bluuebunny/crossref_metadata_2025_split huggingface dataset:
A Comparative Study of Mechanical Properties in Ion-Irradiated A12O3 and MgO·nAl203
Authors: Yasuda K. , Kinoshita C. , Izumi K. 
Published: April 2011

AbstractWe have investigated radiation hardening in alumina (A1203), stoichiometric and nonstoichiometric spinel (MgO·nA1203: n= 1, 2.4) crystals at 300 K irradiated with 100 keV He+ ions by using a ultra-microhardness technique. Al203 shows a remarkable radiation hardening (35% increase in hardness) at a fluence of 5×1019 He+/m2 and saturates at 60 % of the maximum value at fluences higher than 8×1019 He+/m2. In spinel crystals, hardness increases monotonically with fluence, reaching to a saturation at a fluence of 1×1020He+/m2. Analyses of load- displacement curves indicate that both plastic and elastic hardening are responsible for the radiation hardening in A1203, and that plastic hardening is the main cause in MgO'nAl2O3. Microstructure observations and lattice constant measurements showed that point defects are mainly responsible for the radiation hardening in both A1203 and MgO·nAl2O3. The difference in the radiation hardening response is discussed in terms of the difference in recombination rate of point defects among the MgO-A1203 system ceramics.
The Search for Interstitial Dislocation Loops Produced in Displacement Cascades at 20K in Copper
Authors: Kirk M. A. , Jenkins M. L. , Fukushima H. 
Published: April 2011

AbstractA low-temperature in situ ion-irradiation and annealing experiment has been performed by TEM in copper. Most defect clusters which persisted through an anneal to 120 K showed no size changes within the resolution (0.5 nm) of a new weak-beam sizing technique. Of 55 defects measured under a range of weakly diffracting conditions, 7 showed measurable size decreases while 3 showed size increases. We argue that these clusters are likely to be of vacancy and interstitial nature, respectively. Also on annealing to 120 K a fraction of about 25% of the clusters formed by irradiation with 600 kV Cu+ ions at 20 K disappeared, while a similar number of clusters appeared in different locations.
Formation of Voids in Pure Copper and FE-CR-NI Alloys Irradiated by Simultaneous Multi-Ion Beam of Hydrogen, Helium and Ni Ions
Authors: Mukouda I. , Shimomura Y. , Iiyama T. , Katano Y. , Yamaki D. , Nakazawa T. , Noda K. 
Published: April 2011

AbstractPure copper and Fe-15Cr-2ONi alloy were irradiated at 500°C by 5 MeV Ni ions (single beam), Ni ions plus gas atoms (H and He) (dual beam irradiation) or triple beam of Ni, He and H ions (triple beam irradiation) simultaneously. Irradiation was carried out with accelerators TIARA at Takasaki-establishment of JAERI. Thin specimens were prepared with the combined technique of FIB (Focus Ion Beam) and electro-polishing. Damage structure versus the depth from surface was examined by TEM. In Fe-15Cr-20Ni alloy, voids were formed in the range of Ni ion irradiated specimens. In Fe-Cr-Ni alloy which is irradiated by a dual beam of Ni ion and He ion, the number density of voids increased significantly at the stopping range of He atoms. Remarkable results are void formation in specimens irradiated with dual beam of Ni and H ions, only voids of very small size were observed through the range of specimen. In irradiated specimen with triple beam, the size of voids was suppressed to be smaller than that of irradiated specimens with Ni and He ions. In pure copper which is irradiated with dual beam of helium and Ni ions, number density of voids were increased significantly. While in copper irradiated with hydrogen and Ni ions, number density of voids were not so large. Experimental results show that helium atoms have strong effect for void formation, while hydrogen atoms suppress void formation because the remarkable degradation of movement of small vacancy clusters can be induced by trapping hydrogen atoms.
Ion Irradiation of GeSi/Si Strained-Layer Heterostructures
Authors: Glaskol J.M. , Elliman R. G. , Zou J. , Cockayne D.J.H. , Gerald J. D. Fitz 
Published: April 2011

AbstractThe strain in GeSi/Si strained layer heterostructures is studied as a function of ion-irradiation and thermal annealing conditions and correlated with the defect microstructure in the GeSi alloy layer. For room temperature irradiation, compressive strain within the alloy layer increases with increasing ion fluence for both low (projected range of ions within the alloy layer) and high energy (projected range of the ions greater than alloy thickness) irradiation. In contrast, elevated temperature irradiation results in an increase in strain for low-energy irradiation, but a decrease for high-energy irradiation. For example, strain relaxation is observed in layers irradiated with I MeV 28Si+ at 253 °C. During subsequent annealing to 750 °C, the strain is partially recovered but relaxes again at temperatures > 750°C. This behavior is shown to be consistent with the evolution of intrinsic (vacancy-type) defects within the alloy layer.
Atomistic Simulation of Mobile Defect Clusters in Metals
Authors: Osetsky Yu.N. , Bacon D.J. , Serra A. 
Published: April 2011

AbstractThe structure, stability and thermally-activated motion of interstitial and vacancy clusters in Fe and Cu have been studied using atomic scale computer simulation. All studied interstitial clusters and perfect interstitial loops (PILs) in Fe are mobile whereas their mobility in Cu can be suppressed at large sizes (bigger than 49–61 self-interstitials depending on the temperature) due to dissociation. A comparative study of relaxed configurations has shown that the structure of small perfect dislocation loops of vacancy and self-interstitial nature is very similar. Molecular dynamics simulation has demonstrated that small perfect vacancy loops (PVLs) in Fe consisting of more than 37 vacancies are stable over a wide temperature range and produce atomic displacements by a thermally-activated movement in the direction of the Burgers vector. The mechanism is qualitatively similar to that of SIA clusters studied earlier. Motion of vacancy loops in Cu does not occur because they transform into sessile configurations similar to stacking fault tetrahedra. These results point to the possibly important contribution of vacancy loop mobility to the difference in radiation damage between bcc and fcc metals, and between fcc metals with different stacking fault energy.
Annealing Kinetics of Single Displacement Cascades in Ni: An Atomic Scale Computer Simulation
Authors: Almazouzi A. , Caturla M. J. , Rubia T. Diaz de la , Victoria M. 
Published: April 2011

AbstractIn order to describe the long term evolution of the defects produced by a displacement cascade, Molecular dynamics (MD) and Kinetic Monte Carlo (KMC) methods are employed. Using an empirical Ni interatomic potential in MD, the damage resulting from primary knock-on atom (PKA) energies up to 30 keV has been simulated. The annealing kinetics and the fraction of freely migrating defects (FMD) are determined for each single displacement cascade, by a KMC code which is based on a set of parameters extracted mainly from MD simulations. It allows an atomistic study of the evolution of the initial damage over a time scale up to lOOs and the determination of the fraction of the defects that escape the KMC box, compared to those obtained by MD, as function of temperature and PKA energy. It has been found that this fraction depends strongly on the temperature but reaches a saturation value above stage V.
Mechanical Properties of Feedstock Material for Fused Deposition of Ceramics
Authors: Venkataraman N. , McNulty T. , Rangarajan S. , Vidaic M. , Matthewson M. J. , Langrana N. , Safari A. , Danforth S. C. 
Published: April 2011

AbstractA scientific methodology to characterize the critical mechanical properties of feedstock material for fused deposition of ceramics has been developed. A detailed discussion of the methodology of mechanical characterization and results for lead zirconate titanate (PZT) fused deposition of ceramics (FDC) feedstock is presented. The effect of storage time, temperature and crosshead displacement rates on the mechanical properties of the PZT FDC feedstock was studied. The modulus and the failure stress increase with displacement rate. The modulus and failure stress decrease with temperature indicating the necessity for cooling filaments prior to entrance to liquefier. The modulus also decreases with storage time in 50% RH while failure strain increases with storage time in 50% RH.
Direct-Write Precision Resistors for Ceramic Packages
Authors: Yang P. , Dimos D. , Rodriguez M. A. , Huang R. F. , Dai S. , Wilcox D. 
Published: April 2011

AbstractA direct-write approach to fabricate high precision resistors is reported. Special attention is paid to the effect of print thickness on the resistance value of buried resistors after a low temperature co-firing process. The results show that the direct-write approach provides a superior line definition and thickness control over a traditional screen printing process. Microstructural analysis indicates that there is an interdiffused layer developed between the resistor material and the low temperature co-fired ceramic substrate. These observations are consistent with electrical measurements which show that resistance increases as the effective cross-sectional area is reduced. The resistance data show that the standard deviations for resistors printed on a 6” × 6” area are 5% and 15% for the direct-write and the screen-printed patterns, respectively.
Freeform Fabrication of High Performance Titanium Components via SLS/HIP
Authors: Das S. , Beaman J. J. , Wohlert M. , Bourell D. L. 
Published: April 2011

AbstractThis paper presents the development of Selective Laser Sintering/Hot Isostatic Pressing (SLS/HIP) technology for production of functional high performance components in the titanium alloy Ti-6AI-4V. SLS/HIP is a net shape manufacturing technique that combines and exploits the freeform shaping capability of selective laser sintering and the full densification capability of hot isostatic pressing. The advantages of SLS combined with in situ HIP encapsulation include single step net shape canning, full densification by containerless HIP, no container-powder adverse interactions, reduced pre-processing time, and minimal post-process machining compared to conventional HIP of canned powders. Microstructure and mechanical properties of SLS processed and HIP post-processed Ti-6A1-4V are consistent with conventionally processed material. The potential of SLS/HIP technology was demonstrated by net shape fabricating a component to specification, namely the titanium guidance section housing base for the AIM-9 Sidewinder missile.
Direct Materials Deposition: Designed Macro and Microstructure
Authors: Mazumder J. , Schifferer A. , Choi J. 
Published: April 2011

AbstractRapid Fabrication of three-dimensional shapes of engineering materials such as H 13 tool steel and Nickel super alloys are now possible using Direct Materials Deposition (DMD) technique. H 13 tool steel is one of the difficult alloys for deposition due to residual stress accumulation from martensitic transformation. However, it is the material of choice for the die and tool industry. DMD offers Copper chill blocks and water cooling channels as the integral part of the tool. On the other hand ZrO2 was co-deposited with nickel superalloys using DMD. This process thus is amenable to produce both macro and microstructure to a designed specification. This paper briefly reviews the state of the art of DMD and describes the microstructure and mechanical properties of selected engineering alloy systems deposited by DMD.
Processing of Novel Electroceramic Components by SFF Techniques
Authors: Safari A. , Danforth S. C. , Kholkin A. L. , Cornejo I. A. , Mohammadi F. , McNulty T. , Panda R. 
Published: April 2011

AbstractNovel piezoelectric ceramic and ceramic/polymer composite structures were fabricated by solid freeform fabrication (SFF) for sensor and actuator applications. SFF techniques including fused deposition of ceramics (FDC) and Sanders prototyping (SP) were utilized to fabricate a variety of complex structures directly from a computer aided design (CAD) file. Novel composite structures including volume fraction gradients (VFG) and staggered rods, as well as actuator designs such as tubes, spirals and telescopes were made using the flexibility provided by the above processes. VFG composites were made by SP technique with the ceramic content decreasing from the center towards the edges. This resulted in a reduction of side lobe intensity in the acoustic beam pattern. The FDC technique was used to manufacture high authority actuators utilizing novel designs for the amplification of strain under applied electric field. The design, fabrication and electromechanical properties of these composite and actuator structures are discussed in this paper.
Homogeneity, Anisotropy, and Texture In Si3n4 Ceramics made by Fused Deposition
Authors: Rangarajan S. , Pozsgai I. , McIntosh J. , McCuiston R. , Harper B. L. , Langrana N. , Safari A. , Danforth S. C. , Clancy R. B. , Gasdaska C. , Whalen P. J. 
Published: April 2011

AbstractThe Fused Deposition of Ceramics (FDC) process is an extrusion based layered manufacturing technique. In this study, the microstructural and property homogeneity of GS44-Si3N4 parts made by FDC is examined. The feedstock, green, and sintered parts were examined using characterization techniques such as optical and scanning electron microscopy, x-ray radiography, and x-ray diffraction. In addition, mechanical properties (σf, and Klc), shrinkage, and warpage results were used to characterize the FDC parts. It was found that by using proper build parameters and tool paths, dense, homogenous, near-net-shape GS44-Si3N4 parts can be fabricated. While the mechanical properties of these parts are shown to be isotropic, there is some degree of texturing detected with XRD. Si3N4 filament feedstock intentionally textured with 5.5 vol% of β-seed particles has also been made.
Thermoelectric Properties of AgBiTe2-Ag2Te Composite
Authors: Takigawa Y. , Imoto T. , Sakakibara T. , Kurosawa K. 
Published: April 2011

AbstractWe prepared composite materials of AgBiTe2 with several contents of Ag2Te small-size grains for applications to thermoelectric devices. By enhancing long-wavelength phonon scattering at the grain boundaries, lattice thermal conductivity (thermal conductivity due to lattice vibrations) decreased 30% and thus the thermoelectric characteristics were significantly improved.
Experimental Study of Phonon-Folding in Si/Ge and Si/Sige Structures Designed for Thermoelectric Applications
Authors: Liu J. , Balandin A. , Borca-Tascjuc T. , Tang Y. S. , Wang K. L. , Chen G. 
Published: April 2011

AbstractWe report data of Raman study of Si/Ge and Si/SiGe superlattices designed for thermoelectric applications. The obtained Raman spectra clearly indicate the presence of folded doublets from longitudinal acoustic phonons. Due to the significant difference in the sound velocities for Si and Ge the position of the doublets strongly depends on the superlattice layer thickness and ordering. Comparison of the Raman data for different samples with measured thermal and thermoelectric properties allows us to determine a correlation between the strength of the phonon confinement in these structures and their thermoelectric properties. Our experimental results are consistent with recent theoretical prediction of increased thermoelectric figure of merit in semiconductor quantum wells.
The Influence of Silicon Dopant and Processing on Thermoelectric Properties of B4C Ceramics
Authors: Cai Ke-Feng , Nan Ce-Wen , Min Xin-Min 
Published: April 2011

AbstractB4C ceramics doped with various content of Si (0 to 2.03 at%) are prepared via hot pressing. The composition and microstructure of the ceramics are characterized by means of XRD and EPMA. Their electrical conductivity and Seebeck coefficient of the samples are measured from room temperature up to 1500K. The electrical conductivity increases with temperature, and more rapidly after 1300K; the Seebeck coefficient of the ceramics also increases with temperature and rises to a value of about 320μVK−1. The value of the figure of merit of Si-doped B4C rises to about 4 × 10−4K−1 at 1500K.
Thermoelectric Properties of Doped Rhenium Chalcogenides Re6MxTe15 (x = 0, 1, 2; M = Ga, In, Ag)
Authors: Dalafave S. Kilibarda , Barcena H. , Henningsen D. 
Published: April 2011

AbstractTemperature dependencies of the electrical resistivity, ρ, and the thermoelectric power, α, are reported for Re6 MxTe15 (M = Ga, In, Ag; x = 0, 1, 2) between 90–380 K. Theoretical discussion of the results is presented. The materials, synthesized by filling large voids in the Re6Te15 cluster system, may have potential thermoelectric applications around and below room temperatures. The samples are prepared by reacting 99.99% pure elemental powders in evacuated and sealed quartz ampoules at 1070 K for 170 hours. The resistivity data indicate semiconducting behavior for all samples. Possible hopping conduction is present at lower temperatures. The energy gap is observed at higher temperatures in all the samples.Positive values of α in Re6(Ga,In)x Te15 (x = 0, 1, 2) indicate p-type semiconducting behavior in the studied temperature range. For these samples α increases initially with temperature, then levels off to a nearly constant value. The positions of the sharp peaks in a, observed at lower temperatures for x = 1, 2 only, depend on the Ga (In) concentration. High values of a (∼ 300 μV/K) are measured at room temperatures. In Re6AgTe15 α has small positive values (∼ 20–40 μV/K) between 185 K and 270 K. Outside this range α is negative. It reaches local maxima of -340 μV/K at 105 K and -350 μV/K at 370 K. In Re6Ag2Te15 α changes from positive to negative values above 295 K. A maximum positive value of +350 μV/K is reached at 250 K and maximum negative of -250 μV/K at 330 K. The power factor, α2/ρ, increases with temperature for all studied samples. Theoretical fits to α(T) for all samples are discussed. Also discussed is the effect of filling the voids in the rhenium-telluride system on the figure of merit.
Prospects for Bismuth Nanowires as Thermoelectrics
Authors: Dresselhausa M. S. , Zhang Z. , Sun X. , Ying J. Y. , Heremans J. , Dresselhaus G. , Chen G. 
Published: April 2011

AbstractThe small effective mass of Bi, high anisotropy of its Fermi surface, and the high aspect ratio (length/diameter) of Bi nanowires make this an excellent system for studying quantum confinement effects of a one-dimensional (ID) electron gas in relation to electrical conductivity, thermoelectric power, and thermal conductivity. A theoretical model based on the basic electronic band structure of bulk Bi is suitably modified to describe 1D bismuth nanowires and is used to predict the dependence of these transport properties on nanowire diameter, temperature and crystalline orientation of the bismuth nanowires. Experiments have been carried out on ultra-fine single crystal Bi nanowires (10–120 nm diameter) with a packing density as high as 7 × 1010 wires/cm2 to test the quantum confinement assumptions of the model and the occurrence of a quantum confinement-induced semimetal-to-semiconductor transition as the wire diameter becomes less than 100 nm. Prospects for the use of bismuth nanowires for thermoelectric applications are discussed.
Pressure-Tuning in the Search for Improved Thermoelectric Materials
Authors: Polvani D. A. , Meng J. F. , Jones C. D. W. , DiSalvo F. J. , Badding J. V. 
Published: April 2011

AbstractThe traditional approach to the search for improved materials, such as thermoelectric materials, involves the sequential synthesis and characterization of new compounds, followed by the investigation of their properties. Each single solid state compound has materials interaction parameters (e.g., degree of orbital overlap, orbital energy, band energies etc.) that determine its thermoelectric properties. These interaction parameters can be used to define a phase space, in which individual compounds are represented by a single point. Because this phase space can be rapidly explored with pressure, our efforts have focused on the synthesis of complex semiconductors and rare earth based materials, followed by pressure-tuning studies of their thermoelectric properties. This approach to exploring interaction parameter phase space potentially allows the thermoelectric power to be more rapidly and cleanly optimized than is possible with the traditional approach. Here we present some results for rare earth thermoelectric compounds that have been pressure-tuned. Demonstration of the existence of materials with improved ZT at high pressure can also provide insight into the structural and electronic parameters necessary to achieve high figures of merit at ambient pressure.
Properties of Novel Thermoelectrics from First Principles Calculations
Authors: Singh D. J. , Mazin I. I. , Feldman J. L. , Fornari M. 
Published: April 2011

AbstractThe use of first principles methods based on density functional theory to investigate novel thermoelectric materials is illustrated for several empty and filled skutterudite compounds, including CoSb3, COP3, La(Fe,Co)4Sb12 and La(Fe,Co)P12. Band structures and their relationship to transport properties especially as regards optimization of thermoelectric properties is discussed. Phonon models constructed from calculations and existing experimental data for CoSb3 are presented. These have been extended to the filled skutterudites, particularly LaFe4Sb12 using additional first principles calculations to fix the La related parameters in the model. This model allows an interpretation of neutron scattering data as well as an understanding of the low frequency phonon modes that transport heat in these compounds.
Thermoelectric Properties of Single-Wall Carbon Nanotubes
Authors: Grigorian L. , Sumanasekera G. , Eklund P. C 
Published: April 2011

AbstractResults of the temperature dependence of the thermoelectric power and fourprobe resistance of single wall carbon nanotube mats are presented. The data are interpreted in terms of the response of a percolating network of metallic nanotube bundles. To the best of our knowledge, the work represents the first systematic study of the transport properties of a series of samples prepared using different transition metal-Y growth catalysts. Although x-ray diffraction and Raman scattering data indicate these samples are nominally the same, we find that the identity of the catalyst has a pronounced effect on the electrical transport properties. The data are interpreted qualitatively in terms of a dilute Kondo system involving the coupling of the the localized magnetic moments of impurity atoms (derived from the catalyst), and the conduction electron spins in the nanotube walls.
Nickel Substituted Skutterudites: Synthesis and Physical Properties
Authors: Chapon L. , Ravot D. , Tedenac J. C. 
Published: April 2011

AbstractStarting to CeFe4Sb12 and trying to obtain low gap semiconductors with very low thermal conductivity, we have performed in this compound the substitution of Ni for Fe.This substitution induces a reject of cerium from the structure. In this paper we present synthesis and physical properties of CeyFe4-xNixSb12 in which a relationship is existing between x and y to retain the electronic account giving semiconducting character.
Imaging of the Carrier Density of States in Low Dimensional Structures Using Electrostatic Force Microscopy
Authors: Gekhtman D. , Zhang Z. B. , Adderton D. , Dresselhaus M. S. , Dresselhaus G. 
Published: April 2011

AbstractIn this work we show that scanning probe electrostatic force microscopy (EFM) can be applied to low dimensional electronic nanostructures for imaging the density of states of quantum confined carriers. The results on EFM studies are presented for quasione- dimensional (ID) Bi quantum wire arrays and quasi-two-dimensional (2D) GaAs/AlxGa1-x As multiple quantum well structures.