou Hao Shen , Honma Itaru 
Published: April 2011

ABSTRACTIn this paper, we have studied a method of loading 12-tungstophosphoric acid (H3PW12O40; PWA) into blockcopolymer templated (designated EO20PO70EO20; Pluronic P-123) mesoporous SiO2 framework without a disordering of mesostructure and without remarkable decrease of specific surface area through one-step condensation process. A precursor solution is initially prepared by TEOS (tetraethoxysilane) hydrolyzed with templating polymer (eg. triblock copolymer), and then mixed directly with PWA to condense mesoporous silicate products that incorporate PWA clusters in the framework. Heteropolyanions are possibly incorporated in the framework silicates. Electrochemical properties of these PWA impregnated mesoporous silicates were studied as electrode materials of Li ion battery as well as solid proton conductors.
Electrical Conductivity Prediction in Langasite for Optimized Microbalance Performance at Elevated Temperatures
Authors: Seh Huankiat , Tuller Harry , Fritze Holger 
Published: April 2011

ABSTRACTThe performance of the langasite-based crystal microbalance is limited due to reductions in its resistivity at high temperatures and reduced oxygen partial pressures. In this work, we utilize a recently developed defect model to predict the dependence of the ionic and electronic contributions to the total conductivity of langasite on temperature, oxygen partial pressure and acceptor and donor dopants. These results are used to select the type and concentrations of dopants expected to provide extended operating conditions for langasite-based gas sensors and crystal microbalances.
High-Temperature Potentiometric NO2 and CO Sensors Based on Stabilized Zirconia with Oxide Sensing Electrodes
Authors: Di Bartolomeo E. , Grilli M. L. , Kaabbuathong N. , Traversa E. 
Published: April 2011

ABSTRACTThis paper reports the efforts made in our laboratory to develop electrochemical sensors that might detect NO2 and CO at high temperatures for On Board Diagnostic (OBD) application. The non-Nernstian behaviour of zirconia-based electrochemical NO2 sensors with various oxides as sensing electrodes was studied in the temperature range 450–700°C. Both pellets and tape-casted layers (150 μm of thickness) of yttria-stabilized zirconia (YSZ) were used for fabrication of the sensors. Pt electrodes were painted on both sides of the pellets or as two parallel fingers on one face of the layers. One of the Pt electrodes was covered with a thick-film oxide electrode. Various oxides were tested as sensing electrodes, either p- or n-type semiconductors, including WO3 and LaFeO3. The role of ionic conductivity of the oxide electrodes was investigated using Sr-doped perovskite-type oxides, such as LaxSr1-xFeO3, a mixed ionic-electronic conductor. The sensors were tested as potentiometric and amperometric devices. The performance of these devices was promising: fast and stable responses to different NO2 concentrations (20–1000 ppm in synthetic air) were observed at high temperatures. The role of the metallic electrodes is also studied. The sensing mechanism of the sensors is discussed.