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Sample records for earth intermetallic compounds

  1. Intermetallic Compounds

    NASA Astrophysics Data System (ADS)

    Takagiwa, Y.; Matsuura, Y.; Kimura, K.

    2014-06-01

    We have focused on the binary narrow-bandgap intermetallic compounds FeGa3 and RuGa3 as thermoelectric materials. Their crystal structure is FeGa3-type (tetragonal, P42/ mnm) with 16 atoms per unit cell. Despite their simple crystal structure, their room temperature thermal conductivity is in the range 4-5-W-m-1-K-1. Both compounds have narrow-bandgaps of approximately 0.3-eV near the Fermi level. Because their Seebeck coefficients are quite large negative values in the range 350-<-| S 373K|-<-550- μV-K-1 for undoped samples, it should be possible to obtain highly efficient thermoelectric materials both by adjusting the carrier concentration and by reducing the thermal conductivity. Here, we report the effects of doping on the thermoelectric properties of FeGa3 and RuGa3 as n and p-type materials. The dimensionless figure of merit, ZT, was significantly improved by substitution of Sn for Ga in FeGa3 (electron-doping) and by substitution of Zn for Ga in RuGa3 (hole-doping), mainly as a result of optimization of the electronic part, S 2 σ.

  2. Correlation between valence electronic structure and magnetic properties in RCo5 (R = rare earth) intermetallic compound

    NASA Astrophysics Data System (ADS)

    Zhi-Qin, Xue; Yong-Quan, Guo

    2016-06-01

    The magnetisms of RCo5 (R = rare earth) intermetallics are systematically studied with the empirical electron theory of solids and molecules (EET). The theoretical moments and Curie temperatures agree well with experimental ones. The calculated results show strong correlations between the valence electronic structure and the magnetic properties in RCo5 intermetallic compounds. The moments of RCo5 intermetallics originate mainly from the 3d electrons of Co atoms and 4f electrons of rare earth, and the s electrons also affect the magnetic moments by the hybridization of d and s electrons. It is found that moment of Co atom at 2c site is higher than that at 3g site due to the fact that the bonding effect between R and Co is associated with an electron transformation from 3d electrons into covalence electrons. In the heavy rare-earth-based RCo5 intermetallics, the contribution to magnetic moment originates from the 3d and 4f electrons. The covalence electrons and lattice electrons also affect the Curie temperature, which is proportional to the average moment along the various bonds. Project supported by the National Natural Science Foundation of China (Grant No. 11274110).

  3. Photoemission Study of the Rare Earth Intermetallic Compounds: RNi2Ge2 (R=Eu, Gd)

    SciTech Connect

    Jongik Park

    2004-12-19

    EuNi{sub 2}Ge{sub 2} and GdNi{sub 2}Ge{sub 2} are two members of the RT{sub 2}X{sub 2} (R = rare earth, T = transition metal and X = Si, Ge) family of intermetallic compounds, which has been studied since the early 1980s. These ternary rare-earth intermetallic compounds with the tetragonal ThCr{sub 2}Si{sub 2} structure are known for their wide variety of magnetic properties, Extensive studies of the RT{sub 2}X{sub 2} series can be found in Refs [ 1,2,3]. The magnetic properties of the rare-earth nickel germanides RNi{sub 2}Ge{sub 2} were recently studied in more detail [4]. The purpose of this dissertation is to investigate the electronic structure (both valence band and shallow core levels) of single crystals of EuNi{sub 2}Ge{sub 2} and GdNi{sub 2}Ge{sub 2} and to check the assumptions that the f electrons are non-interacting and, consequently, the rigid-band model for these crystals would work [11], using synchrotron radiation because, to the best of our knowledge, no photoemission measurements on those have been reported. Photoemission spectroscopy has been widely used to study the detailed electronic structure of metals and alloys, and especially angle-resolved photoemission spectroscopy (ARPES) has proven to be a powerful technique for investigating Fermi surfaces (FSs) of single-crystal compounds.

  4. Influence of magnetic fluctuations in the magnetocaloric effect on rare-earth intermetallic compounds

    NASA Astrophysics Data System (ADS)

    Álvarez, P.; Gorria, P.; Blanco, J. A.

    2011-07-01

    A theoretical model including both crystal-field and exchange interactions that considers the effect of magnetic fluctuations is developed to evaluate the temperature dependence of the isothermal magnetic entropy changes in ferromagnetic rare-earth-based intermetallic compounds. The Green’s functions are derived from their equation of motion. The magnetic moment correlation functions are determined beyond the random phase approximation by incorporating a measure of magnetic spontaneous fluctuations in a way that ensures self-consistency with regard to the fluctuation-dissipation theorem. In particular, the exact magnitude of the entropy change without magnetic moment fluctuations depends on the ratio of both the crystal-field first- and the crystal-field third-order magnetic susceptibilities at the Curie temperature, TC. These theoretical predictions are compared with experimental data on cubic RM2 (R=rareearth and M=Al and Ni) compounds, where the principal crystal-field and exchange parameters are well known.

  5. A review on the synthesis, crystal growth, structure and physical properties of rare earth based quaternary intermetallic compounds

    NASA Astrophysics Data System (ADS)

    Mumbaraddi, Dundappa; Sarkar, Sumanta; Peter, Sebastian C.

    2016-04-01

    This review highlights the synthesis and crystal growth of quaternary intermetallic compounds based on rare earth metals. In the first part of this review, we highlight briefly about intermetallics and their versatile properties in comparison to the constituent elements. In the next part, we have discussed about various synthesis techniques with more focus on the metal flux technique towards the well shaped crystal growth of novel compounds. In the subsequent parts, several disordered quaternary compounds have been reviewed and then outlined most known ordered quaternary compounds with their complex structure. A special attention has been given to the ordered compounds with structural description and relation to the parent binary and ternary compounds. The importance of electronic and structural feature is highlighted as the key roles in designing these materials for emerging applications.

  6. Review of magnetic properties and magnetocaloric effect in the intermetallic compounds of rare earth with low boiling point metals

    NASA Astrophysics Data System (ADS)

    Ling-Wei, Li

    2016-03-01

    The magnetocaloric effect (MCE) in many rare earth (RE) based intermetallic compounds has been extensively investigated during the last two decades, not only due to their potential applications for magnetic refrigeration but also for better understanding of the fundamental problems of the materials. This paper reviews our recent progress on studying the magnetic properties and MCE in some binary or ternary intermetallic compounds of RE with low boiling point metal(s) (Zn, Mg, and Cd). Some of them exhibit promising MCE properties, which make them attractive for low temperature magnetic refrigeration. Characteristics of the magnetic transition, origin of large MCE, as well as the potential application of these compounds are thoroughly discussed. Additionally, a brief review of the magnetic and magnetocaloric properties in the quaternary rare earth nickel boroncarbides RENi2B2C superconductors is also presented. Project supported by the National Natural Science Foundation of China (Grant Nos. 11374081 and 11004044), the Fundamental Research Funds for the Central Universities, China (Grant Nos. N150905001, L1509006, and N140901001), the Japan Society for the Promotion of Science Postdoctoral Fellowships for Foreign Researchers (Grant No. P10060), and the Alexander von Humboldt (AvH) Foundation (Research stipend to L. Li).

  7. Synthesis of Xenon and Iron/Nickel Intermetallic Compounds Under the Thermodynamic Conditions of the Earth's Core.

    NASA Astrophysics Data System (ADS)

    Stavrou, E.; Zaug, J. M.; Crowhurst, J.; Lobanov, S.; Goncharov, A. F.; Prakapenka, V.; Prescher, C.; Yao, Y.; Liu, H.; Dai, Z.; Oleynik, I.; Steele, B.; Cong, K. N.

    2015-12-01

    The lower Xe abundance in Earth's atmosphere, in comparison to other noble gases like Ar and Kr, is one of the most challenging open questions in geosciences [1]. The origin of the so-called "missing Xe paradox" is usually attributed to the inclusion of Xe in the interior of Earth[2]. Although Xe is known to form compounds (e.g. with hydrogen, oxygen), none of them can be related with Earth's interior. Indeed, only a very low amount of Xe can be incorporated in silica at <1 GPa and 500K [3]. On the other hand, experimental attempts have failed to trace possible formation of Fe-Xe compounds up to 155 GPa and bellow 2500K [4]. A very recent theoretical study, suggests that Xe-Ni and Xe-Fe compounds can form at thermodynamic conditions representative of Earth's outer core [5]. Here we explored the possible formation of stable compounds in the Xe-Fe/Ni system at thermodynamic conditions representative of Earth's outer core starting from the following mixtures: a) Xe-Fe, b) Xe-Ni and c) Xe and an Fe/Ni alloy representative of Earth's core (ca 6% Ni). Using in situ synchrotron X-ray diffraction and Raman spectroscopy we report the formation of: a) a XeNi3 compound, in the form of a CrNi3-type FCC solid solution, above 150 GPa and 1500K, b) a Xe(Fe/Ni)3 compound, tentatively characterized as an orthorhombic NbPd3-type solid solution, above 190 GPa and 2000K and c) a still not completely characterized XeFexcompound above 180 GPa and 2000K. This work provides a plausible explanation of the "missing Xe paradox", and underscores the importance of understanding the novel rules of high-pressure chemistry for an improved understanding of the structure and chemistry of the Earth's core. [1] E. Anders, E. and T. Owen, Science 198, 453 (1977). [2] Caldwell, W. A. et al.,Science 277, 930 (1997). [3] C. Sanloup et al.,Science 310, 1174(2005). [4] D. Nishio-Hamane et al.,Geophys. Res. Lett. 37, L04302 (2010). [5] L. Zhu et al., Nature chemistry 6, 664 (2014).

  8. New twisted intermetallic compound superconductor: A concept

    NASA Technical Reports Server (NTRS)

    Coles, W. D.; Brown, G. V.; Laurence, J. C.

    1972-01-01

    Method for processing Nb3Sn and other intermetallic compound superconductors produces a twisted, stabilized wire or tube which can be used to wind electromagnetics, armatures, rotors, and field windings for motors and generators as well as other magnetic devices.

  9. Magnetic properties and structure of nonstoichiometric rare-earth transition-metal intermetallic compounds TbNi2Mn x (0 ≤ x ≤ 1.5)

    NASA Astrophysics Data System (ADS)

    Mushnikov, N. V.; Gaviko, V. S.; Gerasimov, E. G.; Terent'ev, P. B.; Tkach, I. A.

    2010-09-01

    Crystal structure, magnetization, coercive force, magnetic susceptibility, and anisotropic magnetostriction of nonstoichiometric rare-earth transition-metal intermetallic compounds TbNi2Mn x (0 ≤ x ≤ 1.5) have been studied. The samples with x ≤ 1 have an fcc structure, whereas TbNi2Mn1.25 has a rhombohedral structure of the PuNi3 type. It has been found that the magnetic ordering temperature increases sharply when manganese is added. As the Mn concentration grows, the magnetization and the magnetostriction decrease monotonically, while the coercive force increases. The experimental data obtained have been interpreted on the assumption that a partial substitution of manganese for terbium in TbNi2Mn x leads to local distortions of the crystal field acting on Tb ions, to the appearance of a local uniaxial random anisotropy, and to the formation of a noncollinear magnetic structure in the terbium sublattice.

  10. Comments on the thermoelectric power of intermetallic rare-earth compounds with well localized 4f shells

    NASA Astrophysics Data System (ADS)

    Szukiel, A. E.

    2016-05-01

    The anomalous temperature variation of the thermoelectric power in the metallic rare-earth compounds with well-localized 4f shells is sometimes interpreted as resulting from the conduction electrons scattering in the Born approximation on the acoustic phonons and on the localized spins in the s-f exchange interaction. Such an interpretation relies on the results of some theoretical works where the sign reversal and the maxima of the thermoelectric power were obtained within these simple models. In the present paper we prove that neither the electron-phonon scattering nor the magnetic s-f scattering in the Born approximation (nor both of them) do lead to the effects mentioned above.

  11. Chemical effect on diffusion in intermetallic compounds

    NASA Astrophysics Data System (ADS)

    Chen, Yi-Ting

    With the trend of big data and the Internet of things, we live in a world full of personal electronic devices and small electronic devices. In order to make the devices more powerful, advanced electronic packaging such as wafer level packaging or 3D IC packaging play an important role. Furthermore, ?-bumps, which connect silicon dies together with dimension less than 10 ?m, are crucial parts in advanced packaging. Owing to the dimension of ?-bumps, they transform into intermetallic compound from tin based solder after the liquid state bonding process. Moreover, many new reliability issues will occur in electronic packaging when the bonding materials change; in this case, we no longer have tin based solder joint, instead, we have intermetallic compound ?-bumps. Most of the potential reliability issues in intermetallic compounds are caused by the chemical reactions driven by atomic diffusion in the material; thus, to know the diffusivities of atoms inside a material is significant and can help us to further analyze the reliability issues. However, we are lacking these kinds of data in intermetallic compound because there are some problems if used traditional Darken's analysis. Therefore, we considered Wagner diffusivity in our system to solve the problems and applied the concept of chemical effect on diffusion by taking the advantage that large amount of energy will release when compounds formed. Moreover, by inventing the holes markers made by Focus ion beam (FIB), we can conduct the diffusion experiment and obtain the tracer diffusivities of atoms inside the intermetallic compound. We applied the technique on Ni3Sn4 and Cu3Sn, which are two of the most common materials in electronic packaging, and the tracer diffusivities are measured under several different temperatures; moreover, microstructure of the intermetallic compounds are investigated to ensure the diffusion environment. Additionally, the detail diffusion mechanism was also discussed in aspect of diffusion

  12. Oxygen stabilized zirconium vanadium intermetallic compound

    DOEpatents

    Mendelsohn, Marshall H.; Gruen, Dieter M.

    1982-01-01

    An oxygen stabilized intermetallic compound having the formula Zr.sub.x OV.sub.y where x=0.7 to 2.0 and y=0.18 to 0.33. The compound is capable of reversibly sorbing hydrogen at temperatures from -196.degree. C. to 450.degree. C. at pressures down to 10.sup.-6 Torr. The compound is also capable of selectively sorbing hydrogen from gaseous mixtures in the presence of CO and CO.sub.2.

  13. Forging of FeAl intermetallic compounds

    SciTech Connect

    Flores, O.; Juarez, J.; Campillo, B.; Martinez, L.; Schneibel, J.H.

    1994-09-01

    Much activity has been concentrated on the development of intermetallic compounds with the aim of improving tensile ductility, fracture toughness and high notch sensitivity in order to develop an attractive combination of properties for high and low temperature applications. This paper reports experience in processing and forging of FeAl intermetallic of B2 type. During the experiments two different temperatures were employed, and the specimens were forged after annealing in air, 10{sup {minus}2} torr vacuum and argon. From the results it was learned that annealing FeAl in argon atmosphere prior to forging resulted in better deformation behavior than for the other two environments. For the higher forging temperature used in the experiments (700C), the as-cast microstructure becomes partially recrystallized.

  14. Magnetic field controlled FZ single crystal growth of intermetallic compounds

    NASA Astrophysics Data System (ADS)

    Hermann, R.; Behr, G.; Gerbeth, G.; Priede, J.; Uhlemann, H.-J.; Fischer, F.; Schultz, L.

    2005-02-01

    Intermetallic rare-earth-transition-metal compounds with their coexistence of magnetic ordering and superconductivity are still of great scientific interest. The crystal growth of bulk single crystals is very often unsuccessful due to an unfavorable solid-liquid interface geometry enclosing concave fringes. The aim of the work is the contactless control of heat and material transport during floating-zone single crystal growth of intermetallic compounds. This control is provided by a tailored design of the electromagnetic field and the resulting electromagnetically driven convection. Numerical simulations for the determination of the electromagnetic field configuration induced by the RF heater coil and the solution of the coupled heat and hydrodynamic equations were done for the model substance Ni with and without additional magnetic field. As a result, an innovative magnetic two-phase stirrer system has been developed which enables the controlled influence on the melt ranging from intensive inwards/outwards flows to flows almost at rest. The selection of parameters necessary for the desired fluid flow is determined from numerical simulation. The basis for the calculations are the process-related fluid flow conditions which are determined by the mode of heating, heat radiation at the free surface and material parameters. This treatment of the problem leads to the customised magnetic field for the special intermetallic compound. The application of the new magnetic system leads to a distinct improvement of the solid-liquid interface validated on experiments with the model substance Nickel.

  15. SYNTHESIS AND CHARACTERIZATION OF NEW INTERMETALLIC COMPOUNDS

    SciTech Connect

    Professor Monica Sorescu

    2003-05-07

    This six-month work is focused mainly on the properties of novel magnetic intermetallics. In the first project, we synthesized several 2:17 intermetallic compounds, namely Nd{sub 2}Fe{sub 15}Si{sub 2}, Nd{sub 2}Fe{sub 15}Al{sub 2}2, Nd{sub 2}Fe{sub 15}SiAl and Nd{sub 2}Fe{sub 15}SiMn, as well as several 1:12 intermetallic compounds, such as NdFe{sub 10}Si{sub 2}, NdFe{sub 10}Al{sub 2}, NdFe{sub 10}SiAl and NdFe{sub 10}MnAl. In the second project, seven compositions of Nd{sub x}Fe{sub 100-x-y}B{sub y} ribbons were prepared by a melt spinning method with Nd and B content increasing from 7.3 and 3.6 to 11 and 6, respectively. The alloys were annealed under optimized conditions to obtain a composite material consisting of the hard magnetic Nd{sub 2}Fe{sub 14}B and soft magnetic {alpha}-Fe phases, typical of a spring magnet structure. In the third project, intermetallic compounds of the type Zr{sub 1}Cr{sub 1}Fe{sub 1}T{sub 0.8} with T=Al, Co and Fe were subjected to hydrogenation. In the fourth project, we performed three crucial experiments. In the first experiment, we subjected a mixture of Fe{sub 3}O{sub 4} and Fe(80-20 wt%) to mechanochemical activation by high-energy ball milling, for time periods ranging from 0.5 to 14 hours. In the second experiment, we ball-milled Fe{sub 3}O{sub 4}:Co{sup 2+} (x=0.1) for time intervals between 2.5 and 17.5 hours. Finally, we exposed a mixture of Fe{sub 3}O{sub 4} and Co(80-20 wt%) to mechanochemical activation for time periods ranging from 0.5 to 10 hours. In all cases, the structural and magnetic properties of the systems involved were elucidated by X-ray diffraction (XRD), Moessbauer spectroscopy and hysteresis loop measurements. The four projects resulted in four papers, which are currently being considered for publication in Intermetallics, IEEE Transactions on Magnetics, Journal of Materials Science Letters and Journal of Materials Science. The contributions reveal for the first time in literature the effect of

  16. Roles of Titanium-Intermetallic Compound Layer

    NASA Astrophysics Data System (ADS)

    Lee, Chii-Chang

    Four different configurations have been tested: Al-Cu, Ti/Al-Cu, Al-Cu/Ti, and Ti/Al-Cu/Ti to evaluate the possible contributions of Ti-intermetallic compound layer(s) to enhancement of the lifetime to failure. Basically, the proposed mechanisms can be classified into two groups: shunting effect and effects limited to changes in Al-Cu conducting layer(s). A resistance monitoring technique was adopted to supplement lifetime measurement to separate these two effects. By correlating the first resistance jump (spike) to the happening of a complete open across Al-Cu layer, it was found that the shunting effect contributes to enhancement of the lifetime by 4 times in Ti/Al-Cu, 2 times in Al-Cu/Ti, and 2 times in Ti/Al-Cu/Ti. A Ti underlayer was found to contribute mainly the shunting effect. However, from drift velocity measurements and failure mode analysis, it is possible to deduce that a Ti overlayer contributes not only the shunting effect but also another effect that acts to diminish the grain boundary mass transport rate by a factor of about 76. It is believed that the latter effect is a consequence of the high compressive yield stength conferred by the Ti-intermetallic compound overlayer to the Al-Cu layer. Finally, an important non-destructive technique, based on the characteristic x-rays generated by energetic electrons, to characterize the mass divergences in multilayer interconnects, was developed in this research, called SMEISIS, representing Simultaneous Multiple Elements Intensity Scanning of Interconnecting Stripes. This technique was proved to be capable of revealing detail about the shapes, nature, and location of mass divergence that cannot be revealed by thermal wave image technique and that requires time consuming multiple sectioning in TEM and SEM methods.

  17. Driving magnetostructural transitions in layered intermetallic compounds.

    PubMed

    Wang, J L; Caron, L; Campbell, S J; Kennedy, S J; Hofmann, M; Cheng, Z X; Din, M F Md; Studer, A J; Brück, E; Dou, S X

    2013-05-24

    We report the dramatic effect of applied pressure and magnetic field on the layered intermetallic compound Pr(0.5)Y(0.5)Mn(2)Ge(2). In the absence of pressure or magnetic field this compound displays interplanar ferromagnetism at room temperature and undergoes an isostructural first order magnetic transition (FOMT) to an antiferromagnetic state below 158 K, followed by another FOMT at 50 K due to the reemergence of ferromagnetism as praseodymium orders (T(C)(Pr)). The application of a magnetic field drives these two transitions towards each other, whereas the application of pressure drives them apart. Pressure also produces a giant magnetocaloric effect such that a threefold increase of the entropy change associated with the lower FOMT (at T(C)(Pr)) is seen under a pressure of 7.5 kbar. First principles calculations, using density functional theory, show that this remarkable magnetic behavior derives from the strong magnetoelastic coupling of the manganese layers in this compound. PMID:23745927

  18. SrZn2Sn2 and Ca2Zn3Sn6 — two new Ae-Zn-Sn polar intermetallic compounds (Ae: alkaline earth metal)

    NASA Astrophysics Data System (ADS)

    Stegmaier, Saskia; Fässler, Thomas F.

    2012-08-01

    SrZn2Sn2 and Ca2Zn3Sn6, two closely related new polar intermetallic compounds, were obtained by high temperature reactions of the elements. Their crystal structures were determined with single crystal XRD methods, and their electronic structures were analyzed by means of DFT calculations. The Zn-Sn structure part of SrZn2Sn2 comprises (anti-)PbO-like {ZnSn4/4} and {SnZn4/4} layers. Ca2Zn3Sn6 shows similar {ZnSn4/4} layers and {Sn4Zn} slabs constructed of a covalently bonded Sn scaffold capped by Zn atoms. For both phases, the two types of layers are alternatingly stacked and interconnected via Zn-Sn bonds. SrZn2Sn2 adopts the SrPd2Bi2 structure type, and Ca2Zn3Sn6 is isotypic to the R2Zn3Ge6 compounds (R=La, Ce, Pr, Nd). Band structure calculations indicate that both SrZn2Sn2 and Ca2Zn3Sn6 are metallic. Analyses of the chemical bonding with the electron localization function (ELF) show lone pair like basins at Sn atoms and Zn-Sn bonding interactions between the layers for both title phases, and covalent Sn-Sn bonding within the {Sn4Zn} layers of Ca2Zn3Sn6.

  19. Huge positive hyperfine fields for Sn impurity atoms on R sites of R T intermetallic compounds (R=rare-earth, T=Fe, Co)

    NASA Astrophysics Data System (ADS)

    Krylov, V. I.; Delyagin, N. N.

    2006-10-01

    The magnetic hyperfine field Bhf of the 119Sn impurity atom on the R site of the RFe 2 (R=Sm, Tb, Tm), TbCo 2, RCo 5 (R=Dy, Ho, Er), GdCo 3 and Gd 2Co 7 intermetallic compounds has been investigated by Mössbauer spectroscopy technique. At 5 K, very large hyperfine fields equal to 46-56 T were observed. The B values are several times larger than commonly observed for Sn in 3d-based magnetic hosts. The hyperfine fields are positive (that is parallel to the 3d magnetic moments direction). The results can be interpreted qualitatively in terms of the theory proposed for the impurity atoms in homogeneous ferromagnetic hosts [J. Kanamori, H. Katayama-Yoshida, K. Terakura, Hyperfine Interact. 8 (1981) 573; J. Kanamori, H. Katayama-Yoshida, K. Terakura, Hyperfine Interact. 9 (1981) 363; M. Akai, H. Akai, J. Kanamori, J. Phys. Soc. Jpn. 54 (1985) 4246; S. Blügel, H. Akai, R. Zeller, P.H. Dederichs, Phys. Rev. B 35 (1987) 3271], when it is considered that the splitting between bonding and antibonding hybrid states is strongly dependent on the interatomic distance. As the distance between the probe atom and neighboring magnetic atoms increases, the population of the antibonding states grows and, as a consequence, the corresponding positive contribution to the B increases sharply. For Sn atom the positive contribution to the B dominates when the interatomic distance exceeds 0.28-0.29 nm.

  20. First-principles studies of Al-Ni intermetallic compounds

    SciTech Connect

    Shi Dongmin; Wen Bin; Melnik, Roderick; Yao Shan; Li Tingju

    2009-10-15

    The structural properties, heats of formation, elastic properties, and electronic structures of Al-Ni intermetallic compounds are analyzed here in detail by using density functional theory. Higher calculated absolute values of heats of formation indicate a very strong chemical interaction between Al and Ni for all Al-Ni intermetallic compounds. According to the computational single crystal elastic constants, all the Al-Ni intermetallic compounds considered here are mechanically stable. The polycrystalline elastic modulus and Poisson's ratio have been deduced by using Voigt, Reuss, and Hill (VRH) approximations, and the calculated ratio of shear modulus to bulk modulus indicated that AlNi, Al{sub 3}Ni, AlNi{sub 3} and Al{sub 3}Ni{sub 5} compounds are ductile materials, but Al{sub 4}Ni{sub 3} and Al{sub 3}Ni{sub 2} are brittle materials. With increasing Ni concentration, the bulk modulus of Al-Ni intermetallic compounds increases in a linear manner. The electronic energy band structures confirm that all Al-Ni intermetallic compounds are conductors. - Graphical abstract: Calculated bulk modulus compared to experimental and other theoretical values for the Al-Ni intermetallic compounds.

  1. Containerless automated processing of intermetallic compounds and composites

    NASA Technical Reports Server (NTRS)

    Johnson, D. R.; Joslin, S. M.; Reviere, R. D.; Oliver, B. F.; Noebe, R. D.

    1993-01-01

    An automated containerless processing system has been developed to directionally solidify high temperature materials, intermetallic compounds, and intermetallic/metallic composites. The system incorporates a wide range of ultra-high purity chemical processing conditions. The utilization of image processing for automated control negates the need for temperature measurements for process control. The list of recent systems that have been processed includes Cr, Mo, Mn, Nb, Ni, Ti, V, and Zr containing aluminides. Possible uses of the system, process control approaches, and properties and structures of recently processed intermetallics are reviewed.

  2. Magnetocaloric effect of RM2 (R = rare earth, M = Ni, Al) intermetallic compounds made by centrifugal atomization process for magnetic refrigerator

    NASA Astrophysics Data System (ADS)

    Matsumoto, K.; Asamato, K.; Nishimura, Y.; Zhu, Y.; Abe, S.; Numazawa, T.

    2012-12-01

    RM2 (R = rare earth, M = Al, Ni and Co) compounds have large entropy change and magnetic transition temperatures can be controlled by change of R and/or M so that are suitable to a magnetic refrigerator for hydrogen liquefaction under development. In order to improve refrigerator performance, spherical powdered HoAl2, DyAl2, and GdNi2 compounds with submillimeter diameter were synthesized by centrifugal atomization process. By measuring the magnetization and heat capacity, we obtained entropy change by magnetic fields and entropy as functions of temperature and magnetic field, which are essential for analysing the magnetic refrigeration cycle. All samples showed sharp magnetic transitions and had good potentials for use in magnetic refrigeration.

  3. First-principles studies of Ni-Ta intermetallic compounds

    SciTech Connect

    Zhou Yi; Wen Bin; Ma Yunqing; Melnik, Roderick; Liu Xingjun

    2012-03-15

    The structural properties, heats of formation, elastic properties, and electronic structures of Ni-Ta intermetallic compounds are investigated in detail based on density functional theory. Our results indicate that all Ni-Ta intermetallic compounds calculated here are mechanically stable except for P21/m-Ni{sub 3}Ta and hc-NiTa{sub 2}. Furthermore, we found that Pmmn-Ni{sub 3}Ta is the ground state stable phase of Ni{sub 3}Ta polymorphs. The polycrystalline elastic modulus has been deduced by using the Voigt-Reuss-Hill approximation. All Ni-Ta intermetallic compounds in our study, except for NiTa, are ductile materials by corresponding G/K values and poisson's ratio. The calculated heats of formation demonstrated that Ni{sub 2}Ta are thermodynamically unstable. Our results also indicated that all Ni-Ta intermetallic compounds analyzed here are conductors. The density of state demonstrated the structure stability increases with the Ta concentration. - Graphical abstract: Mechanical properties and formation heats of Ni-Ta intermetallic compounds are discussed in detail in this paper. Highlights: Black-Right-Pointing-Pointer Ni-Ta intermetallic compounds are investigated by first principle calculations. Black-Right-Pointing-Pointer P21/m-Ni{sub 3}Ta and hc-NiTa{sub 2} are mechanically unstable phases. Black-Right-Pointing-Pointer Pmmn-Ni{sub 3}Ta is ground stable phase of Ni{sub 3}Ta polymorphs. Black-Right-Pointing-Pointer All Ni-Ta intermetallic compounds are conducting materials.

  4. Theoretical screening of intermetallic ThMn12-type phases for new hard-magnetic compounds with low rare earth content

    NASA Astrophysics Data System (ADS)

    Körner, Wolfgang; Krugel, Georg; Elsässer, Christian

    2016-04-01

    We report on theoretical investigations of intermetallic phases derived from the ThMn12-type crystal structure. Our computational high-throughput screening (HTS) approach is extended to an estimation of the anisotropy constant K1, the anisotropy field Ha and the energy product (BH)max. The calculation of K1 is fast since it is based on the crystal field parameters and avoids expensive total-energy calculations with many k-points. Thus the HTS approach allows a very efficient search for hard-magnetic materials for which the magnetization M and the coercive field Hc connected to Ha represent the key quantities. Besides for NdFe12N which has the highest magnetization we report HTS results for several intermetallic phases based on Cerium which are interesting as alternative hard-magnetic phases because Cerium is a less ressource-critical element than Neodymium.

  5. Theoretical screening of intermetallic ThMn12-type phases for new hard-magnetic compounds with low rare earth content

    PubMed Central

    Körner, Wolfgang; Krugel, Georg; Elsässer, Christian

    2016-01-01

    We report on theoretical investigations of intermetallic phases derived from the ThMn12-type crystal structure. Our computational high-throughput screening (HTS) approach is extended to an estimation of the anisotropy constant K1, the anisotropy field Ha and the energy product (BH)max. The calculation of K1 is fast since it is based on the crystal field parameters and avoids expensive total-energy calculations with many k-points. Thus the HTS approach allows a very efficient search for hard-magnetic materials for which the magnetization M and the coercive field Hc connected to Ha represent the key quantities. Besides for NdFe12N which has the highest magnetization we report HTS results for several intermetallic phases based on Cerium which are interesting as alternative hard-magnetic phases because Cerium is a less ressource-critical element than Neodymium. PMID:27098547

  6. Theoretical screening of intermetallic ThMn12-type phases for new hard-magnetic compounds with low rare earth content.

    PubMed

    Körner, Wolfgang; Krugel, Georg; Elsässer, Christian

    2016-01-01

    We report on theoretical investigations of intermetallic phases derived from the ThMn12-type crystal structure. Our computational high-throughput screening (HTS) approach is extended to an estimation of the anisotropy constant K1, the anisotropy field Ha and the energy product (BH)max. The calculation of K1 is fast since it is based on the crystal field parameters and avoids expensive total-energy calculations with many k-points. Thus the HTS approach allows a very efficient search for hard-magnetic materials for which the magnetization M and the coercive field Hc connected to Ha represent the key quantities. Besides for NdFe12N which has the highest magnetization we report HTS results for several intermetallic phases based on Cerium which are interesting as alternative hard-magnetic phases because Cerium is a less ressource-critical element than Neodymium. PMID:27098547

  7. First Principles Study of Al-Li Intermetallic Compounds

    NASA Astrophysics Data System (ADS)

    Yu, Hai-li; Duan, Xiao-hui; Ma, Yong-jun; Zeng, Min

    2012-12-01

    The structural properties, heats of formation, elastic properties, and electronic structures of four compositions of binary Al-Li intermetallics, Al3Li, AlLi, Al2Li3, and Al4Li9, are analyzed in detail by using density functional theory. The calculated formation heats indicate a strong chemical interaction between Al and Li for all the Al-Li intermetallics. In particular, in the Li-rich Al-Li compounds, the thermodynamic stability of intermetallics linearly decreases with increasing concentration of Li. According to the computational single crystal elastic constants, all the four Al-Li intermetallic compounds considered here are mechanically stable. The polycrystalline elastic modulus and Poisson's ratio have been deduced by using Voigt, Reuss, and Hill approximations, and the calculated ratios of bulk modulus to shear modulus indicate that the four compositions of binary Al-Li intermetallics are brittle materials. With the increase of Li concentration, the bulk modulus of Al-Li intermetallics decreases in a linear manner.

  8. PAC Studies on Zr-Based Intermetallic Compounds

    NASA Astrophysics Data System (ADS)

    Damonte, L. C.; Mendoza-Zélis, L. A.

    2004-11-01

    The Zr2Al, Zr3Al2 and Zr6NiAl2 intermetallic compounds were characterized by means of time differential perturbed angular correlation (TDPAC) and X-ray diffraction. Our interest in these Zr(Hf) aluminides comes from crystallization studies of Zr(Hf)-based bulk metallic glasses which have a wide supercooled liquid region.

  9. Unique intermetallic compounds prepared by shock wave synthesis

    NASA Technical Reports Server (NTRS)

    Otto, G.; Reece, O. Y.; Roy, U.

    1971-01-01

    Technique compresses fine ground metallic powder mixture beyond crystal fusion point. Absence of vapor pressure voids and elimination of incongruous effects permit application of technique to large scale fabrication of intermetallic compounds with specific characteristics, e.g., semiconduction, superconduction, or magnetic properties.

  10. Explosive reaction pressing of intermetallic compounds from stoichiometric powder mixtures

    SciTech Connect

    Kochsiek, D.; Pruemmer, R.; Brunold, A.

    1995-09-01

    Intermetallic NiAl, TiAl, and TiAl{sub 3} were synthesized by shock compression experiments from stoichiometric powder mixtures of nickel and aluminium as well as of titanium and aluminium. Good consolidation and complete intermetallic reaction were achieved by the direct method of explosive compaction. For each powder mixture, a certain individual threshold pressure has to be exceeded in order to initiate intermetallic reaction. The reacting compounds melted completely with subsequent rapid solidification during the passage of the shock wave. The new material shows high hardness. Pores are formed by gaseous reaction products in the NiAl and TiAl{sub 3} compacts. The TiAl structure is fully-dense and dendritic.

  11. Oxygen-stabilized zirconium-vanadium intermetallic compound

    DOEpatents

    Mendelsohn, M.H.; Gruen, D.M.

    1981-10-06

    An oxygen stabilized intermetallic compound having the formula Zr/sub x/OV/sub y/ where x = 0.7 to 2.0 and y = 0.18 to 0.33 is described. The compound is capable of reversibly sorbing hydrogen at temperatures from - 196/sup 0/C to 450/sup 0/C at pressures down to 10/sup -6/ Torr. The compound is also capable of selectively sorbing hydrogen from gaseous mixtures in the presence of CO and CO/sub 2/.

  12. Magnetism and superconductivity of uranium and intermetallic compounds

    SciTech Connect

    Cooley, J. C.; Gay, E. C.; Hanrahan, R. J.; Hults, W. L.; Lashley, J. C.; Manley, M. E.; McPheeters, C. C.; Schmiedeshoff, G. M.; Thoma, D. J.; Touton, S.; Smith, J. L.

    2001-01-01

    Heat capacity, resistivity, and phonon density of states have been measured on uranium and reported already. Many of the results are on single crystals of purity that has been unavailable before. Some intermetallic compounds have been measured that are in the class of so-called heavy-fermion materials. We present here the latest results along with a discussion of the occurrence of superconductivity or magnetism in these materials.

  13. Magnetic and magnetocaloric properties of the new rare-earth-transition-metal intermetallic compound Gd3Co29Ge4B10

    NASA Astrophysics Data System (ADS)

    Hill, P.; Dubenko, Igor; Samanta, Tapas; Quetz, Abdiel; Ali, Naushad

    2012-04-01

    The compounds Gd3-xYxCo29Ge4B10 (x = 0, 0.5, 1.0, 1.5, and 3.0), Gd3Co29Al4B10, and Gd3Co29Al4B10 were synthesized by arc melting, and their magnetic properties investigated as a function of temperature and applied magnetic field. X-ray measurements showed primarily single-phase samples with the tetragonal crystal structure P4/nmm. It was found that Gd3Co29Ge4B10 orders ferromagnetically at TC = 212 K and shows a compensation point at 128 K, indicating a ferrimagnetic ordering of the Co and Gd moments. An entropy change of -ΔS = 0.5 J/kgK was observed in a 5-T field at TC for this sample, while a change in sign for this quantity was observed both at the maximum value of magnetization (around 200 K) and then again at the compensation point. Substitution of Y for Gd in Gd3Co29Ge4B10 does not affect the Curie temperature, but shifts the compensation point to lower temperatures. This indicates that a decrease in Gd concentration does not affect the d-d exchange interaction, but has a pronounced effect on the f-d exchange interaction.

  14. Extreme Poisson's ratios and their electronic origin in B2 CsCl-type AB intermetallic compounds

    NASA Astrophysics Data System (ADS)

    Wang, X. F.; Jones, Travis E.; Li, W.; Zhou, Y. C.

    2012-04-01

    Negative Poisson's ratios have been observed in a variety of metals and alloys. However, the electronic origin of this effect remains unclear, as is evident by our limited knowledge about intermetallics showing this behavior. In an effort to clarify the electronic origin of a negative Poisson's ratio, we have performed a systematic and comprehensive study of extreme (both positive and negative) Poisson's ratios behavior in the B2 CsCl-type AB intermetallic family (including 14 common intermetallics and 128 rare-earth-metal transition or main-group-metal intermetallics) by way of density functional theory calculations. We found a pronounced correlation between the extreme Poisson's ratios and the elastic anisotropy, with approximately 70% of the B2 intermetallics showing intrinsic auxetic behavior. We went on to examine the topology and geometry of the electron charge density and found that the extreme Poisson's ratios are attributable to the directionality of the bonds of the material. Auxetic materials were found to have nondirectional bonds, and nonauxetic compounds had directional bonds. Our findings provide an essential electronic perspective to forecast the auxetic behavior, and suggest a new application for intermetallic compounds.

  15. Surfaces of complex intermetallic compounds: insights from density functional calculations.

    PubMed

    Hafner, Jürgen; Krajčí, Marian

    2014-11-18

    CONSPECTUS: Complex intermetallic compounds are a class of ordered alloys consisting of quasicrystals and other ordered compounds with large unit cells; many of them are approximant phases to quasicrystals. Quasicrystals are the limiting case where the unit cell becomes infinitely large; approximants are series of periodic structures converging to the quasicrystal. While the unique properties of quasicrystals have inspired many investigations of their surfaces, relatively little attention has been devoted to the surface properties of the approximants. In general, complex intermetallic compounds display rather irregular, often strongly corrugated surfaces, making the determination of their atomic structure a very complex and challenging task. During recent years, scanning tunneling microscopy (STM) has been used to study the surfaces of several complex intermetallic compounds. If atomic resolution can be achieved, STM permits visualization of the local atomistic surface structure. However, the interpretation of the STM images is often ambiguous and sometimes even impossible without a realistic model of the structure of the surface and the distribution of the electronic density above the surface. Here we demonstrate that ab initio density functional theory (DFT) can be used to determine the energetics and the geometric and electronic structures of the stable surfaces of complex intermetallic compounds. Calculations for surfaces with different chemical compositions can be performed in the grand canonical ensemble. Simulated cleavage experiments permit us to determine the formation of the cleavage planes requiring the lowest energy. The investigation of the adsorption of molecular species permits a comparison with temperature-programmed thermal desorption experiments. Calculated surface electronic densities of state can be compared with the results of photoelectron spectroscopy. Simulations of detailed STM images can be directly confronted with the experimental results

  16. Structural and Electronic Investigations of Complex Intermetallic Compounds

    SciTech Connect

    Ko, Hyunjin

    2008-01-01

    In solid state chemistry, numerous investigations have been attempted to address the relationships between chemical structure and physical properties. Such questions include: (1) How can we understand the driving forces of the atomic arrangements in complex solids that exhibit interesting chemical and physical properties? (2) How do different elements distribute themselves in a solid-state structure? (3) Can we develop a chemical understanding to predict the effects of valence electron concentration on the structures and magnetic ordering of systems by both experimental and theoretical means? Although these issues are relevant to various compound classes, intermetallic compounds are especially interesting and well suited for a joint experimental and theoretical effort. For intermetallic compounds, the questions listed above are difficult to answer since many of the constituent atoms simply do not crystallize in the same manner as in their separate, elemental structures. Also, theoretical studies suggest that the energy differences between various structural alternatives are small. For example, Al and Ga both belong in the same group on the Periodic Table of Elements and share many similar chemical properties. Al crystallizes in the fcc lattice with 4 atoms per unit cell and Ga crystallizes in an orthorhombic unit cell lattice with 8 atoms per unit cell, which are both fairly simple structures (Figure 1). However, when combined with Mn, which itself has a very complex cubic crystal structure with 58 atoms per unit cell, the resulting intermetallic compounds crystallize in a completely different fashion. At the 1:1 stoichiometry, MnAl forms a very simple tetragonal lattice with two atoms per primitive unit cell, while MnGa crystallizes in a complicated rhombohedral unit cell with 26 atoms within the primitive unit cell. The mechanisms influencing the arrangements of atoms in numerous crystal structures have been studied theoretically by calculating electronic

  17. Development of New Cryocooler Regenerator Materials-Ductile Intermetallic Compounds

    SciTech Connect

    K.A. Gschneidner; A.O. Pecharsky; V.K. Pecharsky

    2004-09-30

    The volumetric heat capacities of a number of binary and ternary Er- and Tm-based intermetallic compounds, which exhibited substantial ductilities, were measured from {approx}3 to {approx}350 K. They have the RM stoichiometry (where R = Er or Tm, and M is a main group or transition metal) and crystallize in the CsCl-type structure. The heat capacities of the Tm-based compounds are in general larger than the corresponding Er-based materials. Many of them have heat capacities which are significantly larger than those of the low temperature (<15 K) prototype cryocooler regenerator materials HoCu{sub 2}, Er{sub 3}Ni and ErNi. Utilization of the new materials as regenerators in the various cryocoolers should improve the performance of these refrigeration units for cooling below 15 K.

  18. SrZn{sub 2}Sn{sub 2} and Ca{sub 2}Zn{sub 3}Sn{sub 6} - two new Ae-Zn-Sn polar intermetallic compounds (Ae: alkaline earth metal)

    SciTech Connect

    Stegmaier, Saskia; Faessler, Thomas F.

    2012-08-15

    SrZn{sub 2}Sn{sub 2} and Ca{sub 2}Zn{sub 3}Sn{sub 6}, two closely related new polar intermetallic compounds, were obtained by high temperature reactions of the elements. Their crystal structures were determined with single crystal XRD methods, and their electronic structures were analyzed by means of DFT calculations. The Zn-Sn structure part of SrZn{sub 2}Sn{sub 2} comprises (anti-)PbO-like {l_brace}ZnSn{sub 4/4}{r_brace} and {l_brace}SnZn{sub 4/4}{r_brace} layers. Ca{sub 2}Zn{sub 3}Sn{sub 6} shows similar {l_brace}ZnSn{sub 4/4}{r_brace} layers and {l_brace}Sn{sub 4}Zn{r_brace} slabs constructed of a covalently bonded Sn scaffold capped by Zn atoms. For both phases, the two types of layers are alternatingly stacked and interconnected via Zn-Sn bonds. SrZn{sub 2}Sn{sub 2} adopts the SrPd{sub 2}Bi{sub 2} structure type, and Ca{sub 2}Zn{sub 3}Sn{sub 6} is isotypic to the R{sub 2}Zn{sub 3}Ge{sub 6} compounds (R=La, Ce, Pr, Nd). Band structure calculations indicate that both SrZn{sub 2}Sn{sub 2} and Ca{sub 2}Zn{sub 3}Sn{sub 6} are metallic. Analyses of the chemical bonding with the electron localization function (ELF) show lone pair like basins at Sn atoms and Zn-Sn bonding interactions between the layers for both title phases, and covalent Sn-Sn bonding within the {l_brace}Sn{sub 4}Zn{r_brace} layers of Ca{sub 2}Zn{sub 3}Sn{sub 6}. - Graphical abstract: Crystal structures of the new Ae-Zn-Sn polar intermetallic phases SrZn{sub 2}Sn{sub 2} and Ca{sub 2}Zn{sub 3}Sn{sub 6}. Highlights: Black-Right-Pointing-Pointer New polar intermetallic phases SrZn{sub 2}Sn{sub 2} and Ca{sub 2}Zn{sub 3}Sn{sub 6}. Black-Right-Pointing-Pointer Obtained by high temperature reactions of the elements. Black-Right-Pointing-Pointer Single crystal XRD structure determination and DFT electronic structure calculations. Black-Right-Pointing-Pointer Closely related crystal and electronic structures. Black-Right-Pointing-Pointer Metallic conductivity coexisting with lone pairs and covalent bonding

  19. Effects of elastic anisotropy on mechanical behavior of intermetallic compounds

    SciTech Connect

    Yoo, M.H.

    1991-01-01

    Fundamental aspects of the deformation and fracture behavior of ordered intermetallic compounds are examined within the framework of linear anisotropic elasticity theory of dislocations and cracks. The orientation dependence and the tension/compression asymmetry of yield stress are explained in terms of the anisotropic coupling effect of non-glide stresses to the glide strain. The anomalous yield behavior is related to the disparity (edge/screw) of dislocation mobility and the critical stress required for the dislocation multiplication mechanism of Frank-Read type. The slip-twin conjugate relationship, extensive faulting, and pseudo-twinning (martensitic transformation) at a crack tip can be enhanced also by the anisotropic coupling effect, which may lead to transformation toughening of shear type.

  20. Griffiths phase behaviour in a frustrated antiferromagnetic intermetallic compound

    PubMed Central

    Ghosh, Krishanu; Mazumdar, Chandan; Ranganathan, R.; Mukherjee, S.

    2015-01-01

    The rare coexistence of a Griffiths phase (GP) and a geometrically frustrated antiferromagnetism in the non-stoichiometric intermetallic compound GdFe0.17Sn2 (the paramagnetic Weiss temperature θp ~ −59 K) is reported in this work. The compound forms in the Cmcm space group with large structural anisotropy (b/c ~ 4). Interestingly, all the atoms in the unit cell possess the same point group symmetry (Wycoff position 4c), which is rather rare. The frustration parameter, f = |θp|/TN has been established as 3.6, with the Néel temperature TN and Griffiths temperature TG being 16.5 and 32 K, respectively. The TG has been determined from the heat capacity measurement and also from the magnetocaloric effect (MCE). It is also shown that substantial difference in GP region may exist between zero field and field cooled measurements - a fact hitherto not emphasized so far. PMID:26515256

  1. Magnetic Anisotropy and Crystalline Electric Field in Quaternary Intermetallic Compounds

    NASA Astrophysics Data System (ADS)

    Lee, W. C.

    All isostructural compounds RNi2B2C (R =Er, Ho, Dy) show some magnetic transitions in magnetization isotherms at certain applied magnetic fields and temperatures above and below Neel and superconducting temperatures (TN, TC) where TN/TC varies from 0.57 to 1.66 for ErNi2B2C and DyNi2B2C. By using theoretical group analysis of D4h (I4/mmm) to the energy level scheme of crystalline electric field of magnetization isotherms anisotropy at various temperatures, we have obtained some possible ground state energy levels such as singlet Γ4 and first excited doublet state Γ5 in addition to another excited singlet Γ1 . Our crystalline electric field energy scheme analysis shows some qualitative agreement between theoretical calculation and experiments at high magnetic fields regime only, which means the interplay between antiferromagnetsm and superconductivity should be included. Magnetic Anisotropy and Crystalline Electric Field in Quaternary Intermetallic Compounds.

  2. Rare-earth transition-metal intermetallics: Structure-bonding-property relationships

    SciTech Connect

    Han, M.K.

    2006-05-06

    The explorations of rare-earth, transition metal intermetallics have resulted in the synthesis and characterization, and electronic structure investigation, as well as understanding the structure-bonding property relationships. The work has presented the following results: (1) Understanding the relationship between compositions and properties in LaFe{sub 13-x}Si{sub x} system: A detailed structural and theoretical investigation provided the understanding of the role of a third element on stabilizing the structure and controlling the transformation of cubic NaZn{sub 13}-type structures to the tetragonal derivative, as well as the relationship between the structures and properties. (2) Synthesis of new ternary rare-earth iron silicides Re{sub 2-x}Fe{sub 4}Si{sub 14-y} and proposed superstructure: This compound offers complex structural challenges such as fractional occupancies and their ordering in superstructure. (3) Electronic structure calculation of FeSi{sub 2}: This shows that the metal-semiconductor phase transition depends on the structure. The mechanism of band gap opening is described in terms of bonding and structural distortion. This result shows that the electronic structure calculations are an essential tool for understanding the relationship between structure and chemical bonding in these compounds. (4) Synthesis of new ternary rare-earth Zinc aluminides Tb{sub 3}Zn{sub 3.6}Al{sub 7.4}: Partially ordered structure of Tb{sub 3}Zn{sub 3.6}Al{sub 7.4} compound provides new insights into the formation, composition and structure of rare-earth transition-metal intermetallics. Electronic structure calculations attribute the observed composition to optimizing metal-metal bonding in the electronegative (Zn, Al) framework, while the specific ordering is strongly influenced by specific orbital interactions. (5) Synthesis of new structure type of Zn{sub 39}(Cr{sub x}Al{sub 1-x}){sub 81}: These layered structures are similar to icosahedral Mn-Al quasicrystalline

  3. Rare-Earth Transition-Metal Intermetallics: Structure-bonding-Property Relationships

    SciTech Connect

    Mi-Kyung Han

    2006-05-01

    Our explorations of rare-earth, transition metal intermetallics have resulted in the synthesis and characterization, and electronic structure investigation, as well as understanding the structure-bonding-property relationships. Our work has presented the following results: (1) Understanding the relationship between compositions and properties in LaFe{sub 13-x}Si{sub x} system: A detailed structural and theoretical investigation provided the understanding of the role of a third element on stabilizing the structure and controlling the transformation of cubic NaZn{sub 13}-type structures to the tetragonal derivative, as well as the relationship between the structures and properties. (2) Synthesis of new ternary rare-earth iron silicides RE{sub 2-x}Fe{sub 4}Si{sub 14-y} and proposed superstructure: This compound offers complex structural challenges such as fractional occupancies and their ordering in superstructure. (3) Electronic structure calculation of FeSi{sub 2}: This shows that the metal-semiconductor phase transition depends on the structure. The mechanism of band gap opening is described in terms of bonding and structural distortion. This result shows that the electronic structure calculations are an essential tool for understanding the relationship between structure and chemical bonding in these compounds. (4) Synthesis of new ternary rare-earth Zinc aluminides Tb{sub 3}Zn{sub 3.6}Al{sub 7.4}: Partially ordered structure of Tb{sub 3}Zn{sub 3.6}Al{sub 7.4} compound provides new insights into the formation, composition and structure of rare-earth transition-metal intermetallics. Electronic structure calculations attribute the observed composition to optimizing metal-metal bonding in the electronegative (Zn, Al) framework, while the specific ordering is strongly influenced by specific orbital interactions. (5) Synthesis of new structure type of Zn{sub 39}(Cr{sub x}Al{sub 1-x}){sub 81}: These layered structures are similar to icosahedral Mn-Al quasicrystalline

  4. Magnetic and crystallographic structures in UTX intermetallic compounds

    SciTech Connect

    Robinson, R.A.; Lawson, A.C.; Sechovsky, V.; Havela, L.; Kergadallan, Y.; Nakotte, H.; de Boer, F.R.

    1993-08-01

    Uranium, along with other actinides and lanthanides, forms a large group of ternary intermetallic compounds of stoichiometry UTX (T = transition metal, X = p-electron metal). These compounds are formed in several structure types and the occurrence and stability of particular structures with respect to the transition metal content suggests reasonable systematics. The authors have also investigated the magnetic structures of selected UTX compounds and it is revealing to relate the crystallographic and magnetic structures, because of the relationship between the magnetic symmetry and that of the U-atom environment produced by the 5f-ligand hybridization, and the consequent anisotropic exchange. Those of ZrNiAl structure type are collinear, with moments along the hexagonal c-axis. In the orthorhombic NiSiTi structure type, the moments are confined to the b- c plane (perpendicular to the uranium chains) and the structures are often incommensurate. In the hexagonal CaIn{sub 2} (or GaGeLi) structure type, the magnetic structures form in an orthorhombic cell, and at least in the disordered centric group, again the moments lie perpendicular to the nearest-neighbor uranium spacing. This work presents a phenomenology of trends in UTX ternary compounds. It is shown that there is an apparent strong hybridization parallel to nearest neighbor U-U directions, with ferromagnetic coupling in the same directions. There may be a systematic relationship between the hybridization anisotropy and the magnetic anisotropy, in which the quantization axes are the same and the moments point along directions of relatively weak hybridization.

  5. Intermetallic compound formation at Cu-Al wire bond interface

    SciTech Connect

    Bae, In-Tae; Young Jung, Dae; Chen, William T.; Du Yong

    2012-12-15

    Intermetallic compound (IMC) formation and evolution at Cu-Al wire bond interface were studied using focused ion beam /scanning electron microscopy, transmission electron microscopy (TEM)/energy dispersive x-ray spectroscopy (EDS), nano beam electron diffraction (NBED) and structure factor (SF) calculation. It was found that discrete IMC patches were formed at the Cu/Al interface in as-packaged state and they grew toward Al pad after high temperature storage (HTS) environment at 150 Degree-Sign C. TEM/EDS and NBED results combined with SF calculation revealed the evidence of metastable {theta} Prime -CuAl{sub 2} IMC phase (tetragonal, space group: I4m2, a = 0.404 nm, c= 0.580 nm) formed at Cu/Al interfaces in both of the as-packaged and the post-HTS samples. Two feasible mechanisms for the formation of the metastable {theta} Prime -CuAl{sub 2} phase are discussed based on (1) non-equilibrium cooling of wire bond that is attributed to highly short bonding process time and (2) the epitaxial relationships between Cu and {theta} Prime -CuAl{sub 2}, which can minimize lattice mismatch for {theta} Prime -CuAl{sub 2} to grow on Cu.

  6. New Interest in Intermetallic Compound ZnSb

    NASA Astrophysics Data System (ADS)

    Fedorov, M. I.; Prokof'eva, L. V.; Pshenay-Severin, D. A.; Shabaldin, A. A.; Konstantinov, P. P.

    2014-06-01

    The intermetallic compound ZnSb has been known since the 1830s. It has semiconductor properties, but its mechanical, thermal, and chemical properties are very close to those of a metallic alloy. When thermoelectrics based on (BiSb)2(TeSe)3 solid solutions were created, interest in ZnSb subsided. However, the current situation is different, as tellurium has become expensive and rare. Moreover, its compounds are too toxic, and it is too difficult to produce such materials and devices from these solid solutions. Recently, n-type material based on Mg2(SnSi) solid solution was proposed in the Laboratory of Physics for Thermoelements of the Ioffe Physical-Technical Institute. This material together with ZnSb may form a promising couple for creating various thermoelectric modules. In this paper, various properties (Hall and Seebeck coefficients, electrical and thermal conductivities) are reported in the temperature range from 80 K to 797 K. Different acceptor impurities have been tested. The Hall concentration at room temperature varied from 1.5 × 1018 cm-3 to 2.7 × 1019 cm-3. Some features have been discovered in the behavior of the thermoelectric parameters of double-doped ZnSb samples at temperatures above 500 K. Their nature points to a temperature-dependent increase of the Hall concentration. The existence of two temperature ranges with additional doping is revealed by Hall coefficient and electrical conductivity measurements in the range from 80 K to 797 K. The experimental data are discussed based on a model of the energy spectrum with impurity and native defect states localized in the energy gap. It is shown that the dimensionless thermoelectric figure of merit of ZnSb: Cd, Ag, Sn is not less than 1.0 at 600 K.

  7. Identification and control of grinding processes for intermetallic compounds

    NASA Astrophysics Data System (ADS)

    Razavi, Hosein Ali

    2000-10-01

    An intermetallic compound (IMC) is a combination of two or more metals with a particular atomic formula by having either ionic and covalent bonds, or metallic bonds with specific crystal structures. They may be thought of as the intermediate between metals and ceramics. These new materials may combine the best of each class: the ductility, heat and electric conductivity of metals with the strength and oxidation resistance of ceramics. Previous study has proposed that the depth of plastic deformation can be used as a parameter to describe the influence of grinding conditions on other physical properties of subsurface layers. Accordingly, the indentation model has been developed to correlate the depth of plastic deformation with the normal component of grinding force. It has been reported that the under certain grinding conditions the depth of plastic deformation does not follow the indentation model. The primary objective of this research is to explain such deviations and to demonstrate that this model can be used to control and predict the depth of plastic deformation. Elements of this research include the development of an open architecture platform to study grinding process, a signal processing algorithm for gap elimination, introducing and implementation of model reference unfalsification and learning concept, development of a mathematical model for grinding gamma-TiAl, a comparison between conventional and superabrasive grinding, control and prediction of the depth of plastic deformation, and initiation of one of the first databases for grinding gamma-TiAl. This work not only serves as a step toward the use of IMCs in future technology but also serves as a step toward autonomous machining systems using intelligent control and advanced monitoring which is a feature of the future abrasive technology.

  8. Microwave assisted combustion synthesis of non-equilibrium intermetallic compounds.

    PubMed

    Veronesi, Paolo; Rosa, Roberto; Colombini, Elena; Leonelli, Cristina; Poli, Giorgio; Casagrande, Angelo

    2010-01-01

    A simplified model of the microwave-assisted combustion synthesis of Ni and Al metal powders to form the NiAl intermetallic on titanium and steel substrates is presented. The simulation couples an electro-thermal model with a chemical model, accounting for local heat generation due to the highly exothermic nature of the reactions between the powders. Numerical results, validated by experimental values, show that the capability of microwaves to convey energy, and not heat, can be used to alter the temperature profiles during and after the combustion synthesis, leading to unique intermetallic microstructures. This phenomenon is ascribed to the extended existence of high temperature liquid intermetallic phases, which react with the metallic substrates at the interface. Moreover, microwave heating selectivity allows to maintain the bulk of the substrate metallic materials to a much lower temperature, compared to combustion synthesis in conventionally heated furnaces, thus reducing possible unwanted transformations like phase change or oxidation. PMID:21721328

  9. Surface integrity on grinding of gamma titanium aluminide intermetallic compounds

    NASA Astrophysics Data System (ADS)

    Murtagian, Gregorio Roberto

    Gamma-TiAl is an ordered intermetallic compound characterized by high strength to density ratio, good oxidation resistance, and good creep properties at elevated temperatures. However, it is intrinsically brittle at room temperature. This thesis investigates the potential for the use of grinding to process TiAl into useful shapes. Grinding is far from completely understood, and many aspects of the individual mechanical interactions of the abrasive grit with the material and their effect on surface integrity are unknown. The development of new synthetic diamond superabrasives in which shape and size can be controlled raises the question of the influence of those variables on the surface integrity. The goal of this work is to better understand the fundamentals of the abrasive grit/material interaction in grinding operations. Experimental, analytical, and numerical work was done to characterize and predict the resultant deformation and surface integrity on ground lamellar gamma-TiAl. Grinding tests were carried out, by analyzing the effects of grit size and shape, workpiece speed, wheel depth of cut, and wear on the subsurface plastic deformation depth (PDD). A practical method to assess the PDD is introduced based on the measurement of the lateral material flow by 3D non-contact surface profilometry. This method combines the quantitative capabilities of the microhardness measurement with the sensitivity of Nomarski microscopy. The scope and limitations of this technique are analyzed. Mechanical properties were obtained by quasi-static and split Hopkinson bar compression tests. Residual stress plots were obtained by x-ray, and surface roughness and cracking were evaluated. The abrasive grit/material interaction was accounted by modeling the force per abrasive grit for different grinding conditions, and studying its correlation to the PDD. Numerical models of this interaction were used to analyze boundary conditions, and abrasive size effects on the PDD. An explicit 2D

  10. X-Ray Diffraction of Intermetallic Compounds: A Physical Chemistry Laboratory Experiment

    ERIC Educational Resources Information Center

    Varberg, Thomas D.; Skakuj, Kacper

    2015-01-01

    Here we describe an experiment for the undergraduate physical chemistry laboratory in which students synthesize the intermetallic compounds AlNi and AlNi3 and study them by X-ray diffractometry. The compounds are synthesized in a simple one-step reaction occurring in the solid state. Powder X-ray diffractograms are recorded for the two compounds…

  11. Electronic and high pressure elastic properties of RECd and REHg (RE=Sc, La and Yb) intermetallic compounds

    NASA Astrophysics Data System (ADS)

    Devi, Hansa; Pagare, Gitanjali; Chouhan, Sunil S.; Sanyal, Sankar P.

    2015-01-01

    Structural, electronic, elastic and mechanical properties of Cd and Hg based rare earth intermetallics (RECd and REHg; RE=Sc, La and Yb) have been investigated using the full-potential linearized augmented plane-wave (FP-LAPW) method within the density-functional theory (DFT). The ground state properties such as lattice constant (a0), bulk modulus (B) and its pressure derivative (B‧) have been obtained using optimization method and are found in good agreement with the available experimental results. The calculated enthalpy of formation shows that LaHg has the strongest alloying ability and structural stability. The electronic band structures and density of states reveal the metallic character of these compounds. The structural stability mechanism is also explained through the electronic structures of these compounds. The chemical bonding between rare earth atoms and Cd, Hg is interpreted by the charge density plots along (1 1 0) direction. The elastic constants are predicted from which all the related mechanical properties like Poisson's ratio (σ), Young's modulus (E), shear modulus (GH) and anisotropy factor (A) are calculated. The ductility/brittleness of these intermetallics is predicted. Chen's method has been used to predict the Vicker's hardness of RECd and REHg compounds. The pressure variation of the elastic constants is also reported in their B2 phase.

  12. Formation and nitridation of vanadium-aluminum intermetallic compounds.

    PubMed

    Lewalter, H; Bock, W; Kolbesen, B O

    2002-10-01

    V(5)Al(8) and V(3)Al intermetallics have been formed by interdiffusion, by annealing of sputtered V/Al-multilayers at 700 degrees C in vacuo; sapphire (102) was used as substrate. The V/Al intermetallics were nitridated in NH(3) at 900 degrees C for 1 min by RTP (rapid thermal processing). The samples were investigated with XRD (X-ray diffraction), SNMS (secondary neutral mass spectrometry), and AFM (atomic force microscopy). A 5-10 nm thick AlN film (001 textured) was formed by nitridation of V(5)Al(8) (110 textured) and 2-3% nitrogen was incorporated in the V(5)Al(8) bulk. Nitridation of V(3)Al resulted in the formation of VN and AlN. Direct nitridation of V/Al-multilayers showed that near the surface nitridation is faster than intermixing of the V and Al layers. The capability of VN as diffusion barrier for Al could also be shown. PMID:12397502

  13. Modeling of Intermetallic Compounds Growth Between Dissimilar Metals

    NASA Astrophysics Data System (ADS)

    Wang, Li; Wang, Yin; Prangnell, Philip; Robson, Joseph

    2015-09-01

    A model has been developed to predict growth kinetics of the intermetallic phases (IMCs) formed in a reactive diffusion couple between two metals for the case where multiple IMC phases are observed. The model explicitly accounts for the effect of grain boundary diffusion through the IMC layer, and can thus be used to explore the effect of IMC grain size on the thickening of the reaction layer. The model has been applied to the industrially important case of aluminum to magnesium alloy diffusion couples in which several different IMC phases are possible. It is demonstrated that there is a transition from grain boundary-dominated diffusion to lattice-dominated diffusion at a critical grain size, which is different for each IMC phase. The varying contribution of grain boundary diffusion to the overall thickening kinetics with changing grain size helps explain the large scatter in thickening kinetics reported for diffusion couples produced under different conditions.

  14. First-principle studies of Ca-X (X=Si,Ge,Sn,Pb) intermetallic compounds

    SciTech Connect

    Yang Zhiwen; Shi Dongmin; Wen Bin; Melnik, Roderick; Yao Shan; Li Tingju

    2010-01-15

    The structural properties, elastic properties, heats of formation, electronic structures, and densities of states of 20 intermetallic compounds in the Ca-X (X=Si, Ge, Sn, Pb) systems have been systematically investigated by using first-principle calculations. Our computational results indicated that with increasing atomic weight of X, the bulk modulus of Ca-X intermetallic compounds decreases gradually. It was also found that Ca{sub 36}Sn{sub 23} and CaPb are mechanically unstable phases. Results on the electronic energy band and densities of states also indicated that Ca{sub 3}Si{sub 4} is an indirect band gap semiconductor with a band gap of 0.598 eV, and Ca{sub 2}Si, Ca{sub 2}Ge, Ca{sub 2}Sn, and Ca{sub 2}Pb are direct band gap semiconductors with band gaps of 0.324, 0.265, 0.06, and 0.07 eV, respectively. In addition, it is found that the absolute values of heats of formation for all Ca-X intermetallics are larger than 30 kJ/mol atom. - Graphical abstract: Calculated (a) bulk moduli and (b) shear moduli of Ca-X system intermetallic compounds.

  15. Synthesis, Characterization and Properties of Nanoparticles of Intermetallic Compounds

    SciTech Connect

    DiSalvo, Francis J.

    2015-03-12

    The research program from 2010 to the end of the grant focused on understanding the factors important to the synthesis of single phase intermetallic nano-particles (NPs), their size, crystalline order, surface properties and electrochemical activity. The synthetic method developed is a co-reduction of mixtures of single metal precursors by strong, soluble reducing agents in a non-protic solvent, tetrahydrofuran (THF). With some exceptions, the particles obtained by room temperature reduction are random alloys that need to be annealed at modest temperatures (200 to 600 °C) in order to develop an ordered structure. To avoid significant particle size growth and agglomeration, the particles must be protected by surface coatings. We developed a novel method of coating the metal nanoparticles with KCl, a by-product of the reduction reaction if the proper reducing agents are employed. In that case, a composite product containing individual metal nanoparticles in a KCl matrix is obtained. The composite can be heated to at least 600 °C without significant agglomeration or growth in particle size. Washing the annealed product in the presence of catalyst supports in ethylene glycol removes the KCl and deposits the particles on the support. Six publications present the method and its application to producing and studying new catalyst/support combinations for fuel cell applications. Three publications concern the use of related methods to explore new lithium-sulfur battery concepts.

  16. Optical properties of Group X-XII intermetallic compounds studied by HR-EELS.

    PubMed

    Sato, Yohei; Terauchi, Masami; Kameoka, Satoshi; Tsai, An-Pang

    2014-11-01

    Electronic structure of d orbital states in transition metals is a key factor for their physical properties and chemical functions. Copper and intermetallic compound PdZn have good catalysis function for the methanol steam reforming reaction. Tsai et al. showed that from results of XPS measurements the d electronic structure of PdZn was similar with that of copper, and the catalysis function should be related to the d electron states [1]. This similarity of d electronic states leads to another view point of the mechanism for coloring the intermetallic compounds. It is well-known that the characteristic red color of copper is caused by interband transition from the d electrons. Therefore, PdZn and Group X-XII intermetallic compounds are expected to be colored and the optical properties should depend on the d electronic states. In this study, the relations between optical properties and d electron states of Group X-XII intermetallic compounds were investigated by using high energy-resolution electron energy-loss spectroscopy (HR-EELS) based on transmission electron microscopy (TEM). From the relation between optical properties and d electronic states, the mechanism of colored intermetallic compounds will be discussed.Figure shows the optical reflectivity of NiZn, PdZn and PtZn, which were derived from EELS spectra by Kramers-Kronig analysis. Intensity drops (arrows) of the reflectivity were observed in visible energy region. These are caused by the interband transitions from d electronic states. The energy positions of the reflectivity drops have tendency of shifting to higher energy side with increasing atomic number of Group X elements (Ni → Pd → Pt). This indicates that the transition energies of d electrons become larger with the atomic number of the elements. First principle calculations (WIEN2k) confirmed that the interband transitions of d electronic states were excitations from bonding d states to hybrid states of anti-bonding s, p, and d states of Group

  17. Increasing strength and conductivity of Cu alloy through abnormal plastic deformation of an intermetallic compound

    NASA Astrophysics Data System (ADS)

    Han, Seung Zeon; Lim, Sung Hwan; Kim, Sangshik; Lee, Jehyun; Goto, Masahiro; Kim, Hyung Giun; Han, Byungchan; Kim, Kwang Ho

    2016-08-01

    The precipitation strengthening of Cu alloys inevitably accompanies lowering of their electric conductivity and ductility. We produced bulk Cu alloys arrayed with nanofibers of stiff intermetallic compound through a precipitation mechanism using conventional casting and heat treatment processes. We then successfully elongated these arrays of nanofibers in the bulk Cu alloys to 400% of original length without breakage at room temperature using conventional rolling process. By inducing such an one-directional array of nanofibers of intermetallic compound from the uniform distribution of fine precipitates in the bulk Cu alloys, the trade-off between strength and conductivity and between strength and ductility could be significantly reduced. We observed a simultaneous increase in electrical conductivity by 1.3 times and also tensile strength by 1.3 times in this Cu alloy bulk compared to the conventional Cu alloys.

  18. Increasing strength and conductivity of Cu alloy through abnormal plastic deformation of an intermetallic compound

    PubMed Central

    Han, Seung Zeon; Lim, Sung Hwan; Kim, Sangshik; Lee, Jehyun; Goto, Masahiro; Kim, Hyung Giun; Han, Byungchan; Kim, Kwang Ho

    2016-01-01

    The precipitation strengthening of Cu alloys inevitably accompanies lowering of their electric conductivity and ductility. We produced bulk Cu alloys arrayed with nanofibers of stiff intermetallic compound through a precipitation mechanism using conventional casting and heat treatment processes. We then successfully elongated these arrays of nanofibers in the bulk Cu alloys to 400% of original length without breakage at room temperature using conventional rolling process. By inducing such an one-directional array of nanofibers of intermetallic compound from the uniform distribution of fine precipitates in the bulk Cu alloys, the trade-off between strength and conductivity and between strength and ductility could be significantly reduced. We observed a simultaneous increase in electrical conductivity by 1.3 times and also tensile strength by 1.3 times in this Cu alloy bulk compared to the conventional Cu alloys. PMID:27488621

  19. Increasing strength and conductivity of Cu alloy through abnormal plastic deformation of an intermetallic compound.

    PubMed

    Han, Seung Zeon; Lim, Sung Hwan; Kim, Sangshik; Lee, Jehyun; Goto, Masahiro; Kim, Hyung Giun; Han, Byungchan; Kim, Kwang Ho

    2016-01-01

    The precipitation strengthening of Cu alloys inevitably accompanies lowering of their electric conductivity and ductility. We produced bulk Cu alloys arrayed with nanofibers of stiff intermetallic compound through a precipitation mechanism using conventional casting and heat treatment processes. We then successfully elongated these arrays of nanofibers in the bulk Cu alloys to 400% of original length without breakage at room temperature using conventional rolling process. By inducing such an one-directional array of nanofibers of intermetallic compound from the uniform distribution of fine precipitates in the bulk Cu alloys, the trade-off between strength and conductivity and between strength and ductility could be significantly reduced. We observed a simultaneous increase in electrical conductivity by 1.3 times and also tensile strength by 1.3 times in this Cu alloy bulk compared to the conventional Cu alloys. PMID:27488621

  20. Estimation of the effective parameter of spinorbital interaction of electrons in intermetallic Er-In system compounds from the kinetic and magnetic properties

    NASA Astrophysics Data System (ADS)

    Kuvandikov, O. K.; Hamraev, N. S.; Razhabov, R. M.; Éshkulov, A. A.

    2012-05-01

    Normal, R 0 and anomalous, R S components of the Hall coefficient are determined from the results of experimental investigations of temperature dependences of the Hall coefficient, magnetic susceptibility, and specific electrical resistance for intermetallic Er2In, ErIn, and Er3In5 compounds. Effective parameters of spinorbital interaction λSO of intermetallic compounds are calculated from anomalous components RS of the Hall coefficient and specific electrical resistance. The results calculated for the band parameters and effective parameters of spin-orbital interaction λSO for Er-In system intermetallides coincide by orders of magnitude with the results obtained in [4,7,8] from the optical spectra of pure rare-earth metals.

  1. Massive spalling of intermetallic compounds in solder-substrate reactions due to limited supply of the active element

    SciTech Connect

    Yang, S. C.; Ho, C. E.; Chang, C. W.; Kao, C. R.

    2007-04-15

    Massive spalling of intermetallic compounds has been reported in the literature for several solder/substrate systems, including SnAgCu soldered on Ni substrate, SnZn on Cu, high-Pb PbSn on Cu, and high-Pb PbSn on Ni. In this work, a unified thermodynamic argument is proposed to explain this rather unusual phenomenon. According to this argument, two necessary conditions must be met. The number one condition is that at least one of the reactive constituents of the solder must be present in a limited amount, and the second condition is that the soldering reaction has to be very sensitive to its concentration. With the growth of intermetallic, more and more atoms of this constituent are extracted out of the solder and incorporated into the intermetallic. As the concentration of this constituent decreases, the original intermetallic at the interface becomes a nonequilibrium phase, and the spalling of the original intermetallic occurs.

  2. Low temperature properties of some Er-rich intermetallic compounds

    SciTech Connect

    K.A. Gshneidner,jr; A.O. Pecharsky; L.Hale; V.K. Pecharsky

    2004-09-30

    The low temperature volumetric heat capacity ({approx}3.5 to 350 K) and magnetic susceptibility ({approx}4 to 320 K) of Er{sub 3}Rh, Er{sub 3}Ir, Er{sub 3}Pt, Er{sub 2}Al, and Er{sub 2}Sn have been measured. All of the compounds order antiferromagnetically (or ferrimagnetically), and most exhibit more than one magnetic ordering transition. The volumetric heat capacities in general are smaller than those of the prototype magnetic regenerator materials, except for Er{sub 3}Ir in the 12 to 14 K temperature range.

  3. Na-Au intermetallic compounds formed under high pressure at room temperature

    NASA Astrophysics Data System (ADS)

    Takemura, K.; Fujihisa, H.

    2011-07-01

    High-pressure powder x-ray diffraction experiments have revealed that sodium and gold react at room temperature and form Na-Au intermetallic compounds under high pressure. We have identified four intermetallic phases up to 60 GPa. The first phase (phase I) is the known Na2Au with the tetragonal CuAl2-type structure. It changed to the second phase (phase II) at ˜0.8 GPa, which has the composition Na3Au with the trigonal Cu3As-type or hexagonal Cu3P-type structure. Phase II further transformed to phase III at 3.6 GPa. Phase III has the same composition, Na3Au, with the cubic BiF3-type structure. Finally, phase III changed to phase IV at ˜54 GPa. Phase IV gives broad diffraction peaks, indicating large structural disorder.

  4. Electric field gradients at Ta in Zr and Hf inter-metallic compounds

    NASA Astrophysics Data System (ADS)

    Terrazos, L. A.; Petrilli, H. M.; Marszalek, M.; Saitovitch, H.; Silva, P. R. J.; Blaha, P.; Schwarz, K.

    2002-03-01

    Here we calculate the electric field gradient (EFG) at the nucleus of the substitutional Ta impurity site in Zr 2T and Hf 2T (T=Cu, Ag, Au, and Pd) C11 b inter-metallic compounds. We use the ab initio FP-LAPW method as embodied in the Wien97 code in a super-cell approach and include lattice relaxations around the impurity. Our results are compared with EFG values inferred from measurements of the quadrupole coupling constants at the 111Ta probe in these compounds performed with the time differential perturbed angular correlation (TDPAC) technique. We also performed EFG calculations for the pure inter-metallic compounds. Through the comparison of theoretical and experimental EFGs in these cases, we elucidate the role played by the Ta probe in the TDPAC measurements of Hf and Zr compounds. Our results show that, although the EFGs at the Hf site are very similar to the EFGs at the Ta impurity, there is no direct correlation between the Zr and Ta EFGs.

  5. Production method for making rare earth compounds

    DOEpatents

    McCallum, R.W.; Ellis, T.W.; Dennis, K.W.; Hofer, R.J.; Branagan, D.J.

    1997-11-25

    A method of making a rare earth compound, such as a earth-transition metal permanent magnet compound, without the need for producing rare earth metal as a process step, comprises carbothermically reacting a rare earth oxide to form a rare earth carbide and heating the rare earth carbide, a compound-forming reactant (e.g., a transition metal and optional boron), and a carbide-forming element (e.g., a refractory metal) that forms a carbide that is more thermodynamically favorable than the rare earth carbide whereby the rare earth compound (e.g., Nd{sub 2}Fe{sub 14}B or LaNi{sub 5}) and a carbide of the carbide-forming element are formed.

  6. Production method for making rare earth compounds

    DOEpatents

    McCallum, R. William; Ellis, Timothy W.; Dennis, Kevin W.; Hofer, Robert J.; Branagan, Daniel J.

    1997-11-25

    A method of making a rare earth compound, such as a earth-transition metal permanent magnet compound, without the need for producing rare earth metal as a process step, comprises carbothermically reacting a rare earth oxide to form a rare earth carbide and heating the rare earth carbide, a compound-forming reactant (e.g. a transition metal and optional boron), and a carbide-forming element (e.g. a refractory metal) that forms a carbide that is more thermodynamically favorable than the rare earth carbide whereby the rare earth compound (e.g. Nd.sub.2 Fe.sub.14 B or LaNi.sub.5) and a carbide of the carbide-forming element are formed.

  7. Development of Cu alloy anode and separator coated with Al-Ni intermetallic compound

    SciTech Connect

    Toyokura, K.; Hoshino, K.; Yamamoto, M.

    1996-12-31

    Anode made of Cu alloy and separator coated with Al-Ni intermetallic compound have been developed for VCFC. Anode of Ni alloy is usually used. However, the alternative of cost lower than Ni alloy anode should be needed, because Ni is expensive. Cu is attractive as an anode material for VCFC because it is inexpensive and electrochemically noble. However, the creep resistance of Cu is not sufficient, compared with Ni alloy. In this study, strengthening due to oxide-dispersed microstructure has been developed in Cu-Ni-Al alloy with the two-step sintering process. A wet-seal technique has been widely applied for gas-sealing and supporting of electrolyte in MCFC. Since the wet-seal area is exposed to a severe corrosive environment, corrosion resistance of material for wet sealing is related with the cell performance. Al-Ni plating with post-heat treating for stainless steel has been investigated. Stainless steel substrate was plated with Al after being coated with Ni, then heat-treated at 750 {degrees}C for 1 hour in Ar gas atmosphere. Due to the treatment, Al-Ni intermetallic compound ( mainly Al3Ni2 ) layer is formed on stainless steel surface. The long-term immersion test was carried out till 14,500 hours in 62 mol% Li{sub 2}CO{sub 3}-38 mol% K{sub 2}CO{sub 3} at 650 {degrees}C under air-30%CO{sub 2} atmosphere, for the purpose of evaluating the corrosion resistance and thermal stability of Al-Ni intermetallic compound layer in actual generating with VCFC.

  8. Brittle intermetallic compound makes ultrastrong low-density steel with large ductility.

    PubMed

    Kim, Sang-Heon; Kim, Hansoo; Kim, Nack J

    2015-02-01

    Although steel has been the workhorse of the automotive industry since the 1920s, the share by weight of steel and iron in an average light vehicle is now gradually decreasing, from 68.1 per cent in 1995 to 60.1 per cent in 2011 (refs 1, 2). This has been driven by the low strength-to-weight ratio (specific strength) of iron and steel, and the desire to improve such mechanical properties with other materials. Recently, high-aluminium low-density steels have been actively studied as a means of increasing the specific strength of an alloy by reducing its density. But with increasing aluminium content a problem is encountered: brittle intermetallic compounds can form in the resulting alloys, leading to poor ductility. Here we show that an FeAl-type brittle but hard intermetallic compound (B2) can be effectively used as a strengthening second phase in high-aluminium low-density steel, while alleviating its harmful effect on ductility by controlling its morphology and dispersion. The specific tensile strength and ductility of the developed steel improve on those of the lightest and strongest metallic materials known, titanium alloys. We found that alloying of nickel catalyses the precipitation of nanometre-sized B2 particles in the face-centred cubic matrix of high-aluminium low-density steel during heat treatment of cold-rolled sheet steel. Our results demonstrate how intermetallic compounds can be harnessed in the alloy design of lightweight steels for structural applications and others. PMID:25652998

  9. Determining factor of median diameter in intermetallic compound nanoparticles prepared by pulsed wire discharge

    NASA Astrophysics Data System (ADS)

    Nagasawa, Shinobu; Koishi, Tetsuya; Tokoi, Yoshinori; Suzuki, Tsuneo; Nakayama, Tadachika; Suematsu, Hisayuki; Niihara, Koichi

    2014-02-01

    The preparation of NiAl intermetallic compound nanoparticles was carried out by pulsed wire discharge (PWD) using twisted pure Ni and Al wires in N2 ambient gas with varying number of turns of the wire (Nt), energy ratio (K), and ambient gas pressure (P). From the voltage and current waveforms during the wire heating, the energy deposition ratio up to the voltage peak (Kp) was calculated. It increased with an increase in Nt to 0.4 turns/mm and with increases in K and P. Under all the conditions, with an increase in Kp, the Ni composition ratio of the prepared particles (CNi) became closer to that of the wire (= 51.2 mol %). Furthermore, the collection rate (Rc) increased and the median particle diameter (d50) decreased. In particular, the change in d50 due to the change in Nt was not predicted by the relationship of d50 and Dth in our previous report. Single-phase NiAl intermetallic compound nanoparticles were successfully prepared under the condition in which Nt is 0.4 turns/mm, K is 3.4, and P is 100 kPa, where relatively high value of Kp was obtained. From these results, Kp was determined to be an important factor that determines the composition, collection rate, and median diameter of intermetallic compound nanoparticles synthesized by PWD using different kinds of twisted wires under various experimental conditions. This may be because of the selective wire heating in high-resistance parts that are associated with the introduction of lattice defects and/or necks by overwinding.

  10. Brittle intermetallic compound makes ultrastrong low-density steel with large ductility

    NASA Astrophysics Data System (ADS)

    Kim, Sang-Heon; Kim, Hansoo; Kim, Nack J.

    2015-02-01

    Although steel has been the workhorse of the automotive industry since the 1920s, the share by weight of steel and iron in an average light vehicle is now gradually decreasing, from 68.1 per cent in 1995 to 60.1 per cent in 2011 (refs 1, 2). This has been driven by the low strength-to-weight ratio (specific strength) of iron and steel, and the desire to improve such mechanical properties with other materials. Recently, high-aluminium low-density steels have been actively studied as a means of increasing the specific strength of an alloy by reducing its density. But with increasing aluminium content a problem is encountered: brittle intermetallic compounds can form in the resulting alloys, leading to poor ductility. Here we show that an FeAl-type brittle but hard intermetallic compound (B2) can be effectively used as a strengthening second phase in high-aluminium low-density steel, while alleviating its harmful effect on ductility by controlling its morphology and dispersion. The specific tensile strength and ductility of the developed steel improve on those of the lightest and strongest metallic materials known, titanium alloys. We found that alloying of nickel catalyses the precipitation of nanometre-sized B2 particles in the face-centred cubic matrix of high-aluminium low-density steel during heat treatment of cold-rolled sheet steel. Our results demonstrate how intermetallic compounds can be harnessed in the alloy design of lightweight steels for structural applications and others.

  11. Properties Evaluation and Studying Production Mechanism of Nanocrystalline NiAl Intermetallic Compound by Mechanical Alloying

    NASA Astrophysics Data System (ADS)

    Khajesarvi, Ali; Akbari, Golamhossein

    2016-04-01

    Ni50Al50 intermetallic compound was synthesized by mechanical alloying (MA) of elemental mixtures of Ni and Al powders in a planetary ball mill. After 16 hours of milling and obtaining crystallites with a critical size, the initial NiAl compound was formed along with the combustive reaction after opening the vial lid. In the time interval of 16 to 128 hours, the reaction from combustive state reached the explosive state. Finally, after 128 hours of milling, the initial powders were wholly transformed into NiAl before completion of the milling time. Structural changes of powder particles during MA were studied by X-ray diffractometry and scanning electron microscopy. The crystallite size measurements revealed that the grain size of the NiAl phase decreased from 155 to 26 nm with increasing MA time from 8 to 128 hours. Microhardness for nanocrystalline Ni50Al50 intermetallic compound produced after 128 hours of milling was measured as about 350 Hv.

  12. High hardness in the biocompatible intermetallic compound β-Ti3Au.

    PubMed

    Svanidze, Eteri; Besara, Tiglet; Ozaydin, M Fevsi; Tiwary, Chandra Sekhar; Wang, Jiakui K; Radhakrishnan, Sruthi; Mani, Sendurai; Xin, Yan; Han, Ke; Liang, Hong; Siegrist, Theo; Ajayan, Pulickel M; Morosan, E

    2016-07-01

    The search for new hard materials is often challenging, but strongly motivated by the vast application potential such materials hold. Ti3Au exhibits high hardness values (about four times those of pure Ti and most steel alloys), reduced coefficient of friction and wear rates, and biocompatibility, all of which are optimal traits for orthopedic, dental, and prosthetic applications. In addition, the ability of this compound to adhere to ceramic parts can reduce both the weight and the cost of medical components. The fourfold increase in the hardness of Ti3Au compared to other Ti-Au alloys and compounds can be attributed to the elevated valence electron density, the reduced bond length, and the pseudogap formation. Understanding the origin of hardness in this intermetallic compound provides an avenue toward designing superior biocompatible, hard materials. PMID:27453942

  13. High hardness in the biocompatible intermetallic compound β-Ti3Au

    PubMed Central

    Svanidze, Eteri; Besara, Tiglet; Ozaydin, M. Fevsi; Tiwary, Chandra Sekhar; Wang, Jiakui K.; Radhakrishnan, Sruthi; Mani, Sendurai; Xin, Yan; Han, Ke; Liang, Hong; Siegrist, Theo; Ajayan, Pulickel M.; Morosan, E.

    2016-01-01

    The search for new hard materials is often challenging, but strongly motivated by the vast application potential such materials hold. Ti3Au exhibits high hardness values (about four times those of pure Ti and most steel alloys), reduced coefficient of friction and wear rates, and biocompatibility, all of which are optimal traits for orthopedic, dental, and prosthetic applications. In addition, the ability of this compound to adhere to ceramic parts can reduce both the weight and the cost of medical components. The fourfold increase in the hardness of Ti3Au compared to other Ti–Au alloys and compounds can be attributed to the elevated valence electron density, the reduced bond length, and the pseudogap formation. Understanding the origin of hardness in this intermetallic compound provides an avenue toward designing superior biocompatible, hard materials. PMID:27453942

  14. Surface structures of In-Pd intermetallic compounds. II. A theoretical study

    SciTech Connect

    Gaudry, É.; McGuirk, G. M.; Ledieu, J.; Fournée, V.

    2014-08-28

    The (110) surface of the InPd intermetallic compound and the In–Pd surface alloy properties are investigated in the framework of the density functional theory, within the projector augmented plane-wave method. Surface segregation is calculated to be energetically unfavorable at stoichiometric InPd(110) surfaces, while indium antisites are shown to segregate to the surface in off-stoichiometric InPd(110) systems. Concerning surface alloys obtained by burying In-doped Pd layers in Pd(111), we demonstrated that the most stable ones are those presenting atomic indium concentrations below 50 at. % (11 at. %, 25 at. %, 33 at. %). According to our calculations, the In-doped Pd layers with concentration above or equal to 50% lead to In-doped Pd multilayers, each presenting an atomic indium concentration below 50 at. %. Alloying and segregation effects in InPd intermetallic compound and In–Pd surface alloys clearly agree with the larger bonding strength of In–Pd (−0.44 eV) compared to In–In (−0.29 eV) and Pd–Pd (−0.31 eV)

  15. TDPAC Study of the Intermetallic Compound HfCo3B2

    NASA Astrophysics Data System (ADS)

    Yaar, I.; Halevy, I.; Salhov, S.; Caspi, E. N.; Dubman, M.; Kahane, S.; Berant, Z.

    2004-11-01

    The electronic properties of the intermetallic compound HfCo3B2 were investigated using combined TDPAC measurements and first principles LAPW calculations. The V zz value at the hafnium site is determined from dominant positive p p contribution, with less than 20%, negative s d and d d contributions. Based on the calculated density of state (DOS) at 0 K, a band contribution ( γ band) of 7.26 (mJ/mol/K2) to the value of the electronic specific heat coefficient ( γ) was obtained. This relatively low γ band value is attributed to the hybridization between hafnium d-states, boron 2 p-states and cobalt 3 d-states, formed at the energy interval below E Fermi. This hybridization, together with the dip in the DOS around E Fermi, implies a possible reduction of the low temperature magnetic moment in this compound.

  16. First principles calculations of the optical and plasmonic response of Au alloys and intermetallic compounds.

    PubMed

    Keast, V J; Barnett, R L; Cortie, M B

    2014-07-30

    Pure Au is widely used in plasmonic applications even though its use is compromised by significant losses due to damping. There are some elements that are less lossy than Au (e.g. Ag or Al) but they will normally oxidize or corrode under ambient conditions. Here we examine whether alloying Au with a second element would be beneficial for plasmonic applications. In order to evaluate potential alternatives to pure Au, the density of states (DOS), dielectric function and plasmon quality factor have been calculated for alloys and compounds of Au with Al, Cd, Mg, Pd, Pt, Sn, Ti, Zn and Zr. Substitutional alloying of Au with Al, Cd, Mg and Zn was found to slightly improve the plasmonic response. Of the large number of intermetallic compounds studied, only AuAl2, Au3Cd, AuMg, AuCd and AuZn were found to be suitable for plasmonic applications. PMID:25001413

  17. First principles calculations of the optical and plasmonic response of Au alloys and intermetallic compounds

    NASA Astrophysics Data System (ADS)

    Keast, V. J.; Barnett, R. L.; Cortie, M. B.

    2014-07-01

    Pure Au is widely used in plasmonic applications even though its use is compromised by significant losses due to damping. There are some elements that are less lossy than Au (e.g. Ag or Al) but they will normally oxidize or corrode under ambient conditions. Here we examine whether alloying Au with a second element would be beneficial for plasmonic applications. In order to evaluate potential alternatives to pure Au, the density of states (DOS), dielectric function and plasmon quality factor have been calculated for alloys and compounds of Au with Al, Cd, Mg, Pd, Pt, Sn, Ti, Zn and Zr. Substitutional alloying of Au with Al, Cd, Mg and Zn was found to slightly improve the plasmonic response. Of the large number of intermetallic compounds studied, only AuAl2, Au3Cd, AuMg, AuCd and AuZn were found to be suitable for plasmonic applications.

  18. Lattice dynamics of the mixed-conducting intermetallic compound,. beta. -LiAl

    SciTech Connect

    Brun, T.O.; Robinson, J.E.; Susman, S.; Mildner, D.F.R.; Dejus, R.; Skoeld K.

    1983-04-01

    The intermetallic compound, ..beta..-LiAl, that crystallizes in the uncommon Zintl structure is a mixed-conducting electrode and has many unusual properties pointing to the existence of unusual bonding in the semi-metallic compound. In order to elucidate the nature of the bonding in LiAl, we have studied the lattice dynamics of ..beta..-LiAl by inelastic neutron scattering. Results for the phonon dispersion curves have been obtained for the principal symmetry directions. A force constant fit to the results indicates that the Al-Al force constants are unusually large. Pair potentials were constructed by conventional pseudopotential calculations. The pair interactions favoring the Zintl structure were used to compute phonon dispersion curves. Good agreement between theory and experiment can be obtained for the acoustic branches.

  19. Synthesis, crystal structure, and magnetic properties of novel intermetallic compounds R2Co2SiC (R = Pr, Nd).

    PubMed

    Zhou, Sixuan; Mishra, Trinath; Wang, Man; Shatruk, Michael; Cao, Huibo; Latturner, Susan E

    2014-06-16

    The intermetallic compounds R2Co2SiC (R = Pr, Nd) were prepared from the reaction of silicon and carbon in either Pr/Co or Nd/Co eutectic flux. These phases crystallize with a new stuffed variant of the W2CoB2 structure type in orthorhombic space group Immm with unit cell parameters a = 3.978(4) Å, b = 6.094(5) Å, c = 8.903(8) Å (Z = 2; R1 = 0.0302) for Nd2Co2SiC. Silicon, cobalt, and carbon atoms form two-dimensional flat sheets, which are separated by puckered layers of rare-earth cations. Magnetic susceptibility measurements indicate that the rare earth cations in both analogues order ferromagnetically at low temperature (TC ≈ 12 K for Nd2Co2SiC and TC ≈ 20 K for Pr2Co2SiC). Single-crystal neutron diffraction data for Nd2Co2SiC indicate that Nd moments initially align ferromagnetically along the c axis around ∼12 K, but below 11 K, they tilt slightly away from the c axis, in the ac plane. Electronic structure calculations confirm the lack of spin polarization for Co 3d moments. PMID:24898034

  20. Intermetallic nanoparticles

    SciTech Connect

    Singh, Dileep; Yusufoglu, Yusuf; Timofeeva, Elena; Routbort, Jules L.

    2015-11-20

    A process for preparing intermetallic nanoparticles of two or more metals is provided. In particular, the process includes the steps: a) dispersing nanoparticles of a first metal in a solvent to prepare a first metal solution, b) forming a reaction mixture with the first metal solution and a reducing agent, c) heating the reaction mixture to a reaction temperature; and d) adding a second metal solution containing a salt of a second metal to the reaction mixture. During this process, intermetallic nanoparticles, which contain a compound with the first and second metals are formed. The intermetallic nanoparticles with uniform size and a narrow size distribution is also provided. An electrochemical device such as a battery with the intermetallic nanoparticles is also provided.

  1. Intermetallic nanoparticles

    SciTech Connect

    Singh, Dileep; Yusufoglu, Yusuf; Timofeeva, Elena; Routbort, Jules

    2015-07-14

    A process for preparing intermetallic nanoparticles of two or more metals is provided. In particular, the process includes the steps: a) dispersing nanoparticles of a first metal in a solvent to prepare a first metal solution, b) forming a reaction mixture with the first metal solution and a reducing agent, c) heating the reaction mixture to a reaction temperature; and d) adding a second metal solution containing a salt of a second metal to the reaction mixture. During this process, intermetallic nanoparticles, which contain a compound with the first and second metals are formed. The intermetallic nanoparticles with uniform size and a narrow size distribution is also provided. An electrochemical device such as a battery with the intermetallic nanoparticles is also provided.

  2. Absence of the hyperfine magnetic field at the Ru site in ferromagnetic rare-earth intermetallics

    SciTech Connect

    Coffey, D.; DeMarco, M.; Ho, P. C.; Maple, M. B.; Sayles, T.; Lynn, J. W.; Huang, Q.; Toorongian, S.; Haka, M.

    2010-05-01

    The Moessbauer effect (ME) is frequently used to investigate magnetically ordered systems. One usually assumes that the magnetic order induces a hyperfine magnetic field, B{sub hyperfine}, at the ME active site. This is the case in the ruthenates, where the temperature dependence of B{sub hyperfine} at {sup 99}Ru sites tracks the temperature dependence of the ferromagnetic or antiferromagnetic order. However this does not happen in the rare-earth intermetallics, GdRu{sub 2} and HoRu{sub 2}. Specific heat, magnetization, magnetic susceptibility, Moessbauer effect, and neutron diffraction have been used to study the nature of the magnetic order in these materials. Both materials are found to order ferromagnetically at 83.1 and 15.3 K, respectively. Despite the ferromagnetic order of the rare-earth moments in both systems, there is no evidence of a correspondingly large B{sub hyperfine} in the Moessbauer spectrum at the Ru site. Instead the measured spectra consist of a narrow peak at all temperatures which points to the absence of magnetic order. To understand the surprising absence of a transferred hyperfine magnetic field, we carried out ab initio calculations which show that spin polarization is present only on the rare-earth site. The electron spin at the Ru sites is effectively unpolarized and, as a result, B{sub hyperfine} is very small at those sites. This occurs because the 4d Ru electrons form broad conduction bands rather than localized moments. These 4d conduction bands are polarized in the region of the Fermi energy and mediate the interaction between the localized rare-earth moments.

  3. Absence of the hyperfine magnetic field at the Ru site in ferromagnetic rare-earth intermetallics

    NASA Astrophysics Data System (ADS)

    Coffey, D.; Demarco, M.; Ho, P. C.; Maple, M. B.; Sayles, T.; Lynn, J. W.; Huang, Q.; Toorongian, S.; Haka, M.

    2010-05-01

    The Mössbauer effect (ME) is frequently used to investigate magnetically ordered systems. One usually assumes that the magnetic order induces a hyperfine magnetic field, Bhyperfine , at the ME active site. This is the case in the ruthenates, where the temperature dependence of Bhyperfine at R99u sites tracks the temperature dependence of the ferromagnetic or antiferromagnetic order. However this does not happen in the rare-earth intermetallics, GdRu2 and HoRu2 . Specific heat, magnetization, magnetic susceptibility, Mössbauer effect, and neutron diffraction have been used to study the nature of the magnetic order in these materials. Both materials are found to order ferromagnetically at 83.1 and 15.3 K, respectively. Despite the ferromagnetic order of the rare-earth moments in both systems, there is no evidence of a correspondingly large Bhyperfine in the Mössbauer spectrum at the Ru site. Instead the measured spectra consist of a narrow peak at all temperatures which points to the absence of magnetic order. To understand the surprising absence of a transferred hyperfine magnetic field, we carried out ab initio calculations which show that spin polarization is present only on the rare-earth site. The electron spin at the Ru sites is effectively unpolarized and, as a result, Bhyperfine is very small at those sites. This occurs because the 4d Ru electrons form broad conduction bands rather than localized moments. These 4d conduction bands are polarized in the region of the Fermi energy and mediate the interaction between the localized rare-earth moments.

  4. Ab initio calculation of molecular field interactions in rare-earth transition-metal intermetallics (invited)

    NASA Astrophysics Data System (ADS)

    Brooks, M. S. S.; Gasche, T.; Auluck, S.; Nordström, L.; Severin, L.; Trygg, J.; Johansson, B.

    1991-11-01

    The interaction, KRM, between the rare-earth 4f moment and the transition-metal 3d moments in rare-earth transition-metal intermetallics is shown to depend upon the R-5d moment, which is due to 3d-5d hybridization, and local 4f-5d exchange integrals. Both the R-5d moment and KRM may be calculated ab initio from the local spin-density approximation to density functional theory in self-consistent energy-band calculations with the localized 4f-moments fixed at their Russel-Saunders values. Detailed examples are given for the RFe2 (R=Gd-Yb) series. The exchange integrals are similar to those entering into the density functional version of Stoner theory and their energy dependence must be treated carefully. The calculated local exchange integrals are shown to be related to the molecular fields derived from spin Hamiltonians, hence to the spin-wave spectra. Reasonable agreement with values of the molecular fields extracted from inelastic neutron scattering and high field susceptibility measurements is obtained.

  5. Crystallization behavior of iron-containing intermetallic compounds in 319 aluminum alloy

    SciTech Connect

    Narayanan, L.A.; Samuel, F.H. ); Gruzleski, J.E. . Dept. of Mining and Metallurgical Engineering)

    1994-08-01

    The crystallization behavior of iron-containing intermetallic compounds in industrial grade 319 aluminum alloy has been investigated by means of thermal analysis and metallography. In the absence of manganese, the iron compound crystallizes in the [beta] phase, at all cooling rates ranging from 0.1 C/s to 20 C/s under normal casting temperatures (750 C). However, when the melt is superheated to a high temperature (about 200 to 300 degrees above the liquidus temperature), the iron compound crystallizes in the [alpha] phase at high cooling rates. This is due to the fact that [gamma] alumina, which forms at low melt temperatures ([<=]750 C), acts as a nucleus for crystallization of [beta] phase. When the melt is superheated to high temperatures ([>=] 850 C), the [gamma] alumina transforms to [alpha] alumina. This is a poor nucleus for the [beta]-phase crystallization, and as a result, [alpha] phase forms. The importance of nucleation and growth undercooling for the crystallization of iron compounds is highlighted. In the presence of manganese, the iron compound crystallizes in [alpha] phase at low cooling rates and in both the [alpha] and [beta] phases at high cooling rates. This reverse crystallization behavior is explained in terms of phase diagram relationships.

  6. Layered antiferromagnetism with high Neel temperature in the intermetallic compound Mn2Au

    NASA Astrophysics Data System (ADS)

    Khmelevskyi, Sergii; Mohn, Peter

    2008-10-01

    On the basis of earlier experimental studies the intermetallic compound Mn2Au has been characterized as a nonmagnetically ordered material. Here we report the results of first-principles calculations based on local spin-density approximation that describes Mn2Au to have a narrow band ground state with rigid local moments on the Mn sites. Calculations of the interatomic exchange constants based on the magnetic force theorem and a Monte Carlo modeling of the resulting Heisenberg-like Hamiltonian predict a high Neel temperature of ˜1600 K. This temperature is considerably higher than for the other known high-temperature antiferromagnetic L10-type Mn based binary alloys used in magnetic storage applications.

  7. Gas atomization synthesis of refractory or intermetallic compounds and supersaturated solid solutions

    DOEpatents

    Anderson, I.E.; Lograsso, B.K.; Ellis, T.W.

    1994-11-29

    A metallic melt is atomized using a high pressure atomizing gas wherein the temperature of the melt and the composition of the atomizing gas are selected such that the gas and melt react in the atomization spray zone to form a refractory or intermetallic compound in the as-atomized powder particles. A metallic melt is also atomized using a high pressure atomizing gas mixture gas wherein the temperature of the melt and the ratio of a reactive gas to a carrier gas are selected to form powder particles comprising a supersaturated solid solution of the atomic species of the reactive gas in the particles. The powder particles are then heat treated to precipitate dispersoids in-situ therein to form a dispersion strengthened material. 9 figures.

  8. Gas atomization synthesis of refractory or intermetallic compounds and supersaturated solid solutions

    SciTech Connect

    Anderson, Iver E.; Lograsso, Barbara K.; Ellis, Timothy W.

    1994-01-01

    A metallic melt is atomized using a high pressure atomizing gas wherein the temperature of the melt and the composition of the atomizing gas are selected such that the gas and melt react in the atomization spray zone to form a refractory or intermetallic compound in the as-atomized powder particles. A metallic melt is also atomized using a high pressure atomizing gas mixture gas wherein the temperature of the melt and the ratio of a reactive gas to a carrier gas are selected to form powder particles comprising a supersaturated solid solution of the atomic species of the reactive gas in the particles. The powder particles are then heat treated to precipitate dispersoids in-situ therein to form a dispersion strengthened material.

  9. Cutting tool performance characteristics in the machining of a nickel aluminide intermetallic compound

    SciTech Connect

    Chatterjee, S.; Srivatsan, T.S.; Giusti, P.

    1994-05-01

    Ductile nickel aluminide, Ni{sub 3}Al, containing traces of boron, is an intermetallic compound with high strength, making it a promising structural material for elevated, ambient and cryogenic temperature applications. In order to be able to use alloys, they must be capable of being fabricated by machining. The machinability of a cast nickel aluminide, Ni{sub 3}Al, alloy containing boron was studied by conventional machining using the lathe. Three different cutting tool inserts and two types of coolants, namely kerosene oil mist and soluble oil, were chosen. The machining performance of the cutting tool insert and the influence of coolant type were established through measurements of volume of material removed and tool wear. The tool wear analysis was made using microscopic examination of the cutting tool insert in order to elucidate information of the influence of machining parameters and choice of coolant on performance capability of the insert. The overall machinability performance of these materials is rationalized.

  10. Intermetallic compounds, copper and palladium alloys in Au-Pd ore of the Skaergaard pluton, Greenland

    NASA Astrophysics Data System (ADS)

    Rudashevsky, N. S.; Rudashevsky, V. N.; Nielsen, T. F. D.

    2015-12-01

    Copper-palladium intermetallic compounds and alloys (2314 grains) from the Au-Pd ore of the Skaergaard layered gabbroic pluton have been studied. Skaergaardite PdCu, nielsenite PdCu3, (Cu,Pd)β, (Cu,Pd)α, (Pd,Cu,Au,Pt) alloys, and native palladium have been identified as a result of 1680 microprobe analyses. The average compositions and various chemical varieties of these minerals are characterized, as well as vertical and lateral zoning in distribution of noble metals. The primary Pd-Cu alloys were formed within a wide temperature interval broadly synchronously with cooling and crystallization of host gabbro and in close association with separation of Fe-Cu sulfide liquid. In the course of crystallization of residual gabbroic melt enriched in iron, noble and heavy metals and saturated with the supercritical aqueous fluid, PGE and Au are selectively concentrated in the Fe-Cu sulfide phase as Pd-Cu and Cu-Au alloys.

  11. Intermetallic Compound Formation Mechanisms for Cu-Sn Solid-Liquid Interdiffusion Bonding

    NASA Astrophysics Data System (ADS)

    Liu, H.; Wang, K.; Aasmundtveit, K. E.; Hoivik, N.

    2012-09-01

    Cu-Sn solid-liquid interdiffusion (SLID) bonding is an evolving technique for wafer-level packaging which features robust, fine pitch and high temperature tolerance. The mechanisms of Cu-Sn SLID bonding for wafer-level bonding and three-dimensional (3-D) packaging applications have been studied by analyzing the microstructure evolution of Cu-Sn intermetallic compounds (IMCs) at elevated temperature up to 400°C. The bonding time required to achieve a single IMC phase (Cu3Sn) in the final interconnects was estimated according to the parabolic growth law with consideration of defect-induced deviation. The effect of predominantly Cu metal grain size on the Cu-Sn interdiffusion rate is discussed. The temperature versus time profile (ramp rate) is critical to control the morphology of scallops in the IMC. A low temperature ramp rate before reaching the bonding temperature is believed to be favorable in a SLID wafer-level bonding process.

  12. Multiconfigurational nature of 5f orbitals in uranium and plutonium and their intermetallic compounds

    NASA Astrophysics Data System (ADS)

    Booth, Corwin

    2013-03-01

    The structural, electronic, and magnetic properties of U and Pu elements and intermetallics remain poorly understood despite decades of effort, and currently represent an important scientific frontier toward understanding matter. The last decade has seen great progress both due to the discovery of superconductivity in PuCoGa5 and advances in theory that finally can explain fundamental ground state properties in elemental plutonium, such as the phonon dispersion curve, the non-magnetic ground state, and the volume difference between the α and δ phases. A new feature of the recent calculations is the presence not only of intermediate valence of the Pu 5f electrons, but of multiconfigurational ground states, where the different properties of the α and δ phases are primarily governed by the different relative weights of the 5f4, 5f5, and 5f6 electronic configurations. The usual method for measuring multiconfigurational states in the lanthanides is to measure the lanthanide LIII-edge x-ray absorption near-edge structure (XANES), a method that is severely limited for the actinides because the spectroscopic features are not well enough separated. Advances in resonant x-ray emission spectroscopy (RXES) have now allowed for spectra with sufficient resolution to resolve individual resonances associated with the various actinide valence states. Utilizing a new spectrometer at the Stanford Synchrotron Radiation Lightsource (SSRL), RXES data have been collected that show, for the first time, spectroscopic signatures of each of these configurations and their relative changes in various uranium and plutonium intermetallic compounds. In combination with conventional XANES spectra on related compounds, these data indicate such states may be ubiquitous in uranium and plutonium intermetallics, providing a new framework toward understanding properties ranging from heavy fermion behavior, superconductivity, and intermediate valence to mechanical and fundamental bonding behavior in

  13. Fundamental study about CO2 laser welding of titanium aluminide intermetallic compound

    NASA Astrophysics Data System (ADS)

    Kuwahara, Gaku; Yamaguchi, Shigeru; Nanri, Kenzo; Ootani, Masanori; Tetsuka, Masato; Seto, Sachio; Arai, Mikiya; Fujioka, Tomoo

    2000-11-01

    Titanium aluminide intermetallic compound is attracting attentions as heat-resistant and high-specific strength material in the next generation, especially, it is promising material in the field of aerospace components. Conventional machining process including welding, however, can be hardly applied due to its very low ductility. The objective of this study, as a first stage, is to find out paying attention to crack and hardness the fundamental good conditions of the bead-on-plate welding of TiAl intermetallic compound using CO2 laser irradiation. In the experiment, we used the casting gamma titanium aluminide contained iron, vanadium and boron with a thickness of 2mm. We carried out bead-on-plate laser welding in the titanium aluminide material in inert gas environment filled with argon. We measured fused depth, Vickers hardness, transverse crack numbers and so on as major parameters of welding speed from 1000 to 4600 mm/min and initial temperature of specimen from R.T. to 873 K with a beam spot size of 0.5 mm and an output power of 1.5 kW. In addition, the specimens were analyzed by Electron Probe X-ray Micro Analyzer, Energy Dispersive X-ray Spectroscopy and X-ray Diffractometry. As a result of experiments, transverse crack-free welding was achieved, when initial temperature was at 873 K. In every condition, the value of Vickers hardness of fused zone increased compared with base. We think the reason of it is an increase of (alpha) 2(Ti3Al) phase, which is caused by rapid cooling, taking in Oxygen, fine structure and so on.

  14. Hydrogen occupancy in the RNi{sub 4}Mg (R=Y, La, Ce, and Nd) intermetallic compounds and hydrides

    SciTech Connect

    Hahn-Herrera, Otto; Orgaz, Emilio; Aburto, Andrea

    2009-10-15

    We have investigated the effect of hydrogen on the electronic strtucture of the RNi{sub 4}Mg (R=Y, La, Ce, Pr, and Nd) intermetallics. By means of a two-step approach, the projected plane-wave and linearized plane-waves methods, we studied the hydrogen-insertion energetics on the intermetallic matrix and the H-vacancy formation in the hydride compound. We found that particular interstitial sites in the intermetallics are suitable to allocate hydrogen and form a solid solution. The effect of these interstitials on the electronic structure is discussed. In the other hand, the hydrogen-occupied sites in the hydride are found to be energetically equivalent.

  15. Surface structure of the Ag-In-(rare earth) complex intermetallics

    NASA Astrophysics Data System (ADS)

    Hars, S. S.; Sharma, H. R.; Smerdon, J. A.; Yadav, T. P.; Al-Mahboob, A.; Ledieu, J.; Fournée, V.; Tamura, R.; McGrath, R.

    2016-05-01

    We present a study of the surface structure of the Ag-In-RE (RE: rare-earth elements Gd, Tb, and Yb) complex intermetallics using scanning tunneling microscopy and low-energy electron diffraction. The surface of the Ag-In-Yb approximant prepared by sputter-annealing methods under ultrahigh-vacuum conditions produces a flat (100) surface with no facets. However, the Ag-In-Gd and Ag-In-Tb 1/1 approximants, which have a surface miscut of about 12∘ relative to the (100) plane, develop surface facets along various crystallographic directions. The structure of each facet can be explained as a truncation of the rhombic triacontahedral clusters, i.e., the main building blocks of these systems. Despite their differences in atomic structure, symmetry, and density, the facets show common features. The facet planes are In rich. The analysis of the nearest-neighbor atom distances suggests that In atoms form bonds with the RE atoms, which we suggest is a key factor that stabilizes even low-density facet planes.

  16. Atomic disorder induced by mechanical milling in the intermetallic compound CoAl

    NASA Astrophysics Data System (ADS)

    Di, L. M.; Bakker, H.; de Boer, F. R.

    1992-10-01

    The stoichiometric intermetallic compound CoAl with the CsCl-structure was subjected to ball milling. Structural changes during ball milling were studied by measurements of the magnetization and the lattice parameter. The behaviour of Coal upon milling turns out to be quite similar to that of CoGa. The increase of the magnetization and the decrease of the lattice parameter with the milling time show that, similar to CoGa, triple-defect disorder is generated by ball milling. By comparing the measured magnetization to the magnetization of Co xAl 100- x compounds with excess Co, the concentration of defects is derived for milled samples. In order to interpret our results, the existing experimental data of lattice parameters, X-ray densities calculated from the lattice parameters and macroscopic densities for Co xAl 100- x compounds were analyzed according to Edelin's equations. The defect volumes for vacancies and anti-site atoms obtained by fitting these experimental data have reasonable values. By means of the defect concentrations obtained from our magnetization measurements and the defect volumes by fitting the experimental data, the change of the lattice parameter was calculated by means of Edelin's equation. The agreement between the calculated lattice parameter and the measured lattice parameter is quite satisfactory.

  17. Observation of superconductivity in the intermetallic compound β-IrSn4.

    PubMed

    Tran, Vinh Hung; Bukowski, Zbigniew; Wiśniewski, Piotr; Tran, Lan Maria; Zaleski, Andrzej J

    2013-04-17

    Low-temperature dc-magnetization, ac electrical resistivity and specific heat measurements were performed on single crystals of the intermetallic compound β-IrSn4. The compound crystallizes in the tetragonal MoSn4-type structure (space group I41/acd) and exhibits superconductivity below Tc = 0.9 ± 0.05 K. Further, the magnitude of the ratios ΔCp/(γnkBTc) = 1.29, 2Δ/(kBTc) = 3.55 and of the electron-phonon coupling λ[overline](e-ph) = 0.5 imply that superconductivity in β-IrSn4 can be ascribed to a s-wave weak coupling regime. We determined crucial thermodynamic characteristics of the superconducting state. It turned out that depending on the assumption of either a spherical or non-spherical Fermi surface, the superconductivity can be ascribed to either a type-I and type-II/1 or type-II in clean limit, respectively. However, the behavior of the upper critical field and the anisotropic crystalline structure of the studied compound provide strong support to the type-II superconductivity. In the normal state the resistivity exhibits a prominent quadratic temperature dependence, which together with a large Kadowaki-Woods ratio and with the enhanced effective mass indicate that the electrons in β-IrSn4 are strongly correlated. PMID:23529025

  18. Growth of a Au-Ni-Sn intermetallic compound on the solder-substrate interface after aging

    SciTech Connect

    Minor, Andrew M.; Morris, J.W., Jr.

    1999-12-16

    Au/Ni metallization has become increasingly common in microelectronic packaging when Cu pads are joined with Pb-Sn solder. The outermost Au layer serves to protect the pad from corrosion and oxidation and the Ni layer provides a diffusion barrier to inhibit detrimental growth of Cu-Sn intermetallics. As a result of reflowing eutectic Pb-Sn on top of Au/Ni metallization, the as-solidified joints have AuSn{sub 4} precipitates distributed throughout the bulk of the solder joint, and Ni{sub 3}Sn{sub 4} intermetallics at the interface. Recent work has shown that the Au-Sn redeposits onto the interface during aging, compromising the strength of the joint. The present work shows that the redeposited intermetallic layer is a ternary compound with stoichiometry Au{sub 0.5}Ni{sub 0.5}Sn{sub 4}. The growth of this intermetallic layer was investigated, and results show that the ternary compound is observed to grow after as little as 3 hours at 150 C and after 3 weeks at 150 C has grown to a thickness of 10 {micro}m. Additionally, methods for inhibiting the growth of the ternary layer were investigated and it was determined that multiple reflows, both with and without additional aging can substantially limit the thickness of the ternary layer.

  19. Magnetic susceptibility and parameters of electronic structure of Al2REM (Gd, Dy, and Ho) intermetallic compounds at high temperatures

    NASA Astrophysics Data System (ADS)

    Uporova, N. S.; Uporov, S. A.; Sidorov, V. E.

    2011-08-01

    The magnetic susceptibility of Al2REM (REM = Gd, Dy, and Ho) intermetallic compounds is experimentally investigated by the Faraday method in a wide temperature interval (290-2000 K) in different magnetic fields (0.3-1.3 T). In the crystalline state, the temperature dependences of the susceptibility follow the generalized Curie-Weiss law. In the liquid phase, the magnetic susceptibility of these intermetallic compounds above the melting point increases for all examined samples. The parameters of the electronic structure of the compounds are calculated based on the experimental data. It is established that the effective magnetic moment per rareearth metal atom is smaller than that characteristic of the free REM+ ion.

  20. On the site preferences of ternary additions to triple defect B2 intermetallic compounds

    SciTech Connect

    Pike, L.M.; Chen, S.L.; Chang, Y.A.

    1995-12-31

    Knowledge of the site preference of ternary solute additions is essential to developing an understanding of how these solutes affect the properties of B2 intermetallic compounds. A quasichemical model will be presented which is able to predict the site preferences of dilute solute additions to triple defect B2 compounds. The only parameters required are enthalpies of formation at the stoichiometric composition. General equations are developed which can be used to determine site occupations and defect concentrations for dilute as well as non-dilute solute additions. These equations use atom pair bond enthalpies as the parameters. It is found that the site preferences of dilute additions are not always in agreement with predictions based on the solubility lobes in ternary Gibbs isotherms, Predictions for dilute additions to NiAl and FeAl are compared to experimental results found in the literature. Satisfactory correlation is found between the model and the experimental results. In addition, the predictions from the model on vacancy concentrations in Fe doped NiAl are compared to recent experimental results by the authors.

  1. Investigation of Dissolution Behavior of Metallic Substrates and Intermetallic Compound in Molten Lead-free Solders

    NASA Astrophysics Data System (ADS)

    Yen, Yee-Wen; Chou, Weng-Ting; Tseng, Yu; Lee, Chiapyng; Hsu, Chun-Lei

    2008-01-01

    This study investigates the dissolution behavior of the metallic substrates Cu and Ag and the intermetallic compound (IMC)-Ag3Sn in molten Sn, Sn-3.0Ag-0.5Cu, Sn-58Bi and Sn-9Zn (in wt.%) at 300, 270 and 240°C. The dissolution rates of both Cu and Ag in molten solder follow the order Sn > Sn-3.0Ag-0.5Cu >Sn-58Bi > Sn-9Zn. Planar Cu3Sn and scalloped Cu6Sn5 phases in Cu/solders and the scalloped Ag3Sn phase in Ag/solders are observed at the metallic substrate/solder interface. The dissolution mechanism is controlled by grain boundary diffusion. The planar Cu5Zn8 layer formed in the Sn-9Zn/Cu systems. AgZn3, Ag5Zn8 and AgZn phases are found in the Sn-9Zn/Ag system and the dissolution mechanism is controlled by lattice diffusion. Massive Ag3Sn phases dissolved into the solders and formed during solidification processes in the Ag3Sn/Sn or Sn-3.0Ag-0.5Cu systems. AgZn3 and Ag5Zn8 phases are formed at the Sn-9Zn/Ag3Sn interface. Zn atoms diffuse through Ag-Zn IMCs to form (Ag, Zn)Sn4 and Sn-rich regions between Ag5Zn8 and Ag3Sn.

  2. Discovery and characterization of magnetism in sigma-phase intermetallic Fe-Re compounds

    SciTech Connect

    Cieślak, J. Dubiel, S. M.; Tobola, J.; Reissner, M.

    2014-11-14

    Systematic experimental studies (vibrating sample magnetometry) supported by theoretical calculations (electronic structure by spin self-consistent Korringa-Kohn-Rostoker Green's function method) were performed on a series of intermetallic sigma-phase Fe{sub 100−x}Re{sub x} (x = 43–53) compounds. All investigated samples exhibit magnetism with an ordering temperature ranging between ∼65 K for x = 43 and ∼23 K for x = 53. The magnetism was revealed to be itinerant and identified as a spin-glass (SG) possibly having a re-entrant character. The SG was found to be heterogeneous, viz., two regimes could be distinguished as far as irreversibility in temperature dependence of magnetization is concerned: (1) of a weak irreversibility and (2) of a strong one. According to the theoretical calculations, the main contribution to the magnetism comes from Fe atoms occupying all five sub lattices, while Re atoms have rather small magnetic moments. However, the calculated average magnetic moments highly (ferromagnetic ordering model) or moderately (antiparallel ordering model) overestimate the experimental data.

  3. Layered antiferromagnetism with high Neel temperature in the intermetallic compound Mn2Au

    NASA Astrophysics Data System (ADS)

    Khmelevskyi, Sergii; Mohn, Peter

    2009-03-01

    On the basis of earlier experimental studies the intermetallic compound Mn2Au has been characterized as a non-magnetically ordered material. Here we report the results of first-principles calculations based on Local Spin-Density Approximation which describe Mn2Au to have a narrow band antiferromagnetic ground state with rigid local moments on the Mn sites. Calculations of the inter-atomic exchange constants based on the magnetic force theorem and a Monte-Carlo modeling of the resulting Heisenberg-like Hamiltonian predict a very high Neel-temperature of ˜1580K. This temperature is considerably higher than for the other known high-temperature antiferromagnetic L10-type Mn based binary alloys, which are widely used in magnetic storage applications. The source of the difficulties in determining magnetic order from the earlier experiments is discussed. The observed meta-magnetic like behavior and a susceptibility anomaly at low temperatures are linked to the frustrated magnetism on Mn anti-site impurities. We believe that the high temperature antiferromagnetism of Mn2Au may have quite an impact in technology. In particular, it can be considered as a candidate for the application as a ``pinning'' layer in GMR devices.

  4. Oxidation behavior of plasma sintered beryllium-titanium intermetallic compounds as an advanced neutron multiplier

    NASA Astrophysics Data System (ADS)

    Kim, Jae-Hwan; Nakamichi, Masaru

    2013-07-01

    Beryllium intermetallic compounds (beryllides) such as Be12Ti are very promising candidates for advanced neutron multiplier materials in a demonstration fusion power reactor (DEMO). However, beryllides are too brittle to be fabricated either into pebble-type or rod-type shapes via conventional methods (i.e. arc melting and hot isostatic pressing). We have proposed a plasma sintering technique as a new method for beryllide fabrication, and our studies on the properties of plasma sintered beryllides are ongoing. In the present work, the oxidation properties of plasma sintered beryllides were investigated at 1273 K for 24 h in a dry air atmosphere to evaluate the high temperature properties of this material. Thermal gravimetry measurements indicate that specimens with larger fractions of Be12Ti phase corresponding to samples that have been sintered for longer time periods, exhibit superior oxidation properties. Our evaluation of the oxidation behavior of each phase in our beryllide samples is as follows: Be12Ti and Be17Ti2 both have good oxidation resistance, owing to the formation of dense and protective scales, while the Be and Be2Ti phases are mainly responsible for thermal-gravimetry (TG) weight gains, which is indicative of severe oxidation. We attribute the degradation in oxidation resistance specifically to Be2Ti that transforms into TiO2, and also find this phase to be the cause of deterioration in the mechanical properties of samples, owing to cracks near Be2Ti phase conglomerates.

  5. Investigation of the Growth of Intermetallic Compounds Between Cu Pillars and Solder Caps

    NASA Astrophysics Data System (ADS)

    Lin, Jui-Ching; Qin, Yi; Woertink, Julia

    2014-11-01

    In flip chip applications, Cu pillars with solder caps are regarded as next-generation electronic interconnection technology, because of high input/output density. However, because of diffusion and reaction of Sn and Cu during the high-temperature reflow process, intermetallic compounds (IMC) are formed, and grow, at the interface between the cap and the pillar. Understanding the growth behavior of interfacial IMC is critical in the design of solder interconnections, because excessive growth of IMC can reduce the reliability of connections. In this study, the growth of IMC during thermal cycling, an accelerated method of testing the service environment of electronic devices, was studied by use of focused ion beam-scanning electron microscopy. Under alternating high and low-temperature extremes, growth of Cu6Sn5 ( η-phase) and Cu3Sn ( ɛ-phase) IMC was imaged and measured as a function of the number of cycles. The total IMC layer grew significantly thicker but became more uniform during thermal cycling. The Cu3Sn layer was initially thinner than the Cu6Sn5 layer but outgrew the Cu6Sn5 layer after 1000 cycles. It was found that, with limited Cu and Sn diffusion, consumption of Cu6Sn5 for growth of the Cu3Sn layer can result in a thinner Cu6Sn5 layer after thermal cycling.

  6. Intermetallic compound layer growth kinetics in non-lead bearing solders

    SciTech Connect

    Vianco, P.T.; Kilgo, A.C.; Grant, R.

    1995-04-01

    The introduction of alternative, non-lead bearing solders into electronic assemblies requires a thorough investigation of product manufacturability and reliability. Both of these attributes can be impacted by the excessive growth of intermetallic compound (IMC) layers at the solder/substrate interface. An extensive study has documented the stoichiometry and solid state growth kinetics of IMC layers formed between copper and the lead-free solders: 96.5Sn-3.5Ag (wt.%), 95Sn-5Sb, 100Sn, and 58Bi-42Sn. Aging temperatures were 70--205 C for the Sn-based solders and 55--120 C for the Bi-rich solder. Time periods were 1--400 days for all of the alloys. The Sn/Cu, Sn-Ag/Cu, and Sn-Sb/Cu IMC layers exhibited sub-layers of Cu{sub 6}Sn{sub 5} and Cu{sub 3}Sn; the latter composition was present only following prolonged aging times or higher temperatures. The total layer growth exhibited a time exponent of n = 0.5 at low temperatures and a value of n = 0.42 at higher temperatures in each of the solder/Cu systems. Similar growth kinetics were observed with the low temperature 58Bi-42Sn solder; however, a considerably more complex sub-layer structure was observed. The kinetic data will be discussed with respect to predicting IMC layer growth based upon solder composition.

  7. Heat and mass transfer in the sorption of hydrogen by intermetallic compounds

    SciTech Connect

    Svinarev, S.V.; Trushevskii, S.N.

    1984-06-01

    Intermetallic compounds (IMC), which reversibly absorb hydrogen, are currently the subject of many investigations re their possible use in hydrogen accumulators, thermal machines, thermal pumps and accumulators, sorptional compressors, etc. The dynamics of hydrogen sorption in IMC must be investigated for the analysis and design of such devices. Trends in such studies can be distinguished: the study of the true chemical kinetics of sorption; the investigation of the sorption dynamics in extended IMC layers of dimensions characteristic for practical applications. However, these do not give criteria by which the experimental conditions may be chosen, and often the conditions themselves are not completely described. In connection with this, calculations of the sorption process in which the heat liberation and filtration of hydrogen through the IMC layer are taken into account are of interest both for practical applications and for the elucidation of the conditions in which the process may be regarded as purely kinetic or controlled by the heat and mass transfer in the layer. The authors devote themselves to this aspect in this presentation.

  8. Model-based predictions of solid state intermetallic compound layer growth in hybrid microelectronic circuits

    SciTech Connect

    Vianco, P.T.; Erickson, K.L.; Hopkins, P.L.

    1997-12-31

    A mathematical model was developed to quantitatively describe the intermetallic compound (IMC) layer growth that takes place between a Sn-based solder and a noble metal thick film conductor material used in hybrid microcircuit (HMC) assemblies. The model combined the reaction kinetics of the solder/substrate interaction, as determined from ancillary isothermal aging experiments, with a 2-D finite element mesh that took account of the porous morphology of the thick film coating. The effect of the porous morphology on the IMC layer growth when compared to the traditional 1-D computations was significant. The previous 1-D calculations under-predicted the nominal IMC layer thickness relative to the 2-D case. The 2-D model showed greater substrate consumption by IMC growth and lesser solder consumption that was determined with the 1-D computation. The new 2-D model allows the design engineer to better predict circuit aging and hence, the reliability of HMC hardware that is placed in the field.

  9. Growth kinetics of Al–Fe intermetallic compounds during annealing treatment of friction stir lap welds

    SciTech Connect

    Movahedi, M.; Kokabi, A.H.; Seyed Reihani, S.M.; Najafi, H.; Farzadfar, S.A.; Cheng, W.J.; Wang, C.J.

    2014-04-01

    In this study, we explored the growth kinetics of the Al–Fe intermetallic (IM) layer at the joint interface of the St-12/Al-5083 friction stir lap welds during post-weld annealing treatment at 350, 400 and 450 °C for 30 to 180 min. Optical microscope (OM), field emission gun scanning electron microscope (FEG-SEM) and transmission electron microscope (TEM) were employed to investigate the structure of the weld zone. The thickness and composition of the IM layers were evaluated using image analysis system and electron back-scatter diffraction (EBSD), respectively. Moreover, kernel average misorientation (KAM) analysis was performed to evaluate the level of stored energy in the as-welded state. The results showed that the growth kinetics of the IM layer was not governed by a parabolic diffusion law. Presence of the IM compounds as well as high stored energy near the joint interface of the as-welded sample was recognized to be the origin of the observed deviation from the parabolic diffusion law. - Highlights: • This work provided a new insight into growth kinetics of Al–Fe IM thickness. • The growth kinetics of IM layer was not governed by a parabolic diffusion law. • IM near the joint interface was the origin of deviation from the parabolic law. • High stored energy at joint interface was origin of deviation from parabolic law.

  10. Theoretical and positron annihilation study of point defects in intermetallic compound Ni{sub 3}Al

    SciTech Connect

    Jian Sun; Dongliang Lin

    1994-01-01

    The equilibrium equation of point defects in Ll{sub 2} types of intermetallic compounds was established in a new simple method, which is independent of the chemical potentials. The formation energies of the relevant point defects in Ni{sub 3}Al were calculated by EAM potentials and statical relaxations. The concentration of point defects at 1,000 K as a function of bulk composition and the effect of temperature on them were studied for Ni{sub 3}Al alloy. The results show that the Al-antisites are the constitutional defects in hypostoichiometric Ni{sub 3}Al, and the Ni-antisite defects in hyperstoichiometric Ni{sub 3}Al. The two types of vacancies belong to thermal defects. The positron annihilation technique was also conducted to measure the concentration of vacancies in Ni{sub 3}Al alloys with and without boron. Although vacancies interact with the boron dopant, the changes of vacancy concentration Ni{sub 3}Al alloys can not be considered as the main reason in explaining the effect of stoichiometry on the segregation of boron. The effect of stoichiometry on diffusion in Ni{sub 3}Al alloys was discussed additionally.

  11. Kinetics of accumulation of the intermetallic compound of nickel and cadmium during storage of charged cadmium electrodes in alkali

    SciTech Connect

    Reshetov, V.A.; Grachev, D.K.; Pen'kova, L.I.; L'vova, L.A.; Ryabskaya, I.A.; Logvinets, N.P.

    1983-05-20

    When charged cadmium electrodes containing nickelous hydroxide (NHO) are stored in alkali an intermetallic compound (IMC) of the composition Ni/sub 5/Cd/sub 21/ is formed. The appearance of a step corresponding to oxidation of the IMC at a potential more positive by 0.12-0.18 V than the potential of the principal discharge process leads to appreciable lowering of the electrode capacity after storage. A systematic study was carried out of the kinetics of accumulation of the IMC at various temperatures and with additions of various amounts of NHO in order to elucidate the mechanism of formation of the intermetallic compound and to examine the possibility of predicting the loss of capacity of cadmium electrodes during storage. A kinetic equation, which can be used for predicting capacity losses of charged cadmium electrodes because of formation of the intermetallic compound Ni/sub 5/Cd/sub 21/ in them during storage, is proposed. The two-step form of the kinetic curves indicates that the IMC can be formed in cadmium electrodes during storage by two parallel mechanisms, involving both Ni/sup 0/ and Ni/sup 2 +/.

  12. Interaction of Oxygen and Carbon Monoxide with Cerium and Lanthanum Intermetallic Compounds

    NASA Astrophysics Data System (ADS)

    Wu, Ming

    In intermetallic compounds of Ce, the hybridization of the Ce 4f states and the conduction electron states generally results in an increase of the density of states at the Fermi level and has a profound effect on the transport, thermal, magnetic, and other physical properties of these compounds. In an attempt to determine whether these modifications are reflected in the catalytic properties, Auger electron spectroscopy (AES) and temperature programmed desorption (TPD) have been employed for an investigation of the interaction of O_2 and CO with CeIr _2 and its isostructural counterpart LaIr _2. Results from CeIr_2 and LaIr_2 show the following differences: (1) oxygen and carbon penetrate into CeIr _2<=ss deeply than LaIr _2; (2) O_2 and CO exhibit high temperature peaks (at 610 K for O _2 and at 740 and 900 K for CO) in the TPD spectra from the CeIr_2 sample not present in those from the LaIr_2 sample; (3) when the compounds are predosed with CO, substantial thermal desorption of CO_2 occurs from LaIr_2, but none from CeIr _2. Considering that La and Ce are chemically almost identical and the CeIr_2 and LaIr_2 bulk compounds are isostructural, the above differences suggest that the intermediate valence of CeIr_2 affects the interaction with gases. However, no direct relation has been established between the large density of states at the Fermi level and the differences in the interactions, due to the complications related to the presence of CeO _2. Unusual properties discussed are the formation of surface and near-surface oxide species upon exposure to O_2 or CO, the dissociative adsorption of CO and recombination of CO, the production of CO _2, thermal segregation, and subsurface "reservoir" of C and O. Surface and subsurface processes, such as adsorption and penetration, or thermal segregation, recombination, and desorption, are strongly coupled together. A consistent interpretation of the AES data requires consideration of the C and O concentrations occurring in

  13. Electric field gradients in nanoparticles of HfAl2 and HfAl3 intermetallic compounds

    NASA Astrophysics Data System (ADS)

    Kulińska, Agnieszka; Wodniecki, Paweł

    2010-06-01

    Perturbed angular correlation (PAC) method was applied to study the electric field gradients in nanopowders of the HfAl2 and HfAl3 intermetallic compounds, obtained via mechanical alloying or after ball milling of the thermally alloyed compound. The influence of the ball milling procedure on the experimentally obtained hyperfine interaction parameters was determined. A strong dependence of the PAC pattern on the milling time was evidenced and attributed to the structural disorder. The thickness of the outer damaged part of the grains depends on the crystallographic structure of the milled material. In HfAl3 sample the influence of the milling procedure on the phase transformation was observed.

  14. The atomic structure of low-index surfaces of the intermetallic compound InPd

    SciTech Connect

    McGuirk, G. M.; Ledieu, J.; Gaudry, É.; Weerd, M.-C.; Fournée, V. de; Hahne, M.; Gille, P.; Ivarsson, D. C. A.; Armbrüster, M.; Ardini, J.; Held, G.; Maccherozzi, F.; Bayer, A.; Lowe, M.; Pussi, K.; Diehl, R. D.

    2015-08-21

    The intermetallic compound InPd (CsCl type of crystal structure with a broad compositional range) is considered as a candidate catalyst for the steam reforming of methanol. Single crystals of this phase have been grown to study the structure of its three low-index surfaces under ultra-high vacuum conditions, using low energy electron diffraction (LEED), X-ray photoemission spectroscopy (XPS), and scanning tunneling microscopy (STM). During surface preparation, preferential sputtering leads to a depletion of In within the top few layers for all three surfaces. The near-surface regions remain slightly Pd-rich until annealing to ∼580 K. A transition occurs between 580 and 660 K where In segregates towards the surface and the near-surface regions become slightly In-rich above ∼660 K. This transition is accompanied by a sharpening of LEED patterns and formation of flat step-terrace morphology, as observed by STM. Several superstructures have been identified for the different surfaces associated with this process. Annealing to higher temperatures (≥750 K) leads to faceting via thermal etching as shown for the (110) surface, with a bulk In composition close to the In-rich limit of the existence domain of the cubic phase. The Pd-rich InPd(111) is found to be consistent with a Pd-terminated bulk truncation model as shown by dynamical LEED analysis while, after annealing at higher temperature, the In-rich InPd(111) is consistent with an In-terminated bulk truncation, in agreement with density functional theory (DFT) calculations of the relative surface energies. More complex surface structures are observed for the (100) surface. Additionally, individual grains of a polycrystalline sample are characterized by micro-spot XPS and LEED as well as low-energy electron microscopy. Results from both individual grains and “global” measurements are interpreted based on comparison to our single crystals findings, DFT calculations and previous literature.

  15. The atomic structure of low-index surfaces of the intermetallic compound InPd

    NASA Astrophysics Data System (ADS)

    McGuirk, G. M.; Ledieu, J.; Gaudry, É.; de Weerd, M.-C.; Hahne, M.; Gille, P.; Ivarsson, D. C. A.; Armbrüster, M.; Ardini, J.; Held, G.; Maccherozzi, F.; Bayer, A.; Lowe, M.; Pussi, K.; Diehl, R. D.; Fournée, V.

    2015-08-01

    The intermetallic compound InPd (CsCl type of crystal structure with a broad compositional range) is considered as a candidate catalyst for the steam reforming of methanol. Single crystals of this phase have been grown to study the structure of its three low-index surfaces under ultra-high vacuum conditions, using low energy electron diffraction (LEED), X-ray photoemission spectroscopy (XPS), and scanning tunneling microscopy (STM). During surface preparation, preferential sputtering leads to a depletion of In within the top few layers for all three surfaces. The near-surface regions remain slightly Pd-rich until annealing to ˜580 K. A transition occurs between 580 and 660 K where In segregates towards the surface and the near-surface regions become slightly In-rich above ˜660 K. This transition is accompanied by a sharpening of LEED patterns and formation of flat step-terrace morphology, as observed by STM. Several superstructures have been identified for the different surfaces associated with this process. Annealing to higher temperatures (≥750 K) leads to faceting via thermal etching as shown for the (110) surface, with a bulk In composition close to the In-rich limit of the existence domain of the cubic phase. The Pd-rich InPd(111) is found to be consistent with a Pd-terminated bulk truncation model as shown by dynamical LEED analysis while, after annealing at higher temperature, the In-rich InPd(111) is consistent with an In-terminated bulk truncation, in agreement with density functional theory (DFT) calculations of the relative surface energies. More complex surface structures are observed for the (100) surface. Additionally, individual grains of a polycrystalline sample are characterized by micro-spot XPS and LEED as well as low-energy electron microscopy. Results from both individual grains and "global" measurements are interpreted based on comparison to our single crystals findings, DFT calculations and previous literature.

  16. The atomic structure of low-index surfaces of the intermetallic compound InPd.

    PubMed

    McGuirk, G M; Ledieu, J; Gaudry, É; de Weerd, M-C; Hahne, M; Gille, P; Ivarsson, D C A; Armbrüster, M; Ardini, J; Held, G; Maccherozzi, F; Bayer, A; Lowe, M; Pussi, K; Diehl, R D; Fournée, V

    2015-08-21

    The intermetallic compound InPd (CsCl type of crystal structure with a broad compositional range) is considered as a candidate catalyst for the steam reforming of methanol. Single crystals of this phase have been grown to study the structure of its three low-index surfaces under ultra-high vacuum conditions, using low energy electron diffraction (LEED), X-ray photoemission spectroscopy (XPS), and scanning tunneling microscopy (STM). During surface preparation, preferential sputtering leads to a depletion of In within the top few layers for all three surfaces. The near-surface regions remain slightly Pd-rich until annealing to ∼580 K. A transition occurs between 580 and 660 K where In segregates towards the surface and the near-surface regions become slightly In-rich above ∼660 K. This transition is accompanied by a sharpening of LEED patterns and formation of flat step-terrace morphology, as observed by STM. Several superstructures have been identified for the different surfaces associated with this process. Annealing to higher temperatures (≥750 K) leads to faceting via thermal etching as shown for the (110) surface, with a bulk In composition close to the In-rich limit of the existence domain of the cubic phase. The Pd-rich InPd(111) is found to be consistent with a Pd-terminated bulk truncation model as shown by dynamical LEED analysis while, after annealing at higher temperature, the In-rich InPd(111) is consistent with an In-terminated bulk truncation, in agreement with density functional theory (DFT) calculations of the relative surface energies. More complex surface structures are observed for the (100) surface. Additionally, individual grains of a polycrystalline sample are characterized by micro-spot XPS and LEED as well as low-energy electron microscopy. Results from both individual grains and "global" measurements are interpreted based on comparison to our single crystals findings, DFT calculations and previous literature. PMID:26298146

  17. Atomic jump frequencies in intermetallic compounds studied using perturbed angular correlation of gamma rays

    NASA Astrophysics Data System (ADS)

    Newhouse, Randal Leslie

    Atomic jump frequencies were determined in a variety of intermetallic compounds through analysis of nuclear relaxation of spectra measured using the nuclear hyperfine technique, perturbed angular correlation (PAC) of gamma rays. Observed at higher temperatures, this relaxation is attributed to fluctuations in the orientation or magnitude of electric field gradients (EFG) at nuclei of 111In/Cd probe atoms as the atoms make diffusive jumps. Jump frequencies were obtained by fitting dynamically relaxed PAC spectra using either an empirical relaxation function or using ab initio relaxation models created using the program PolyPacFit. Jump frequency activation enthalpies were determined from measurements over a range of temperatures. Diffusion was studied in the following systems: 1) Pseudo-binary alloys having the L12 crystal structure such as In3(La1-xPrx). The goal was to see how jump frequencies were affected by random disorder. 2) The family of layered phases, LanCoIn3n+2 ( n=0,1,2,3…∞). The goal was to see how jump frequencies varied with the spacing of Co layers, which were found to block diffusion. 3) Phases having the FeGa3 structure. The goal was to analyze dynamical relaxation for probe atoms having multiple inequivalent jump vectors. 4) Phases having the tetragonal Al4Ba structure. The goal was to search for effects in the PAC spectra caused by fluctuations in magnitudes of EFGs without fluctuations in orientations. Ab initio relaxation models were developed to simulate and fit dynamical relaxation for PAC spectra of FeGa3, and several phases with the Al4Ba structure in order to determine underlying microscopic jump frequencies. In the course of this work, site preferences also were observed for 111In/Cd probe atoms in several FeGa 3 and Al4Ba phases.

  18. Polar intermetallic compounds of the silicon and arsenic family elements and their ternary hydrides and fluorides

    SciTech Connect

    Leon-Escamilla, E.A.

    1996-10-17

    An investigation has been made on the effects of hydrogen and fluoride in the solid state chemistry of alkaline-earth and divalent rare-earth metal pnictide (Pn) and tetrelide (Tt) phases A{sub 5}(Pn,Tt,){sub 3}Z{sub x}, where A = Ca, Sr, Ba, Sm, Eu, Yb; Pn = As, Sb, Bi; Tt = Si, Ge, Sn, Pb and Z = H, F. Several trivalent rare-earth-metal pnictides, RE{sub 5}Pn{sub 3} (RE = Y, La, Gd, Tb, Dy, Ho, Er, Tm) and alkaline-earth-metal trielides, A{sub 5}Tr{sub 3}Z{sub x} (Tr = Ga, In, Tl) have been included in an effort to complete observed structural trends. Two main experimental techniques were followed throughout this work, (a) reactions in absence of hydrogen or under continuous high vacuum, and (b) reactions with binary metal hydrides, AH{sub x}, in closed containers. The results demonstrate that all the phases reported with the {beta}-Yb{sub 5}Sb{sub 3}-type structure in the A{sub 5}Pn{sub 3} systems are hydrogen-stabilized compounds. Reactions in absence of hydrogen lead to compounds with the Mn{sub 5}Si{sub 3}-type structure. The structure type {beta}-Yb{sub 5}Sb{sub 3} (= Ca{sub 5}SB{sub 3}F) was found to be characteristic of ternary systems and inaccurately associated with phases that form in the Y{sub 5}Bi{sub 3}-type. A new series of isomorphous Zintl compounds with the Ca{sub 16}Sb{sub 11}-type structure were prepared and studied as well. All the alkaline-earth-metal tetrelides, A{sub 5}Tt{sub 3}, that crystallize in the Cr{sub 5}B{sub 3}-type structure can be interstitially derivatized by hydrogen or fluoride. Binary and ternary compounds were characterized by Guinier powder patterns, single crystal X-ray and powder neutron diffraction techniques. In an effort to establish property-structure relationships, electrical resistivity and magnetic measurements were performed on selected systems, and the results were explained in terms of the Zintl concepts, aided by extended Hueckel band calculations.

  19. Formation of GaPd2 and GaPd intermetallic compounds on GaN(0001)

    NASA Astrophysics Data System (ADS)

    Grodzicki, M.; Mazur, P.; Pers, J.; Brona, J.; Zuber, S.; Ciszewski, A.

    2015-09-01

    Palladium was deposited gradually under ultrahigh vacuum onto a well-defined surface of (0001)-oriented n-type GaN, at room temperature. Each deposition step was followed by annealing. Physicochemical properties of the Pd adlayers were in situ investigated prior to and after annealing by the X-ray photoelectron spectroscopy, ultraviolet photoelectron spectroscopy, low-energy electron diffraction, scanning tunneling microscopy and atomic force microscopy techniques. Annealing resulted in the formation of GaPd2 and GaPd intermetallic compounds at 550 °C and at 800 °C. Even for thicker layers, the compounds were strongly dispersed, forming 3D nanostructures. The substrate uncovered by the compounds revealed Ga-rich GaN(0001)-(1 × 1) surface. Formation of Ga-Pd-N bonds or Pd nitrides was not detected at the surface. The Ga-Pd intermetallic compound surface engineered on the GaN(0001) substrate can be used as the strongly dispersed catalyst or a model catalyst.

  20. Hydride Properties and IRON-57 Mossbauer Effect Studies in TITANIUM(COPPER(1-Y)IRON(Y)) Intermetallic Compounds.

    NASA Astrophysics Data System (ADS)

    Zakaria, Ahmad

    1987-12-01

    The hydrogen absorption properties of the Ti(Cu _{rm 1-y}Fe _{rm y}) (0 <=q y <=q 1) intermetallic compound were systematically investigated. X-ray diffraction data indicated that the intermetallic compound adopted the gammaTiCu structure for 0 <=q y <=q.1 and crystallized in the TiFe structure for.5 <=q y <=q 1. A mixture of these two phases was observed for 0.1 < y <.5. The lattice parameters for the pure intermetallic compounds and hydrided samples were measured. The heat of hydride formation, DeltaH, as a function of Fe content was determined from pressure-composition isotherms and the Van't Hoff relation. In the composition range 0 <=q y <=q.1 the value of DeltaH varied from -74.3 kJ (mole H_{2 })^{-1} to -59.1 kJ (mole H_{2})^{ -1}. For.5 <=q y <=q 1 it went from -49.5 kJ (mole H_{2})^{-1} to -27.3 kJ (mole H_ {2})^{-1}. We have found that DeltaH values derived from a model proposed by Shilov et al. for calculating DeltaH of the multicomponent hydrides were in good agreement with the experimental data by about 3%. Other properties of the hydride such as hydrogen storage capacity and hysteresis effect were also found to be y dependent. Systematic ^{57}Fe Mossbauer effect studies were also carried out in the intermetallic compound and hydride systems with the emphasis on the isomer shift measurements. The total s-electron densities at the Fe nucleus (|psi_{ rm s}({rm o})|^ {2}) increases when the Fe content y decreases in the pure intermetallic compounds. | psi_{rm s}({rm o })|^{2} decreases with the introduction of the hydrogen. In the hydride system |psi_{rm s}({rm o})|^{2 } was found to be y independent. Interpretation of the data was based on the changes in | psi_{rm s}({rm o })|^{2} due to expansion and contraction of the host lattice and the electronic structure differences. The decrease in | psi_{rm s}({rm o })|^{2} due to the hydrogenation in the TiCu-like hydride (0 <=q y <=q.1) could be accounted for by the volume effect only. For TiFe-like hydride

  1. Characterization of radiation-induced lattice vacancies in intermetallic compounds by means of positron-lifetime studies

    NASA Astrophysics Data System (ADS)

    Würschum, R.; Badura-Gergen, K.; Kümmerle, E. A.; Grupp, C.; Schaefer, H.-E.

    1996-07-01

    In the present paper a characterization of atomic vacancies in intermetallic compounds is given by means of positron-lifetime measurements after electron irradiation and comparison with the states after preparation, after long-time annealing, or in high-temperature equilibrium. In TiAl, Ti3Al, and Ni3Al no structural vacancies (detection limit CV=10-6) are observed at ambient temperature. This confirms that in these compounds slight deviations from stoichiometry are compensated by antisite atoms. In the Al-poor B2 alloys FeAl and NiAl, on the other hand, remnant vacancies exist due to the high thermal equilibrium vacancy concentrations and their slow diffusivities. The kinetics of vacancy elimination in FeAl and NiAl is discussed. A substantial temperature dependence of the positron lifetime in vacancies is detected in close-packed intermetallics which is attributed to an increased atomic relaxation or partial positron detrapping at high temperatures. In contrast to that, the temperature dependence of the positron lifetime in vacancies is small in the open-structured B2 aluminides. The lifetimes τf of free delocalized positrons in transition-metal aluminides and in NiZr and NiTi can be correlated to those of the pure components, taking into account the densities of valence electrons. For the positron lifetimes τ1 of vacancies in intermetallic compounds, values of τ1/τf=1.5-1.7 are observed similar as in the pure metals. Annealing studies of B2-FeAl after electron irradiation yield time constants for the disappearance of vacancies identical to those deduced recently for the equilibration of thermal vacancies. In electron-irradiated Ti aluminides annealing processes at 250 K and 450 K are observed where the latter process is tentatively attributed to long-range migration of vacancies.

  2. Effects of metallic nanoparticle doped flux on the interfacial intermetallic compounds between lead-free solder ball and copper substrate

    SciTech Connect

    Sujan, G.K. Haseeb, A.S.M.A. Afifi, A.B.M.

    2014-11-15

    Lead free solders currently in use are prone to develop thick interfacial intermetallic compound layers with rough morphology which are detrimental to the long term solder joint reliability. A novel method has been developed to control the morphology and growth of intermetallic compound layers between lead-free Sn–3.0Ag–0.5Cu solder ball and copper substrate by doping a water soluble flux with metallic nanoparticles. Four types of metallic nanoparticles (nickel, cobalt, molybdenum and titanium) were used to investigate their effects on the wetting behavior and interfacial microstructural evaluations after reflow. Nanoparticles were dispersed manually with a water soluble flux and the resulting nanoparticle doped flux was placed on copper substrate. Lead-free Sn–3.0Ag–0.5Cu solder balls of diameter 0.45 mm were placed on top of the flux and were reflowed at a peak temperature of 240 °C for 45 s. Angle of contact, wetting area and interfacial microstructure were studied by optical microscopy, field emission scanning electron microscopy and energy-dispersive X-ray spectroscopy. It was observed that the angle of contact increased and wetting area decreased with the addition of cobalt, molybdenum and titanium nanoparticles to flux. On the other hand, wettability improved with the addition of nickel nanoparticles. Cross-sectional micrographs revealed that both nickel and cobalt nanoparticle doping transformed the morphology of Cu{sub 6}Sn{sub 5} from a typical scallop type to a planer one and reduced the intermetallic compound thickness under optimum condition. These effects were suggested to be related to in-situ interfacial alloying at the interface during reflow. The minimum amount of nanoparticles required to produce the planer morphology was found to be 0.1 wt.% for both nickel and cobalt. Molybdenum and titanium nanoparticles neither appear to undergo alloying during reflow nor have any influence at the solder/substrate interfacial reaction. Thus, doping

  3. Structure and mechanical properties of cement and intermetallic compounds via ab-initio simulations

    NASA Astrophysics Data System (ADS)

    Dharmawardhana, Chamila Chathuranga

    structural material such as cement. However, it is far too early to be applicable for cement. Thus, this study used intermetallic compounds as a test case to develop new AIMD methods. In light of this objective, a direct method to calculate high temperature mechanical properties was devised for Mo5Si3 (T1 phase) and Mo5B2Si 3 (T2 phase). It was found that thermal expansion anisotropy (TEA) of T1 phase is captured by this simulation. It was also found an AIMD method to reduce TEA of Mo5Si3 (T1 phase) by strategic alloying. With further research these methods may be transferrable to cement and may allow optimizing the performance of hydraulic cements.

  4. NMR spectroscopy of intermetallic compounds: an experimental and theoretical approach to local atomic arrangements in binary gallides.

    PubMed

    Haarmann, Frank; Koch, Katrin; Jeglič, Peter; Pecher, Oliver; Rosner, Helge; Grin, Yuri

    2011-06-27

    The results of the investigation of MGa(2) with M = Ca, Sr, Ba and of MGa(4) with M = Na, Ca, Sr, Ba by a combined application of NMR spectroscopy and quantum mechanical calculations are comprehensively evaluated. The electric-field gradient (EFG) was identified as the most reliable measure to study intermetallic compounds, since it is accessible with high precision by quantum mechanical calculations and, for nuclear spin I>1/2, by NMR spectroscopy. The EFG values obtained by NMR spectroscopy and quantum mechanical calculations agree very well for both series of investigated compounds. A deconvolution of the calculated EFGs into their contributions reveals its sensitivity to the local environment of the atoms. The EFGs of the investigated di- and tetragallides are dominated by the population of the p(x)-, p(y)-, and p(z)-like states of the Ga atoms. A general combined approach for the investigation of disordered intermetallic compounds by application of diffraction methods, NMR spectroscopy, and quantum mechanical calculations is suggested. This scheme can also be applied to other classes of crystalline disordered inorganic materials. PMID:21590820

  5. Enthalpies of formation of Cd–Pr intermetallic compounds and thermodynamic assessment of the Cd–Pr system

    PubMed Central

    Reichmann, Thomas L.; Richter, Klaus W.; Delsante, Simona; Borzone, Gabriella; Ipser, Herbert

    2014-01-01

    In the present study standard enthalpies of formation were measured by reaction and solution calorimetry at stoichiometric compositions of Cd2Pr, Cd3Pr, Cd58Pr13 and Cd6Pr. The corresponding values were determined to be −46.0, −38.8, −35.2 and −24.7 kJ/mol(at), respectively. These data together with thermodynamic data and phase diagram information from literature served as input data for a CALPHAD-type optimization of the Cd–Pr phase diagram. The complete composition range could be described precisely with the present models, both with respect to phase equilibria as well as to thermodynamic input data. The thermodynamic parameters of all intermetallic compounds were modelled following Neumann–Kopp rule. Temperature dependent contributions to the individual Gibbs energies were used for all compounds. Extended solid solubilities are well described for the low- and high-temperature modifications of Pr and also for the intermetallic compound CdPr. A quite good agreement with all viable data available from literature was found and is presented. PMID:25540475

  6. Radiation-induced crystalline-to-amorphous transition in intermetallic compounds of the Cu-Ti alloy system

    SciTech Connect

    Lam, N.Q.; Okamoto, P.R.; Devanathan, R. ); Sabochick, M.J. . Computer Applications Div.)

    1992-02-01

    Recent progress in molecular-dynamics studies of radiation-induced crystalline-to-amorphous transition in the ordered intermetallic compounds of the Cu-Ti system is discussed. The effect of irradiation was simulated by the generation of Frenkel pairs,which resulted in both the formation of stable point defects and chemical disorder upon defect recombination. The thermodynamic, structural and mechanical responses of the compounds during irradiation were determined by monitoring changes in the system potential energy, volume expansion, pair correlation function, diffraction patterns, and elastic constants. It was found that the intermetallics Cu{sub 4}Ti{sub 3}, CuTi, and CuTi{sub 2} could be rendered amorphous by the creation of Frenkel pairs, but Cu{sub 4}Ti could not, consistent with experimental observations during electron irradiation. However, the simulations showed that Cu{sub 4}Ti did become amorphous when clusters of Frenkel pairs were introduced, indicating that this compound may be susceptible to amorphization by heavy-ion bombardment. A generalization of the Lindemann criterion was used to develop a thermodynamic description of solid-state amorphization as a disorder- induced melting process.

  7. Stability of molybdenum nanoparticles in Sn-3.8Ag-0.7Cu solder during multiple reflow and their influence on interfacial intermetallic compounds

    SciTech Connect

    Haseeb, A.S.M.A. Arafat, M.M. Johan, Mohd Rafie

    2012-02-15

    This work investigates the effects of molybdenum nanoparticles on the growth of interfacial intermetallic compound between Sn-3.8Ag-0.7Cu solder and copper substrate during multiple reflow. Molybdenum nanoparticles were mixed with Sn-3.8Ag-0.7Cu solder paste by manual mixing. Solder samples were reflowed on a copper substrate in a 250 Degree-Sign C reflow oven up to six times. The molybdenum content of the bulk solder was determined by inductive coupled plasma-optical emission spectrometry. It is found that upon the addition of molybdenum nanoparticles to Sn-3.8Ag-0.7Cu solder, the interfacial intermetallic compound thickness and scallop diameter decreases under all reflow conditions. Molybdenum nanoparticles do not appear to dissolve or react with the solder. They tend to adsorb preferentially at the interface between solder and the intermetallic compound scallops. It is suggested that molybdenum nanoparticles impart their influence on the interfacial intermetallic compound as discrete particles. The intact, discrete nanoparticles, by absorbing preferentially at the interface, hinder the diffusion flux of the substrate and thereby suppress the intermetallic compound growth. - Highlights: Black-Right-Pointing-Pointer Mo nanoparticles do not dissolve or react with the SAC solder during reflow. Black-Right-Pointing-Pointer Addition of Mo nanoparticles results smaller IMC thickness and scallop diameter. Black-Right-Pointing-Pointer Mo nanoparticles influence the interfacial IMC through discrete particle effect.

  8. Exploring phase stability, electronic and mechanical properties of Ce-Pb intermetallic compounds using first-principles calculations

    NASA Astrophysics Data System (ADS)

    Tao, Xiaoma; Wang, Ziru; Lan, Chunxiang; Xu, Guanglong; Ouyang, Yifang; Du, Yong

    2016-05-01

    The phase stability, electronic and mechanical properties of Ce-Pb intermetallics have been investigated by using first-principles calculations. Five stable and four metastable phases of Ce-Pb intermetallics were verified. Among them, CePb2 has been confirmed as HfGa2-type structure. For Ce5Pb3, the high pressure phase transformation from D8m to D88 with trivalent Ce has been predicted to occur at P=1.2 GPa and a high temperature phase transformation has been predicted from D8m to D88 with tetravalent Ce at 531.5 K. The calculated lattice constants of the five stable phases are in good agreement with experimental values. The electronic density of states, charge density and electron localization function of Ce3Pb have been calculated, which indicated that the Ce and Pb show ionic behavior. The polycrystalline bulk modulus, shear modulus, Young's modulus, and Poisson's ratio are also estimated from the calculated single crystalline elastic constants. All of the calculated elastic constants satisfy mechanical stability criteria. The microhardness and mechanical anisotropy are predicted. The anisotropic nature of the Ce-Pb intermetallic compounds are demonstrated by the three-dimensional orientation dependent surfaces of Young's moduli and linear compressibility are also demonstrated. The longitudinal, transverse and average sound velocities and the Debye temperatures are also obtained in this work. The Ce3Pb has the largest Debye temperature of 192.6 K, which means the Ce3Pb has a highest melting point and high thermal conductivity than other compounds.

  9. The role of zinc on the chemistry of complex intermetallic compounds

    SciTech Connect

    Xie, Weiwei

    2014-01-01

    Combining experiments and electronic structure theory provides the framework to design and discover new families of complex intermetallic phases and to understand factors that stabilize both new and known phases. Using solid state synthesis and multiple structural determinations, ferromagnetic β-Mn type Co8+xZn12–x was analyzed for their crystal and electronic structures.

  10. Estimation of the composition of intermetallic compounds in LiCl-KCl molten salt by cyclic voltammetry.

    PubMed

    Liu, Ya L; Liu, Kui; Yuan, Li Y; Chai, Zhi F; Shi, Wei Q

    2016-08-15

    In this work, the compositions of Ce-Al, Er-Al and La-Bi intermetallic compounds were estimated by the cyclic voltammetry (CV) technique. At first, CV measurements were carried out at different reverse potentials to study the co-reduction processes of Ce-Al, Er-Al and La-Bi systems. The CV curves obtained were then re-plotted with the current as a function of time, and the coulomb number of each peak was calculated. By comparing the coulomb number of the related peaks, the compositions of the Ce-Al, Er-Al and La-Bi intermetallic compounds formed in the co-reduction process could be estimated. The results showed that Al11Ce3, Al3Ce, Al2Ce and AlCe could be formed by the co-reduction of Ce(iii) and Al(iii). For the co-reduction of Er(iii) and Al(iii), Al3Er2, Al2Er and AlEr were formed. In a La(iii) and Bi(iii) co-existing system in LiCl-KCl melts, LaBi2, LaBi and Li3Bi were the major products as a result of co-reduction. PMID:27203295

  11. Growth behavior of intermetallic compounds during reactive diffusion between aluminum alloy 1060 and magnesium at 573-673 K

    NASA Astrophysics Data System (ADS)

    Xiao, Lin; Wang, Ning

    2015-01-01

    A potential new research reactor fuel design proposes to use U-Mo fuel in a Mg matrix clad with Al. Interdiffusion between the Mg containing fuel core and Al cladding can result in the formation of intermetallic compounds that can be detrimental to fuel element performance. The kinetics of the reactive diffusion in the binary Al-Mg system was experimentally studied. Layers of the intermetallic compounds, β (Al3Mg2) and γ (Al12Mg17) phases, were formed between the Al alloy 1060 and Mg during annealing. The β layer was observed to grow faster than the γ phase. The thickness of each layer can be expressed by a power function of the annealing time with the exponent n close to 0.5 for the β phase and less than 0.5 for the γ phase. The results suggest that the growth of β phase is controlled by lattice diffusion and that of the γ phase by grain boundary and lattice diffusion. Metallographic examination showed the grain boundary diffusion in the form of columnar growth of γ phase during annealing. Based on the reactive diffusion equation developed in this work, in the absence of irradiation effects, it will take more than 110 h to consume a half thickness of 400 μm of the cladding.

  12. Microstructure study of the rare-earth intermetallic compounds R5(SixGe1-x)4 and R5(SixGe1-x)3

    SciTech Connect

    Cao, Qing

    2012-01-01

    The unique combination of magnetic properties and structural transitions exhibited by many members of the R5(SixGe1-x)4 family (R = rare earths, 0 ≤ x ≤ 1) presents numerous opportunities for these materials in advanced energy transformation applications. Past research has proven that the crystal structure and magnetic ordering of the R5(SixGe1-x)4 compounds can be altered by temperature, magnetic field, pressure and the Si/Ge ratio. Results of this thesis study on the crystal structure of the Er5Si4 compound have for the first time shown that the application of mechanical forces (i.e. shear stress introduced during the mechanical grinding) can also result in a structural transition from Gd5Si4-type orthorhombic to Gd5Si2Ge2-type monoclinic. This structural transition is reversible, moving in the opposite direction when the material is subjected to low-temperature annealing at 500 °C.

  13. Lattice structure transformation and change in surface hardness of Ni3Nb and Ni3Ta intermetallic compounds induced by energetic ion beam irradiation

    NASA Astrophysics Data System (ADS)

    Kojima, H.; Yoshizaki, H.; Kaneno, Y.; Semboshi, S.; Hori, F.; Saitoh, Y.; Okamoto, Y.; Iwase, A.

    2016-04-01

    Ni3Nb and Ni3Ta intermetallic compounds, which show the complicated lattice structures were irradiated with 16 MeV Au5+ ions at room temperature. The X-ray diffraction measurement revealed that the lattice structure of these intermetallic compounds changed from the ordered structures to the amorphous state by the ion irradiation. The irradiation-induced amorphization caused the increase in Vickers hardness. The result was compared with our previous results for Ni3Al and Ni3V, and was discussed in terms of the intrinsic lattice structures of the samples.

  14. Structural, electronic and elastic properties of RERu2 (RE=Pr and Nd) Laves phase intermetallic compounds

    NASA Astrophysics Data System (ADS)

    Shrivastava, Deepika; Sanyal, Sankar P.

    2016-05-01

    We have performed the first-principles calculations to study the structural, electronic and elastic properties of RERu2 (RE = Pr and Nd) Laves phase intermetallic compounds using full-potential linearized augmented plane wave (FP-LAPW) method based on density functional theory (DFT) within the generalized gradient approximation (GGA) for exchange and correlation potential. The optimized lattices constant are in reasonable agreement with available experimental data. The electronic properties are analyzed in terms of band structures, total and partial density of states, which confirm their metallic character. The calculated elastic constants infer that these compounds are mechanically stable in C15 (MgCu2 type) structure and found to be ductile in nature.

  15. Catalytic properties of intermetallic compounds Ln(NiM)/sub 5/ and their hydrides in hydrogenation reactions

    SciTech Connect

    Konenko, I.R.; Starodubtseva, E.V.; Urazbaeva, K.A.; Fedorovskaya, E.A.; Klabunovskii, E.I.; Slinkin, A.A.; Mordovin, V.P.

    1989-02-01

    The catalytic (hydrogenation of propylene), asymmetric (enantioselective hydrogenation of ethyl acetoacetate), and magnetic properties of intermetallic compounds with the composition Ln(NiM)/sub 5/(IMC), where Ln = La, Sm, Gd; M = Ti, V, Cr, Mn, Cu, and of their hydrides have been studied. The data obtained indicate that the catalytic activity of the above compounds in both reactions is due to structural peculiarities of IMC and to the affinity of IMC to H/sub 2/. The observed changes in the total and the optical yield of the product of hydrogenation in the presence of IMC hydrides, modified with R,R-(+) tartaric acid, as functions of the nature of d-metals and their combinations, in the initial complex catalyst lead to the assumption that different metal tartrate complexes are formed on the hydride surface which act as centers of enantioselective hydrogenation.

  16. On the formation of Al{sub 3}Ni{sub 2} intermetallic compound by aluminothermic reduction of nickel oxide

    SciTech Connect

    Parsa, M.R.; Soltanieh, M.

    2011-07-15

    Simultaneous reduction of NiO and formation of Al{sub 3}Ni{sub 2} intermetallic compound at 880, 940 and 1000 deg. C were investigated by means of the thermal reduction method. The optimal Ni contents for the starting samples were determined at different times and temperatures through the compositional analysis. The microstructure of the metallic quenched samples was observed by scanning electron microscope. Moreover, the X-ray diffraction analysis and energy disperse spectrometry were applied to characterize the formation of the phases. The results showed that the metallic samples consisted of Al{sub 3}Ni{sub 2}, Al{sub 3}Ni and Al phases and that there was no trace of Ni, NiO and Al{sub 2}O{sub 3}. It was found that after 10 min at the applied temperatures, the reaction completed. For the longer time, the dispersed Al{sub 3}Ni{sub 2} nuclei were grown and its continuous network formed. By increasing the temperature, the thickness of the Al{sub 3}Ni precipitation around Al{sub 3}Ni{sub 2} phase is enhanced in the samples with the same Ni content. A model was proposed for these reactions. - Research Highlights: {yields} Simultaneous reduction of NiO, and Al{sub 3}Ni{sub 2} intermetallics formation at temperatures lower than Ni melting point. {yields} Presently a mechanism for such a process. {yields} Parametric study of microstructure and formed phases.

  17. Characterization of High-Temperature Abrasive Wear of Cold-Sprayed FeAl Intermetallic Compound Coating

    NASA Astrophysics Data System (ADS)

    Li, Chang-Jiu; Wang, Hong-Tao; Yang, Guan-Jun; Bao, Chong-Gao

    2011-01-01

    FeAl intermetallic compound coating was prepared by cold spraying using a mechanically alloyed Fe(Al) alloy powder followed by post-spray annealing at 950 °C. The high-temperature abrasive wear test was carried out for the FeAl coating at a temperature range from room temperature to 800 °C. The high-temperature abrasive wear of a heat-resistant stainless steel 2520 was performed for comparison. It was observed that the abrasive wear weight loss of FeAl coating was proportional to wear cycles in terms of sample revolutions at the tested temperatures. It was found that with the increase of the test temperature higher than 400 °C, the wear rate of cold-sprayed FeAl coating decreased with the increase of test temperature, while the wear rate of the heat-resistant steel increased significantly. The results indicate that the high-temperature abrasive wear resistance of the cold-sprayed FeAl intermetallic coating increased with the increase of the wear temperature in a temperature range from 400 to 800 °C. The wear resistance of cold-sprayed FeAl coating was higher than that of heat-resistant 2520 stainless steel under 800 °C by a factor of 3.

  18. FP-LAPW based investigation of structural, electronic and mechanical properties of CePb{sub 3} intermetallic compound

    SciTech Connect

    Pagare, Gitanjali Jain, Ekta; Abraham, Jisha Annie; Sanyal, Sankar P.

    2015-08-28

    A theoretical study of structural, electronic, elastic and mechanical properties of CePb{sub 3} intermetallic compound has been investigated systematically using first principles density functional theory. The calculations are carried out within the three different forms of generalized gradient approximation (GGA) and LSDA for the exchange correlation potential. The ground state properties such as lattice parameter (a{sub 0}), bulk modulus (B) and its pressure derivative (B′) are calculated and obtained lattice parameter of this compound shows well agreement with the experimental results. We have calculated three independent second order elastic constants (C{sub 11}, C{sub 12} and C{sub 44}), which has not been calculated and measured yet. From energy dispersion curves, it is found that the studied compound is metallic in nature. Ductility of this compound is analyzed using Pugh’s criteria and Cauchy's pressure (C{sub 11}-C{sub 12}). The mechanical properties such as Young's modulus, shear modulus, anisotropic ratio, Poison's ratio have been calculated for the first time using the Voigt–Reuss–Hill (VRH) averaging scheme. The average sound velocities (v{sub m}), density (ρ) and Debye temperature (θ{sub D}) of this compound are also estimated from the elastic constants.

  19. Elastic, Electronic and Thermodynamic Properties of Rh3X(X = Zr, Nb and Ta) Intermetallic Compounds

    NASA Astrophysics Data System (ADS)

    Ould Kada, M.; Seddik, T.; Sayede, A.; Khenata, R.; Bouhemadou, A.; Deligoz, E.; Alahmed, Z. A.; Bin Omran, S.; Rached, D.

    2014-11-01

    Structural, electronic, elastic and thermodynamic properties of Rh3X(X = Zr, Nb, Ta) intermetallic compounds are investigated in the framework of density functional theory (DFT). The exchange-correlation (XC) potential is treated with the generalized gradient approximation (GGA) and local density approximation (LDA). The computed ground state properties agree well with the available theoretical and experimental values. The elastic constants are obtained by calculating the total energy versus volume conserving strains using Mehl model. The electronic and bonding properties are discussed from the calculations of band structures (BSs), densities of states and electron charge densities. The volume and bulk modulus at high pressure and temperature are investigated. Additionally, thermodynamic properties such as the heat capacity, thermal expansion and Debye temperature at high pressures and temperatures are also analyzed.

  20. Experimental investigation on the corrosion behavior of Al3Ti-based intermetallic compounds in nuclear reactor normal operation conditions

    NASA Astrophysics Data System (ADS)

    Park, Jeong-Yong; Kim, Il-Hyun; Kim, Hyun-Gil; Jung, Yang-Il; Park, Dong-Jun; Park, Jung-Hwan; Koo, Yang-Hyun

    2015-12-01

    The corrosion behavior of Al3Ti-based intermetallic compounds was investigated under nuclear reactor normal operation conditions. The corrosion test was performed for Al-25Ti-10Cr and Al-21Ti-23Cr (at.%) in 633 K water and 673 K steam. The corroded surface was analyzed to identify the corrosion products. Both alloys showed a weight loss in 633 K water with no appreciable difference between the alloys. The corroded layer formed in water was shown to be the mixture of AlO(OH), TiO2, and Cr2O3. In 673 K steam, the corrosion behaviors of both alloys were similar with a small amount of weight gain. A thin, stable Al2O3 layer was formed on the surface as result of oxidation in 673 K steam.

  1. Boron-modified Ni3Al intermetallic compound formed by spark plasma sintering of mechanically activated Ni and Al powders

    NASA Astrophysics Data System (ADS)

    Shevtsova, L. I.; Ogneva, T. S.; Mul, D. O.; Esikov, M. A.; Larichkin, A. Yu; Malikov, V. N.

    2016-04-01

    A Ni3Al intermetallic compound was obtained by spark plasma sintering of mechanically activated Ni and Al powders in atomic ratio 3:1 respectively. Samples with boron addition of 0.1 and 0.2% (wt.) and samples without boron were obtained. The maximum value of the relative density (~99 %) has been obtained for the material by sintering of mechanically activated mixture powders modified with 0.1% of boron. No differences have been found between the structure of boron-modified Ni3Al and Ni3Al without boron addition. The maximum level of bending strength (2200 MPa) has been achieved for Ni3Al with 0.1% (wt.) of boron. This value is almost 3 times the bending strength of the sample of Ni3Al sintered without boron addition.

  2. Wear Properties of Intermetallic Compound Reinforced Functionally Graded Materials Fabricated by Centrifugal Solid-particle and In-Situ Methods

    NASA Astrophysics Data System (ADS)

    Watanabe, Yoshimi; Sato, Hisashi; Fukui, Yasuyoshi

    One of the functionally graded material (FGM) fabrication methods is a centrifugal method, which is an application of the centrifugal casting technique. The centrifugal force applied to a homogeneous molten composite assists the formation of the desired gradation. In this paper, the wear properties of two kinds of Al base FGMs, namely Al-Al3Ti FGM and Al-Al3Ni FGM, are reported. The former and the latter hold the oriented intermetallic compound platelets and the particle size gradient, respectively. Here, volume fraction, size, shape and orientation of the reinforcements in the composite play an important role in improving the mechanical properties of the materials, whereby FGMs with oriented platelets or particle size gradient may have special mechanical properties such as increased wear resistance. Based on the experimental results, the origin of anisotropic wear resistance and the effect of particle size on the wear properties are discussed.

  3. Effect of electron doping on thermoelectric properties for narrow-bandgap intermetallic compound RuGa2

    NASA Astrophysics Data System (ADS)

    Takagiwa, Y.; Kitahara, K.; Kimura, K.

    2013-01-01

    The maximum dimensionless figure of merit, ZTmax, as a function of the chemical potential of the narrow-bandgap intermetallic compound RuGa2 was calculated by using the Boltzmann transport equation with a simple rigid band approach under the constant relaxation time assumption. The calculation, including the effect of the group velocity, indicates that ZTmax over unity would be achieved by electron doping rather than hole doping. Based on this calculation, the effects of Ir substitution for Ru on the thermoelectric properties for RuGa2 have been investigated in the temperature range from 373 K to 973 K. Indeed, a relatively large ZT value of 0.31 for n-type material was obtained in the nominal composition of Ir3.0Ru30.4Ga66.6. The discussion includes the validity of the rigid band approximation and further enhancement of ZT from theoretical and experimental aspects.

  4. Fracture Behaviors of Sn-Cu Intermetallic Compound Layer in Ball Grid Array Induced by Thermal Shock

    NASA Astrophysics Data System (ADS)

    Shen, Jun; Zhai, Dajun; Cao, Zhongming; Zhao, Mali; Pu, Yayun

    2014-02-01

    In this work, thermal shock reliability testing and finite-element analysis (FEA) of solder joints between ball grid array components and printed circuit boards with Cu pads were used to investigate the failure mechanism of solder interconnections. The morphologies, composition, and thickness of Sn-Cu intermetallic compounds (IMC) at the interface of Sn-3.0Ag-0.5Cu lead-free solder alloy and Cu substrates were investigated by scanning electron microscopy and transmission electron microscopy. Based on the experimental observations and FEA results, it can be recognized that the origin and propagation of cracks are caused primarily by the difference between the coefficient of thermal expansion of different parts of the packaged products, the growth behaviors and roughness of the IMC layer, and the grain size of the solder balls.

  5. Investigations of the (R)nickel germanide intermetallic compounds by X-ray resonant magnetic scattering

    NASA Astrophysics Data System (ADS)

    Kim, Jong-Woo

    2005-11-01

    The x-ray magnetic scattering (XRMS) intensities of the Gd, Tb, Dy, Ho, Er, and Tm L2,3 edges were investigated using two isostructural samples [Gd1/4Tb1/4Dy1/4Ho 1/4]Ni2Ge2 and [Gd1/3Er1/3Tm 1/3]Ni2Ge2 in order to elucidate systematics in the underlying resonance process. Taken together with theoretical linearized augmented planewave (LAPW) calculations employing LDA + U, we found that the XRMS intensity at the heavy rare-earth L edges is strongly related to the 4f-5d exchange interaction and that the branching ratio arises from the effects of spin orbit coupling in the 5d band. For Gd, the 4f-5 d exchange interaction is large and dominant over not only the spin orbit coupling but also other interactions. Therefore, the XRMS intensity of Gd L3 and L2 edges most closely reflects the state of 4f moments. In the pure GdNi2Ge2 compound, large antiferromagnetic (AFM) domains were found, comparable to the x-ray beam size. Single domain scattering was measured carefully with a very small beam size for various azimuth angles and temperatures. From this measurement, a second transition at 16 K in bulk measurements was identified as a transformation from a collinear squared-up structure at high temperature, to a tilted helical structure below 16 K. Since the XRMS scattering cross-section is strongly dependent on the magnetic moment direction, the AFM domain structure was imaged by the XRMS intensity. From single domain scattering data, the ratio of the spin moments in the collinear and the spiral structure of GdNi2Ge2 at the second magnetic transition temperature were derived and used to estimate the magnetic anisotropy energy of Gd. Surprisingly, the estimated magnetic anisotropy energy of Gd in this compound is much higher than that of pure Gd metal (about a order of magnitude). This is expected to be the effect of the anisotropy in 5d conduction band. More theoretical study is necessary to understand this observation.

  6. Ab initio calculations on elastic properties in L12 structure Al3X and X3Al-type (X=transition or main group metal) intermetallic compounds

    NASA Astrophysics Data System (ADS)

    Tian, T.; Wang, X. F.; Li, W.

    2013-03-01

    As high-temperature structural materials, L12 intermetallic compounds have attracted the strong interest from both fundamental and industrial aspects. Understanding of elastic property is a basis for the complete investigations of mechanical behavior of L12 alloys. In an effort to explore the electronic origin of elastic properties of L12 intermetallics, we have performed a systematic study on elastic constants for single crystals, and Young's modulus, shear modulus, bulk modulus and Poisson's ratio for poly-crystals of 22 known Al3X and X3Al-type (X=transition or main group metal) intermetallics using the ab initio calculations. Based on the calculations of elastic constants and extreme (both positive and negative) Poisson's ratios, we found a pronounced correlation between the extreme Poisson's ratio and the elastic anisotropy, i.e., approximate 40% of the investigated L12 intermetallics exhibit intrinsic auxetic behavior. Furthermore, based on the distribution of bonding charge densities, we revealed that the ductility and extreme Poisson's ratios were attributable to the directionality of bonds of these alloys. Our findings provide a new method to predict mechanical behavior of intermetallics.

  7. Rattling-enhanced superconductivity in M V2A l20(M =Sc ,Lu ,Y ) intermetallic cage compounds

    NASA Astrophysics Data System (ADS)

    Winiarski, M. J.; Wiendlocha, B.; Sternik, M.; Wiśniewski, P.; O'Brien, J. R.; Kaczorowski, D.; Klimczuk, T.

    2016-04-01

    Polycrystalline samples of four intermetallic compounds: M V2A l20 (M =Sc , Y, La, and Lu) were synthesized using an arc-melting technique. The crystal structures were analyzed by means of powder x-ray diffraction and Rietveld analysis, and the physical properties were studied by means of heat capacity, electrical resistivity, and magnetic susceptibility measurements down to 0.4 K. For Sc V2A l20 , Lu V2A l20 , and Y V2A l20 , superconductivity was observed with critical temperatures Tc=1.00 , 0.57, and 0.60 K, respectively. Superconductivity for the Lu compound is reported. Theoretical calculations of the electronic and phonon structures were conducted in order to analyze the superconductivity and dynamics in Sc V2A l20 , Y V2A l20 , and Lu V2A l20 and to explain the lack of a superconducting transition in La V2A l20 down to 0.4 K. The results of the experimental and theoretical studies show that all the compounds are weakly coupled type-II BCS superconductors, and reveal the importance of the M -atom anharmonic "rattling" modes for the superconductivity in these materials, which seem to enhance Tc, especially for Sc V2A l20 .

  8. The evolution of γ-Mg17Al12 intermetallic compound during accumulative back extrusion and subsequent ageing treatment

    NASA Astrophysics Data System (ADS)

    Maghsoudi, M. H.; Zarei-Hanzaki, A.; Abedi, H. R.; Shamsolhodaei, A.

    2015-11-01

    Accumulative back extrusion (ABE) processing, as a novel severe plastic deformation (SPD) method, has been recently justified to be capable of modifying the microstructural characteristics of alloys. In line to its ongoing researches, the present work has been planned to study the evolution of γ-Mg17Al12 intermetallic phase during ABE and subsequent ageing treatment in a high Al-bearing Mg-Al-Zn alloy. The behaviour of γ intermetallic has been systematically examined as following points of view: (i) strain-temperature-dependent morphology changes, (ii) strain-induced dissolution, and (iii) re-ageing behaviour as a function of time and temperature. Aiming to analyse the morphology of eutectic γ compound with respect to the strain and temperature, 2D projections of effective diameter, shape factor and globularity have been made in strain/temperature graphs. The processing conditions (strain and temperature) corresponding to the desired and undesired morphologies are introduced and microstructurally explained through underlying plasticity mechanisms, i.e., 'necking-thinning-particle separation' and 'brittle fragmentation.' The former mechanism is suggested to be in relation with partial strain-induced dissolution of eutectic γ phase, leading to generation of a supersaturated solid solution. This has resulted to the observation of 'off-stoichiometry' phenomena in Mg17Al12 phase and has been justified through dislocation-assisted deformation mechanism at elevated temperature. Surprisingly, a unique re-ageing behaviour has been found for the obtained solid solutions, where a modified kinetics and morphology of γ phase precipitation were characterized. The altered precipitation behaviour is attributed to the specific defect structure achieved by SPD acting as fast diffusion channel for Al solutes.

  9. A new approach to study vacancy defects in high-temperature intermetallic compounds

    SciTech Connect

    Collins, G.S.; Sinha, P.

    1995-08-01

    Perturbed angular correlations of gamma rays (PAC) is being applied to study defects in ordered intermetallic alloys. Vacancies on both Pd and In sublattices in the B2 system PdIn were detected after quenching through quadrupole interactions induced at nearby {sup 111}In probe atoms. Fractions of probe atoms having each type of neighboring defect were observed to increase monotonically with quenching temperature over the range 825--1,500 K. For compositions close to 50.15 at.% Pd, nearly equal site fractions were observed for Pd and In vacancies, indicating that the Schottky vacancy-pair defect is the thermal defect at high temperature. The formation enthalpy of the Schottky defect was determined to be 1.3(2) eV through analysis of quenching data from in the range 825--1,200 K. Above 1200 K, however, the vacancy concentration was observed to saturate at a value of 1.4(2) atomic percent, perhaps due to breakdown of the law of mass action for high defect concentrations.

  10. Effects of Bonding Wires and Epoxy Molding Compound on Gold and Copper Ball Bonds Intermetallic Growth Kinetics in Electronic Packaging

    NASA Astrophysics Data System (ADS)

    Gan, C. L.; Classe, F. C.; Chan, B. L.; Hashim, U.

    2014-04-01

    This paper discusses the influence of bonding wires and epoxy mold compounds (EMC) on intermetallic compound (IMC) diffusion kinetics and apparent activation energies ( E aa) of CuAl and AuAl IMCs in a fineline ball grid array package. The objective of this study is to study the CuAl and AuAl IMC growth rates with different epoxy mold compounds and to determine the apparent activation energies of different combination of package bills of materials. IMC thickness measurement has been carried out to estimate the coefficient of diffusion ( D o) and E aa various aging conditions of different EMCs and bonding wires. Apparent activation energies ( E aa) of both wire types were investigated after high temperature storage life tests (HTSL) for both molding compounds. Au bonds were identified to have faster IMC formation, compared to slower IMC growth of Cu. The E aa obtained for CuAl IMC diffusion kinetics are 1.08 and 1.04 eV with EMC A and EMC B, respectively. For AuAl IMC diffusion kinetics, the E aa obtained are 1.04 and 0.98 eV, respectively, on EMC A and EMC B. These values are close to previous HTSL studies conducted on Au and Cu ball bonds and are in agreement to the theory of HTSL performance of Au and Cu bonding wires.Overall, EMC B shows slightly lower apparent activation energy ( E aa) valueas in CuAl and AuAl IMCs. This proves that the different types of epoxy mold compounds have some influence on IMC growth rates.

  11. Rare earth-transition metal-magnesium compounds-An overview

    SciTech Connect

    Rodewald, Ute Ch.; Chevalier, Bernard Poettgen, Rainer

    2007-05-15

    Intermetallic rare earth-transition metal-magnesium compounds play an important role as precipitations in modern light weight alloys and as host materials for hydrogen storage applications. Recent results on the crystal chemistry, the chemical bonding peculiarities, physical properties, and hydrogenation behavior of these materials are reviewed. - Graphical abstract: View of the Sm{sub 4}RhMg crystal structure approximately along the direction. Samarium, rhodium, and magnesium atoms are drawn as medium gray, filled (hidden in the trigonal prisms), and open circles, respectively. The three-dimensional network of corner-sharing RhSm{sub 6} trigonal prisms and the Mg{sub 4} tetrahedra are emphasized. The Sm1 atoms do not participate in the network of condensed trigonal prisms.

  12. Multiscale Study of Interfacial Intermetallic Compounds in a Dissimilar Al 6082-T6/Cu Friction-Stir Weld

    NASA Astrophysics Data System (ADS)

    Avettand-Fenoël, M. N.; Taillard, R.; Ji, G.; Goran, D.

    2012-12-01

    The objective of this work was to characterize the Al x Cu y intermetallic compounds (IMCs) formed at the abutting interface during solid-state friction-stir welding (FSW) of 6082 aluminum alloy and pure copper. As IMCs are potential sources of flaws in case of mechanical loading of welds, their study is essential at various scale lengths. In the present case, they have been identified by neutron diffraction, electron backscattered diffraction, and transmission electron microscopy. Neutron diffraction analyses have shown that a shift of the tool from the interface, in particular towards the Cu part, generates an increase of the IMCs' volume fraction. In accordance with an exacerbation of its kinetics of formation by FSW, a 4- μm-thick layer has precipitated at the interface despite the shortness of the thermal cycle. This layer is composed of two sublayers with the Al4Cu9 and Al2Cu stoichiometry, respectively. Convergent beam electron diffraction analyses have, however, disclosed that the crystallography of the current Al2Cu compound does not comply with the usual tetragonal symmetry of this phase. The Al2Cu phase formation results from both the local chemical composition and thermodynamics, whereas the development of Al4Cu9 is rather due to both the local chemical composition and the shortness of the local FSW thermal cycle.

  13. Studies of magnetostriction and spin polarized band structures of rare earth intermetallics

    NASA Technical Reports Server (NTRS)

    Wallace, W. E.

    1979-01-01

    Anisotropic magnetostriction measurements of R6Fe23, R = (Tb, Dy, Ho, and Er) were carried out from 77 K to room temperature. Magnetic fields up to 2.1 Tesla were applied. All the compounds exhibited large magnetostrictions at 77 K, the largest effect being obtained for Tb6Fe23. Saturation magnetostriction values for the compounds were also determined for 77 K and room temperature. Results of the temperature dependence of magnetostriction for Er6Fe23 are in good agreement with Callen and Callen's single ion theory. Therefore, the main sources of magnetostriction in this compound is the Er ion. The spin-up and spin-down electronic energy bands, the density of states and the magnetic moments of YCo5, SmCo5, and GdCo5 were calculated by the spin polarized augmented plane wave technique. The calculations obtained show the origin of the moment, provide good estimates of its magnitude and variation, and the reasons for those variations. They also show the important role of partial charge transfer and of d-d electronic coupling. Calculations for LaNi5 and GdNi5 systems are discussed.

  14. New insights into rare-earth intermetallic alloys for cryogenic Peltier cooling

    NASA Astrophysics Data System (ADS)

    Boona, Stephen; Morelli, Donald

    2013-03-01

    Strongly correlated materials such as intermediate valence CePd3 have long been considered attractive candidates for cryogenic Peltier cooling due to the combination of metallic electrical resistivity concurrent with Seebeck coefficient values on the order of 100 μ V/K at low temperatures. This behavior is a direct result of the strong hybridization of localized 4f states with delocalized conduction electrons, which gives rise to several unusual structural, electronic, thermal, and magnetic properties. Our recent work on this compound has helped to unravel some of the complex ways in which these properties are correlated, and we have successfully utilized this improved understanding to enhance ZT up to 0.3. We present a broad overview of these new insights and provide suggestions for how they may be exploited to achieve enhanced thermoelectric performance in other strongly correlated materials. Work supported by AFOSR-MURI ``Cryogenic Peltier Cooling'' Contract #FA9550-10-1-0533.

  15. Elastic and Thermodynamic Properties of Complex Mg-Al Intermetallic Compounds via Orbital-Free Density Functional Theory

    NASA Astrophysics Data System (ADS)

    Zhuang, Houlong; Chen, Mohan; Carter, Emily A.

    2016-06-01

    Magnesium-aluminum (Mg-Al) alloys are important metal alloys with a wide range of engineering applications. We investigate the elastic and thermodynamic properties of Mg, Al, and four stoichiometric Mg-Al compounds including Mg17Al12 , Mg13Al14 , and Mg23Al30 , and MgAl2 with orbital-free density-functional theory (OFDFT). We first calculate the lattice constants, zero-temperature formation energy, and independent elastic constants of these six materials and compare the results to those computed via Kohn-Sham DFT (KSDFT) benchmarks. We obtain excellent agreement between these two methods. Our calculated elastic constants of hexagonal close-packed Mg and face-centered-cubic Al are also consistent with available experimental data. We next compute their phonon spectra using the force constants extracted from the very fast OFDFT calculations, because such calculations are computationally challenging using KSDFT. This is especially the case for the Mg23Al30 compound, whose 3 ×3 ×3 supercell consists of 1431 atoms. We finally employ the quasiharmonic approximation to investigate temperature-dependent thermodynamic properties, including formation energies, heat capacities, and thermal expansion of the four Mg-Al intermetallic compounds. The calculated heat capacity and thermal expansion of both Mg and Al agree well with experimental data. We additionally find that Mg13Al14 and MgAl2 are both unstable, consistent with their absence from the equilibrium Mg-Al phase diagram. Our work demonstrates that OFDFT is an efficient and accurate quantum-mechanical computational tool for predicting elastic and thermodynamic properties of complicated Mg-Al alloys and also should be applicable to many other engineering alloys.

  16. New method for computer analysis of complex intermetallic compounds and nanocluster model of the samson phase Cd{sub 3}Cu{sub 4}

    SciTech Connect

    Blatov, V. A.; Ilyushin, G. D.

    2010-12-15

    A new method is proposed for the computer analysis of crystal structures of complex intermetallic compounds (with more than 1000 atoms per unit cell) using a developed algorithm of the complete decomposition of the 3D graph of the structure into nanocluster substructures. This method has been implemented in the TOPOS software package and approved successfully in an analysis of the complex Cu{sub 3}Cd{sub 4} structure (Samson phase). Cu{sub 3}Cd{sub 4} structure models were used to establish a structural relationship between nanoclusters in this intermetallic compound and nanoclusters in other complex crystal structures: ZrZn{sub 22}, Ru{sub 7}Mg{sub 44}, NaCd{sub 2}, and Mg{sub 2}Al{sub 3}.

  17. Nanoclusters based on pentagondodecahedra with shells in the form of D32, D42, and D50 deltahedra in crystal structures of intermetallic compounds

    SciTech Connect

    Pankova, A. A.; Ilyushin, G. D.; Blatov, V. A.

    2012-01-15

    The TOPOS software package has been used to form a database of intermetallic compounds containing pentagondodecahedral d clusters (528 crystal structures of intermetallic compounds, 111 topological types, and 47 space symmetry groups). On the whole, 606 atomic d configurations have been selected which are described by 14 point symmetry groups. Examples of nanoclusters are presented which are precursors of the crystal structures of intermetallic compounds with the outer shell in the form of deltahedra D, which are formed above dodecahedra. These nanoclusters are identified in the automatic mode of structural data processing: D32 (K{sub 8}In{sub 6}Ge{sub 40}, Cs{sub 30}Na{sub 3}Sn{sub 162}), D{sub 42} (Ru{sub 3}Be{sub 17}, Y{sub 3}Cd{sub 18}, Ca{sub 3}(Cd{sub 17}Al)), and D{sub 50} (Yb{sub 3}Zn{sub 18}, Ce{sub 3}(Au{sub 14}Sn{sub 3}), Pr{sub 3}Cd{sub 18}, Eu{sub 4}Cd{sub 25}), where 32, 42, and 50 are the numbers of atoms in the shell. Similar deltahedra were found previously in icosahedral nanoclusters (precursors of intermetallic compounds). Structures with the dodecahedral nanocluster precursors containing D42 and D50 deltahedra are approximants of MCd{sub 5.7} (M = Yb or Ca) quasicrystals and belong to the family of MCd{sub 6} (M = Ce, Pr, Nd, Sm, Eu, Gd, Dy, Yb, Y, or Ca).

  18. Theoretical Calculations for Magnetic Property of FeRh Inter-Metallic Compound with Site-Exchange Defects

    NASA Astrophysics Data System (ADS)

    Kaneta, Yasunori; Ishino, Shiori; Chen, Ying; Iwata, Shuichi; Iwase, Akihiro

    2011-10-01

    To clarify the relationship between a magnetic property and a defect structure in FeRh inter-metallic compound theoretically, energy band calculations are performed based on the density functional theory. Under the assumption that the majority of defect structure is a type of site-exchanged one between Fe and Rh atoms, total energy for various magnetic structures is evaluated within a super-cell of 2×2×2 cubic cells. Due to the site-exchange defect pair of nearest neighbor Fe and Rh atoms in 12.5%/f.u. (f.u.: formula unit) density, the total energy increases by 1.91 eV/pair in the anti-ferromagnetic structure and 0.88 eV/pair in the ferromagnetic structure. Although the anti-ferromagnetic structure is the stable state at low temperatures in defect-free FeRh, it becomes unstable with an amount of the site-exchange defect density. Threshold defect density to stabilize ferromagnetic state is estimated to be 0.8%/f.u. This phenomenon is expected in ion irradiated FeRh.

  19. Micromagnetic analysis of the hardening mechanisms of nanocrystalline MnBi and nanopatterned FePt intermetallic compounds.

    PubMed

    Kronmüller, H; Yang, J B; Goll, D

    2014-02-12

    The uniaxial intermetallic compounds of L10-FePt and the low temperature NiAs structure of MnBi are suitable alloys for application as high-density recording materials or as high-coercivity permanent magnets. Single domain particles of these materials are characterized by coercive fields above 1 T over a large temperature range. In particular MnBi shows a coercive field of 2 T at 450 K. Its extraordinary magnetic properties in the temperature range up to 600 K are due to an increase of the magnetocrystalline anisotropy constant from 1.2 MJ m(-3) at 300 K to 2.4 MJ m(-3) at 450 K. In spite of the large coercivities obtained for both type of materials their experimental values deviate considerably from the theoretical values Hc = 2K1/Js valid for a homogeneous rotation process in spherical particles. As is well known these discrepancies are due to the deteriorating effects of the microstructure. For an analysis of the coercive fields the Stoner-Wohlfarth theory has to be expanded with respect to higher anisotropy constants and to microstructural effects such as misaligned grains and grain surfaces with reduced anisotropy constants. It is shown that the temperature dependence and the angular dependence of Hc for FePt as well as MnBi can be quantitatively interpreted by taking into account the above mentioned intrinsic and microstructural effects. PMID:24469256

  20. The magnetic behavior of the intermetallic compound NdMn2Ge2 studied by magnetization and hyperfine interactions measurements

    NASA Astrophysics Data System (ADS)

    Bosch-Santos, B.; Carbonari, A. W.; Cabrera-Pasca, G. A.; Saxena, R. N.; Freitas, R. S.

    2015-05-01

    The magnetic behavior of the intermetallic compound NdMn2Ge2 was investigated by bulk magnetization measurements and measurements of hyperfine interactions using perturbed γ-γ angular correlation (PAC) spectroscopy. Magnetization measurements indicate the presence of four magnetic transitions associated with the Mn and Nd magnetic sublattices. At high temperatures, magnetic measurements show a change in the slope of the magnetization due to an antiferromagnetic transition around TN ˜ 425 K and a well defined ferromagnetic transition at TC ˜ 320 K. Moreover, at ˜210 K a peak is observed in the magnetization curve, which is assigned to the reorientation of the Mn spin, and at ˜25 K an increase in the magnetic moment is also observed, which is ascribed to the ordering of Nd ions. PAC measurements using 140La(140Ce) and 111In(111Cd) probe nuclei allowed the determination of the temperature dependence of the magnetic hyperfine field (Bhf) at Nd and Mn sites, respectively. PAC results with 111Cd probe nuclei at Mn sites show that the dependence of Bhf with temperature follows the expected behavior for the host magnetization associated with the magnetic ordering of Mn ions. From these results, the antiferromagnetic transition followed by a ferromagnetic ordering is clearly observed. PAC results with 140Ce probe nuclei at Nd sites, however, showed a strong deviation from the Brillouin function, which is attributed to the Ce 4f-electron contribution to Bhf.

  1. Atomistic simulation of radiation-induced amorphization of the B2 ordered intermetallic compound NiTi

    SciTech Connect

    Sabochick, M.J. . Dept. of Engineering Physics); Lam, N.Q. )

    1990-12-01

    Amorphization of the B2 intermetallic compound NiTi under electron irradiation has been investigated using molecular dynamics. The effect of irradiation was simulated using two processes: (1) Ni and Ti atoms were exchanged, resulting in chemical disorder, and (2) Frenkel pairs were introduced, leading to the formation of stable point defects and also chemical disorder upon mutual recombination of interstitials and vacancies. After {approximately}0.4 exchanges per atom, the first process resulted in an energy increase of approximately 0.11 eV/atom and a volume increase of 1.91%. On the other hand, after introducing {approximately}0.5 Frenkel pairs per atom, the second process led to smaller increases of 0.092 eV/atom in energy and 1.43% in volume. The calculated radial distribution functions (RDFs) were essentially identical to each other and to the calculated RDF of a quenched liquid. The structure factor, however, showed that long-range order was still present after atom exchanges, while the introduction of Frenkel pairs resulted in the loss of long-range order. It was concluded that point defects are necessary for amorphization to occur in NiTi, although chemical disorder alone is capable of storing enough energy to make the transition possible. 18 refs., 3 figs.

  2. In situ study on the effect of thermomigration on intermetallic compounds growth in liquid-solid interfacial reaction

    SciTech Connect

    Qu, Lin; Zhao, Ning; Ma, Haitao Zhao, Huijing; Huang, Mingliang

    2014-05-28

    Synchrotron radiation real-time imaging technology was carried out in situ to observe and characterize the effect of thermomigration on the growth behavior of interfacial intermetallic compounds (IMCs) in Cu/Sn/Cu solder joint during soldering. The thermomigration resulted in asymmetrical formation and growth of the interfacial IMCs. Cu{sub 6}Sn{sub 5} and Cu{sub 3}Sn IMCs formed at the cold end and grew rapidly during the whole soldering process. However, only Cu{sub 6}Sn{sub 5} IMC formed at the hot end and remained relatively thin until solidification. The IMCs at the cold end were nearly seven times thicker than that at the hot end after solidification. The Cu dissolution at the cold end was significantly restrained, while that at the hot end was promoted, which supplied Cu atoms to diffuse toward the cold end under thermomigration to feed the rapid IMC growth. Moreover, the thermomigration also caused asymmetrical morphology of the interfacial IMCs at the cooling stage, i.e., the Cu{sub 6}Sn{sub 5} IMC at the cold end transformed into facet structure, while that at the hot end remained scallop-type. The asymmetrical growth behavior of the interfacial IMCs was analyzed from the view point of kinetics.

  3. Evidence of ferromagnetism in vanadium substituted layered intermetallic compounds RE (Co1-xVx) 2 Si2 (RE=Pr and Nd; 0 ≤ x ≤ 0.35)

    NASA Astrophysics Data System (ADS)

    Chowdhury, R. Roy; Dhara, S.; Bandyopadhyay, B.

    2016-03-01

    In intermetallic compounds RECo2Si2 (RE=Pr and Nd), cobalt has been partially substituted by vanadium to obtain RE(Co1-xVx)2Si2 (0 ≤ x ≤ 0.35). The parent compounds are antiferromagnetic below about 30 K due to the ordering of localized magnetic moments that are present only on rare-earth ions, cobalt being non-magnetic in the parent compounds. The present study demonstrates that in these compounds where 3 d and 4 f ions occupy different layers in the crystal structure, V substitution and subsequent lattice expansion results in the occurrence of inequivalent magnetic ions and complex interactions that lead to multiple magnetic transitions. At temperatures around 40-50 K, the temperature dependence of magnetization indicates a ferrimagnetic transition which is accompanied by a rapid decrease in the temperature dependence of resistivity. Below temperatures ∼30 K, the samples begin to show ferromagnetic-like behavior with the appearance of a coercive field and saturation in the magnetization at magnetic fields above ∼2 T. These two magnetic transitions are indicated also by prominent λ-like peaks in specific heat measurements. At around 10 K, a sharp drop in the resistivity indicates another magnetic transition which is followed by a rapid increase in coercive field with decrease in temperature. In a magnetic field of 9 T, the latter transition shifts to a lower temperature and that leads to a positive magnetoresistance. The onset of ferromagnetism at ∼30 K is accompanied with an exchange bias field which is observed for the first time in layered intermetallic compounds. The exchange bias field increases rapidly below the transition at ∼10 K and reaches ∼16% of coercive field at 2 K.

  4. Ultrarapid formation of homogeneous Cu6Sn5 and Cu3Sn intermetallic compound joints at room temperature using ultrasonic waves.

    PubMed

    Li, Zhuolin; Li, Mingyu; Xiao, Yong; Wang, Chunqing

    2014-05-01

    Homogeneous intermetallic compound joints are demanded by the semiconductor industry because of their high melting point. In the present work, ultrasonic vibration was applied to Cu/Sn foil/Cu interconnection system at room temperature to form homogeneous Cu6Sn5 and Cu3Sn joints. Compared with other studies based on transient-liquid-phase soldering, the processing time of our method was dramatically reduced from several hours to several seconds. This ultrarapid intermetallic phase formation process resulted from accelerated interdiffusion kinetics, which can be attributed to the sonochemical effects of acoustic cavitation at the interface between the liquid Sn and the solid Cu during the ultrasonic bonding process. PMID:24279981

  5. Structural transformations in the deuterium-containing intermetallic compound (Ti3Al)D1.2 induced by high-pressure torsion

    NASA Astrophysics Data System (ADS)

    Eshchenko, R. N.; Elkina, O. A.; Patselov, A. M.; Pilyugin, V. P.

    2009-06-01

    The intermetallic compound Ti3Al (which is a very brittle material) with a high deuterium concentration ( x = 1.2) is fabricated in a monolithic state by high-pressure torsion at room temperature. The structure of the intermetallic samples is studied by X-ray diffraction and transmission electron microscopy after deformation at various degrees. Under certain conditions, the main volume of the material is found to transform into an amorphous state, and areas 1-2 nm in size with an atomic arrangement close to the initial arrangement are also present in the material. The possible causes of the deformation-induced amorphization of the material alloyed with interstitial atoms are discussed.

  6. Magnetotransport and magnetothermal properties of the ternary intermetallic compound TbFe2Al10.

    PubMed

    Khandelwal, Ashish; Chattopadhyay, M K; Roy, S B

    2016-09-01

    We have studied the temperature and field dependences of electrical resistivity and heat capacity of TbFe2Al10, and have also complimented the above studies with low field magnetization measurements. In zero magnetic field, TbFe2Al10 exhibits paramagnetic (PM) to ferrimagnetic (Ferri-I) and Ferri-I to antiferromagnetic (AFM) phase transitions below 17.6 and 10 K respectively. We have found that the electrical resistivity of TbFe2Al10 exhibits a sharp rise across the PM to Ferri-I phase transition in this compound. Our analysis indicates that this sharp rise of electrical resistivity is related to the formation of new zone boundaries (across the PM to Ferri-I phase transition) that reduce the area of the Fermi surface. We have found that TbFe2Al10 exhibits large magnetoresistance (MR) below 100 K. Overall, the MR behaviour of TbFe2Al10 below 17.6 K in different magnetic fields reveals strong competition between AFM and ferromagnetic (FM) correlations, which seems to be quite intrinsic to the magnetic structure of the compound. Our analysis indicates that the large MR and magnetocaloric effect persisting deep inside the PM regime of TbFe2Al10 is mainly related to the presence of FM spin fluctuations and the formation of a Griffiths like (GL) phase consisting of FM clusters within the PM regime. The formation of the GL phase may be mediated by the static crystal defects in the midst of the competing inter and intra layer magnetic interactions. PMID:27385638

  7. Magnetotransport and magnetothermal properties of the ternary intermetallic compound TbFe2Al10

    NASA Astrophysics Data System (ADS)

    Khandelwal, Ashish; Chattopadhyay, M. K.; Roy, S. B.

    2016-09-01

    We have studied the temperature and field dependences of electrical resistivity and heat capacity of TbFe2Al10, and have also complimented the above studies with low field magnetization measurements. In zero magnetic field, TbFe2Al10 exhibits paramagnetic (PM) to ferrimagnetic (Ferri-I) and Ferri-I to antiferromagnetic (AFM) phase transitions below 17.6 and 10 K respectively. We have found that the electrical resistivity of TbFe2Al10 exhibits a sharp rise across the PM to Ferri-I phase transition in this compound. Our analysis indicates that this sharp rise of electrical resistivity is related to the formation of new zone boundaries (across the PM to Ferri-I phase transition) that reduce the area of the Fermi surface. We have found that TbFe2Al10 exhibits large magnetoresistance (MR) below 100 K. Overall, the MR behaviour of TbFe2Al10 below 17.6 K in different magnetic fields reveals strong competition between AFM and ferromagnetic (FM) correlations, which seems to be quite intrinsic to the magnetic structure of the compound. Our analysis indicates that the large MR and magnetocaloric effect persisting deep inside the PM regime of TbFe2Al10 is mainly related to the presence of FM spin fluctuations and the formation of a Griffiths like (GL) phase consisting of FM clusters within the PM regime. The formation of the GL phase may be mediated by the static crystal defects in the midst of the competing inter and intra layer magnetic interactions.

  8. Theoretical studies of strongly correlated rare-earth intermetallics RIn₃ and RSn₃ (R=Sm, Eu, and Gd)

    SciTech Connect

    Shafiq, M.; Ahmad, Iftikhar E-mail: dr.iftikhar@uom.edu.pk; Jalali Asadabadi, S.

    2014-09-14

    In this paper, the structural, elastic, and electronic properties of RIn₃ and RSn₃ (R = Sm, Eu, Gd) compounds have been investigated using the full potential linearized augmented plane wave plus local orbital method within the density functional theory. The structural properties are investigated using the LDA, GGA, and the band correlated LDA+U and GGA+U schemes. The lattice parameters are in good agreement with the available experimental results and the divalent state of Eu is also verified. The spin-orbit coupling is included in order to predict the correct electronic properties and splitting of 4f states of the rare earth elements is also incorporated. We calculated Bulk modulus, shear modulus, Young's modulus, anisotropic ratio, Kleinman parameters, Poisson's ratio, Lame's co-efficient, sound velocities for shear and longitudinal waves, and Debye temperature. We also predict the Cauchy pressure and B/G ratio in order to explore the ductile and brittle behaviors of these compounds.

  9. Solid state phase equilibria and intermetallic compounds of the Al-Cr-Ho system

    SciTech Connect

    Pang, Mingjun; Zhan, Yongzhong; Du, Yong

    2013-02-15

    The solid state phase equilibria of the Al-Cr-Ho ternary system at 500 Degree-Sign C were experimentally investigated. The phase relations at 500 Degree-Sign C are governed by 14 three-phase regions, 29 two-phase regions and 15 single-phase regions. The existences of 10 binary compounds and 2 ternary phases have been confirmed. Al{sub 11}Cr{sub 2}, Al{sub 11}Cr{sub 4} and Al{sub 17}Ho{sub 2} were not found at 500 Degree-Sign C. Crystal structures of Al{sub 9}Cr{sub 4} and Al{sub 8}Cr{sub 4}Ho were determined by the Rietveld X-ray powder data refinement. Al{sub 9}Cr{sub 4} was found to exhibit cubic structure with space group I4-bar 3m (no. 217) and lattice parameters a=0.9107(5) nm. Al{sub 8}Cr{sub 4}Ho crystallizes in ThMn{sub 12} structure type with space group I4/mmm (no. 139) and lattice parameters a=0.8909(4) nm, c=0.5120(5) nm. It is concluded that the obtained Al{sub 4}Cr phase in this work should be {mu}-Al{sub 4}Cr by comparing with XRD pattern of the hexagonal {mu}-Al{sub 4}Mn compound. - Graphical abstract: The solid state phase equilibria of the Al-Cr-Ho ternary system at 500 Degree-Sign C. Highlights: Black-Right-Pointing-Pointer Al-Cr-Ho system has been investigated. Black-Right-Pointing-Pointer Al{sub 9}Cr{sub 4} has cubic structure with space group I4-bar 3m. Black-Right-Pointing-Pointer Al{sub 8}Cr{sub 4}Ho crystallizes in ThMn{sub 12} type with space group I4/mmm. Black-Right-Pointing-Pointer Al{sub 4}Cr phase is {mu}-type at 500 Degree-Sign C.

  10. The structural, elastic and thermodynamic properties of intermetallic compound CeGa2

    NASA Astrophysics Data System (ADS)

    Çiftci, Yasemin; Çolakoǧlu, Kemal; Çoban, Cansu; Deligöz, Engin

    2012-02-01

    The structural, elastic and thermodynamic characteristics of CeGa2 compound in the AlB2 (space group: P6/mmm) and the omega trigonal (space group: P-3m1) type structures are investigated using the methods of density functional theory within the generalized gradient approximation (GGA). The thermodynamic properties of the considered structures are obtained through the quasi-harmonic Debye model. The results on the basic physical parameters, such as the lattice constant, the bulk modulus, the pressure derivative of bulk modulus, the phase-transition pressure (P t) from P6/mmm to P-3m1 structure, the second-order elastic constants, Zener anisotropy factor, Poisson's ratio, Young's modulus, and the isotropic shear modulus are presented. In order to gain further information, the pressure and temperature-dependent behavior of the volume, the bulk modulus, the thermal expansion coefficient, the heat capacity, the entropy, Debye temperature and Grüneisen parameter are also evaluated over a pressure range of 0-6 GPa and a wide temperature range of 0-1800 K. The obtained results are in agreement with the available experimental and the other theoretical values.

  11. The structural, elastic and thermodynamic properties of intermetallic compound CeGa2

    NASA Astrophysics Data System (ADS)

    Çiftci, Yasemin Ö.; Çolakoǧlu, Kemal; Çoban, Cansu; Deligöz, Engin

    2012-02-01

    The structural, elastic and thermodynamic characteristics of CeGa2 compound in the AlB2 (space group: P6/mmm) and the omega trigonal (space group: P-3m1) type structures are investigated using the methods of density functional theory within the generalized gradient approximation (GGA). The thermodynamic properties of the considered structures are obtained through the quasi-harmonic Debye model. The results on the basic physical parameters, such as the lattice constant, the bulk modulus, the pressure derivative of bulk modulus, the phase-transition pressure ( P t ) from P6/mmm to P-3m1 structure, the second-order elastic constants, Zener anisotropy factor, Poisson's ratio, Young's modulus, and the isotropic shear modulus are presented. In order to gain further information, the pressure and temperature-dependent behavior of the volume, the bulk modulus, the thermal expansion coefficient, the heat capacity, the entropy, Debye temperature and Grüneisen parameter are also evaluated over a pressure range of 0-6 GPa and a wide temperature range of 0-1800 K. The obtained results are in agreement with the available experimental and the other theoretical values.

  12. Positron annihilation study of the influence of doping on the 3 d electron states in the Ni3Al intermetallic compound

    NASA Astrophysics Data System (ADS)

    Druzhkov, A. P.; Perminov, D. A.; Stepanova, N. N.

    2010-10-01

    The 3 d electron states in Ni3Al single crystals doped with Fe, Co, and Nb have been investigated using angular correlation of annihilation radiation (ACAR). The ACAR spectra contain information on the momentum distribution of valence electrons and strongly bound 3 d electrons of the intermetallic compound. It has been established that the positrons in the Ni3Al crystals predominantly annihilate in the nickel sublattice from delocalized states. The doping of the compound by the third element leads to a variation in the momentum distribution of Ni 3 d electrons due to the change in the character of interatomic bonds. An analysis of the momentum distribution has demonstrated that the niobium atoms increase the covalent component of the chemical bond as compared to the binary compound due to the d Nb- d Ni hybridization. The doping with cobalt atoms also enhances the tendency toward the formation of the covalent bond. At the same time, iron atoms have a weak effect on the electronic structure of the intermetallic compound.

  13. Hydrogenation of Zr0.9Ti0.1CrxFe2-x Intermetallic Compounds: Free Electron Model for Magnetic Susceptibility and Thermoelectric Power

    NASA Astrophysics Data System (ADS)

    Niyomsoan, S.; Termsuksawad, P.; Goldfarb, R. B.; Olson, D. L.; Mishra, B.; Kaydanov, V.; Gavra, Z.

    2008-02-01

    The magnetic susceptibility and thermoelectric power of Zr0.9Ti0.1CrxFe2-x intermetallic compounds were investigated as functions of hydrogen content. The alloys are paramagnetic, with magnetic susceptibility and Seebeck coefficient increasing with the amount of stored hydrogen. The susceptibility is proportional to the Seebeck coefficient and to the d-electron concentration, consistent with a free-electron model. The susceptibility of alloys with lower iron concentration suggests exchange-enhanced Pauli paramagnetism. However, Curie-Weiss paramagnetism likely coexists in alloys with higher iron content. Magnetic and electronic measurements may be used to assess the ability of an alloy to store hydrogen.

  14. Radiation-induced amorphization of intermetallic compounds: A molecular-dynamics study of CuTi and Cu sub 4 Ti sub 3

    SciTech Connect

    Lam, N.Q.; Okamoto, P.R. ); Sabochick, M.J. . Dept. of Engineering Physics)

    1991-06-01

    In the present paper, important results of our recent computer simulation of radiation-induced amorphization in the ordered compounds CuTi and Cu{sub 4}Ti{sub 3} are summarized. The energetic, structural, thermodynamic and mechanical responses of these intermetallics during chemical disordering, point-defect production and heating were simulated, using molecular dynamics and embedded-atom potentials. From the atomistic details obtained, the critical role of radiation-induced structural disorder in driving the crystalline-to-amorphous phase transformation is discussed. 25 refs., 4 figs.

  15. Crystal structure and chemical bonding of novel Li-containing polar intermetallic compound La{sub 11}Li{sub 12}Ge{sub 16}

    SciTech Connect

    Jung, Yaho; Nam, Gnu; Jeon, Jieun; Kim, Youngjo; You, Tae-Soo

    2012-12-15

    A novel Li-containing polar intermetallic compound La{sub 11}Li{sub 12}Ge{sub 16} has been synthesized using the high-temperature reaction method and characterized by both powder and single-crystal X-ray diffractions. The title compound crystallized in the orthorhombic crystal system (space group Immm, Z=2, Pearson symbol oI78) with fifteen crystallographically unique atomic positions in the asymmetric unit, and the lattice parameters are refined as a=4.5244(4) A, b=6.9932(6) A, and c=53.043(5) A. The complex crystal structure of the title compound can be described as a 2:1 intergrowth of two closely related compounds: La{sub 2}Li{sub 2}Ge{sub 3} (Ce{sub 2}Li{sub 2}Ge{sub 3}-type) and La{sub 3}Li{sub 4}Ge{sub 4} (Zr{sub 3}Cu{sub 4}Si{sub 4}-type) acting like 'building-blocks' along the c-axis. Six La sites are categorized into three distinct types based on the local coordination environment showing the coordination numbers of 12-14. Three unique Li sites are placed in the centers of local tetrahedra formed by four Ge atoms which eventually construct Ge{sub 2} dimers or 1-dimensional cis-/trans-Ge chains. Theoretical investigations using the tight-binding linear muffin-tin orbital (LMTO) method provide rationales for an improved structural stability and for unique local coordination geometries established by anionic elements including [LiGe{sub 4}] tetrahedra, cis-/trans-Ge chain and Ge{sub 2} dimers. - Graphical abstract: Reported is a novel ternary Li-containing polar intermetallic compound La{sub 11}Li{sub 12}Ge{sub 16}. The complex crystal structure can be viewed as a simple combination of two closely related known compounds acting as 'building-blocks', La{sub 2}Li{sub 2}G{sub 3} and La{sub 3}Li{sub 4}Ge{sub 4}, in a 2:1 stoichiometric ratio. Highlights: Black-Right-Pointing-Pointer A novel Li-containing polar intermetallic compound La{sub 11}Li{sub 12}Ge{sub 16} was synthesized. Black-Right-Pointing-Pointer The complex crystal structure was easily explained as

  16. Surface structures of In-Pd intermetallic compounds. I. Experimental study of In thin films on Pd(111) and alloy formation

    SciTech Connect

    McGuirk, G. M.; Ledieu, J.; Gaudry, É.; Weerd, M.-C. de; Fournée, V.

    2014-08-28

    A combination of experimental methods was used to study the structure of In thin films deposited on the Pd(111) surface and the alloying behavior. X-ray photoelectron spectroscopy (XPS), low-energy electron diffraction (LEED), and scanning tunneling microscopy results indicate that surface alloying takes place at room temperature. Below 2 monolayer equivalents (MLEs), the LEED patterns show the formation of three rotational domains of InPd(110) of poor structural quality on top of the Pd(111) substrate. Both core-levels and valence band XPS spectra show that the surface alloy does not yet exhibit the electronic structure characteristic of the 1:1 intermetallic compound under these conditions. Annealing the 1 MLE thin film up to 690 K yields to a transition from a multilayer InPd near-surface intermetallic phase to a monolayer-like surface alloy exhibiting a well ordered (√(3)×√(3)) R30{sup ∘} superstructure and an estimated composition close to In{sub 2}Pd{sub 3}. Annealing above 690 K leads to further In depletion and a (1 × 1) pattern is recovered. The (√(3)×√(3)) R30{sup ∘} superstructure is not observed for thicker films. Successive annealing of the 2 MLE thin film leads the progressive disappearance of the InPd diffraction spots till a sharp (1 × 1) pattern is recovered above 690 K. In the high coverage regime (from 4 to 35 MLE), the formation of three rotational domains of a bcc-In{sub 7}Pd{sub 3} compound with (110) orientation is observed. This In-rich phase probably grows on top of interfacial InPd(110) domains and is metastable. It transforms into a pure InPd(110) near-surface intermetallic phase in a temperature range between 500 and 600 K depending on the initial coverage. At this stage, the surface alloy exhibits core-level chemical shifts and valence band (VB) spectra identical to those of the 1:1 InPd intermetallic compound and resembling Cu-like density of states. Annealing at higher temperatures yields to a decrease of the In

  17. Electrocatalytic mechanism and kinetics of SOMs oxidation on ordered PtPb and PtBi intermetallic compounds: DEMS and FTIRS study.

    PubMed

    Wang, Hongsen; Alden, Laif; Disalvo, F J; Abruña, Héctor D

    2008-07-01

    The electrocatalytic activities and mechanisms of PtPb and PtBi ordered intermetallic phases towards formic acid, formaldehyde and methanol oxidation have been studied by DEMS and FTIRS, and the results compared to those for a pure polycrystalline platinum electrode. While PtPb exhibits an enhanced electrocatalytic activity for the oxidation of all three organic molecules when compared to a Pt electrode, PtBi exhibits an enhanced catalytic activity towards formic acid and formaldehyde oxidation, but not methanol. FTIRS data indicate that adsorbed CO does not form on PtPb or PtBi intermetallic compounds during the oxidation of formic acid, formaldehyde and methanol, and therefore their oxidation on both PtPb and PtBi intermetallic compounds proceeds via a non-CO(ads) pathway. Quantitative DEMS measurements indicate that only CO(2) was detected as a final product during formic acid oxidation on Pt, PtPb and PtBi electrodes. At a smooth polycrystalline platinum electrode, the oxidation of formaldehyde and methanol produces mainly intermediates (formaldehyde and formic acid), while CO(2) is a minor product. In contrast, CO(2) is the major product for formaldehyde and methanol oxidation at a PtPb electrode. The high current efficiency of CO(2) formation for methanol and formaldehyde oxidation at a PtPb electrode can be ascribed to the complete dehydrogenation of formaldehyde and formic acid due to electronic effects. The low onset potential, high current density and high CO(2) yield make PtPb one of the most promising electrocatalysts for fuel cell applications using small organic molecules as fuels. PMID:18563235

  18. Interfacial reaction of intermetallic compounds of ultrasonic-assisted brazed joints between dissimilar alloys of Ti6Al4V and Al4Cu1Mg.

    PubMed

    Ma, Zhipeng; Zhao, Weiwei; Yan, Jiuchun; Li, Dacheng

    2011-09-01

    Ultrasonic-assisted brazing of Al4Cu1Mg and Ti6Al4V using Zn-based filler metal (without and with Si) has been investigated. Before brazing, the Ti6Al4V samples were pre-treated by hot-dip aluminizing and ultrasonic dipping in a molten filler metal bath in order to control the formation of intermetallic compounds between the Ti6Al4V samples and the filler metal. The results show that the TiAl(3) phase was formed in the interface between the Ti6Al4V substrate and the aluminized coating. For the Zn-based filler metal without Si, the Ti6Al4V interfacial area of the brazed joint did not change under the effect of the ultrasonic wave, and only consisted of the TiAl(3) phase. For the Zn-based filler metal with Si, the TiAl(3) phase disappeared and a Ti(7)Al(5)Si(12) phase was formed at the interfacial area of the brazed joints under the effect of the ultrasonic wave. Due to the TiAl(3) phase completely changing to a Ti(7)Al(5)Si(12) phase, the morphology of the intermetallic compounds changed from a block-like shape into a lamellar-like structure. The highest shear strength of 138MPa was obtained from the brazed joint free of the block-like TiAl(3) phase. PMID:21489846

  19. PyDII: A python framework for computing equilibrium intrinsic point defect concentrations and extrinsic solute site preferences in intermetallic compounds

    NASA Astrophysics Data System (ADS)

    Ding, Hong; Medasani, Bharat; Chen, Wei; Persson, Kristin A.; Haranczyk, Maciej; Asta, Mark

    2015-08-01

    Point defects play an important role in determining the structural stability and mechanical behavior of intermetallic compounds. To help quantitatively understand the point defect properties in these compounds, we developed PyDII, a Python program that performs thermodynamic calculations of equilibrium intrinsic point defect concentrations and extrinsic solute site preferences in intermetallics. The algorithm implemented in PyDII is built upon a dilute-solution thermodynamic formalism with a set of defect excitation energies calculated from first-principles density-functional theory methods. The analysis module in PyDII enables automated calculations of equilibrium intrinsic antisite and vacancy concentrations as a function of composition and temperature (over ranges where the dilute solution formalism is accurate) and the point defect concentration changes arising from addition of an extrinsic substitutional solute species. To demonstrate the applications of PyDII, we provide examples for intrinsic point defect concentrations in NiAl and Al3 V and site preferences for Ti, Mo and Fe solutes in NiAl.

  20. A COMPOUND MODEL FOR THE ORIGIN OF EARTH'S WATER

    SciTech Connect

    Izidoro, A.; Winter, O. C.; De Souza Torres, K.; Haghighipour, N.

    2013-04-10

    One of the most important subjects of debate in the formation of the solar system is the origin of Earth's water. Comets have long been considered as the most likely source of the delivery of water to Earth. However, elemental and isotopic arguments suggest a very small contribution from these objects. Other sources have also been proposed, among which local adsorption of water vapor onto dust grains in the primordial nebula and delivery through planetesimals and planetary embryos have become more prominent. However, no sole source of water provides a satisfactory explanation for Earth's water as a whole. In view of that, using numerical simulations, we have developed a compound model incorporating both the principal endogenous and exogenous theories, and investigating their implications for terrestrial planet formation and water delivery. Comets are also considered in the final analysis, as it is likely that at least some of Earth's water has cometary origin. We analyze our results comparing two different water distribution models, and complement our study using the D/H ratio, finding possible relative contributions from each source and focusing on planets formed in the habitable zone. We find that the compound model plays an important role by showing greater advantage in the amount and time of water delivery in Earth-like planets.

  1. Structural, stability and electronic properties of C15-AB2 (A = Ti, Zr; B = Cr) intermetallic compounds and their hydrides: An ab initio study

    NASA Astrophysics Data System (ADS)

    Sarhaddi, Reza; Arabi, Hadi; Pourarian, Faiz

    2014-05-01

    The structural, stability and electronic properties of C15-AB2 (A = Ti, Zr; B = Cr) isomeric intermetallic compounds were systematically investigated by using density functional theory (DFT) and plane-wave pseudo-potential (PW-PP) method. The macroscopic properties including the lattice constant, bulk modulus and stability for these compounds were studied before and after hydrogenation. For parent compounds, the enthalpy of formation was evaluated with regard to their bulk modules and electronic structures. After hydrogenation of compounds at different interstitial tetrahedral sites (A2B2, A1B3, B4), a volume expansion was found for hydrides. The stability properties of hydrides characterized the A2B2 sites as the site preference of hydrogen atoms for both compounds. The Miedema's "reverse stability" rule is also satisfied in these compounds as lower the enthalpy of formation for the host compound, the more stable the hydride. Analysis of microscopic properties (electronic structures) after hydrogenation at more stable interstitial site (A2B2) shows that the H atoms interact stronger with the weaker (or non) hydride forming element B (Cr) than the hydride forming element A (Ti/Zr). A correlation was also found between the stability of the hydrides and their electronic structure: the deeper the hydrogen band, the less stable the hydride.

  2. The adsorption, catalytic and structural characteristics of LaNi /SUB 5-x/ Co /SUB x/ intermetallic compounds and their hydrides -

    SciTech Connect

    Konenko, I.R.; Fedorovskaya, E.A.; Klabunovskii, E.I.; Slinkin, A.A.; Starodubtseva, E.V.; Stepanov, Y.P.

    1986-10-01

    The hydrogen adsorption, propylene hydrogenation catalysis, and magnetic properties of LaNi /SUB 5-x/ Co /SUB x/ (0 intermetallic compounds (IMC) and their hydrides were studied. An extremal dependence of the specific catalytic activity on the catalyst composition was found. The rate of propylene hydrogenation obeys a kinetic equation which is zero-order in hydrogen and first-order relative to the olefin. Comparison of the data for the catalytic, magnetic, and physicochemical properties of the IMC and their hydrides showed that the catalytic activity of these compounds is related to the hydrogen affinity of the IMC and their structural features related to the ratio of the nickel and cobalt atoms.

  3. The easy magnetization directions in R{sub 6}Fe{sub 23} intermetallic compounds: A crystal field analysis

    SciTech Connect

    Bowden, G.J.; Cadogan, J.M.; de Leon, H.; Ryan, D.H.

    1997-04-01

    X-ray diffraction patterns on magnetically aligned powder samples of R{sub 6}Fe{sub 23} (R=Dy, Er, Ho, and Tm) show that these compounds all magnetize along a [111] easy direction. At first sight it is difficult to reconcile the common easy magnetization direction of Er{sub 6}Fe{sub 23} and Tm{sub 6}Fe{sub 23} on one hand, with Dy{sub 6}Fe{sub 23} and Ho{sub 6}Fe{sub 23} on the other, since the respective B{sub 20} rare earth crystal field parameters of these pairs of compounds are opposite in sign. In this article we show that the crystal field stabilization energy of the [111] direction, relative to either [100] or [110], varies as the square of the crystal field term B{sub 20}, thereby providing an explanation for the common [111] direction of easy magnetization. {copyright} {ital 1997 American Institute of Physics.}

  4. Random-anisotropy ferromagnetic state in the C u5G d0.54C a0.42 intermetallic compound

    NASA Astrophysics Data System (ADS)

    Krnel, M.; Vrtnik, S.; Koželj, P.; Kocjan, A.; Jagličić, Z.; Boulet, P.; de Weerd, M. C.; Dubois, J. M.; Dolinšek, J.

    2016-03-01

    By applying the alloy design concept that stable intermetallic phases between two immiscible elements can be formed by adding a third element that forms stable compounds with both elements, we have synthesized the first known stable intermetallic compound of Cu, Gd, and Ca, where copper acts as the mediating element between the immiscible Gd and Ca. A compound with the composition C u84G d9C a7 (equivalent to C u5G d0.54C a0.42 ) was synthesized by the Czochralski technique in the form of a large single crystal of high structural perfection, and the structural model was determined by x-ray diffraction (XRD). The compound crystallizes in the hexagonal system, space group P 6 /mmm, and the crystal structure is isotypic to the C u5.44T b0.78 . The unit cell contains inherent disorder due to partial occupation of the Cu3 site and the substitutional disorder at the Gd/Ca mixed site located at the vertices of the hexagonal unit cell, where Gd and Ca randomly substitute each other. The random substitution of magnetic Gd by nonmagnetic Ca atoms makes the magnetic Gd lattice disordered, which leads to interesting magnetic ordering at low temperatures that occurs below TC=24 K in zero and low external magnetic fields. By performing a large set of complementary experiments along two perpendicular crystallographic directions (the [001] hexagonal-axis direction and the [100] hexagonal-plane direction), we show that the zero-field collective magnetic state can be described as a random-anisotropy ferromagnetic state, where random magnetic anisotropies originate from the magnetic dipole interactions between the Gd moments in the magnetically disordered lattice. The random-anisotropy ferromagnetic state in the C u84G d9C a7 is characterized by randomness and frustration of magnetic interactions, which are the two ingredients that allow classifying this state into the generic class of spin glasses. Our paper opens the possibility to search for new ternary intermetallic phases in the

  5. Finite Element Modeling of Stress Evolution in Sn Films due to Growth of the Cu6Sn5 Intermetallic Compound

    NASA Astrophysics Data System (ADS)

    Buchovecky, Eric; Jadhav, Nitin; Bower, Allan F.; Chason, Eric

    2009-12-01

    We use finite element simulations to quantitatively evaluate different mechanisms for the generation of stress in Sn films due to growth of the Cu6Sn5 intermetallic phase at the Cu-Sn interface. We find that elastic and plastic behavior alone are not sufficient to reproduce the experimentally measured stress evolution. However, when grain boundary diffusion is included, the model results agree well with experimental observations. Examination of conditions necessary to produce the observed stresses provides insight into potential strategies for minimizing stress generation and thus mitigating Sn whisker growth.

  6. Comparison of Sn-Ag-Cu Solder Alloy Intermetallic Compound Growth Under Different Thermal Excursions for Fine-Pitch Flip-Chip Assemblies

    NASA Astrophysics Data System (ADS)

    Tian, Ye; Liu, Xi; Chow, Justin; Wu, Yi Ping; Sitaraman, Suresh K.

    2013-08-01

    The intermetallic compound (IMC) evolution in Cu pad/Sn-Ag-Cu solder interface and Sn-Ag-Cu solder/Ni pad interface was investigated using thermal shock experiments with 100- μm-pitch flip-chip assemblies. The experiments show that low standoff height of solder joints and high thermomechanical stress play a great role in the interfacial IMC microstructure evolution under thermal shock, and strong cross-reaction of pad metallurgies is evident in the intermetallic growth. Furthermore, by comparing the IMC growth during thermal aging and thermal shock, it was found that thermal shock accelerates IMC growth and that kinetic models based on thermal aging experiments underpredict IMC growth in thermal shock experiments. Therefore, new diffusion kinetic parameters were determined for the growth of (Cu,Ni)6Sn5 using thermal shock experiments, and the Cu diffusion coefficient through the IMC layer was calculated to be 0.2028 μm2/h under thermal shock. Finite-element models also show that the solder stresses are higher under thermal shock, which could explain why the IMC growth is faster and greater under thermal shock cycling as opposed to thermal aging.

  7. Structural and physical properties of the new intermetallic compound Yb{sub 3}Pd{sub 2}Sn{sub 2}

    SciTech Connect

    Solokha, P.; Curlik, I.; Giovannini, M.; Lee-Hone, N.R.; Reiffers, M.; Ryan, D.H.; Saccone, A.

    2011-09-15

    The crystal structure of the ternary intermetallic compound Yb{sub 3}Pd{sub 2}Sn{sub 2} has been determined ab initio from powder X-ray diffraction data. The compound crystallizes as a new structure type in the orthorhombic space group Pbcm and lattice constants a=0.58262(3), b=1.68393(8), c=1.38735(7) nm. Yb{sub 3}Pd{sub 2}Sn{sub 2} is composed of a complex {sub {infinity}}[Pd{sub 2}Sn{sub 2}]{sup {delta}-} polyanionic network in which the Yb ions are embedded. A comparison between this structure and those of Eu{sub 3}Pd{sub 2}Sn{sub 2} and Ca{sub 3}Pd{sub 2}Sn{sub 2}, other novel polar intermetallic compounds, was made. DC susceptibility and {sup 170}Yb Moessbauer spectroscopic measurements indicate a close-to divalent Yb behavior. Moreover, a hybridization between 4f and conduction electrons is suggested by electronic structure calculations and heat capacity measurements. - Graphical Abstract: Polyanionic networks for Yb{sub 3}Pd{sub 2}Sn{sub 2} and Eu{sub 3}Pd{sub 2}Sn{sub 2}. Highlights: > We determined ab initio the crystal structure of the novel ternary Yb{sub 3}Pd{sub 2}Sn{sub 2} stannide. > This structure has been compared with those of other polar 3:2:2 stannides discovered in this work. > Measurements of physical properties on Yb{sub 3}Pd{sub 2}Sn{sub 2} point to a close-to-divalent Yb ion. > Electron structure calculation and heat capacity indicate some hybridization between 4f and conduction electrons.

  8. Blocking hillock and whisker growth by intermetallic compound formation in Sn-0.7Cu flip chip solder joints under electromigration

    NASA Astrophysics Data System (ADS)

    Liang, S. W.; Chen, Chih; Han, J. K.; Xu, Luhua; Tu, K. N.; Lai, Yi-Shao

    2010-05-01

    Mass extrusion occurs in electromigration at the anode in cross-sectioned Sn-0.7Cu flip-chip solder joints. In a pair of joints, the hillock squeezed out at the anode on the board side is more serious than the whisker grown at the anode on the chip side. The difference of mass extrusion has been found to be affected by the amount of intermetallic compound (IMC) formation in the solder bump. It is found that when a large amount of Cu-Sn IMCs form in the grain boundaries of Sn grains, small hillocks are extruded on the anode end. It is proposed that the excessive IMC formation may be able to block the diffusion path of Sn atoms, so the growth of both the Sn whiskers and hillocks are retarded.

  9. Influence of nanoparticle addition on the formation and growth of intermetallic compounds (IMCs) in Cu/Sn-Ag-Cu/Cu solder joint during different thermal conditions

    NASA Astrophysics Data System (ADS)

    Tan, Ai Ting; Tan, Ai Wen; Yusof, Farazila

    2015-06-01

    Nanocomposite lead-free solders are gaining prominence as replacements for conventional lead-free solders such as Sn-Ag-Cu solder in the electronic packaging industry. They are fabricated by adding nanoparticles such as metallic and ceramic particles into conventional lead-free solder. It is reported that the addition of such nanoparticles could strengthen the solder matrix, refine the intermetallic compounds (IMCs) formed and suppress the growth of IMCs when the joint is subjected to different thermal conditions such as thermal aging and thermal cycling. In this paper, we first review the fundamental studies on the formation and growth of IMCs in lead-free solder joints. Subsequently, we discuss the effect of the addition of nanoparticles on IMC formation and their growth under several thermal conditions. Finally, an outlook on the future growth of research in the fabrication of nanocomposite solder is provided.

  10. Intermetallic compounds formed at the interface between Cu substrate and an Sn-9Zn-0.5Ag lead-free solder

    SciTech Connect

    Chang, T.-C.; Hon, M.-H.; Wang, M.-C

    2003-04-30

    The intermetallic compounds (IMCs) formed at the interface between Cu substrate and an Sn-9Zn-0.5Ag lead-free solder alloy have been investigated by X-ray diffraction (XRD), transmission electron microscopy (TEM) and electron diffraction (ED). The XRD patterns show that the main IMCs formed at the interface of Sn-9Zn-0.5Ag/Cu are {gamma}-Cu{sub 5}Zn{sub 8} and {eta}'-Cu{sub 6}Sn{sub 5}. The Ag{sub 3}Sn IMC with orthorhombic structure was also observed at the Sn-9Zn-0.5Ag/Cu interface by TEM and ED analyses. The interfacial adhesion strength between the Cu substrate and Sn-9Zn-0.5Ag lead-free solder alloy is higher than that of the Sn-9Zn alloy due to the formation of Ag{sub 3}Sn IMC at the interface.

  11. Enhancement on wettability and intermetallic compound formation with an addition of Al on Sn-0.7Cu lead-free solder fabricated via powder metallurgy method

    NASA Astrophysics Data System (ADS)

    Adli, Nisrin; Razak, Nurul Razliana Abdul; Saud, Norainiza

    2016-07-01

    Due to the toxicity of lead (Pb), the exploration of another possibility for lead-free solder is necessary. Nowadays, SnCu alloys are being established as one of the lead-free solder alternatives. In this study, Sn-0.7Cu lead-free solder with an addition of 1wt% and 5wt% Al were investigated by using powder metallurgy method. The effect of Al addition on the wettability and intermetallic compound thickness (IMC) of Sn-0.7Cu-Al lead-free solder were appraised. Results showed that Al having a high potential to enhance Sn-0.7Cu lead-free solder due to its good wetting and reduction of IMC thickness. The contact angle and IMC of the Sn-0.7Cu-Al lead-free solder were decreased by 14.32% and 40% as the Al content increased from 1 wt% to 5 wt%.

  12. Structural, electronic and elastic properties of the B2-ScM (M =Au, Hg and Tl) intermetallic compounds: Ab initio calculations

    NASA Astrophysics Data System (ADS)

    Mousa, Ahmad A.; Khalifeh, Jamil M.

    2015-10-01

    Structural, electronic, elastic and mechanical properties of ScM (M =Au, Hg and Tl) intermetallic compounds are studied using the full potential-linearized augmented plane wave (FP-LAPW) method based on the density functional theory (DFT), within the generalized gradient approximation (GGA) and the local density approximation (LDA) to the exchange-correlation approximation energy as implemented in the Wien2k code. The ground state properties including lattice parameters, bulk modulus and elastic constants were all computed and compared with the available previous theoretical and experimental results. The lattice constant was found to increase in contrast to the bulk modulus which was found to decrease with every substitution of the cation (M) starting from Au till Tl in ScM. Both the electronic band structure and density-of-states (DOS) calculations show that these compounds possess metallic properties. The calculated elastic constants (C11, C12 and C44) confirmed the elastic stability of the ScM compounds in the B2-phase. The mechanical properties and ductile behaviors of these compounds are also predicted based on the calculated elastic constants.

  13. Double-exchange mechanism in rare-earth compounds

    SciTech Connect

    Gulacsi, M.

    2015-03-15

    We show that double-exchange mechanism is responsible for ferromagnetism in low dimensional rare-earth compounds. We use the bosonized version of the one-dimensional Anderson lattice model in Toulouse limit to characterize the properties of the emerging ferromagnetic phase. We give a comprehensive description of the ferromagnetic ordering of the correlated electrons which appears at intermediate couplings and doping. The obtained ferromagnetic phase transitions have been identified to be an order–disorder transition of the quantum random transverse-field Ising type.

  14. Electric Field Gradient at Nb Site in the Intermetallic Compounds Nb3X (X = AI, In, Si, Ge, Sn) Measured by PAC

    NASA Astrophysics Data System (ADS)

    Junqueira, A. C.; Carbonari, A. W.; Filho, J. Mestnik; Saxena, R. N.

    2000-02-01

    The electric field gradient (efg) at the Nb site in the intermetallic compounds Nb3X (X = Al, In, Si, Ge, Sn) was measured by the Perturbed Angular Correlation (PAC) method using the well-known gamma-gamma cascade of 133 -482 keV in 181Ta from the β- decay of 181Hf, substituting approximately 0.1 atom percent of Nb. The PAC results show that Vzz drops by nearly 40% when X changes from Al to In, and by about 25% when X changes from Si to Ge and Sn. This behavior is most probably related to the change in the degree of sp hybridization in these compounds. The Vzz values of the studied compounds do not follow the well known universal correlation for the efg's in non-cubic metals but the observed trend is well reproduced by results of ab-initio electronic structure calculations. In the case of Nb3 Al a linear temperature dependence of the quadrupole frequencies was observed in the temperature range of 6.5 to 1210 K.

  15. Evolution of the magnetic properties along the RCuBi2 (R = Ce, Pr, Nd, Gd, Sm) series of intermetallic compounds

    NASA Astrophysics Data System (ADS)

    Jesus, C. B. R.; Piva, M. M.; Rosa, P. F. S.; Adriano, C.; Pagliuso, P. G.

    2014-05-01

    In this paper, the evolution of the magnetic properties along the series of intermetallic compounds RCuBi2 (R = Ce, Pr, Nd, Gd, Sm) is discussed. These compounds crystallize in a tetragonal ZrCuSi2 (P4/nmm) structure, and our single crystals of RCuBi2 grown from Bi-flux show no evidence for Cu-deficiency [Ye et al., Acta Crystallogr. C 52, 1325 (1996)] as previously reported for R = Ce. For R = Ce, Pr, Gd, and Sm, we found an antiferromagnetic ordering at TN ˜ 16 K, 4.2 K, 13.6 K, and 4.9 K, respectively. For R = Nd, we saw no evidence for a magnetic phase transition down to T = 2 K. These values of TN clearly show a dramatic breakdown of the De Gennes factor in this series. We discuss our data taken into account the tetragonal crystalline electrical field and the anisotropic Ruderman-Kittel-Kasuya-Yoshida magnetic interaction between the R-ions in this family of compounds.

  16. Effect of Laser Processing Parameters on the Formation of Intermetallic Compounds in Fe-Al Dissimilar Welding

    NASA Astrophysics Data System (ADS)

    Meco, Sonia; Ganguly, Supriyo; Williams, Stewart; McPherson, Norman

    2014-09-01

    Fusion welding of steel to aluminum is difficult due to formation of different types of Fe-Al intermetallics (IMs). In this work, 2 mm-thick steel was joined to 6 mm aluminum in overlap configuration using a 8 kW CW fiber laser. A defocused laser beam was used to control the energy input and allow melting of the aluminum alone and form the bond by wetting of the steel substrate. Experimentally, the process energy was varied by changing the power density (PD) and interaction time separately to understand the influence of each of these parameters on the IM formation. It was observed that the IM formation is a complex function of PD and interaction time. It was also found that the mechanical strength of such joint could not be simply correlated to the IM layer thickness but also depends on the area of wetting of the steel substrate by molten aluminum. In order to form a viable joint, PD needs to be over a threshold value where although IM growth will increase, the strength will be better due to increased wetting. Any increase in interaction time, with PD over the threshold, will have negative effect on the bond strength.

  17. Magnetic interactions in equi-atomic rare-earth intermetallic alloys RScGe (R = Ce, Pr, Nd and Gd) studied by time differential perturbed angular correlation spectroscopy and ab initio calculations

    NASA Astrophysics Data System (ADS)

    Mishra, S N

    2009-03-01

    Applying the time differential perturbed angular correlation (TDPAC) technique we have measured electric and magnetic hyperfine fields of the 111Cd impurity in equi-atomic rare-earth intermetallic alloys RScGe (R = Ce, Pr and Gd) showing antiferro- and ferromagnetism with unusually high ordering temperatures. The Cd nuclei occupying the Sc site show high magnetic hyperfine fields with saturation values Bhf(0) = 21 kG, 45 kG and 189 kG in CeScGe, PrScGe and GdScGe, respectively. By comparing the results with the hyperfine field data of Cd in rare-earth metals and estimations from the RKKY model, we find evidence for the presence of additional spin density at the probe nucleus, possibly due to spin polarization of Sc d band electrons. The principal electric field gradient component Vzz in CeScGe, PrScGe and GdScGe has been determined to be 5.3 × 1021 V m-2, 5.5 × 1021 V m-2 and 5.6 × 1021 V m-2, respectively. Supplementing the experimental measurements, we have carried out ab initio calculations for pure and Cd-doped RScGe compounds with R = Ce, Pr, Nd and Gd using the full potential linearized augmented plane wave (FLAPW) method based on density functional theory (DFT). From the total energies calculated with and without spin polarization we find ferrimagnetic ground states for CeScGe and PrScGe while NdScGe and GdScGe are ferromagnetic. In addition, we find a sizable magnetic moment at the Sc site, increasing from ≈0.10 μB in CeScGe to ≈0.3 μB in GdScGe, confirming the spin polarization of Sc d band electrons. The calculated electric field gradient and magnetic hyperfine fields of the Cd impurity closely agree with the experimental values. We believe spin polarization of Sc 3d band electrons, strongly hybridized with spin polarized 5d band electrons of the rare-earth, enables a long range Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction between RE 4f moments which in turn leads to high magnetic ordering temperatures in RScGe compounds.

  18. Magnetic interactions in equi-atomic rare-earth intermetallic alloys RScGe (R = Ce, Pr, Nd and Gd) studied by time differential perturbed angular correlation spectroscopy and ab initio calculations.

    PubMed

    Mishra, S N

    2009-03-18

    Applying the time differential perturbed angular correlation (TDPAC) technique we have measured electric and magnetic hyperfine fields of the (111)Cd impurity in equi-atomic rare-earth intermetallic alloys RScGe (R = Ce, Pr and Gd) showing antiferro- and ferromagnetism with unusually high ordering temperatures. The Cd nuclei occupying the Sc site show high magnetic hyperfine fields with saturation values B(hf)(0) = 21 kG, 45 kG and 189 kG in CeScGe, PrScGe and GdScGe, respectively. By comparing the results with the hyperfine field data of Cd in rare-earth metals and estimations from the RKKY model, we find evidence for the presence of additional spin density at the probe nucleus, possibly due to spin polarization of Sc d band electrons. The principal electric field gradient component V(zz) in CeScGe, PrScGe and GdScGe has been determined to be 5.3 × 10(21) V m(-2), 5.5 × 10(21) V m(-2) and 5.6 × 10(21) V m(-2), respectively. Supplementing the experimental measurements, we have carried out ab initio calculations for pure and Cd-doped RScGe compounds with R = Ce, Pr, Nd and Gd using the full potential linearized augmented plane wave (FLAPW) method based on density functional theory (DFT). From the total energies calculated with and without spin polarization we find ferrimagnetic ground states for CeScGe and PrScGe while NdScGe and GdScGe are ferromagnetic. In addition, we find a sizable magnetic moment at the Sc site, increasing from ≈0.10 μ(B) in CeScGe to ≈0.3 μ(B) in GdScGe, confirming the spin polarization of Sc d band electrons. The calculated electric field gradient and magnetic hyperfine fields of the Cd impurity closely agree with the experimental values. We believe spin polarization of Sc 3d band electrons, strongly hybridized with spin polarized 5d band electrons of the rare-earth, enables a long range Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction between RE 4f moments which in turn leads to high magnetic ordering temperatures in

  19. Instrumentation for Measuring Thermodynamic Properties of Rare-Earth Compounds

    NASA Astrophysics Data System (ADS)

    Urbina, Ulises I.; Thompson, Jonathon; Ho, Pei-Chun

    2010-03-01

    Current models on some Rare-Earth compounds cannot fully account for their strongly correlated electron behavior, which give rise to phenomenon such as unconventional superconductivity, heavy Fermion, and quantum critical behavior. The specific heat, thermopower, and thermal conductivity measurements give important thermodynamic properties, such as effective electronic mass, stiffness of the lattice (Debye temperature), entropy, density of states of charge carriers, and phase transitions which are crucial in characterizing these materials of interest in our laboratory. A calorimeter and a thermopower-thermal conductivity probe, which are using a modified relaxation method and standard steady-state heat flow technique, respectively, are constructed for the above purpose. Detailed schematic diagram and operating principles will be discussed in the report.

  20. Exposure, metabolism, and toxicity of rare earths and related compounds.

    PubMed Central

    Hirano, S; Suzuki, K T

    1996-01-01

    For the past three decades, most attention in heavy metal toxicology has been paid to cadmium, mercury, lead, chromium, nickel, vanadium, and tin because these metals widely polluted the environment. However, with the development of new materials in the last decade, the need for toxicological studies on those new materials has been increasing. A group of rare earths (RE) is a good example. Although some RE have been used for superconductors, plastic magnets, and ceramics, few toxicological data are available compared to other heavy metals described above. Because chemical properties of RE are very similar, it is plausible that their binding affinities to biomolecules, metabolism, and toxicity in the living system are also very similar. In this report, we present an overview of the metabolism and health hazards of RE and related compounds, including our recent studies. Images Figure 1. A Figure 1. B Figure 1. C PMID:8722113

  1. The structure and composition of chromate conversion coatings formed on aluminum-copper alloy AA2024-T3 and thin film analogs of constituent intermetallic compounds

    NASA Astrophysics Data System (ADS)

    Vasquez, Marvin Jaime

    2002-01-01

    A comprehensive suite of spectroscopy have been used to study the composition and structure of Chromate Conversion Coatings (CCC) formed on Aluminum Copper (Al-Cu) alloy AA2024-T3 and constituent Intermetallic Compounds (IMCs). Based on previous work the CCC formed over the IMCs is expected to be thinner and therefore different in structure and composition than the CCC formed on the matrix. The formation of the CCC over the different IMCs is expected to be dependent on the chemistry and the interaction of the IMCs with accelerators such as ferricyanide. Surface chemical and structural data determined by X-ray Photoelectron Spectroscopy (XPS), Synchrotron Infrared Microspectroscopy, X-ray Absorption Near Edge Spectroscopy (XANES), Extended X-ray Absorption Fine Structure (EXAFS), Secondary Ion Mass Spectrometry (SIMS), and Secondary Electron Microscopy/Energy Dispersive Analysis of X-rays (SEM/EDAX) have been developed to refine an existing model for the CCC formed on the AA2024-T3 surface, an Al-Cu aircraft alloy, by considering the composition and structure of the CCC formed on constituent intermetallic compounds (IMCs). The limited corrosion behavior of AA2024-T3 aluminum alloy is generally attributed to the presence of a variety of constituent IMC. These IMC particles are of the order of 1--20 mum which makes their direct analysis exceedingly difficult and has lead to a limited understanding of their surface chemical properties relative to CCC formation. To overcome this limitation, it was necessary to develop for the first time large area samples composed of compositionally homogenous thin films of the various IMCs found on the AA2024-T3 surface, which were galvanically attached to thin films of Al-4.2wt%Cu (representative of the AA2024-T3 matrix). This was performed in a two-step process: Disks of IMC compositions were formed by Reactive Arc Melting (RAM), followed by ultra-fast laser ablation of the RAM IMCs resulting in the formation of homogenous thin films

  2. Soft X-ray appearance potential study of rare earth-manganese compounds

    SciTech Connect

    Chourasia, A. R.; Deshpande, S. D.

    1999-06-10

    Soft X-ray appearance potential spectroscopy (SXAPS) has been employed to study the changes in the electronic structure of RMn{sub 2} compounds (where R=Pr, Sm, Gd and Dy). In this technique the total x-ray emission associated with the thresholds for the excitation of core levels of the atoms in the surface region of the materials is measured. The SXAPS spectra of the Mn L{sub 2,3} levels in these intermetallics are compared with the corresponding elemental manganese spectrum. The normalized spectra exhibit an increasing trend in the unoccupied density of states at the Fermi level as the atomic number of R increases. This has been interpreted as increasing hybridization between the R 5d and Mn 3d bands. The hybridization is found to influence the magnetic properties of these intermetallics. The core levels are also found to display crystal field splitting that seems to disappear for DyMn{sub 2}. This correlates very well with the disappearance of the Mn magnetic moment at Dy in these intermetallics.

  3. Growth Behavior of Intermetallic Compounds in Cu/Sn3.0Ag0.5Cu Solder Joints with Different Rates of Cooling

    NASA Astrophysics Data System (ADS)

    Yang, Linmei; Zhang, Z. F.

    2015-01-01

    The growth behavior of intermetallic compounds (IMC) in Cu/Sn3.0Ag0.5Cu solder joints, including the interfacial Cu6Sn5 layer and Ag3Sn, and Cu6Sn5 in the solder, were investigated when different cooling methods—quenched water, cooling in air, and cooling in a furnace after reflow—were used. For the solder joint quenched in water, no obvious Cu6Sn5 or Ag3Sn was detected in the solder, and the thickness of interfacial Cu6Sn5 layer was slightly thinner than that of the joint cooled in air. On the basis of results from scanning electron microscopy and energy-dispersive spectrometry, a mechanism is proposed for growth of IMC in Sn3.0Ag0.5Cu solder during solidification. The rate of cooling has a substantial effect on the morphology and size of Ag3Sn, which evolved into large plate-like shapes when the joint was cooled slowly in a furnace. However, the morphology of Ag3Sn was branch-like or particle-like when the joint was cooled in air. This is attributed to re-growth of Ag3Sn grains via substantial atomic diffusion during the high-temperature stage of furnace cooling.

  4. Perpendicular Growth Characteristics of Cu-Sn Intermetallic Compounds at the Surface of 99Sn-1Cu/Cu Solder Interconnects

    NASA Astrophysics Data System (ADS)

    Chen, Zhiwen; Liu, Changqing; Wu, Yiping; An, Bing

    2015-12-01

    The growth of intermetallic compounds (IMCs) on the free surface of 99Sn-1Cu solder joints perpendicular to the interdiffusion direction has been investigated in this work. The specimens were specifically designed and polished to reveal a flat free surface at the solder/Cu interface for investigation. After aging at 175°C for progressively increased durations, the height of the perpendicular IMCs was examined and found to follow a parabolic law with aging duration that could be expressed as y = 0.11√ t, where t is the aging duration in hours and y is the height of the perpendicular IMCs in μm. For comparison, the planar growth of IMCs along the interdiffusion direction was also investigated in 99Sn-1Cu/Cu solder joints. After prolonged aging at 175°C, the thickness of the planar interfacial IMC layers also increased parabolically with aging duration and could be expressed as h_{{IMC}} = 0.27√ t + 4.6, where h is the thickness in μm and t is the time in hours. It was found that both the planar and perpendicular growth of the IMCs were diffusion-controlled processes, but the perpendicular growth of the IMCs was much slower than their planar growth due to the longer diffusion distance. It is proposed that Cu3Sn forms prior to the formation of Cu6Sn5 in the perpendicular IMCs, being the reverse order compared with the planar IMC growth.

  5. Asymmetrical Precipitation of Ag3Sn Intermetallic Compounds Induced by Thermomigration of Ag in Pb-Free Microbumps During Solid-State Aging

    NASA Astrophysics Data System (ADS)

    Su, Yu-Ping; Wu, Chun-Sen; Ouyang, Fan-Yi

    2016-01-01

    Three-dimensional integrated circuit technology has become a major trend in electronics packaging in the microelectronics industry. To effectively remove heat from stacked integrated circuitry, a temperature gradient must be established across the chips. Furthermore, because of the trend toward higher device current density, Joule heating is more serious and temperature gradients across soldered joints are expected to increase. In this study we used heat-sink and heat-source devices to establish a temperature gradient across SnAg microbumps to investigate the thermomigration behavior of Ag in SnAg solder. Compared with isothermal conditions, small Ag3Sn particles near the hot end were dissolved and redistributed toward the cold end under a temperature gradient. The results indicated that temperature gradient-induced movement of Ag atoms occurred from the hot side toward the cold side, and asymmetrical precipitation of Ag3Sn resulted. The mechanism of growth of the intermetallic compound (IMC) Ag3Sn, caused by thermomigration of Ag, is discussed. The rate of growth Ag3Sn IMC at the cold side was found to increase linearly with solid-aging time under a temperature gradient. To understand the force driving Ag diffusion under the temperature gradient, the molar heat of transport ( Q*) of Ag in Sn was calculated as +13.34 kJ/mole.

  6. Intermetallic compounds LaNi/sub 5/- /SUB x/ Cu /SUB x/ and their hydrides in the sorption of hydrogen and the hydrogenation of olefins

    SciTech Connect

    Konenko, I.R.; Fedorovskaya, E.A.; Slinkin, A.A.; Starodubtseva, E.V.; Stepanov, Y.P.

    1985-09-01

    This paper studies the sorptive and catalytic properties of the intermetallic compounds (IMC) LaNi /SUB 5-x/ Cu /SUB x/ and also of their hydrides in the hydrogenation of propylene. The existence of an inverse dependence between the bond strength in the IMC-H system and the rate of formation of the alpha-phase of the hydrides was established. It was shown that the observed extremal dependence of the specific catalytic activity of the hydrides on composition is determined by the optimum value of the bond energy of the hydrogen in the IMC matrix. It was found that the rate of hydrogenation of an olefin on IMC hydrides follows a rate equation zero-order in hydrogen and first-order in olefin. In the case of the same IMC, on the contrary, the rate is first-order in H/sub 2/ and zero-order in C/sub 3/H/sub 6/. It is proposed that the sorptive and catalytic properties of the catalysts show the effect of the structure on the surface active center - a cluster.

  7. Hyperfine field at Mn in the intermetallic compound LaMnSi2 measured by PAC using 111Cd nuclear probe

    NASA Astrophysics Data System (ADS)

    Domienikan, C.; Bosch-Santos, B.; Cabrera Pasca, G. A.; Saxena, R. N.; Carbonari, A. W.

    2015-04-01

    Magnetic hyperfine field at Mn site has been measured in the orthorhombic intermetallic compound LaMnSi2 with PAC spectroscopy using radioactive 111In- 111Cd nuclear probe. Samples of LaMnSi2 were prepared by melting pure metallic components in stoichiometric proportion in an arc furnace under argon atmosphere. The samples were sealed in a quartz tube under helium atmosphere, annealed at 1000 °C for 60 h and quenched in water. Samples were analyzed with X-ray diffraction method. 111In was introduced in the samples by thermal diffusion at 1000 °C for 60 h. PAC measurements were carried out with a six BaF2 detector spectrometer at several temperatures between 50 K and 410 K. Results show well defined quadrupole and magnetic interactions at all temperatures. The magnetic hyperfine field (Bhf) measured at 50 K is 7.1(1) T. The temperature dependence of Bhf follows the normal Brillouin-like behavior expected for a simple ferromagnetic ordering. The ferromagnetic transition temperature (Tc) was determined to be 401(1) K.

  8. Different Cation Arrangements in Au-In Networks. Syntheses and Structures of Six Intermetallic Compounds in Alkali-Metal-Au-In Systems

    SciTech Connect

    Bin Li; John D. Corbett

    2007-06-20

    Six robust intermetallic compounds with cations in three different tunnel-like structures have been synthesized in alkali-metal-Au-In systems via high-temperature solid-state methods and characterized by X-ray diffraction: AAu{sub 4}-In{sub 6} [A = K (I), Rb (II), F6m2, Z = 1], K{sub 1.76(6)}Au{sub 6}Ln{sub 4} (III,; 4/mcm, Z = 4), and A{sub x}Au{sub 2}In{sub 2} [x{approx} 0.7, A = K (IV), Rb (V), Cs (VI), P4{sub 2}/nmc, Z = 8]. The first type is constructed from a single cage unit: an alkali-metal-centered 21-vertex polyhedron A@AugIn12 with 6-9-6 arrangement of planar rings. The others contain uniaxial arrays of tunnels built of differently puckered eight- and four-member Au/In rings. The largely different cation distributions depend on the tunnel constitutions and cation sizes. Tight-binding electronic structure calculations by linear muffin-tin-orbital (LMTO) methods were performed for I and idealized III in order to help understand their chemical bonding. These also reveal large differences in relativistic effects for Au d orbitals, as well as for different Au sites in each structure.

  9. Different Cation Arrangements in Au-In Networks. Syntheses and Structures of Six Intermetallic compounds in Alkali-Metal-Au-In Systems

    SciTech Connect

    Li, Bin; Corbett, John D.

    2007-06-20

    Six robust intermetallic compounds with cations in three different tunnel-like structures have been synthesized in alkali-metal-Au-In systems via high-temperature solid-state methods and characterized by X-ray diffraction: AAu{sub 4}-In{sub 6} [A = K (I), Rb (II), F6m2, Z = 1], K{sub 1.76(6)}Au{sub 6}Ln{sub 4} (III, /4/mcm, Z = 4), and A{sub x}Au{sub 2}In{sub 2} [x {approx} 0.7, A = K (IV), Rb (V), Cs (VI), P4{sub 2}/nmc, Z = 8]. The first type is constructed from a single cage unit: an alkali-metal-centered 21-vertex polyhedron A{at}AugIn{sub 12} with 6-9-6 arrangement of planar rings. The others contain uniaxial arrays of tunnels built of differently puckered eight- and four-member Au/In rings. The largely different cation distributions depend on the tunnel constitutions and cation sizes. Tight-binding electronic structure calculations by linear muffin-tin-orbital (LMTO) methods were performed for I and idealized III in order to help understand their chemical bonding. These also reveal large differences in relativistic effects for Au d orbitals, as well as for different Au sites in each structure.

  10. A tale of two metals: new cerium iron borocarbide intermetallics grown from rare-earth/transition metal eutectic fluxes.

    PubMed

    Tucker, Patricia C; Nyffeler, Jason; Chen, Banghao; Ozarowski, Andrew; Stillwell, Ryan; Latturner, Susan E

    2012-07-25

    R(33)Fe(14-x)Al(x+y)B(25-y)C(34) (R = La or Ce; x ≤ 0.9; y ≤ 0.2) and R(33)Fe(13-x)Al(x)B(18)C(34) (R = Ce or Pr; x < 0.1) were synthesized from reactions of iron with boron, carbon, and aluminum in R-T eutectic fluxes (T = Fe, Co, or Ni). These phases crystallize in the cubic space group Im3m (a = 14.617(1) Å, Z = 2, R(1) = 0.0155 for Ce(33)Fe(13.1)Al(1.1)B(24.8)C(34), and a = 14.246(8) Å, Z = 2, R(1) = 0.0142 for Ce(33)Fe(13)B(18)C(34)). Their structures can be described as body-centered cubic arrays of large Fe(13) or Fe(14) clusters which are capped by borocarbide chains and surrounded by rare earth cations. The magnetic behavior of the cerium-containing analogs is complicated by the possibility of two valence states for cerium and possible presence of magnetic moments on the iron sites. Temperature-dependent magnetic susceptibility measurements and Mössbauer data show that the boron-centered Fe(14) clusters in Ce(33)Fe(14-x)Al(x+y)B(25-y)C(34) are not magnetic. X-ray photoelectron spectroscopy data indicate that the cerium is trivalent at room temperature, but the temperature dependence of the resistivity and the magnetic susceptibility data suggest Ce(3+/4+) valence fluctuation beginning at 120 K. Bond length analysis and XPS studies of Ce(33)Fe(13)B(18)C(34) indicate the cerium in this phase is tetravalent, and the observed magnetic ordering at T(C) = 180 K is due to magnetic moments on the Fe(13) clusters. PMID:22731682

  11. Rare Earth Metal/semiconductor Interfaces and Compounds

    NASA Astrophysics Data System (ADS)

    Nogami, Jun

    Interfaces formed at room temperature by incremental deposition of rare earth metals onto semiconductor substrates have been studied with surface sensitive soft X-ray photoelectron spectroscopy. The trends in core level lineshape and intensity with increasing metal coverage have been used to deduce an outline of the evolution and the final morphology of the interfacial region on a microscopic scale. Measurements were taken for Ytterbium (Yb) on Silicon (Si), Germanium, and Gallium Arsenide, and for Gadolinium (Gd) and Europium (Eu) on Silicon. The Yb/Si interface work was supported by comparable measurements of bulk Yb silicide samples of known composition and crystal structure. In a general sense, the behavior of all the systems studied is similar. At very low metal coverages, the metal atoms chemisorb and are weakly bonded to the substrate. The 4f core levels indicate that the metal-metal atom coordination is relatively low at this stage. The interaction with the substrate strengthens with increasing coverage, culminating in the formation of a strongly reacted phase at between 1 and 3 monolayers (ML). The strong reaction is limited to a narrow region at room temperature. At less than 10 ML coverage, the surface of the sample is almost indistinguishable from the pure metal. Details of the behavior such as the reactivity at low coverage, the compounds formed at the interface, the morphology at the surface at intermediate coverages, the final interfacial width, and the amount of substrate atom outdiffusion and surface segregation can all vary from system to system. It is in explaining the causes of some of these differences that insight about what governs the behavior of all of these rare earth metal/semiconductor systems has been obtained. The divalent metals (Yb, Eu) are significantly less reactive than trivalent Gd at sub-monolayer coverages. For the divalent metals the formation of a metal-rich phase is strongly favored in the reaction at the interface, whereas

  12. Synthesis and characterization of Fe-Ti-Sb intermetallic compounds: Discovery of a new Slater-Pauling phase

    NASA Astrophysics Data System (ADS)

    Naghibolashrafi, N.; Keshavarz, S.; Hegde, Vinay I.; Gupta, A.; Butler, W. H.; Romero, J.; Munira, K.; LeClair, P.; Mazumdar, D.; Ma, J.; Ghosh, A. W.; Wolverton, C.

    2016-03-01

    Compounds of Fe, Ti, and Sb were prepared using arc melting and vacuum annealing. Fe2TiSb , expected to be a full Heusler compound crystallizing in the L 21 structure, was shown by XRD and SEM analyses to be composed of weakly magnetic grains of nominal composition Fe1.5TiSb with iron-rich precipitates in the grain boundaries. FeTiSb, a composition consistent with the formation of a half-Heusler compound, also decomposed into Fe1.5TiSb grains with Ti-Sb rich precipitates and was weakly magnetic. The dominant Fe1.5TiSb phase appears to crystallize in a defective L 21 -like structure with iron vacancies. Based on this finding, a first-principles DFT-based binary cluster expansion of Fe and vacancies on the Fe sublattice of the L 21 structure was performed. Using the cluster expansion, we computationally scanned >103 configurations and predict a novel, stable, nonmagnetic semiconductor phase to be the zero-temperature ground state. This new structure is an ordered arrangement of Fe and vacancies, belonging to the space group R 3 m , with composition Fe1.5TiSb , i.e., between the full- and half-Heusler compositions. This phase can be visualized as alternate layers of L 21 phase Fe2TiSb and C 1b phase FeTiSb, with layering along the [111] direction of the original cubic phases. Our experimental results on annealed samples support this predicted ground-state composition, but further work is required to confirm that the R 3 m structure is the ground state.

  13. Electronic Properties of MoSi2-Type Hf2X Intermetallic Compounds (X=Pd, Ag, Cd)

    NASA Astrophysics Data System (ADS)

    Yaar, I.; Maytal-Beck, S.; Berant, Z.

    2001-11-01

    The Hf z coordinate and the value of the electric field gradient (efg) main component (V zz ), were calculated for three Hf2X compounds (X = Pd, Ag, Cd) on a first-principle basis, using the full potential linear augmented plane wave (LAPW) method. Exchange and correlation effects were treated either by the local spine density approximation (LSDA) or by the more advanced generalized gradient approximation (GGA). The calculated V zz values, in the Hf site, were in very good agreement with available 181Hf TDPAC experimental results.

  14. The analysis of the magnetic properties in the intermetallic YxGd1-xNi3 compounds

    NASA Astrophysics Data System (ADS)

    Bajorek, Anna; Chrobak, Artur; Chełkowska, Grażyna; Kwiecień-Grudziecka, Marzena

    2012-12-01

    In the paper an influence of Gd/Y substitution on the magnetic properties and exchange interactions of the YxGd1-xNi3 (x=0.0, 0.2, 0.4, 0.6, 0.8, 1.0) polycrystalline compounds have been studied. The partial replacement of Gd by Y atoms is reflected in decreasing of the Curie temperature (TC) as well as decreasing of effective the magnetic moment (μeff). It has been shown that such a behaviour strongly depends on the magnetic interactions. Exchange coupling parameters of R-R (ARR), T-T (ATT) and R-T (ART) have been evaluated from M(T) magnetization curves (2-300 K, 2 T) based on the mean field theory (MFT) calculation. The magnetocaloric effect (MCE) has been estimated from the family of magnetic isotherms. The magnetic entropy indicates relatively small change with the Gd/Y substitution. The value of ΔSm(T,H) is higher for Gd-rich compounds and, respectively, decreases with Gd/Y substitution.

  15. The effect of intermetallic compound evolution on the fracture behavior of Au stud bumps joined with Sn-3.5Ag solder

    NASA Astrophysics Data System (ADS)

    Lee, Young-Kyu; Ko, Yong-Ho; Kim, Jun-Ki; Lee, Chang-Woo; Yoo, Sehoon

    2013-01-01

    The microstructure and joint properties of Au stud bumps joined with Sn-3.5Ag solder were investigated as functions of flip chip bonding temperature and aging time. Au stud bumps were bonded on solder-onpad (SOP) at bonding temperature of 260°C and 300°C for 10 s, respectively. Aging treatment was carried out at 150°C for 100 h, 300 h, and 500 h, respectively. After flip chip bonding, intermetallic compounds (IMCs) of AuSn, AuSn2, and AuSn4 were formed at the interface between the Au stud bump and Sn-3.5Ag solder. At a bonding temperature of 300°C, AuSn2 IMC clusters, which were surrounded by AuSn4 IMCs, were observed in the Sn-3.5Ag solder bump. After flip chip bonding, bonding strength was approximately 220.5mN/bump. As aging time increased, the bonding strength decreased. After 100 h of aging treatment, the bonding strength of the joint bonded at 300°C was lower than that bonded at 260°C due to the fast growth rate of the AuSn2 IMCs. The main failure modes were interface fractures between the AuSn2 IMCs and AuSn4 IMCs, fractures through the AuSn2 IMCs and pad lift. Initial joint microstructures after flip chip bonding strongly affected the bonding strengths of aged samples.

  16. e/a determination for 4d- and 5d-transition metal elements and their intermetallic compounds with Mg, Al, Zn, Cd and In

    NASA Astrophysics Data System (ADS)

    Mizutani, U.; Sato, H.; Inukai, M.; Zijlstra, E. S.

    2013-08-01

    The present work is devoted to the determination of the effective electrons per atom ratio e/a by means of first-principles full-potential linearized augmented plane wave-Fourier method for elements from Rb to Ag in Period 5 and from Cs to Au in Period 6 of the periodic table and is regarded as a continuation of the preceding work done for elements from K to Cu in Period 4. The value of e/a was determined by reading off the square of the Fermi diameter, ? from the dispersion relation for electrons outside the Muffin-Tin spheres. A straightforward reading of the ordinate at the Fermi level, i.e. local reading method was validated for Rb and Cs in Group 1, Sr in Group 2, Y in Group 3, Pd and Pt in Group 10 and Ag and Au in Group 11. Instead, the nearly free electron (NFE) method was found to be indispensable for TM elements from Zr to Rh in Period 5 and those from Ba to Ir in Period 6. The composition dependence of e/a values for intermetallic compounds in X-TM (X = Mg, Al, Zn, Cd and In) alloy systems was also studied. The new Hume-Rothery electron concentration rule was established by constructing e/uc, the number of electrons per unit cell, vs. square of critical reciprocal lattice vector, ? , diagram for structurally complex metallic alloys having a pseudogap at the Fermi level. A proper use of either the local reading- or the NFE-e/a for the elements as indicated above is found to be essential.

  17. NFE approximation for the e/a determination for 3d-transition metal elements and their intermetallic compounds with Al and Zn

    NASA Astrophysics Data System (ADS)

    Sato, H.; Inukai, M.; Zijlstra, E. S.; Mizutani, U.

    2013-08-01

    First-principles full-potential linearized augmented plane wave (FLAPW) band calculations with subsequent FLAPW-Fourier analyses have been performed for elements from K to Cu in period 4 of the periodic table to determine the effective electrons per atom ratio (e/a). For the series of 3d-transition metals (TM), the determination of the square of the Fermi diameter ? , from which e/a is derived, has been recognized not to be straightforward because of the presence of a huge anomaly associated with the TM-d states across the Fermi level in the energy dispersion relation for electrons outside the muffin-tin sphere. The nearly free electron (NFE) approximation is newly devised to circumvent this difficulty. The centre of gravity energy ? is calculated from the energy distribution of the square of the Fourier coefficients for the FLAPW state ? . The NFE dispersion relation is constructed for the set of ? and ? in combination with the tetrahedron method. The resulting e/a values are distributed over positive numbers in the vicinity of unity for elements from Ti to Co. Instead, the e/a values for the early elements K, Ca and Sc and the late TM elements Ni and Cu were determined to be close to one, two, three, 0.50 and unity, respectively, using our previously designed local reading method. In addition, the composition dependence of e/a values for intermetallic compounds in X-TM (X = Al and Zn) alloy systems was studied to justify an appropriate choice between the local reading and NFE methods for respective elements.

  18. The magnetic behavior of the intermetallic compound NdMn{sub 2}Ge{sub 2} studied by magnetization and hyperfine interactions measurements

    SciTech Connect

    Bosch-Santos, B. Carbonari, A. W.; Cabrera-Pasca, G. A.; Saxena, R. N.; Freitas, R. S.

    2015-05-07

    The magnetic behavior of the intermetallic compound NdMn{sub 2}Ge{sub 2} was investigated by bulk magnetization measurements and measurements of hyperfine interactions using perturbed γ–γ angular correlation (PAC) spectroscopy. Magnetization measurements indicate the presence of four magnetic transitions associated with the Mn and Nd magnetic sublattices. At high temperatures, magnetic measurements show a change in the slope of the magnetization due to an antiferromagnetic transition around T{sub N} ∼ 425 K and a well defined ferromagnetic transition at T{sub C} ∼ 320 K. Moreover, at ∼210 K a peak is observed in the magnetization curve, which is assigned to the reorientation of the Mn spin, and at ∼25 K an increase in the magnetic moment is also observed, which is ascribed to the ordering of Nd ions. PAC measurements using {sup 140}La({sup 140}Ce) and {sup 111}In({sup 111}Cd) probe nuclei allowed the determination of the temperature dependence of the magnetic hyperfine field (B{sub hf}) at Nd and Mn sites, respectively. PAC results with {sup 111}Cd probe nuclei at Mn sites show that the dependence of B{sub hf} with temperature follows the expected behavior for the host magnetization associated with the magnetic ordering of Mn ions. From these results, the antiferromagnetic transition followed by a ferromagnetic ordering is clearly observed. PAC results with {sup 140}Ce probe nuclei at Nd sites, however, showed a strong deviation from the Brillouin function, which is attributed to the Ce 4f-electron contribution to B{sub hf}.

  19. Effect of Ni layer thickness and soldering time on intermetallic compound formation at the interface between molten Sn-3.5Ag and Ni/Cu substrate

    SciTech Connect

    Choi, W.K.; Lee, H.M.

    1999-11-01

    The binary eutectic Sn-3.5wt.%Ag alloy was soldered on the Ni/Cu plate at 250 C, the thickness of the Ni layer changing from 0 through 2 and 4 {micro}m to infinity, and soldering time changing from 30 to 120 s at intervals of 30 s. The infinite thickness was equivalent to the bare Ni plate. The morphology, composition and phase identification of the intermetallic compound (IMC, hereafter) formed at the interface were examined. Depending on the initial Ni thickness, different IMC phases were observed at 30 s: Cu{sub 6}Sn{sub 5} on bare Cu, detestable NiSn{sub 3} + Ni{sub 3}Sn{sub 4} on Ni(2 {micro}m)/Cu, Ni{sub 3}Sn{sub 4} on Ni(4 {micro}m)/Cu, and Ni{sub 3}Sn + Ni{sub 3}Sn{sub 4} on bare Ni. With increased soldering time, a Cu-Sn-based {eta}-(Cu{sub 6}Sn{sub 5}){sub 1{minus}x}Ni{sub x} phase formed under the pre-formed Ni-Sn IMC layer both at 60s in the Ni(2 {micro}m)/Cu plate and at 90s in the Ni(4 {micro}m)/Cu plate. The two-layer IMC pattern remained thereafter. The wetting behavior of each joint was different and it may have resulted from the type of IMC formed on each plate. The thickness of the protective Ni layer over the Cu plate was found to be an important factor in determining the interfacial reaction and the wetting behavior.

  20. Growth kinetics of Cu6Sn5 intermetallic compound at liquid-solid interfaces in Cu/Sn/Cu interconnects under temperature gradient

    NASA Astrophysics Data System (ADS)

    Zhao, N.; Zhong, Y.; Huang, M. L.; Ma, H. T.; Dong, W.

    2015-08-01

    The growth behavior of intermetallic compounds (IMCs) at the liquid-solid interfaces in Cu/Sn/Cu interconnects during reflow at 250 °C and 280 °C on a hot plate was investigated. Being different from the symmetrical growth during isothermal aging, the interfacial IMCs showed clearly asymmetrical growth during reflow, i.e., the growth of Cu6Sn5 IMC at the cold end was significantly enhanced while that of Cu3Sn IMC was hindered especially at the hot end. It was found that the temperature gradient had caused the mass migration of Cu atoms from the hot end toward the cold end, resulting in sufficient Cu atomic flux for interfacial reaction at the cold end while inadequate Cu atomic flux at the hot end. The growth mechanism was considered as reaction/thermomigration-controlled at the cold end and grain boundary diffusion/thermomigration-controlled at the hot end. A growth model was established to explain the growth kinetics of the Cu6Sn5 IMC at both cold and hot ends. The molar heat of transport of Cu atoms in molten Sn was calculated as + 11.12 kJ/mol at 250 °C and + 14.65 kJ/mol at 280 °C. The corresponding driving force of thermomigration in molten Sn was estimated as 4.82 × 10-19 N and 6.80 × 10-19 N.

  1. Effects of post-reflow cooling rate and thermal aging on growth behavior of interfacial intermetallic compound between SAC305 solder and Cu substrate

    NASA Astrophysics Data System (ADS)

    Hu, Xiaowu; Xu, Tao; Jiang, Xiongxin; Li, Yulong; Liu, Yi; Min, Zhixian

    2016-04-01

    The interfacial reactions between Cu and Sn3Ag0.5Cu (SAC305) solder reflowed under various cooling rates were investigated. It is found that the cooling rate is an important parameter in solder reflow process because it influences not only microstructure of solder alloy but also the morphology and growth of intermetallic compounds (IMCs) formed between solder and Cu substrate. The experimental results indicate that only scallop-like Cu6Sn5 IMC layer is observed between solder and Cu substrate in case of water cooling and air cooling, while bilayer composed of scallop-like Cu6Sn5 and thin layer-like Cu3Sn is detected under furnace cooling due to sufficient reaction time to form Cu3Sn between Cu6Sn5 IMC and Cu substrate which resulted from slow cooling rate. Samples with different reflow cooling rates were further thermal-aged at 423 K. And it is found that the thickness of IMC increases linearly with square root of aging time. The growth constants of interfacial IMC layer during aging were obtained and compared for different cooling rates, indicating that the IMC layer thickness increased faster in samples under low cooling rate than in the high cooling rate under the same aging condition. The long prismatic grains were formed on the existing interfacial Cu6Sn5 grains to extrude deeply into solder matrix with lower cooling rate and long-term aging, and the Cu6Sn5 grains coarsened linearly with cubic root of aging time.

  2. Controlling Interfacial Reactions and Intermetallic Compound Growth at the Interface of a Lead-free Solder Joint with Layer-by-Layer Transferred Graphene.

    PubMed

    Ko, Yong-Ho; Lee, Jong-Dae; Yoon, Taeshik; Lee, Chang-Woo; Kim, Taek-Soo

    2016-03-01

    The immoderate growth of intermetallic compounds (IMCs) formed at the interface of a solder metal and the substrate during soldering can degrade the mechanical properties and reliability of a solder joint in electronic packaging. Therefore, it is critical to control IMC growth at the solder joints between the solder and the substrate. In this study, we investigated the control of interfacial reactions and IMC growth by the layer-by-layer transfer of graphene during the reflow process at the interface between Sn-3.0Ag-0.5Cu (in wt %) lead-free solder and Cu. As the number of graphene layers transferred onto the surface of the Cu substrate increased, the thickness of the total IMC (Cu6Sn5 and Cu3Sn) layer decreased. After 10 repetitions of the reflow process for 50 s above 217 °C, the melting temperature of Sn-3.0Ag-0.5Cu, with a peak temperature of 250 °C, the increase in thickness of the total IMC layer at the interface with multiple layers of graphene was decreased by more than 20% compared to that at the interface of bare Cu without graphene. Furthermore, the average diameter of the Cu6Sn5 scallops at the interface with multiple layers of graphene was smaller than that at the interface without graphene. Despite 10 repetitions of the reflow process, the growth of Cu3Sn at the interface with multiple layers of graphene was suppressed by more than 20% compared with that at the interface without graphene. The multiple layers of graphene at the interface between the solder metal and the Cu substrate hindered the diffusion of Cu atoms from the Cu substrate and suppressed the reactions between Cu and Sn in the solder. Thus, the multiple layers of graphene transferred at the interface between dissimilar metals can control the interfacial reaction and IMC growth occurring at the joining interface. PMID:26856638

  3. Growth kinetics of Cu6Sn5 intermetallic compound at liquid-solid interfaces in Cu/Sn/Cu interconnects under temperature gradient

    PubMed Central

    Zhao, N.; Zhong, Y.; Huang, M.L.; Ma, H.T.; Dong, W.

    2015-01-01

    The growth behavior of intermetallic compounds (IMCs) at the liquid-solid interfaces in Cu/Sn/Cu interconnects during reflow at 250 °C and 280 °C on a hot plate was investigated. Being different from the symmetrical growth during isothermal aging, the interfacial IMCs showed clearly asymmetrical growth during reflow, i.e., the growth of Cu6Sn5 IMC at the cold end was significantly enhanced while that of Cu3Sn IMC was hindered especially at the hot end. It was found that the temperature gradient had caused the mass migration of Cu atoms from the hot end toward the cold end, resulting in sufficient Cu atomic flux for interfacial reaction at the cold end while inadequate Cu atomic flux at the hot end. The growth mechanism was considered as reaction/thermomigration-controlled at the cold end and grain boundary diffusion/thermomigration-controlled at the hot end. A growth model was established to explain the growth kinetics of the Cu6Sn5 IMC at both cold and hot ends. The molar heat of transport of Cu atoms in molten Sn was calculated as + 11.12 kJ/mol at 250 °C and + 14.65 kJ/mol at 280 °C. The corresponding driving force of thermomigration in molten Sn was estimated as 4.82 × 10−19 N and 6.80 × 10−19 N. PMID:26311323

  4. Structural, mechanical, thermo-physical and electronic properties of η‧-(CuNi)6Sn5 intermetallic compounds: First-principle calculations

    NASA Astrophysics Data System (ADS)

    Yang, Jian; Huang, Jihua; Fan, Dongyu; Chen, Shuhai; Zhao, Xingke

    2016-05-01

    First-principle calculations have been performed to investigate the structural, mechanical, thermo-physical and electronic properties of η‧-(CuNi)6Sn5 intermetallic compounds. The results indicated that, the doped Ni atom can not only enhance the stability of the η‧-Cu6Sn5, but also improve the mechanical and thermo-physical properties, which are more dependent on the Ni atom doping number than the doping position. In all the η‧-(CuNi)6Sn5, Cu3Ni3Sn5 (Cu1+Cu3 site) shows the best stability, the most excellent deformation resistance and the highest hardness. The Cu6Sn5, Cu3Ni3Sn5, Cu4Ni2Sn5, Cu1Ni5Sn5 and Ni6Sn5 are ductile while the Cu5Ni1Sn5 and Cu4Ni2Sn5 are brittle. The anisotropies of η‧-(CuNi)6Sn5 are all mainly due to the uneven distribution of Young's modulus at (001) planes, moreover, the anisotropy of Cu1Ni5Sn5 (Cu1+Cu2+Cu4 site) is the strongest while that of Ni6Sn5 is the weakest. The calculated Debye temperature and heat capacity showed that Cu4Ni2Sn5 (Cu2 site) possesses the best thermal conductivity (ΘD = 356.9 K) and Cu2Ni4Sn5 (Cu1+Cu2 site) possesses the largest heat capacity. From the electronic property analysis results, the Ni s and Ni p states can replace the Cu s and Cu p states to hybridize with Sn s states at -7.98 eV. Moreover, with the increasing number of the doped Ni atom, the hybridization between Cu d states at different positions is receded, while that between Ni d states is enhanced gradually.

  5. FORMATION OF INTERMETALLIC COMPOUND DISPERSIONS

    DOEpatents

    Bryner, J.S.

    1959-12-01

    BS>A method is presented for preparing dispersions containing thorium bismuthide in equiaxed form and having an average particle size of about 30 microns. Thorium particles having one dimension not greater than 0.015 in. are immersed in liquid bismuth at a temperature between 500 and 600 deg C, the quantity of thorium being in excess of its solubility in the bismuth.

  6. Magnetoresistance in magnetic and nonmagnetic rare earth compounds

    NASA Astrophysics Data System (ADS)

    Gratz, E.; Maikis, M.; Bauer, E.; Nowotny, H.

    1995-02-01

    The temperature dependence of the magnetoresistance Δρ/ ρ of selected magnetic and nonmagnetic RE compounds in fields up to 10 T has been measured. The discussion of the positive magnetoresistance is based on Kohler's rule. It was found that deviations from Kohler's rule at low temperatures depend on the magnitude of the individual residual resistivity. Ferromagnetic compounds exhibit negative values and a minimum in the vicinity of the Curie temperature in accordance to a model calculation of Yamada and Takada. The positive Δρ/ ρ contribution in the low temperature region, observed in all magnetic compounds, is due to the dominating classical magnetoresistance in this temperature range.

  7. SEPARATION OF TRANSURANIC ELEMENTS FROM RARE EARTH COMPOUNDS

    DOEpatents

    Kohman, T.P.

    1961-11-21

    A process of separating neptunium and plutonium values from rare earths and alkaline earth fission products present on a solid mixed actinide carrier (Th or U(IV) oxalate or fluoride) --fission product carrier (LaF/sub 3/, CeF/sub 3/, SrF/sub 2/, CaF/sub 2/, YF/sub 3/, La oxalate, cerous oxalate, Sr oxalate, Ca oxalate or Y oxalate) by extraction of the actinides at elevated temperature with a solution of ammonium fluoride and/or ammonium oxalate is described. Separation of the fission-product-containing carriers from the actinide solution formed and precipitation of the neptunium and plutonium from the solution with mineral acid are also accomplished. (AEC)

  8. Reaction synthesis of intermetallics

    SciTech Connect

    Deevi, S.C.; Sikka, V.K.

    1994-12-31

    Exothermicity associated with the synthesis of aluminides was utilized to obtain nickel, iron, and cobalt aluminides. Combustion synthesis, extrusion, and hot pressing were utilized to obtain intermetallics and their composites. Extrusion conditions, reduction ratios, and hot-pressing conditions of the intermetallics and their composites are discussed.

  9. The composition of the primitive atmosphere and the synthesis of organic compounds on the early Earth

    NASA Technical Reports Server (NTRS)

    Bada, J. L.; Miller, S. L.

    1985-01-01

    The generally accepted theory for the origin of life on the Earth requires that a large variety of organic compounds be present to form the first living organisms and to provide the energy sources for primitive life either directly or through various fermentation reactions. This can provide a strong constraint on discussions of the formation of the Earth and on the composition of the primitive atmosphere. In order for substantial amounts of organic compounds to have been present on the prebiological Earth, certain conditions must have existed. There is a large body of literature on the prebiotic synthesis of organic compounds in various postulated atmospheres. In this mixture of abiotically synthesized organic compounds, the amino acids are of special interest since they are utilized by modern organisms to synthesize structural materials and a large array of catalytic peptides.

  10. Superconductivity in RNi 2B 2C (R = rare earth) compounds

    NASA Astrophysics Data System (ADS)

    Tomy, C. V.; Chang, L. J.; Balakrishnan, G.; Paul, D. M. c.K.

    1994-12-01

    A series of compounds in the recently discovered RNi 2B 2C family of superconductors have been prepared in order to investigate their magnetic and transport properties. Compounds of the form (Y 1-xA x)Ni 2B 2C (A=Sm,Dy) were examined to study the effects of magnetic pair breaking. Resistance measurements show that the lighter rare earth Sm depresses T c faster than the heavier rare earth Dy. Solid solutions of the type (Er 1-xHo x)Ni 2B 2C have also been studied for the possible coexistence of superconductivity and magnetism in these compounds. Even though the magnetic ordering of the rare earth moments can be deduced from our susceptibility measurements, resistance measurements showed no reetrant behavior in any of these compounds down to 1.2 K.

  11. Electromigration enhanced kinetics of copper-tin intermetallic compounds in lead-free solder joints and copper low-k dual damascene processing using step and flash imprint lithography

    NASA Astrophysics Data System (ADS)

    Chao, Huang-Lin

    This dissertation constitutes two major sections. In the first major section, a kinetic analysis was established to investigate the electromigration (EM), enhanced intermetallic compound (IMC) growth and void formation for Sn-based Pb-free solder joints to Cu under bump metallization (UBM). The model takes into account the interfacial intermetallic reaction, Cu-Sn interdiffusion, and current stressing. A new approach was developed to derive atomic diffusivities and effective charge numbers based on Simulated Annealing (SA) in conjunction with the kinetic model. The finite difference (FD) kinetic model based on this approach accurately predicted the intermetallic compound growth when compared to empirical observation. The ultimate electromigration failure of the solder joints was caused by extensive void formation at the intermetallic interface. The void formation mechanism was analyzed by modeling the vacancy transport under electromigration. The effects of current density and Cu diffusivity in Sn solder were also investigated with the kinetic model. The second major section describes the integration of Step and Flash Imprint Lithography (S-FILRTM) into an industry standard Cu/low-k dual damascene process. The yield on a Back End Of the Line (BEOL) test vehicle that contains standard test structures such as via chains with 120 nm vias was established by electrical tests. S-FIL shows promise as a cost effective solution to patterning sub 45 nm features and is capable of simultaneously patterning two levels of interconnect structures, which provides a low cost BEOL process. The critical processing step in the integration is the reactive ion etching (RIE) process that transfers the multilevel patterns to the inter-level dielectrics (ILD). An in-situ, multistep etch process was developed that gives excellent pattern structures in two industry standard Chemical Vapor Deposited (CVD) low-k dielectrics. The etch process showed excellent pattern fidelity and a wide process

  12. One-dimensional rare earth compounds and complexes: preparation and improved photoluminescence properties.

    PubMed

    Song, Hongwei; Pan, Guohui; Bai, Xue; Li, Suwen; Yu, Hongquan; Zhang, Hui

    2008-03-01

    One-dimensional nanosized phosphors demonstrate special structural and photoluminescence properties, which have application potential in some optical fields. In this article, we present our recent progress on preparation and luminescence properties of some one-dimensional rare earth compounds and complexes, the core-shell oxide nanowires prepared by a two-step hydrothermal route, the nanowires of some inorganic compounds doped with rare earths and rare earth complexes/PVP composites prepared by the electrospinning method, and the rare earth complexes in the SBA-15 mesoporous molecule sieves. In these systems, some novel or improved photoluminescence properties are observed such as improved luminescence quantum yield, thermal stability and/or photostability, and depressed thermal effect in upconversion luminescence. PMID:18468146

  13. Chemistry and Properties of Complex Intermetallics from Metallic Fluxes

    SciTech Connect

    Kanatzidis, Mercouri G.

    2015-03-28

    This project investigated the reaction chemistry and synthesis of new intermetallic materials with complex compositions and structures using metallic fluxes as solvents. It was found that the metallic fluxes offer several key advantages in facilitating the formation and crystal growth of new materials. The fluxes mostly explored were liquid aluminum, gallium and indium. The main purpose of this project was to exploit the potential of metallic fluxes as high temperature solvent for materials discovery in the broad class of intermetallics. This work opened new paths to compound formation. We discovered many new Si (or Ge)-based compounds with novel structures, bonding and physicochemical properties. We created new insights about the reaction chemistry that is responsible for stabilizing the new materials. We also studied the structural and compositional relationships to understand their properties. We investigated the use of Group-13 metals Al, Ga and In as solvents and have generated a wide variety of new results including several new ternary and quaternary materials with fascinating structures and properties as well as new insights as to how these systems are stabilized in the fluxes. The project focused on reactions of metals from the rare earth element family in combination with transition metals with Si and Ge. For example molten gallium has serves both as a reactive and non-reactive solvent in the preparation and crystallization of intermetallics in the system RE/M/Ga/Ge(Si). Molten indium behaves similarly in that it too is an excellent reaction medium, but it gives compounds that are different from those obtained from gallium. Some of the new phase identified in the aluminide class are complex phases and may be present in many advanced Al-matrix alloys. Such phases play a key role in determining (either beneficially or detrimentally) the mechanical properties of advanced Al-matrix alloys. This project enhanced our basic knowledge of the solid state chemistry

  14. The effect of pH on the corrosion behavior of intermetallic compounds Ni{sub 3}(Si,Ti) and Ni{sub 3}(Si,Ti) + 2Mo in sodium chloride solutions

    SciTech Connect

    Priyotomo, Gadang Nuraini, Lutviasari; Kaneno, Yasuyuki

    2015-12-29

    The corrosion behavior of the intermetallic compounds, Ni{sub 3}(Si,Ti) (L1{sub 2}: single phase) and Ni{sub 3}(Si,Ti) + 2Mo (L1{sub 2} and (L12 + Ni{sub ss}) mixture region), has been investigated using an immersion test, electrochemical method and surface analytical method (SEM; scanning electron microscope and EDAX: Energy Dispersive X-ray) in 0.5 kmol/m{sup 3} NaCl solutions at various pH. The corrosion behavior of nickel alloy C-276 was studied under the same experimental conditions as a reference. It was found that the uniform attack was observed on Ni{sub 3}(Si,Ti) for the immersion test at lower pH, while the pitting attack was observed on this compound for this test at neutral solution. Furthermore, Ni{sub 3}(Si,Ti)+2Mo had the preferential dissolution of L1{sub 2} compared to (L1{sub 2} + Ni{sub ss}) mixture region at lower pH, while pitting attack occurred in (L1{sub 2} + Ni{sub ss}) mixture region at neutral solution. For both intermetallic compounds, the magnitude of pitting and uniform attack decrease with increasing pH of solutions. From the immersion test and polarization curves, the corrosion resistance of Ni{sub 3}(Si,Ti)+2Mo is lower than that of Ni{sub 3}(Si,Ti), while the nickel alloy C-276 is the highest one at various pH of solutions. On the other hand, in the lower pH of solutions, the corrosion resistance of tested materials decreased significantly compared to those in neutral and higher pH of solutions.

  15. Comment on: Ab initio calculations of B2 type RHg (R = Ce,Pr,Eu and Gd) intermetallic compounds. Eur. Phys. J. B 87, 268 (2014), DOI: 10.1140/epjb/e2014-50521-6

    NASA Astrophysics Data System (ADS)

    Daoud, Salah

    2016-02-01

    In a recent article by Devi et al. [Eur. Phys. J. B 87, 268 (2014)], the structural, electronic, elastic and some thermal properties of B2 type RHg (R = Ce, Pr, Eu and Gd) intermetallic compounds have been studied by ab initio calculations. After the study of their article I found that there are some mistakes in predicted crystal density, longitudinal, transverse and average elastic wave velocities, and Debye temperature data. The crystal density has been found multiplied per 4. Also the longitudinal, transverse and average elastic wave velocities and Debye temperature are different from my reexamined values (all results represented by Devi et al. have been found divided per 2). Although these small mistakes do not influence their conclusion, it is better to correct them. In the present work, I reexamined all data again by using the right formulas, based on the lattice parameters and the elastic constants obtained in the work of Devi et al.

  16. Discontinuous coarsening behavior of Ni(2)MnAl intermetallic compound during isothermal aging treatment of Fe-Mn-Ni-Al alloys.

    PubMed

    Heo, Yoon-Uk; Takeguchi, Masaki; Furuya, Kazuo; Lee, Hu-Chul

    2010-08-01

    The discontinuous reaction of the Ni(2)MnAl intermetallic phase was investigated during the aging of a solution-treated Fe-8.3Mn-8.2Ni-4.2Al alloy. During aging, Ni(2)MnAl lamellae formed at the prior austenite grain boundaries and twin boundaries and grew into the neighboring grains. The presence of continuously precipitated fine Ni(2)MnAl particles before the growth of the discontinuously precipitated lamellae was confirmed by dark-field transmission electron microscopy, and it was concluded that the present reaction is a type of discontinuous coarsening process, alpha' + Ni(2)MnAl (continuous precipitation) --> alpha + Ni(2)MnAl (discontinuous coarsening). The chemical driving force and the reduction of the total coherent strain energy were suggested to be the driving force for the discontinuous coarsening reaction. PMID:20551447

  17. Fermi surface and magnetic structure of rare-earth-Ga3 compounds

    NASA Astrophysics Data System (ADS)

    Biasini, Maurizio; Kontrym-Sznajd, Grazyna; Ferro, Gianclaudio; Czopnik, Andrzej

    2002-03-01

    The measurement of the 2-dimensional angular correlation of the positron annihilation radiation (2D-ACAR), providing a 2D projection of the two-photon electron-positron momentum density, ρ(p), is a powerful tool to investigate the electronic structure of intermetallic compounds. Utilising tomographic reconstruction techniques (G Kontrym-Sznajd et al Mat. Scie. Forum 255-257) 754 (1997) and references therein., the experiment has the unique ability to sample the Brillouin Zone of truly 3-dimensional systems in a cartesian mesh, thus determining their Fermi surface (FS). Our studies have addressed the commensurate and incommensurate antiferromagnetic structures of TmGa3 and ErGa_3, respectively. For both compounds the FSs resulting from the 2D-ACAR experiments are in fair agreement with de Haas van Alphen measurements and with band structure calculations which constrain the 4f electrons to retain a local atomic character (M Biasini at al Phys. Rev. Lett 86), 4616, (2001).. Nevertheless, we discover different nesting features along the [110] directions which can account for the magnetic structures of the two compounds. Moreover, we propose methods to estimate the density of states at the Fermi energy (E_F) and the electronic contribution to the specific heat, γ. We obtain N(E_F)=17 states/ (Ryd cell), γ=2.8 (mJ/mole K^2) and N(E_F)=16 states/ (Ryd cell), γ=2.7 (mJ/mole K^2) for TmGa3 and ErGa_3, respectively.

  18. Carbonaceous meteorites as a source of sugar-related organic compounds for the early Earth

    NASA Technical Reports Server (NTRS)

    Cooper, G.; Kimmich, N.; Belisle, W.; Sarinana, J.; Brabham, K.; Garrel, L.

    2001-01-01

    The much-studied Murchison meteorite is generally used as the standard reference for organic compounds in extraterrestrial material. Amino acids and other organic compounds important in contemporary biochemistry are thought to have been delivered to the early Earth by asteroids and comets, where they may have played a role in the origin of life. Polyhydroxylated compounds (polyols) such as sugars, sugar alcohols and sugar acids are vital to all known lifeforms-they are components of nucleic acids (RNA, DNA), cell membranes and also act as energy sources. But there has hitherto been no conclusive evidence for the existence of polyols in meteorites, leaving a gap in our understanding of the origins of biologically important organic compounds on Earth. Here we report that a variety of polyols are present in, and indigenous to, the Murchison and Murray meteorites in amounts comparable to amino acids. Analyses of water extracts indicate that extraterrestrial processes including photolysis and formaldehyde chemistry could account for the observed compounds. We conclude from this that polyols were present on the early Earth and therefore at least available for incorporation into the first forms of life.

  19. Metal Based Synthetic Strategies and the Examination of Structure Determining Factors in Alkaline Earth Metal Compounds

    NASA Astrophysics Data System (ADS)

    Takahashi, Yuriko

    Last decades have witnessed a large expansion of the organometallic heavier alkaline earth metal species. However, continued growth of this promising area of chemistry has been slowed by severe restrictions and limitations in viable synthetic methodologies leading to difficulties in preparing and characterizing the target compounds. There is clearly a need for the further development of synthetic methodologies and detailed structure function analysis that will promote the further advancement of organoalkaline earth metal chemistry in applications as diverse as materials chemistry and catalysis. This thesis work greatly extends the synthetic options currently available towards organoalkaline earth metal species by introducing redox transmetallation protolysis (RTP), a reaction based on the readily available Ph3Bi as a non-toxic transmetallation agent. Based on a straightforward one-pot procedure and work-up, Ph3Bi based RTP presents a powerful synthetic alternative for the facile preparation of a large variety of heavy alkaline earth metal compounds. The second part of the thesis explores the effect of secondary non covalent interactions on the coordination chemistry as well as thermal properties of a series of novel alkali, alkaline earth, rare earth as well as heterobimetallic alkali/alkaline earth fluoroalkoxides. These compounds showcase the significance of non-covalent M···F-C and agostic interactions on metal stabilization and structural features, providing critical input on ligand design for the design of advanced metal organic vapor deposition (MOCVD) precursor materials. This work also showcases the impact of M···F-C interactions over M---co-ligand coordination, a critical precursor design element as well.

  20. Magnesium silicide intermetallic alloys

    NASA Astrophysics Data System (ADS)

    Li, Gh.; Gill, H. S.; Varin, R. A.

    1993-11-01

    Methods of induction melting an ultra-low-density magnesium silicide (Mg2Si) intermetallic and its alloys and the resulting microstructure and microhardness were studied. The highest quality ingots of Mg2Si alloys were obtained by triple melting in a graphite crucible coated with boron nitride to eliminate reactivity, under overpressure of high-purity argon (1.3 X 105 Pa), at a temperature close to but not exceeding 1105 °C ± 5 °C to avoid excessive evaporation of Mg. After establishing the proper induction-melting conditions, the Mg-Si binary alloys and several Mg2Si alloys macroalloyed with 1 at. pct of Al, Ni, Co, Cu, Ag, Zn, Mn, Cr, and Fe were induction melted and, after solidification, investigated by optical microscopy and quantitative X-ray energy dispersive spectroscopy (EDS). Both the Mg-rich and Si-rich eutectic in the binary alloys exhibited a small but systematic increase in the Si content as the overall composition of the binary alloy moved closer toward the Mg2Si line compound. The Vickers microhardness (VHN) of the as-solidified Mg-rich and Si-rich eutectics in the Mg-Si binary alloys decreased with increasing Mg (decreasing Si) content in the eutectic. This behavior persisted even after annealing for 75 hours at 0.89 pct of the respective eutectic temperature. The Mg-rich eutectic in the Mg2Si + Al, Ni, Co, Cu, Ag, and Zn alloys contained sections exhibiting a different optical contrast and chemical composition than the rest of the eutectic. Some particles dispersed in the Mg2Si matrix were found in the Mg2Si + Cr, Mn, and Fe alloys. The EDS results are presented and discussed and compared with the VHN data.

  1. A magnetization study of RCo 12B 6 intermetallics

    NASA Astrophysics Data System (ADS)

    Mittag, M.; Rosenberg, M.; Buschow, K. H. J.

    1989-11-01

    The magnetic properties of polycrystalline intermetallics RCo 12B 6 with R = Y, La, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er and Tm have been studied in the temperature range 3-300 K and in fields up to 2 T. All compounds order magnetically between Tc=134.3 K for CeCo 12B 6 and Tc=162 K for GdCo 12B 6. YCo 12B 6 has an average Co moment of 0.42μ B. Since the Co moment is constant for all samples the R moments can be easily obtained and they are in good agreement with free R 3+ ion values. Ce is quadripositive in CeCo 12B 6 and therefore nonmagnetic. All light rare-earth compounds are ferromagnetic, while all heavy rare-earth compounds are ferrimagnetic with compensation points between Tcomp=11.6 K ( TmCo12B6) and Tcomp=82.8 K ( TbCo12B6). In the paramagnetic state an effective magnetic moment of 1.94μ B per Co atom has been found. The mean-field approximation yields a 3d-3d exchange integral of {J CoCo}/{k B}=110 K . The 3d-4f exchange integral is much smaller and equal to about {J RCo}/{k B}=6 K .

  2. Effects of Annealing, Thermomigration, and Electromigration on the Intermetallic Compounds Growth Kinetics of Cu/Sn-2.5Ag Microbump.

    PubMed

    Kim, Seung-Hyun; Park, Gyu-Tae; Park, Jong-Jin; Park, Young-Bae

    2015-11-01

    The effects of annealing, thermomigration (TM), and electromigration (EM) on the intermetallic com- pound (IMC) growth kinetics of Cu/Sn-2.5Ag microbumps were investigated using in-situ scanning electron microscopy at 120-165 degrees C with a current density of 1.5 x 10(5) A/cm2. The IMC growth kinetics was controlled by a diffusion-dominant mechanism and a chemical-reaction-dominant mechanism with annealing and current-stressing conditions, respectively. Before all of the Sn was fully transformed into IMCs, the activation energies of the Cu3Sn IMCs were 0.54 eV, 0.50 eV, and 0.40 eV for annealing, TM, and EM, respectively, which is closely related to the acceleration effect of the interfacial reaction by electron wind force under current stressing. After all of the Sn was fully transformed into IMCs by reacting with Cu, the Cu3Sn IMC growth rates of the three structures became similar due to the reduced and similar diffusion rates inside the IMCs with and without current stressing. PMID:26726558

  3. Comets and the formation of biochemical compounds on the primitive earth - A review

    NASA Technical Reports Server (NTRS)

    Oro, J.; Mills, T.; Lazcano, A.

    1992-01-01

    Thirty years ago it was suggested that comets impacting on the primitive earth may have represented a significant source of terrestrial volatiles, including some important precursors for prebiotic synthesis (Oro, 1961). This possibility is strongly supported not only by models of the collisional history of the early earth, but also by astronomical evidence that suggests that frequent collisions of cometlike bodies from the circumstellar disk around the star Beta Pictoris are taking place. Although a significant fraction of the complex organic compounds that appear to be present in cometary nuclei were probably destroyed during impact, it is argued that cometary collisions with the primitive earth represented an important source of both free-energy and volatiles, and may have created transient, gaseous environments in which prebiotic synthesis may have taken place.

  4. Method for preparing high cure temperature rare earth iron compound magnetic material

    DOEpatents

    Huang, Yuhong; Wei, Qiang; Zheng, Haixing

    2002-01-01

    Insertion of light elements such as H,C, or N in the R.sub.2 Fe.sub.17 (R=rare earth metal) series has been found to modify the magnetic properties of these compounds, which thus become prospective candidates for high performance permanent magnets. The most spectacular changes are increases of the Curie temperature, T.sub.c, of the magnetization, M.sub.s, and of coercivity, H.sub.c, upon interstitial insertion. A preliminary product having a component R--Fe--C,N phase is produced by a chemical route. Rare earth metal and iron amides are synthesized followed by pyrolysis and sintering in an inert or reduced atmosphere, as a result of which, the R--Fe--C,N phases are formed. Fabrication of sintered rare earth iron nitride and carbonitride bulk magnet is impossible via conventional process due to the limitation of nitridation method.

  5. Origin of organic compounds on the primitive earth and in meteorites

    NASA Technical Reports Server (NTRS)

    Miller, S. L.; Urey, H. C.; Oro, J.

    1976-01-01

    The paper examines the role and relative contributions of different forms of energy to the synthesis of amino acids and other organic compounds on the primitive earth and in the solar nebula. Attention is directed mainly to the activation steps and formation of reactive intermediate compounds. Electric discharges appear to be not only the most efficient energy for amino acid synthesis but also yield a mixture of amino acids that is qualitatively and quantitatively the same as that found in the Murchison carbonaceous chondrite. Ultraviolet light is likely to have played a major role in prebiotic synthesis. The reaction of CO plus H2 plus NH3 on the surface of a Fischer-Tropsch catalyst produces reactive intermediates which lead to amino acids and other organic compounds in a much less efficient way than electric discharges.

  6. X-ray diffraction study of the phase purity, order, and texture of ductile B2 intermetallics

    SciTech Connect

    Mulay, Rupalee; Wollmershauser, J.A. A.; Heisel, M A; Bei, Hongbin; Russell, A M; Agnew, S R

    2010-01-01

    Representatives (AgY, CuY, AgEr, CuDy, MgY and MgCe) of the newly discovered family of ductile stoichiometric B2 intermetallic (metal-rare-earth element, MR) compounds were characterized by X-ray diffraction, to determine if their anomalous ductility is related to an exceptional level of phase purity, lack of chemical ordering or a strong crystallographic texture. Brittle NiAl served as an anti-type in this study. We found that all of the rare-earth compounds, except MgY, have a significant volume fraction (-5-20vol.%) of second phases (M{sub 2}R intermetallics and R{sub 2}O{sub 3} oxides), which has not been reported in previous studies of these materials. The most ductile of observed MR compounds, AgY, is highly ordered. A moderate texture was observed in AgY, which may explain its higher ductility (using polycrystal modeling) as compared to other MR compounds. However, the intrinsic polycrystalline ductility of these compounds in the randomly textured state (like that observed in CuY) still has no specific, definitive explanation.

  7. Synchrotron Diffraction Studies of Spontaneous Magnetostriction in Rare Earth Transition Metal Compounds

    SciTech Connect

    Ning Yang

    2004-12-19

    Thermal expansion anomalies of R{sub 2}Fe{sub 14}B and R{sub 2}Fe{sub 17}C{sub x} (x = 0,2) (R = Y, Nd, Gd, Tb, Er) stoichiometric compounds are studied with high-energy synchrotron X-ray powder diffraction using Debye-Schemer geometry in temperature range 10K to 1000K. Large spontaneous magnetostriction up to their Curie temperatures (T{sub c}) is observed. The a-axes show relatively larger invar effects than c-axes in the R{sub 2}Fe{sub 14}B compounds whereas the R{sub 2}Fe{sub 17}C{sub x} show the contrary anisotropies. The iron sub-lattice is shown to dominate the spontaneous magnetostriction of the compounds. The contribution of the rare earth sublattice is roughly proportional to the spin magnetic moment of the rare earth in the R{sub 2}Fe{sub 14}B compounds but in R{sub 2}Fe{sub 17}C{sub x}, the rare earth sub-lattice contribution appears more likely to be dominated by the local bonding. The calculation of spontaneous magnetostrain of bonds shows that the bonds associated with Fe(j2) sites in R{sub 2}Fe{sub 14}B and the dumbbell sites in R{sub 2}Fe{sub 17}C{sub x} have larger values, which is strongly related to their largest magnetic moment and Wigner-Seitz atomic cell volume. The roles of the carbon atoms in increasing the Curie temperatures of the R{sub 2}Fe{sub 17} compounds are attributed to the increased separation of Fe hexagons. The R{sub 2}Fe{sub 17} and R{sub 2}Fe{sub 14}B phases with magnetic rare earth ions also show anisotropies of thermal expansion above T{sub c}. For R{sub 2}Fe{sub 17} and R{sub 2}Fe{sub 14}B the a{sub a}/a{sub c} > 1 whereas the anisotropy is reversed with the interstitial carbon in R{sub 2}Fe{sub 17}. The average bond magnetostrain is shown to be a possible predictor of the magnetic moment of Fe sites in the compounds. Both of the theoretical and phenomenological models on spontaneous magnetostriction are discussed and a Landau model on the spontaneous magnetostriction is proposed.

  8. High temperature rare earth compounds: Synthesis, characterization and applications in device fabrication

    NASA Astrophysics Data System (ADS)

    Brewer, Joseph Reese

    As the area of nanotechnology continues to grow, the development of new nanomaterials with interesting physical and electronic properties and improved characterization techniques are several areas of research that will be remain vital for continued improvement of devices and the understanding in nanoscale phenomenon. In this dissertation, the chemical vapor deposition synthesis of rare earth (RE) compounds is described in detail. In general, the procedure involves the vaporization of a REClx (RE = Y, La, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho) in the presence of hydride phase precursors such as decaborane and ammonia at high temperatures and low pressures. Unlike traditional single source precursor techniques such as metal-organic chemical vapor deposition, the materials produced are of extremely high chemical purity. The crystallographic orientation of as-synthesized rare earth hexaboride nanostructures and gadolinium nitride thin films was controlled by judicious choice of specific growth substrates and modeled by analyzing x-ray diffraction powder patterns and crystallographic models. The vapor-liquid-solid mechanism was used in combination with the chemical vapor deposition process to synthesize single crystalline rare earth hexaboride nanostructures. Unlike previously reported synthetic techniques to generate rare earth hexaborides, my synthesis provided control over the tip diameter of the nanomaterials, was applicable to all available rare earth metals and utilized a chemical scheme that was much less toxic. Furthermore, the synthesis provided the first ever doped rare earth hexaboride nanowires. The as produced materials showed excellent electronic properties and could be applicable to many different types of electronic applications. The rare earth hexaboride nanostructures were then implemented into two existing technologies to enhance their characterization capabilities. First, the rare earth hexaboride nanowires were used as a test material for the development

  9. Electronic structure, phase stability, and vibrational properties of Ir-based intermetallic compound IrX (X=Al, Sc, and Ga)

    NASA Astrophysics Data System (ADS)

    Arıkan, N.; Charifi, Z.; Baaziz, H.; Uğur, Ş.; Ünver, H.; Uğur, G.

    2015-02-01

    The phase stability and mechanical properties of B2 type IrX (X=Al, Sc and Ga) compounds are investigated. Self-consistenttotal-energy calculations in the framework of density functional theory using the Generalized Gradient Approximation (GGA) to determine the equations of state and the elastic constants of IrX (X=Al, Sc, and Ga) in the B2 phase have been performed. The calculations predicted the equilibrium lattice constants, which are about 1% greater than experiments for IrAl, 1.81% for IrGa, and 0.71% for IrSc compound. IrAl is shown to be the least compressible, and it is followed by IrGa and the IrSc compound. The phase stability of the studied compounds is checked. The brittleness and ductility properties of IrX (X=Al, Sc, and Ga) are determined by Poisson's ratio σ criterion and Pugh's criterion. IrGa compound is a ductile material; however, IrAl and IrSc show brittleness. The band structure and density of states (DOS), and phonon dispersion curves have been obtained and analyzed. The position of the Fermi level and the contribution of d electrons to the density of states near EF is studied and discussed in detail. We also used the phonon density of states and quasiharmonic approximation to calculate and predict some thermodynamic properties such as constant-volume specific heat capacity of the B2 phase of IrX (X=Al, Sc and Ga) compounds.

  10. Integrating giant microwave absorption with magnetic refrigeration in one multifunctional intermetallic compound of LaFe11.6Si1.4C0.2H1.7

    PubMed Central

    Song, Ning-Ning; Ke, Ya-Jiao; Yang, Hai-Tao; Zhang, Hu; Zhang, Xiang-Qun; Shen, Bao-Gen; Cheng, Zhao-Hua

    2013-01-01

    Both microwave absorption and magnetocaloric effect (MCE) are two essential performances of magnetic materials. We observe that LaFe11.6Si1.4C0.2H1.7 intermetallic compound exhibits the advantages of both giant microwave absorption exceeding −42 dB and magnetic entropy change of −20 Jkg−1K−1. The excellent electromagnetic wave absorption results from the large magnetic loss and dielectric loss as well as the efficient complementarity between relative permittivity and permeability. The giant MCE effect in this material provides an ideal technique for cooling the MAMs to avoid temperature increase and infrared radiation during microwave absorption. Our finding suggests that we can integrate the giant microwave absorption with magnetic refrigeration in one multifunctional material. This integration not only advances our understanding of the correlation between microwave absorption and MCE, but also can open a new avenue to exploit microwave devices and electromagnetic stealth. PMID:23887357

  11. A {sup 151}Eu Moessbauer spectroscopic and magnetic susceptibility investigation of the intermetallic compounds EuTIn (T = Zn, Pd, Pt, Au)

    SciTech Connect

    Muellmann, R.; Mosel, B.D.; Eckert, H.; Kotzyba, G.; Poettgen, R.

    1998-04-01

    The title compounds were investigated by magnetic susceptibility measurements and {sup 151}Eu Moessbauer spectroscopy. EuZnIn and EuPtIn show Curie-Weiss behavior above 60 K with experimental magnetic moments of 7.80(5) and 8.0(1) {mu}{sub B}/Eu, respectively, indicating divalent europium. The zinc compound orders antiferromagnetically at T{sub N} = 8.0(5) k and two metamagnetic transitions are detected at the critical field strengths B{sub C1} = 1.1(1) T and B{sub C2} = 2.6(2) T. At 5 K the saturation magnetic moment amounts to 7.0(1) {mu}{sub B}/Eu, suggesting a full parallel spin alignment. EuPdIn and EuAuIn order antiferromagnetically at 13.0(5) and 21.0(5) K in low external magnetic fields, respectively. The four compounds are metallic conductors. The Moessbauer measurements of the EuTIn compounds show {sup 151}Eu isomer shifts typical of divalent europium. The isomer shifts are found to linearly correlated with the closest Eu-Eu distance in the structure. Based on the Moessbauer data the onset of magnetic order is observed at T{sub N}(EuZnIn) = 9.5(5) K, T{sub N}(EuPdIn) = 15.5(5) K, T{sub N}(EuAuIn) = 20.0(5) K, and T{sub N}(EuPtIn) = 20.0(5) K, respectively. The magnetically split spectrum of EuZnIn reveals evidence of Eu site inequivalence.

  12. Origin of organic compounds on the primitive earth and in meteorites.

    PubMed

    Miller, S L; Urey, H C; Oró, J

    1976-12-31

    The role and relative contributions of different forms of energy to the synthesis of amino acids and other organic compounds on the primitive earth, in the parent bodies or carbonaceous chondrites, and in the solar nebula are examined. A single source of energy or a single process would not account for all the organic compounds synthesized in the solar system. Electric discharges appear to produce amino acids more efficiently than other sources of energy and the composition of the synthesized amino acids is qualitatively similar to those found in the Murchison meteorite. Ultraviolet light is also likely to have played a major role in prebiotic synthesis. Although the energy in the sun's spectrum that can be absorbed by the major constituents of the primitive atmosphere is not large, reactive trace components such as H2S and formaldehyde absorb at longer wavelengths where greater amounts of energy are available and produce amino acids by reactions involving hot hydrogen atoms. The thermal reaction of CO + H2 + NH3 on Fischer-Tropsch catalysts generates intermediates that lead to amino acids and other organic compounds that have been found in meteorites. However, this synthesis appears to be less efficient than electric discharges and to require a special set of reaction conditions. It should be emphasized that after the reactive organic intermediates are generated by the above processes, the subsequent reactions which produce the more complete biochemical compounds are low temperature homogenous reactions occurring in an aqueous environment. PMID:1018332

  13. A high pressure low temperature study on rare earth compounds: Semiconductor to metal transition

    NASA Astrophysics Data System (ADS)

    Neuenschwander, J.; Wachter, P.

    1990-01-01

    This work studies the pressure induced semiconductor to metal transition (SMT) in several rare earth compounds. This SMT is accompanied by a valence instability. Single crystalline semiconducting TmSe 1- xTe x, Tm 1- xEu xSe and SmS 1- xSe x alloys are investigated under high pressure at low temperatures. Measurements of electrical resistivity, magnetic susceptibility, neutron diffraction, volume and optical properties are presented and discussed. A very unusual peak structure in the resistivity-pressure relation of TmSe 1- xTe x at low temperatures is observed. A discussion of the novel feature involves the concept of the excitonic insulator and f-d hybridization. The magnetic behavior of the Tm and Eu based compounds is significantly influenced by the SMT. This is thought to be mainly due to the additional coupling between the rare earth moments via free carriers which are present in the metallic state. In SmS 1- xSe x a considerable softening of the lattice is observed before the valence transition occurs. It is speculated that Poisson's ratio might become negative already in the semiconducting state.

  14. A high pressure low temperature study on rare earth compounds: Semiconductor to metal transition

    NASA Astrophysics Data System (ADS)

    Neuenschwander, J.; Wachter, P.

    1989-12-01

    This work studies the pressure induced semiconductor to metal transition (SMT) in several rare earth compounds. This SMT is accompanied by a valence instability. Single crystalline semiconducting TmSe1-xTex, Tm1-xEuxSe and SmS1-xSex alloys are investigated under high pressure at low temperatures. Measurements of electrical resistivity, magnetic susceptibility, neutron diffraction, volume and optical properties are presented and discussed. A very unusual peak structure in the resistivity-pressure relation of TmSe1-xTex at low temperatures is observed. A discussion of the novel feature involves the concept of the excitonic insulator and f-d hybridization. The magnetic behavior of the Tm and Eu based compounds is significantly influenced by the SMT. This is thought to be mainly due to the additional coupling between the rare earth moments via free carriers which are present in the metallic state. In SmS1-xSex a considerable softening of the lattice is observed before the valence transition occurs. It is speculated that Poisson's ratio might become negative already in the semiconducting state.

  15. Magnetic hyperfine interactions on Cd sites of the rare-earth cadmium compounds R Cd (R =Ce , Pr, Nd, Sm, Gd, Tb, Dy, Ho, and Er)

    NASA Astrophysics Data System (ADS)

    Cavalcante, F. H. M.; Leite Neto, O. F. L. S.; Saitovitch, H.; Cavalcante, J. T. P. D.; Carbonari, A. W.; Saxena, R. N.; Bosch-Santos, B.; Pereira, L. F. D.; Mestnik-Filho, J.; Forker, M.

    2016-08-01

    This paper reports the investigation of the magnetic hyperfine field Bh f in a series of rare-earth (R ) cadmium intermetallic compounds R Cd and GdCd2 measured by perturbed angular correlation (PAC) spectroscopy using 111In/111Cd as probe nuclei at Cd sites as well as first-principles calculations of Bh f at Cd sites in the studied compounds. Vapor-solid state reaction of R metals with Cd vapor and the 111In radioisotope was found to be an appropriate route of doping rare-earth cadmium compounds with the PAC probe 111In/111Cd. The observation that the hyperfine parameters depend on details of the sample preparation provides information on the phase preference of diffusing 111In in the rare-earth cadmium phase system. The 111Cd hyperfine field has been determined in the compounds R Cd for the R constituents Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, and Er, in several cases as a function of temperature. For most R constituents, the temperature dependence Bh f(T ) of 111Cd:R Cd is consistent with ferromagnetic order of the compound. DyCd, however, presents a remarkable anomaly: a finite magnetic hyperfine field is observed only in the temperature interval 35 K ≤ T ≤ 80 K which indicates a transition from ferromagnetic order to a spin arrangement where all 4 f -induced contributions to the magnetic hyperfine field at the Cd site cancel. First-principles calculation results for DyCd show that the (π , π , 0) antiferromagnetic configuration is energetically more favorable than the ferromagnetic. The approach used in the calculations to simulate the R Cd system successfully reproduces the experimental values of Bh f at Cd sites and shows that the main contribution to Bh f comes from the valence electron polarization. The de Gennes plot of the hyperfine field Bh f of 111Cd:R Cd vs the 4 f -spin projection (g -1 )J reflects a decrease of the strength of indirect 4 f -4 f exchange across the R series. Possible mechanisms are discussed and the experimental results indicate that

  16. The intersublattice exchange interactions in the R 2Co 7B 3 compounds (R = heavy rare earth)

    NASA Astrophysics Data System (ADS)

    Kowalczyk, A.

    1997-07-01

    The experimental values of Curie temperatures of hexagonal R 2Co 7B 3 (R = heavy rare earth) compounds are used to calculate the effective intersublattice exchange interactions, JRCo, between R and Co sublattices. A mean field approximation is used. The compounds belong to the R n+1Co 3 n+5B 2 n family. The R 2Co 7B 3 is a combination of CaCu 5 and CeCo 3B 2-type structures. The JRCo has a tendency to decrease with increasing atomic number of the rare earth partner. A similar tendency has been found for other Fe and Co-based compounds.

  17. The impact of quadrupole moment of 4f shell on the hyperfine interactions anisotropy in RAl2 (R=Sm, Tb) intermetallic compounds

    NASA Astrophysics Data System (ADS)

    Delyagin, N. N.; Erzinkyan, A. L.

    2016-03-01

    The magnetic hyperfine interactions for 119Sn impurity atoms in SmAl2 and TbAl2 ferromagnetic compounds have been investigated by Mössbauer spectroscopy technique. These compounds have the same structure but differ in the sign of the quadrupole moment of the R3+ ion. In both cases, the spectrum contains two magnetic subspectra with the ratio of the intensities 1:3, which correspond to a and b Al sites with significantly different hyperfine parameters. The phenomenon change the order the component of inversion component of the Mössbauer spectra was found. This phenomenon is explained by the influence of the quadrupole moment 4f-shell of R3+ ions on the electron density distribution in the valence band. The degree of overlap of electron wave functions being on hybrid orbitals greatly depends on the sign of the 4f-shell quadrupole moment, which gives rise to huge anisotropy in the hyperfine magnetic field and the electric field gradient. Quadrupole deformation induced by the 4f quadrupole moment and the electric field gradient, greatly affects the d-like and p-like components of the electron wave functions, but little effect on the its s-components.

  18. Structures of stable and metastable Ge2Sb2Te5, an intermetallic compound in GeTe-Sb2Te3 pseudobinary systems.

    PubMed

    Matsunaga, Toshiyuki; Yamada, Noboru; Kubota, Yoshiki

    2004-12-01

    The most widely used memory materials for rewritable phase-change optical disks are the GeTe-Sb2Te3 pseudobinary compounds. Among these compounds, Ge2Sb2Te5 crystallizes into a cubic close-packed structure with a six-layer period (metastable phase) in the non-thermal equilibrium state, and a trigonal structure with a nine-layer period (stable phase) in the thermal equilibrium state. The structure of the stable phase has Ge/Sb layers in which Ge and Sb are randomly occupied, as does the structure of the metastable phase, while the conventionally estimated structure had separate layers of Ge and Te. The metastable and stable phases are very similar in that Te and Ge/Sb layers stack alternately to form the crystal. The major differences between these phases are: (i) the stable phase has pairs of adjacent Te layers that are not seen in the metastable phase and (ii) only the metastable phase contains vacancies of ca 20 at. % in the Ge/Sb layers. PMID:15534378

  19. Neutron Scattering Studies of Structural and Magnetic Properties of Rare-Earth - COPPER(6) Compounds

    NASA Astrophysics Data System (ADS)

    Vrtis, Mary Louise

    The structure of the RECu(,6) series (RE = La,Ce,Pr,Nd) has been studied at various temperatures from 10 K to 573 K by time-of-flight neutron powder diffraction. The high temperature orthorhombic cell transforms to a monoclinic cell at a temperature determined by the rare earth ion. Rietveld structural refinements at each temperature give details of the structural distortion associated with the transition. The space groups and the temperature dependence of the monoclinic strain for each compound are consistent with a second order phase transition driven by a soft acoustic phonon mode. By comparing the structural transition in these compounds, we see that the force constants acting on the rare-earth ion in this structure are significantly different for cerium, presumably due to its more delocalized 4f electrons. Polarized neutron scattering techniques have beem used to study the spatial distribution and temperature dependence of the magnetization induced by an externally applied magnetic field in a single crystal of CeCu(,6). This heavy fermion compound remains paramagnetic and non-superconducting down to (TURN)10 mK. The measurements were performed at 4.2 K and 92 K in an applied magnetic field of 50 KGauss. We found that the induced magnetization is predominately of 4f electronic character and exhibits Pauli-like behavior in the 4.2 K to 92 mK temperature region. The value of (chi)(0,0), which was obtained from extrapolating the form factor to the forward direction, is somewhat smaller than the bulk susceptibility measured in the same sample.

  20. Recent advances in ordered intermetallics

    SciTech Connect

    Liu, C.T.

    1992-12-31

    This paper briefly summarizes recent advances in intermetallic research and development. Ordered intermetallics based on aluminides and silicides possess attractive properties for structural applications at elevated temperatures in hostile environments; however, brittle fracture and poor fracture resistance limit their use as engineering materials in many cases. In recent years, considerable efforts have been devoted to the study of the brittle fracture behavior of intermetallic alloys; as a result, both intrinsic and extrinsic factors governing brittle fracture have been identified. Recent advances in first-principles calculations and atomistic simulations further help us in understanding atomic bonding, dislocation configuration, and alloying effects in intermetallics. The basic understanding has led to the development of nickel, iron, and titanium aluminide alloys with improved mechanical and metallurgical properties for structural use. Industrial interest in ductile intermetallic alloys is high, and several examples of industrial involvement are mentioned.

  1. Recent advances in ordered intermetallics

    SciTech Connect

    Liu, C.T.

    1994-12-31

    Ordered intermetallic alloys based on aluminides and silicides offer many advantages for structural use at high temperatures in hostile environments. Attractive properties include excellent oxidation and corrosion resistance, light weight, and superior strength at high temperatures. The major concern for structural use of intermetallics was their low ductility and poor fracture resistance at ambient temperatures. For the past 10 years, considerable effort was devoted to R&D of ordered intermetallic alloys, and progress has been made on understanding intrinsic and extrinsic factors controlling brittle fracture in intermetallic alloys based on aluminides and silicides. Parallel effort on alloy design has led to the development of a number of ductile and strong intermetallic alloys based on Ni{sub 3}Al, NiAl, Fe{sub 3}Al, FeAl, Ti{sub 3}Al, and TiAl systems for structural applications.

  2. Crystal structure and magnetic properties of new Fe3Co3 X 2 (X  =  Ti, Nb) intermetallic compounds

    NASA Astrophysics Data System (ADS)

    Zhang, Jie; Nguyen, Manh Cuong; Balasubramanian, Balamurugan; Das, Bhaskar; Sellmyer, David J.; Zeng, Zhi; Ho, Kai-Ming; Wang, Cai-Zhuang

    2016-05-01

    The structure and magnetic properties of new magnetic Fe3Co3 X 2 (X  =  Ti, Nb) compounds are studied by genetic algorithm, first-principles density functional theory (DFT) calculations, and experiments. The atomic structure of a hexagonal structure with P-6m2 symmetry is determined. The simulated x-ray diffraction (XRD) spectra of the P-6m2 structures agree well with experimental XRD data for both Fe3Co3Ti2 and Fe3Co3Nb2. The magnetic properties of these structures as well as the effect of the disorder of Fe and Co on their magnetic properties are also investigated. The magnetocrystalline anisotropy energy is found to be very sensitive to the occupancy disorder between Fe and Co.

  3. First-principles point defect models in Zr7Ni10 and Zr2Ni7 binary intermetallic compounds and their implications in nickel-metal hydride batteries

    NASA Astrophysics Data System (ADS)

    Wong, Diana F.

    Zr-Ni-based alloys as nickel-metal hydride battery anode materials offer low-cost, flexible and tunable battery performance. Zr7Ni 10 is an important secondary phase found in multi-phased AB2 Laves-phase-based metal hydride alloys, and the synergetic effect between the Zr-Ni and the Laves phases allows access to the high hydrogen storage of the Zr-Ni phases despite the lower absorption/desorption kinetics. Zr7Ni10 displays a small solubility window for Zr-rich compositions, while Zr2Ni7, with no solubility window, shows poor capacity with good kinetics. Stability of point defects within the crystal structure allows Zr7Ni10 to maintain the same structure at off-stoichiometric compositions, thus it is theorized that defects may play a role in the difference between the electrochemical behaviors in Zr7Ni10 and Zr2Ni7. Defect models in Zr7Ni10 and Zr2Ni7 compounds computed using a combination of density functional theory and statistical mechanics offer a starting point for understanding the possible roles that point defects have on the performance of Zr-Ni based active negative electrode materials in Ni/MH batteries. Theoretical vacancy and anti-site defect formation energies are calculated and reported for Zr-rich, Ni-rich, and stoichiometric compounds of Zr7Ni 10 and Zr2Ni7, and the implications of the defect models on nickel-metal hydride negative electrode active material design and performance are discussed.

  4. Structures and physical properties of R2TX3 compounds

    NASA Astrophysics Data System (ADS)

    Pan, Zhi-Yan; Cao, Chong-De; Bai, Xiao-Jun; Song, Rui-Bo; Zheng, Jian-Bang; Duan, Li-Bing

    2013-05-01

    Rare-earth compounds have been an attractive subject based on the unique electronic structures of the rare-earth elements. Novel ternary intermetallic compounds R2TX3 (R = rare-earth element or U, T = transition-metal element, X = Si, Ge, Ga, In) are a significant branch of this research field due to their complex and intriguing physical properties, such as magnetic order at low temperature, spin-glass behavior, Kondo effect, heavy fermion behavior, and so on. The unique physical properties of R2TX3 compounds are related to distinctive electronic structures, crystal structures, microinteraction, and external environment. Most R2TX3 compounds crystallize in AlB2-type or derived AlB2-type structures and exhibit many similar properties. This paper gives a concise review of the structures and physical properties of these compounds. Spin glass, magnetic susceptibility, resistivity, and specific heat of R2TX3 compounds are discussed.

  5. Codetermination of crystal structures at high pressure: Combined application of theory and experiment to the intermetallic compound AuGa2

    NASA Astrophysics Data System (ADS)

    Godwal, B. K.; Stackhouse, S.; Yan, J.; Speziale, S.; Militzer, Burkhard; Jeanloz, R.

    2013-03-01

    A combination of x-ray diffraction at high pressures and first-principles calculations reveals the sequence of crystal-structural phase transitions in AuGa2 from cubic (Fm3¯m) to orthorhombic (Pnma) at 10 (±4) GPa and then to monoclinic (P21/n) at 33 (±6) GPa. Neither theory nor experiment would have been adequate, on their own, in documenting this sequence of phases, but together they confirm a sequence differing from the Fm3¯m→Pnma→P63/mmc transitions predicted for CaF2 and Pnma → P1121/a transition reported for PbCl2 and SnCl2. The combined results from theory and experiment also allow us to constrain the equations of state of the three phases of AuGa2. Calculations on the analog PbCl2 predict a transition to the P21/n phase seen in AuGa2 that could, therefore, be a common high-pressure phase for PbCl2-structured compounds.

  6. Synthesis, structure, and bonding in K12Au21Sn4. A polar intermetallic compound with dense Au20 and open AuSn4 layers

    SciTech Connect

    Li, Bin; Kim, Sung-Jin; Miller, Gordon J.; and Corbett, John D.

    2009-10-29

    The new phase K{sub 12}Au{sub 21}Sn{sub 4} has been synthesized by direct reaction of the elements at elevated temperatures. Single crystal X-ray diffraction established its orthorhombic structure, space group Pmmn (No. 59), a = 12.162(2); b = 18.058(4); c = 8.657(2) {angstrom}, V = 1901.3(7) {angstrom}{sup 3}, and Z = 2. The structure consists of infinite puckered sheets of vertex-sharing gold tetrahedra (Au{sub 20}) that are tied together by thin layers of alternating four-bonded-Sn and -Au atoms (AuSn{sub 4}). Remarkably, the dense but electron-poorer blocks of Au tetrahedra coexist with more open and saturated Au-Sn layers, which are fragments of a zinc blende type structure that maximize tetrahedral heteroatomic bonding outside of the network of gold tetrahedra. LMTO band structure calculations reveal metallic properties and a pseudogap at 256 valence electrons per formula unit, only three electrons fewer than in the title compound and at a point at which strong Au-Sn bonding is optimized. Additionally, the tight coordination of the Au framework atoms by K plays an important bonding role: each Au tetrahedra has 10 K neighbors and each K atom has 8-12 Au contacts. The appreciably different role of the p element Sn in this structure from that in the triel members in K{sub 3}Au{sub 5}In and Rb{sub 2}Au{sub 3}Tl appears to arise from its higher electron count which leads to better p-bonding (valence electron concentrations = 1.32 versus 1.22).

  7. Dual-emitting nanocomposites derived from rare-earth compound nanotubes for ratiometric fluorescence sensing applications.

    PubMed

    Sun, Tian-Ying; Zhang, Da-Quan; Yu, Xue-Feng; Xiang, Yang; Luo, Min; Wang, Jia-Hong; Tan, Guo-Long; Wang, Qu-Quan; Chu, Paul K

    2013-02-21

    A new class of ratiometric fluorescence sensors composed of rare-earth (RE) compound nanotubes is described. Polyethylenimine-coated yttrium hydroxide fluoride nanotubes (YHF NTs) that were synthesized hydrothermally exhibit highly efficient fluorescence when doped with RE ions. The polyethylenimine on the NTs facilitates the incorporation of phosphors such as quantum dots or organic dyes onto the NT surface to produce dual-emitting nanocomposites which are excellent ratiometric fluorescence sensors. The phosphor layer and underlying tubes in the nanocomposites act as the indicator and reference probes, respectively. This ratiometric fluorescence method which can be applied to the detection of heavy metals in solutions, temperature sensing, and pH sensing boasts high sensitivity and selectivity as well as better accuracy than traditional intensity-based fluorescence methods. PMID:23334204

  8. Dual-emitting nanocomposites derived from rare-earth compound nanotubes for ratiometric fluorescence sensing applications

    NASA Astrophysics Data System (ADS)

    Sun, Tian-Ying; Zhang, Da-Quan; Yu, Xue-Feng; Xiang, Yang; Luo, Min; Wang, Jia-Hong; Tan, Guo-Long; Wang, Qu-Quan; Chu, Paul K.

    2013-01-01

    A new class of ratiometric fluorescence sensors composed of rare-earth (RE) compound nanotubes is described. Polyethylenimine-coated yttrium hydroxide fluoride nanotubes (YHF NTs) that were synthesized hydrothermally exhibit highly efficient fluorescence when doped with RE ions. The polyethylenimine on the NTs facilitates the incorporation of phosphors such as quantum dots or organic dyes onto the NT surface to produce dual-emitting nanocomposites which are excellent ratiometric fluorescence sensors. The phosphor layer and underlying tubes in the nanocomposites act as the indicator and reference probes, respectively. This ratiometric fluorescence method which can be applied to the detection of heavy metals in solutions, temperature sensing, and pH sensing boasts high sensitivity and selectivity as well as better accuracy than traditional intensity-based fluorescence methods.A new class of ratiometric fluorescence sensors composed of rare-earth (RE) compound nanotubes is described. Polyethylenimine-coated yttrium hydroxide fluoride nanotubes (YHF NTs) that were synthesized hydrothermally exhibit highly efficient fluorescence when doped with RE ions. The polyethylenimine on the NTs facilitates the incorporation of phosphors such as quantum dots or organic dyes onto the NT surface to produce dual-emitting nanocomposites which are excellent ratiometric fluorescence sensors. The phosphor layer and underlying tubes in the nanocomposites act as the indicator and reference probes, respectively. This ratiometric fluorescence method which can be applied to the detection of heavy metals in solutions, temperature sensing, and pH sensing boasts high sensitivity and selectivity as well as better accuracy than traditional intensity-based fluorescence methods. Electronic supplementary information (ESI) available: EA and TGA profiles, emission spectra of YHF:Eu NTs. See DOI: 10.1039/c2nr33217e

  9. Earth

    NASA Technical Reports Server (NTRS)

    Carr, M. H.

    1984-01-01

    The following aspects of the planet Earth are discussed: plate tectonics, the interior of the planet, the formation of the Earth, and the evolution of the atmosphere and hydrosphere. The Earth's crust, mantle, and core are examined along with the bulk composition of the planet.

  10. On the R 5d band polarization in rare-earth-transition metal compounds.

    PubMed

    Burzo, E; Chioncel, L; Tetean, R; Isnard, O

    2011-01-19

    Magnetic measurements and band structure calculations were performed on RT(2) and RT(5) compounds, where R is a heavy rare-earth and T = Fe, Co, Ni, Al, as well as on pseudobinary compounds GdCo(2 - x)A(x) (A = Ni, Cu, Si), YFe(2 - x)V(x) and YCo(4 - x)Ni(x)B. The calculated moments per formula unit described well the experimentally determined magnetizations. By considering the 4f-5d-3d exchange interactions, we evaluate the contributions of local 4f-5d and short range 5d-3d interactions to R 5d and Y 4d band polarizations. The 4f-5d induced polarizations are proportional to the De Gennes factor and are the same for a given R and a similar type structure. The R 5d and Y 4d band polarizations induced by R 5d-T3d or Y 4d-T3d hybridizations are proportional to the number of neighbouring T atoms, to a given R, and their magnetic moments. Previous results on the matter are also discussed. PMID:21406851

  11. Electronic structure of graphite intercalation compounds of rare-earths and uranium

    NASA Astrophysics Data System (ADS)

    Danzenbächer, S.; Molodtsov, S. L.; Boysen, J.; Gantz, Th.; Laubschat, C.; Shikin, A. M.; Gorovikov, S. A.; Richter, M.

    1999-01-01

    Graphite intercalation compounds (GICs) of rare-earths and U reveal interesting anisotropic electronic properties related to their characteristic layered structure. In this contribution we present a comparative angle-resolved photoemission (PE) study of single-crystalline R-GICs (R=La, Eu, Yb, U) together with band-structure calculations. The samples where prepared in situ by deposition of R metals onto clean graphite (0 0 0 1) substrates and subsequent annealing. Stage-2 GICs are formed with a B-A-R-A-B-R structure changing the A-B-A-B stacking sequence of graphite. The electron structure may be described in a first approach by simple charge transfer from the R metals to unoccupied π* orbitals of graphite leading to a shift of all graphite-derived PE features to higher binding energies and to the appearance of an additional narrow feature at EF. For uranium, this Fermi-level peak is superimposed by a sharp U 5f signal, that is located directly at EF and reveals no trace of multiplet splittings. Since the band-structure calculation gives clear evidence for a localized character of the U 5f states, we assume that uranium behaves mixed-valent in this compound and can be described in the framework of a single-impurity Anderson model.

  12. Intermetallic Layers in Soldered Joints

    Energy Science and Technology Software Center (ESTSC)

    1998-12-10

    ILAG solves the one-dimensional partial differential equations describing the multiphase, multicomponent, solid-state diffusion-controlled growth of intermetallic layers in soldered joints. This software provides an analysis capability for materials researchers to examine intermetallic growth mechanisms in a wide variety of defense and commercial applications involving both traditional and advanced materials. ILAG calculates the interface positions of the layers, as well as the spatial distribution of constituent mass fractions, and outputs the results at user-prescribed simulation times.

  13. Intermetallics as Novel Supports for Pt Monolayer O2 Reduction Electrocatalysts: Potential for Significantly Improving Properties

    SciTech Connect

    Ghosh, T.; Vukmirovic, M.; DiSalvo, F.J.; Adzic, R.R.

    2010-01-27

    We report on a new class of core-shell electrocatalysts for the oxygen-reduction reaction. These electrocatalysts comprise a Pt monolayer shell and ordered intermetallic compounds cores and have enhanced activity and stability compared with conventional ones. These advantages are derived from combining the unique properties of Pt monolayer catalysts (high activity, low metal content) and of the intermetallic compounds (high stability and, possibly, low price). This method holds excellent potential for creating efficient fuel cell electrocatalysts.

  14. Quaternary borocarbides: New class of intermetallic superconductors

    NASA Technical Reports Server (NTRS)

    Nagarajan, R.; Gupta, L. C.; Dhar, S. K.; Mazumdar, Chandan; Hossain, Zakir; Godart, C.; Levy-Clement, C.; Padalia, B. D.; Vijayaraghavan, R.

    1995-01-01

    Our recent discovery of superconductivity (SC) in the four-element multiphase Y-Ni-B-C system at an elevated temperature (TC approximately 12 K) has opened up great possibilities of identifying new superconducting materials and generating new physics. Superconductivity with Tc (greater than 20 K) higher than that known so far in bulk intermetallics has been observed in multiphase Y-Pd-B-C and Th-Pd-B-C systems and a family of single phase materials RENi2B2C (RE= Y, rare earth) have been found. Our investigations show YNi2B2C to be a strong coupling hard type-II SC. HC2(T) exhibits an unconventional temperature dependence. Specific heat and magnetization studies reveal coexistence of SC and magnetism in RNi2B2C (R = Ho, Er, Tm) with magnetic ordering temperatures (Tc approximately 8 K, 10.5 K, 11 K and Tm approximately 5 K, approximately 7K, approximately 4 K respectively) that are remarkably higher than those in known magnetic superconductors . Mu-SR studies suggest the possibility of Ni atoms carrying a moment in TmNi2B2C. Resistivity results suggests a double re-entrant transition (SC-normal-SC) in HoNi2B2C. RENi2B2C (RE = Ce, Nd, Gd) do not show SC down to 4.2 K. The Nd- and Gd-compounds order magnetically at approximately 4.5 K and approximately 19.5 K, respectively. Two SC transitions are observed in Y-Pd-B-C (Tc approximately 22 K, approximately 10 K) and in Th-Pd-B-C (Tc approximately 20 K, approximately 14 K) systems, which indicate that there are at least two structures which support SC in these borocarbides. In our multiphase ThNi2B2C we observe SC at approximately 6 K. No SC was seen in multiphase UNi2B2C, UPd2B2C, UOs2Ge2C and UPd5B3C(0.35) down to 4.2 K. Tc in YNi2B2C is depressed by substitutions (Gd, Th and U at Y-sites and Fe, Co at Ni-sites).

  15. Quaternary borocarbides: New class of intermetallic superconductors

    NASA Astrophysics Data System (ADS)

    Nagarajan, R.; Gupta, L. C.; Dhar, S. K.; Mazumdar, Chandan; Hossain, Zakir; Godart, C.; Levy-Clement, C.; Padalia, B. D.; Vijayaraghavan, R.

    1995-04-01

    Our recent discovery of superconductivity (SC) in the four-element multiphase Y-Ni-B-C system at an elevated temperature (TC approximately 12 K) has opened up great possibilities of identifying new superconducting materials and generating new physics. Superconductivity with Tc (greater than 20 K) higher than that known so far in bulk intermetallics has been observed in multiphase Y-Pd-B-C and Th-Pd-B-C systems and a family of single phase materials RENi2B2C (RE= Y, rare earth) have been found. Our investigations show YNi2B2C to be a strong coupling hard type-II SC. HC2(T) exhibits an unconventional temperature dependence. Specific heat and magnetization studies reveal coexistence of SC and magnetism in RNi2B2C (R = Ho, Er, Tm) with magnetic ordering temperatures (Tc approximately 8 K, 10.5 K, 11 K and Tm approximately 5 K, approximately 7K, approximately 4 K respectively) that are remarkably higher than those in known magnetic superconductors . Mu-SR studies suggest the possibility of Ni atoms carrying a moment in TmNi2B2C. Resistivity results suggests a double re-entrant transition (SC-normal-SC) in HoNi2B2C. RENi2B2C (RE = Ce, Nd, Gd) do not show SC down to 4.2 K. The Nd- and Gd-compounds order magnetically at approximately 4.5 K and approximately 19.5 K, respectively. Two SC transitions are observed in Y-Pd-B-C (Tc approximately 22 K, approximately 10 K) and in Th-Pd-B-C (Tc approximately 20 K, approximately 14 K) systems, which indicate that there are at least two structures which support SC in these borocarbides. In our multiphase ThNi2B2C we observe SC at approximately 6 K. No SC was seen in multiphase UNi2B2C, UPd2B2C, UOs2Ge2C and UPd5B3C(0.35) down to 4.2 K. Tc in YNi2B2C is depressed by substitutions (Gd, Th and U at Y-sites and Fe, Co at Ni-sites).

  16. Computational mechanistic elucidation of the intramolecular aminoalkene hydroamination catalysed by iminoanilide alkaline-earth compounds.

    PubMed

    Tobisch, Sven

    2015-04-27

    A comprehensive computational exploration of plausible alternative mechanistic pathways for the intramolecular hydroamination (HA) of aminoalkenes by a recently reported class of kinetically stabilised iminoanilide alkaline-earth silylamido compounds [{N^N}Ae{N(SiMe3)2}⋅(thf)n] ({N^N} = iminoanilide; Ae = Ca, Sr, Ba) is presented. On the one hand, a proton-assisted concerted N-C/C-H bond-forming pathway to afford the cycloamine in a single step can be invoked and on the other hand, a stepwise σ-insertive pathway that involves a fast, reversible migratory olefin 1,2-insertion step linked to a less rapid, irreversible metal-C azacycle tether σ-bond aminolysis. Notably, these alternative mechanistic avenues are equally consistent with reported key experimental features. The present study, which employs a thoroughly benchmarked and reliable DFT methodology, supports the prevailing mechanism to be a stepwise σ-insertive pathway that sees an initial conversion of the {N^N}Ae silylamido into the catalytically competent {N^N}Ae amidoalkene compound and involves thereafter facile and reversible insertive N-C bond-forming ring closure, linked to irreversible intramolecular Ae-C tether σ-bond aminolysis at the transient {N^N}Ae alkyl intermediate. Turnover-limiting protonolysis accounts for the substantial primary kinetic isotope effect observed; its DFT-derived barrier satisfactorily matches the empirically determined Eyring parameter and predicts the decrease in rate observed across the series Ca>Sr>Ba correctly. Non-competitive kinetic demands militate against the operation of the concerted proton-assisted pathway, which describes N-C bond-forming ring closure triggered by concomitant amino proton delivery at the C=C linkage evolving through a multi-centre TS structure. Valuable insights into the catalytic structure-activity relationships are unveiled by a detailed comparison of [{N^N}Ae(NHR)] catalysts. Moreover, the intriguingly opposite trends in reactivity

  17. Extraction of rare-earth metal(III) nitrates by neutral organophosphorus compounds from concentrated aqueous salt solutions

    SciTech Connect

    Pyartman, A.K.; Puzikov, E.A.

    1995-07-20

    Equations describing isotherms of extraction of rare-earth metal(III) nitrates by neutral organo-phosphorus compounds over a wide range of component concentrations in aqueous and organic phases have been proposed. Constants of phase extraction and empirical parameters characterizing the influence of organic phase composition on the activity coefficients of the components have been presented.

  18. Mechanism of corrosion inhibition of AA2024 by rare-earth compounds.

    PubMed

    Yasakau, Kiryl A; Zheludkevich, Mikhail L; Lamaka, Sviatlana V; Ferreira, Mario G S

    2006-03-23

    The mechanism of corrosion protection of the widely used 2024-T3 aluminum alloy by cerium and lanthanum inhibitors in chloride media is described in detail in the present work. The corrosion process was investigated by means of scanning Kelvin probe force microscopy (SKPFM), in situ atomic force microscopy, and scanning electron microscopy coupled with energy dispersive spectroscopy. Employment of the high-resolution and in situ techniques results in a deep understanding of the details of the physical chemistry and mechanisms of the corrosion processes. The applicability of the SKPFM for mechanistic analysis of the effect of different corrosion inhibitors is demonstrated for the first time. The inhibitors under study show sufficient hindering of the localized corrosion processes especially in the case of pitting formation located around the intermetallic S-phase particles. The main role of Ce(3+) and La(3+) in the corrosion protection is formation of hydroxide deposits on S-phase inclusions buffering the local increase of pH, which is responsible for the acceleration of the intermetallics dealloying. The formed hydroxide precipitates can also act as a diffusion barrier hindering the corrosion processes in active zones. Cerium nitrate exhibits higher inhibition efficiency in comparison with lanthanum nitrate. The higher effect in the case of cerium is obtained due to lower solubility of the respective hydroxide. A detailed mechanism of the corrosion process and its inhibition is proposed based on thermodynamic analysis. PMID:16539491

  19. Intermetallics for structural applications

    SciTech Connect

    Sikka, V.K.; Deevi, S.C.

    1995-09-01

    Intermetallics are introduced as possible structural materials. The attributes and useful temperature limits of eight of the most likely candidates have been described. In addition, detailed descriptions are given for chemical compositions, corrosion properties, mechanical properties, melting and processing, and applications of Ni{sub 3}Al and Fe{sub 3}Al-based alloys. Mechanical properties of Ni{sub 3}Al-based alloys are compared with commercially used HU alloys in the cast condition and Haynes 214 in the wrought condition. The mechanical properties of Fe{sub 3}Al-based alloys are compared with an oxide-dispersion-strengthened (ODS) Inco alloy MA-956. Comparisons have shown that Ni{sub 3}Al-based alloys offer the best combination of oxidation and carburization resistance and are significantly stronger than the commercially used HU alloy for many of the furnace-fixture applications. However, the Fe{sub 3}Al-based alloys, which offer the best sulfidation resistance of the commercially available alloys, are significantly weaker in creep than the ODS MA-956 alloy. Even with the current strength level, Fe{sub 3}Al-based alloys are superior as porous, sintered metal filters for hot-gas cleanup in coal gasification systems. Oxide-dispersion strengthening of the Fe{sub 3}Al-based alloys is currently under way to improve their creep strength.

  20. The atmosphere of the primitive earth and the prebiotic synthesis of organic compounds

    NASA Technical Reports Server (NTRS)

    Miller, S. L.; Schlesinger, G.

    1983-01-01

    The prebiotic synthesis of organic compounds is investigated using a spark discharge on various simulated prebiotic atmospheres at 25 C. It is found that glycine is almost the only amino acid produced from the model atmospheres containing CO and CO2. These results show that the maximum yield is about the same for the three carbon sources (CO, CO2, and CH4) at high H2/carbon ratios, but that CH4 is superior at low H2/carbon ratios. CH4 is found to yield a much greater variety of amino acids than either CO or CO2. If it is assumed that amino acids more complex than glycine were required for the origin of life, then these findings indicate the need for CH4 in the primitive atmosphere. The yields of cyanide and formaldehyde are shown to parallel the amino acid results, with yields of HCN and H2CO as high as 13 percent based on carbon. Ammonia is also found to be produced from N2 in experiments with no added NH3 in yields as high as 4.9 percent. These results indicate that large amounts of NH3 would have been synthesized on the primitive earth by electric discharges.

  1. Thermodynamic, Magnetic, and Superconductivity Properties of Selected Rare Earth - Transition Metal Compounds.

    NASA Astrophysics Data System (ADS)

    Higgins, Bill Edward

    Selected material problems relating to R _2T_{14}B (R = rare earth T = transition metal) and RBa_2 Cu_3O_{ rm x} type materials are studied. Properties central to a basic understanding of desirable characteristics of the material were chosen for study and methods for improving the characteristics devised. Common to both systems is an investigation of the metal gas reactions which each compound undergoes. In R_2T_ {14}B, oxidation is destructive of the material and ways to minimize it, including substitution of chromium at the transition metal site, are developed. Second, the temperature dependence of coercivity in R_2 T_{14}B was shown to depend on the temperature dependence of anisotropy. Materials with a stable temperature dependence of coercivity designed on the basis of this relationship were prepared, and characterized. Finally, the potential of R_2T _{14}B for use as magnetooptic recording media is considered. The R_2 T_{14}B family is promising for this application as it has a large Kerr rotation among other desirable properties. In the RBa_2Cu _3O_{rm x} system oxygen content is important to superconducting properties. Oxygen uptake kinetics are measured for YBa _2Cu_3O _{rm x} as well as Y _{0.5}Na_{0.5 }Ba_2Cu_3 O_{rm x}, YBa_2Cu_{2.5 }Fe_{0.5}O _{rm x} and the Y _{rm 1-y}La _{rm y}Ba_2 Cu_3O_{ rm x} family. Substitution at the rare earth site is found to have little effect on the activation energy of the oxygenation reaction, but substitution at the chain copper site, such as in YBa_2 Cu_{2.5}Fe _{0.5}O_{rm x}, is found to cause a large decrease in the activation energy of oxygen uptake. In addition, the Y_{rm 1-y}La_{rm y} Ba_2Cu_3O _{rm x} system was studied, in order to determine the reason for the anomalously low superconducting transition temperature of LaBa _2Cu_3O_ {rm x} when it is prepared by conventional means. It is likely that the reduced transition temperature comes from disorder of the barium and lanthanum.

  2. Multi-component intermetallic electrodes for lithium batteries

    DOEpatents

    Thackeray, Michael M; Trahey, Lynn; Vaughey, John T

    2015-03-10

    Multi-component intermetallic negative electrodes prepared by electrochemical deposition for non-aqueous lithium cells and batteries are disclosed. More specifically, the invention relates to composite intermetallic electrodes comprising two or more compounds containing metallic or metaloid elements, at least one element of which can react with lithium to form binary, ternary, quaternary or higher order compounds, these compounds being in combination with one or more other metals that are essentially inactive toward lithium and act predominantly, but not necessarily exclusively, to the electronic conductivity of, and as current collection agent for, the electrode. The invention relates more specifically to negative electrode materials that provide an operating potential between 0.05 and 2.0 V vs. metallic lithium.

  3. Alkaline earth lead and tin compounds Ae2Pb, Ae2Sn, Ae=Ca,Sr,Ba, as thermoelectric materials

    SciTech Connect

    Parker, David S; Singh, David J

    2013-01-01

    We present a detailed theoretical study of three alkaline earth compounds Ca2Pb, Sr2Pb and Ba2Pb, which have undergone little previous study, calculating electronic band structures and Boltzmann transport and bulk moduli using density functional theory. We also study the corresponding tin compounds Ca2 Sn, Sr2 Sn and Ba2 Sn. We find that these are all narrow band gap semiconductors with an electronic structure favorable for thermoelectric performance, with substantial thermopowers for the lead compounds at temperature ranges from 300 to 800 K. For the lead compounds, we further find very low calculated bulk moduli - roughly half of the values for the lead chalcogenides, suggestive of soft phonons and hence low lattice thermal conductivity. All these facts indicate that these materials merit experimental investigation as potential high performance thermoelectrics. We find good potential for thermoelectric performance in the environmentally friendly stannide materials, particularly at high temperature.

  4. Role of Ag in the formation of interfacial intermetallic phases in Sn-Zn soldering

    NASA Astrophysics Data System (ADS)

    Song, Jenn-Ming; Liu, Pei-Chi; Shih, Chia-Ling; Lin, Kwang-Lung

    2005-09-01

    This study explored the effect of Ag as the substrate or alloying element of solders on the interfacial reaction in Sn-Zn soldering. Results show that instead of Ag-Sn compounds, ζ-AgZn and γ-Ag5Zn8 form at the Sn-Zn/Ag interface. The addition of Ag in Sn-Zn solders leads to the precipitation of ɛ-AgZn3 from the liquid solder on preformed interfacial intermetallics. The morphology of this additional AgZn3 is closely related to the solidification process of Ag-Zn intermetallics and the under intermetallic layer.

  5. Fundamentals of mechanical behavior in structural intermetallics: A synthesis of atomistic and continuum modeling

    SciTech Connect

    Yoo, M.H.; Fu, C.L.

    1993-08-01

    After a brief account of the recent advances in computational research on mechanical behavior of structural intermetallics, currently unresolved problems and critical issues are addressed and the knowledge base for potential answers to these problems is discussed. As large-scale problems (e.g., dislocation core structures, grain boundaries, and crack tips) are treated by atomistic simulations, future development of relevant interatomic potentials should be made consistent with the results of first-principles calculations. The bulk and defect properties calculated for intermetallic compounds, both known and as yet untested, can furnish insights to alloy designers in search of new high-temperature structural intermetallics.

  6. Three interesting coordination compounds based on metalloligand and alkaline-earth ions: Syntheses, structures, thermal behaviors and magnetic property

    NASA Astrophysics Data System (ADS)

    Zhou, Qiang; Qian, Jun; Zhang, Chi

    2016-09-01

    Based on metalloligand LCu ([Cu(2,4-pydca)2]2-, 2,4-pydca2- = pyridine-2,4-dicarboxylate) and alkaline-earth ions (Ca2+, Sr2+, and Ba2+), three interesting coordination compounds, [Ca(H2O)7][LCu·H2O]·H2O (1), {Sr[LCu·H2O]·4H2O}n (2), and {Ba[LCu·H2O]·8H2O}n (3), have been synthesized and well-characterized by elemental analysis, infrared spectroscopy, thermogravimetric and single-crystal X-ray diffraction analysis. X-ray crystallographic studies reveal that 1 features a discrete 0D coordination compound, while 2 and 3 exhibit the 2D network and 1D chain structures, respectively. Compound 2 is constructed from {LCu}2 dimers connected with {Sr2} units, which is fabricated by two Sr2+ ions bridged via two μ2-O bridges, while compound 3 is formed by 1D {Ba}n chain linked with metalloligands LCu and exhibits an interesting sandwich like chain structure. It is noted that the coordination numbers of alkaline-earth ions are in positive correlation with their radiuses. Moreover, the magnetic property of compound 2 has been studied.

  7. Third Intermetallic Matrix Composites Symposium, volume 350

    SciTech Connect

    Graves, J.A.; Bowman, R.R.; Lewandowski, J.J.

    1994-04-01

    Partial contents include: issues in potential IMC application for aerospace structures; powder metallurgy processing of intermetallic matrix composites; microstructure and properties of intermetallic matrix composites produced by reaction synthesis; combustion synthesis of niobium aluminide matrix composites; ambient temperature synthesis of bulk intermetallics; wear behavior of SHS intermetallic matrix composites; fracture characteristics of metal-intermetallic laminates produced by SHS reactions; and vapor phase synthesis of Ti aluminides and the interfacial bonding effect on the mechanical property of micro-composites reinforced by pyrolized SiC fibers.

  8. Magnetic properties of RT2Zn20; R = rare earth, T = Fe, Co, Ru, Os and Ir

    SciTech Connect

    Jia, Shuang

    2008-01-01

    It is well known that rare earth intermetallic compounds have versatile, magnetic properties associated with the 4f electrons: a local moment associated with the Hund's rule ground state is formed in general, but a strongly correlated, hybridized state may also appear for specific 4f electronic configuration (eg. for rare earth elements such as Ce or Yb). On the other hand, the conduction electrons in rare earth intermetallic compounds, certainly ones associated with non hybridizing rare earths, usually manifest non-magnetic behavior and can be treated as a normal, non-interacted Fermi liquid, except for some 3d-transition metal rich binary or ternary systems which often manifest strong, itinerant, d electron dominant magnetic behavior. Of particular interest are examples in which the band filling of the conduction electrons puts the system in the vicinity of a Stoner transition: such systems, characterized as nearly or weakly ferromagnet, manifest strongly correlated electronic properties [Moriya, 1985]. For rare earth intermetallic compounds, such systems provide an additional versatility and allow for the study of the behaviors of local moments and hybridized moments which are associated with 4f electron in a correlated conduction electron background.

  9. Phosphorus Redox on the Early Earth: First Identification of Low-Oxidation State Phosphorus Compounds in Terrestrial Samples

    NASA Astrophysics Data System (ADS)

    Block, K. M.; Pasek, M. A.

    2008-12-01

    Phosphorus is one of the key elements in biochemical systems, playing an important role in metabolism as ATP and other coenzymes, in replication as DNA and RNA, and in cellular structure as phospholipids. The geochemical cycling of phosphorus on the Earth is usually confined to the rock cycle- redox reactions of phosphorus are never considered. However, it has been proposed that redox reactions of phosphorus were important on the early Earth (Pasek, PNAS 2008). Indeed, such a suggestion is buttressed by the discovery of condensed phosphate formation linked to the oxidation of reduced P compounds. However, prior to the present work, there has been no report of these P compounds in geologic samples. Here we report the first occurrence of reduced P in samples of fulgurites, the glassy material resulting from the fusion of sand, soil, or rock during a lightning strike. On average, lightning strikes the Earth's surface at a rate of approximately 65 times per second (Krider et al., J. Geophys. Res.,1968) exposing target areas to extreme energy dissipation and temperatures. Through electron microprobe analyses and NMR we have identified naturally formed metal droplets containing Fe and P within several fulgurite samples and Ca-phosphite compounds. These droplets are highly reduced compared to the original material and are not naturally present in the target area, rather they were formed through the rapid, intense heating and quenching experienced during fulgurite formation. This process provides a natural means to create localized environments with greater than normal abundances of reduced Fe and P, less commonly found on Earth's surface than their oxidized counterparts. In particular, small areas that receive repeated lightning strikes due to topography or local weather patterns (e.g. hilltops) could potentially house unique microhabitats with reduced elements available for biological use.

  10. High Temperature Chemistry of Rare Earth Compounds: Dramatic Examples of Periodicity.

    ERIC Educational Resources Information Center

    Cater, E. David

    1978-01-01

    Reports that energy required to promote a 4f electron to the 5d level has a profound and predictable influence on the systematics of reactions involving conversion of rare earth atoms from combined to free states. (Author/MA)

  11. Tetranuclear and Pentanuclear Compounds of the Rare-Earth Metals: Synthesis and Magnetism.

    PubMed

    Yadav, Munendra; Mondal, Abhishake; Mereacre, Valeriu; Jana, Salil Kumar; Powell, Annie K; Roesky, Peter W

    2015-08-17

    The Schiff-base proligand 4-tert-butyl-2,6-bis-[(2-hydroxy-phenylimino)methyl]phenol (H3L) was prepared in situ from 4-tert-butyl-2,6-diformylphenol and 2-aminophenol. The proligand (H3L) was used with dibenzoylmethane (DBMH) or acetylacetone (acacH) with lanthanides giving compounds with varying arrangements of metal atoms and nuclearities. The tetranuclear compound {[Dy4(L)3(DBM)4][Et3NH]} (1) and pentanuclear compound {[Dy5(μ3-OH)2(L)3(DBM)4(MeOH)4]·4(MeOH)} (2) were obtained from the ligand (L)(3-) and dibenzoylmethane. The tetranuclear compounds {[Dy4(μ4-OH)(L)2(acac)4(MeOH)2(EtOH)(H2O)]·(NO3)·2(MeOH)·3(EtOH)} (3) and {[Ln4(μ3-OH)2(L)(HL)(acac)5(H2O)] (HNEt3)(NO3)·2(Et2O)} (Ln = Tb (4), Dy (5), Ho (6), and Tm (7)) resulted when the ligand (L)(3-) was used in the presence of acetylacetone. In the solid state structures, the tetranuclear compound 1 adopts a linear arrangement of metal atoms, while tetranuclear compound 3 has a square grid arrangement of metal atoms, and tetranuclear compounds 4-7 have a seesaw-shaped arrangement of metal atoms. The composition found from single-crystal X-ray analysis of compound 1 and 3-7 is supported by electrospray ionization mass spectrometry (ESI-MS). The magnetic studies on compounds 1 suggest the presence of weak ferromagnetic interactions, whereas compounds 2-6 exhibit weak antiferromagnetic interactions between neighboring metal centers. Compounds 1, 2, and 3 also show single-molecule magnet behavior under an applied dc field. PMID:26218434

  12. Thermomechanical processing of plasma sprayed intermetallic sheets

    DOEpatents

    Hajaligol, Mohammad R.; Scorey, Clive; Sikka, Vinod K.; Deevi, Seetharama C.; Fleischhauer, Grier; Lilly, Jr., A. Clifton; German, Randall M.

    2001-01-01

    A powder metallurgical process of preparing a sheet from a powder having an intermetallic alloy composition such as an iron, nickel or titanium aluminide. The sheet can be manufactured into electrical resistance heating elements having improved room temperature ductility, electrical resistivity, cyclic fatigue resistance, high temperature oxidation resistance, low and high temperature strength, and/or resistance to high temperature sagging. The iron aluminide has an entirely ferritic microstructure which is free of austenite and can include, in weight %, 4 to 32% Al, and optional additions such as .ltoreq.1% Cr, .gtoreq.0.05% Zr .ltoreq.2% Ti, .ltoreq.2% Mo, .ltoreq.1% Ni, .ltoreq.0.75% C, .ltoreq.0.1% B, .ltoreq.1% submicron oxide particles and/or electrically insulating or electrically conductive covalent ceramic particles, .ltoreq.1% rare earth metal, and/or .ltoreq.3% Cu. The process includes forming a non-densified metal sheet by consolidating a powder having an intermetallic alloy composition such as by roll compaction, tape casting or plasma spraying, forming a cold rolled sheet by cold rolling the non-densified metal sheet so as to increase the density and reduce the thickness thereof and annealing the cold rolled sheet. The powder can be a water, polymer or gas atomized powder which is subjecting to sieving and/or blending with a binder prior to the consolidation step. After the consolidation step, the sheet can be partially sintered. The cold rolling and/or annealing steps can be repeated to achieve the desired sheet thickness and properties. The annealing can be carried out in a vacuum furnace with a vacuum or inert atmosphere. During final annealing, the cold rolled sheet recrystallizes to an average grain size of about 10 to 30 .mu.m. Final stress relief annealing can be carried out in the B2 phase temperature range.

  13. Synthesis and Structure of ACa 9(VO 4) 7 Compounds, A=Bi or a Rare Earth

    NASA Astrophysics Data System (ADS)

    Evans, J. S. O.; Huang, J.; Sleight, A. W.

    2001-03-01

    Phases of the type ACa9(VO4)7 have been prepared where A can be a trivalent rare earth cation or Bi3+. The structure of BiCa9(VO4)7 was determined from single crystal X-ray diffraction data. The space group is R3 with a=10.8511(2) and c=38.0505(9) at 120 K and Z=6. The structure is related to that of Ca3(VO4)2, but a site partially occupied by Ca in Ca3(VO4)2 is completely vacant in BiCa9(VO4)7. All the ACa9(VO4)7 phases prepared showed a significant second harmonic signal. For the rare-earth compounds, the magnitude of the signal was comparable to that of KH2PO4; a value three times higher was found for BiCa9(VO4)7.

  14. Low-Temperature Synthesis Routes to Intermetallic Superconductors

    SciTech Connect

    Schaak, Raymond E

    2008-01-08

    Over the past few years, our group has gained expertise at developing low-temperature solution-based synthetic pathways to complex nanoscale solids, with particular emphasis on nanocrystalline intermetallic compounds. Our synthetic capabilities are providing tools to reproducibly generate intermetallic nanostructures with simultaneous control over crystal structure, composition, and morphology. This DOE-funded project aims to expand these capabilities to intermetallic superconductors. This could represent an important addition to the tools that are available for the synthesis and processing of intermetallic superconductors, which traditionally utilize high-temperature, high-pressure, thin film, or gas-phase vacuum deposition methods. Our current knowledge of intermetallic superconductors suggests that significant enhancements could result from the inherent benefits of low-temperature solution synthesis, e.g. metastable phase formation, control over nanoscale morphology to facilitate size-dependent property studies, robust and inexpensive processability, low-temperature annealing and consolidation, and impurity incorporation (for doping, stoichiometry control, flux pinning, and improving the critical fields). Our focus is on understanding the superconducting properties as a function of synthetic route, crystal structure, crystallite size, and morphology, and developing the synthetic tools necessary to accomplish this. This research program can currently be divided into two classes of superconducting materials: intermetallics (transition metal/post transition metal) and metal carbides/borides. Both involve the development and exploitation of low-temperature synthesis routes followed by detailed characterization of structures and properties, with the goal of understanding how the synthetic pathways influence key superconducting properties of selected target materials. Because of the low-temperature methods used to synthesize them and the nanocrystalline morphologies

  15. Intermetallic-Based High-Temperature Materials

    SciTech Connect

    Sikka, V.K.

    1999-04-25

    The intermetallic-based alloys for high-temperature applications are introduced. General characteristics of intermetallics are followed by identification of nickel and iron aluminides as the most practical alloys for commercial applications. An overview of the alloy compositions, melting processes, and mechanical properties for nickel and iron aluminizes are presented. The current applications and commercial producers of nickel and iron aluminizes are given. A brief description of the future prospects of intermetallic-based alloys is also given.

  16. Total energy calculations of correlated electron compounds: theory and application to rare earth nickelates

    NASA Astrophysics Data System (ADS)

    Park, Hyowon; Millis, Andrew; Marianetti, Chris

    2013-03-01

    We use density functional theory (DFT) plus dynamical mean field theory (DMFT) method, along with DFT+U and Hartree-Fock methods to compute the electronic energy as a function of crystal structure for rare earth nickelates. We show that full charge self-consistency can be essential for obtaining qualitative agreement with experiment and that the choice of double counting correction has an important effect on the energy. Furthermore, the precise definition (projector vs Wannier) of the correlated d-orbitals has a minimal effect. We show that charge self-consistent DFT+DMFT, as opposed to DFT+U, is critical to describing the magnetic-insulator to paramagnetic-metal phase boundary in the rare earth nickelate phase diagram. The authors acknowledge funding from the U. S. Army Research Office via grant No. W911NF0910345 56032PH.

  17. Method for making devices having intermetallic structures and intermetallic devices made thereby

    DOEpatents

    Paul, Brian Kevin; Wilson, Richard Dean; Alman, David Eli

    2004-01-06

    A method and system for making a monolithic intermetallic structure are presented. The structure is made from lamina blanks which comprise multiple layers of metals which are patternable, or intermetallic lamina blanks that are patternable. Lamina blanks are patterned, stacked and registered, and processed to form a monolithic intermetallic structure. The advantages of a patterned monolithic intermetallic structure include physical characteristics such as melting temperature, thermal conductivity, and corrosion resistance. Applications are broad, and include among others, use as a microreactor, heat recycling device, and apparatus for producing superheated steam. Monolithic intermetallic structures may contain one or more catalysts within the internal features.

  18. Suppressors made from intermetallic materials

    DOEpatents

    Klett, James W; Muth, Thomas R; Cler, Dan L

    2014-11-04

    Disclosed are several examples of apparatuses for suppressing the blast and flash produced as a projectile is expelled by gases from a firearm. In some examples, gases are diverted away from the central chamber to an expansion chamber by baffles. The gases are absorbed by the expansion chamber and desorbed slowly, thus decreasing pressure and increasing residence time of the gases. In other examples, the gases impinge against a plurality of rods before expanding through passages between the rods to decrease the pressure and increase the residence time of the gases. These and other exemplary suppressors are made from an intermetallic material composition for enhanced strength and oxidation resistance at high operational temperatures.

  19. High-temperature ordered intermetallic alloys II; Proceedings of the Second Symposium, Boston, MA, Dec. 2-4, 1986

    NASA Technical Reports Server (NTRS)

    Stoloff, N. S. (Editor); Koch, C. C. (Editor); Liu, C. T. (Editor); Izumi, O. (Editor)

    1987-01-01

    The papers presented in this volume provide on overview of recent theoretical and experimental research in the field of high-temperature ordered intermetallic alloys. The papers are gouped under the following headings: ordering behavior and theory, microstructures, mechanical behavior, alloy design and microstructural control, and metallurgical properties. Specific topics discussed include antiphase domains, disordered films and the ductility of ordered alloys based on Ni3Al; kinetics and mechanics of formation of Al-Ni intermetallics; deformability improvements of L1(2)-type intermetallic compounds; B2 aluminides for high-temperature applications; and rapidly solidified binary TiAl alloys.

  20. Cerium-based, intermetallic-strengthened aluminum casting alloy: High-volume co-product development

    DOE PAGESBeta

    Sims, Zachary C.; Weiss, D.; McCall, S. K.; McGuire, M. A.; Ott, R. T.; Geer, Tom; Rios, Orlando; Turchi, P. A. E.

    2016-05-23

    Here, several rare earth elements are considered by-products to rare earth mining efforts. By using one of these by-product elements in a high-volume application such as aluminum casting alloys, the supply of more valuable rare earths can be globally stabilized. Stabilizing the global rare earth market will decrease the long-term criticality of other rare earth elements. The low demand for Ce, the most abundant rare earth, contributes to the instability of rare earth extraction. In this article, we discuss a series of intermetallic-strengthened Al alloys that exhibit the potential for new high-volume use of Ce. The castability, structure, and mechanicalmore » properties of binary, ternary, and quaternary Al-Ce based alloys are discussed. We have determined Al-Ce based alloys to be highly castable across a broad range of compositions. Nanoscale intermetallics dominate the microstructure and are the theorized source of the high ductility. In addition, room-temperature physical properties appear to be competitive with existing aluminum alloys with extended high-temperature stability of the nanostructured intermetallic.« less

  1. Cerium-Based, Intermetallic-Strengthened Aluminum Casting Alloy: High-Volume Co-product Development

    NASA Astrophysics Data System (ADS)

    Sims, Zachary C.; Weiss, D.; McCall, S. K.; McGuire, M. A.; Ott, R. T.; Geer, Tom; Rios, Orlando; Turchi, P. A. E.

    2016-07-01

    Several rare earth elements are considered by-products to rare earth mining efforts. By using one of these by-product elements in a high-volume application such as aluminum casting alloys, the supply of more valuable rare earths can be globally stabilized. Stabilizing the global rare earth market will decrease the long-term criticality of other rare earth elements. The low demand for Ce, the most abundant rare earth, contributes to the instability of rare earth extraction. In this article, we discuss a series of intermetallic-strengthened Al alloys that exhibit the potential for new high-volume use of Ce. The castability, structure, and mechanical properties of binary, ternary, and quaternary Al-Ce based alloys are discussed. We have determined Al-Ce based alloys to be highly castable across a broad range of compositions. Nanoscale intermetallics dominate the microstructure and are the theorized source of the high ductility. In addition, room-temperature physical properties appear to be competitive with existing aluminum alloys with extended high-temperature stability of the nanostructured intermetallic.

  2. Cerium-Based, Intermetallic-Strengthened Aluminum Casting Alloy: High-Volume Co-product Development

    NASA Astrophysics Data System (ADS)

    Sims, Zachary C.; Weiss, D.; McCall, S. K.; McGuire, M. A.; Ott, R. T.; Geer, Tom; Rios, Orlando; Turchi, P. A. E.

    2016-05-01

    Several rare earth elements are considered by-products to rare earth mining efforts. By using one of these by-product elements in a high-volume application such as aluminum casting alloys, the supply of more valuable rare earths can be globally stabilized. Stabilizing the global rare earth market will decrease the long-term criticality of other rare earth elements. The low demand for Ce, the most abundant rare earth, contributes to the instability of rare earth extraction. In this article, we discuss a series of intermetallic-strengthened Al alloys that exhibit the potential for new high-volume use of Ce. The castability, structure, and mechanical properties of binary, ternary, and quaternary Al-Ce based alloys are discussed. We have determined Al-Ce based alloys to be highly castable across a broad range of compositions. Nanoscale intermetallics dominate the microstructure and are the theorized source of the high ductility. In addition, room-temperature physical properties appear to be competitive with existing aluminum alloys with extended high-temperature stability of the nanostructured intermetallic.

  3. Exchange Interactions for R Co B (R=Rare-Earth) Compounds

    NASA Astrophysics Data System (ADS)

    Maruyama, Fumio

    1999-03-01

    To compare the strength of the exchange interactions between R and Co spins and between Co spins for R Co B compounds, we calculated the molecular field coefficients, nRCo and nCoCo, for Rn+1Co3n+5B2n with n=1(RCo4B), n=2(R3Co11B4), n=3(R2Co7B3) and R2Co14B using the experimental Curie temperature. The calculated nRCo values decrease with increasing atomic number of R and Co concentration. The calculated nCoCo values increase with increasing Co concentration.

  4. Magnetism in rare earth Co{sub 2} compounds under high pressures

    SciTech Connect

    Syshchenko, O.; Sechovsky, V.; Divis, M.; Fujita, T.; Hauser, R.; Fujii, H.

    2001-06-01

    We have studied electrical resistivity anomalies connected with magnetism in RECo{sub 2} (RE=Nd,Tb,Er,Ho) compounds in pressures up to 8 GPa. At ambient pressure the former two compounds exhibit a second order magnetic phase transition (SOMPT) at T{sub C,} whereas a first order magnetic phase transition (FOMPT) is observed in the latter two. Although T{sub C} decreases with pressure in all four compounds, the T{sub C}(P) dependence for NdCo{sub 2} and TbCo{sub 2} differs considerably from this for HoCo{sub 2} and ErCo{sub 2}. For the latter two, T{sub c} vs P data deviate dramatically from the initial linear dependence above a critical pressure P{sub c} to become almost pressure independent at higher pressures. We propose that this is reflecting the loss of Co metamagnetism that is also indicated by the vanishing resistivity drop at T{sub c} for P{gt}4GPa and by the change from a FOMPT to a SOMPT. A scenario is discussed assuming that for P{gt}P{sub c} the projected Co3d density of states at E{sub F} decreases. Hence the Co moment collapses because the RE-Co-RE exchange channel becomes ineffective to induce the itinerant 3d electron metamagnetism. The localized RE moments, however, order at a {open_quotes}residual{close_quotes} T{sub C} due to the persisting Ruderman{endash}Kittel{endash}Kasuya{endash}Yosida-type exchange interaction. For NdCo{sub 2} and TbCo{sub 2} the T{sub c} values decrease with pressure by an exponential law but remain rather high in the highest applied pressures. Results of first-principles electronic structure calculations using the full-potential linearized augmented plane wave method are presented for HoCo{sub 2} and NdCo{sub 2} compounds, as well. {copyright} 2001 American Institute of Physics.

  5. The preparation of the Ti-Al alloys based on intermetallic phases

    NASA Astrophysics Data System (ADS)

    Kosova, N.; Sachkov, V.; Kurzina, I.; Pichugina, A.; Vladimirov, A.; Kazantseva, L.; Sachkova, A.

    2016-01-01

    This article deals with a method of obtaining materials in the Ti-Al system. Research was carried out in accordance with the phase diagram of the system state. It was established, that both single-phase and multiphase systems, containing finely dispersed intermetallic compositions of phases Ti3Al, TiAl and TiAl3, are formed. Additionally, it was found that the pure finely dispersed (coherent-scattering region (CSR) up to 100 nm) intermetallic compound TiAl3 is formed at molar ratio of Ti:Al = 1:3. Experimentally proved the possibility of produce the complex composition of alloys and intermetallic compounds and products based on them.

  6. Fracture toughness of Cu-Sn intermetallic thin films

    NASA Astrophysics Data System (ADS)

    Balakrisnan, B.; Chum, C. C.; Li, M.; Chen, Z.; Cahyadi, T.

    2003-03-01

    Intermetallic compounds (IMCs) are formed as a result of interaction between solder and metallization to form joints in electronic packaging. These joints provide mechanical and electrical contacts between components. The knowledge of fracture strength of the IMCs will facilitate predicting the overall joint property, as it is more disposed to failure at the joint compared to the solder because of its brittle characteristics. The salient feature of this paper is the measurement of the fracture toughness and the critical energy-release rate of Cu3Sn and Cu6Sn5 intermetallic thin films, which is the result of the interaction between Sn from the solder and Cu from the metallization. To achieve the objective, a controlled buckling test was used. A buckling test in the current work refers to one that displays large transverse displacement caused by axial compressive loading on a slender beam. The stress and strain along the beam can be easily calculated by the applied displacement. Fracture-toughness values of Cu3Sn and Cu6Sn5 are 2.85 MPa √m ± 0.17 MPa √m and 2.36 MPa √m ± 0.15 MPa √m, respectively. Corresponding critical energy-release rate values are 65.5 J/m2 ± 8.0 J/m2 and 55.9 J/m2 ± 7.3 J/m2, respectively. The values obtained were much higher than the ones measured in bulk intermetallic samples but correlated well with those values obtained from conventional fracture-toughness specimens when fracture was confined within the intermetallic layers. Hence, the controlled buckling test is a promising fast and effective way to elucidate mechanical properties of thin films.

  7. A diffraction based study of the deformation mechanisms in anomalously ductile B2 intermetallics

    NASA Astrophysics Data System (ADS)

    Mulay, Rupalee Prashant

    For many decades, the brittle nature of most intermetallic compounds (e.g. NiAl) has been the limiting factor in their practical application. Many B2 (CsCl prototypical structure) intermetallics are known to exhibit slip on the <001>{110} slip mode, which provides only 3 independent slip systems and, hence, is unable to satisfy the von Mises (a.k.a. Taylor) criterion for polycrystalline ductility. As a result, inherent polycrystalline ductility is unexpected. Recent discovery of a number of ductile B2 intermetallics has raised questions about possible violation of the von Mises criterion by these alloys. These ductile intermetallic compounds are MR (metal (M) combined with a rare earth metal or group IV refractory metal (R)) alloys and are stoichiometric, ordered compounds. Single crystal slip trace analyses have only identified the presence of <100>{011} or <100>{010} slip systems. More than 100 other B2 MR compounds are known to exist and many of them have already been shown to be ductile (e.g., CuY, AgY, CuDy, CoZr, CoTi, etc.). Furthermore, these alloys exhibit a large Bauschinger effect. The present work uses several diffraction based techniques including electron back scattered diffraction (EBSD), X-ray diffraction (XRD) and in-situ neutron diffraction; in conjunction with scanning electron microscopy (SEM), transmission electron microscopy (TEM), mechanical testing, and crystal plasticity modeling, to elucidate the reason for ductility in select B2 alloys, explore the spread of this ductility over the B2 family, and understand the Bauschinger effect in these alloys. Several possible explanations (e.g., slip of <111> dislocations, strong texture, phase transformations and twinning) for the anomalous ductility were explored. An X-ray diffraction based analysis ruled out texture, phase purity and departure from order as explanations for the anomalous ductility in MR alloys. In-situ neutron diffraction and post deformation SEM, EBSD, and TEM were unable to

  8. Adsorption characterization of gaseous volatile organic compound on mesoporous silica particles prepared from spent diatomaceous earth.

    PubMed

    Bei, Lei-Lei; Tao, Hong; Ma, Chih-Ming; Shiue, Angus; Chang, Chang-Tang

    2014-04-01

    This study used spent diatomaceous earth (SDE) from drink processing as source of Si and cationic surfactant (CTAB) as a template for the synthesis of mesoporous silica Materials (MSM) through hydrothermal method. The MSM was characterized by Small-angle X-ray Diffraction (SXRD), Scanning Electron Microscopy (SEM), Thermo Gravimetric Analysis (TGA), Fourier Transform Infrared (FT-IR) spectroscopy and N2 adsorption-desorption analyzer. The results showed that the surface area, pore volume and pore size was roughly ranged from 880 to 1060 m2 g(-1), 1.05 cm3 g(-1) and 4.0 nm, respectively. The properties of the synthesized MSM were also compared with those prepared from pure silica sources (MCM-41) and got almost the same characteristics. The synthesized MSM was used as adsorbent at 25 degrees C with carrier gas of air. The adsorption equilibrium revealed that adsorption capacity of MSM was 59.6, 65.7, 69.6, 84.9 mg g(-1) while the acetone concentration was 600, 800, 1000 ppm, 1600 ppm respectively. Results showed that breakthrough curves correlate to the challenge vapor concentration, adsorbent loading, and the flow rate. The results obtained in the present work demonstrated that it was feasibility of using the SDE as a potential source of silica to prepare MSM. PMID:24734749

  9. Structure Defect Property Relationships in Binary Intermetallics

    NASA Astrophysics Data System (ADS)

    Medasani, Bharat; Ding, Hong; Chen, Wei; Persson, Kristin; Canning, Andrew; Haranczyk, Maciej; Asta, Mark

    2015-03-01

    Ordered intermetallics are light weight materials with technologically useful high temperature properties such as creep resistance. Knowledge of constitutional and thermal defects is required to understand these properties. Vacancies and antisites are the dominant defects in the intermetallics and their concentrations and formation enthalpies could be computed by using first principles density functional theory and thermodynamic formalisms such as dilute solution method. Previously many properties of the intermetallics such as melting temperatures and formation enthalpies were statistically analyzed for large number of intermetallics using structure maps and data mining approaches. We undertook a similar exercise to establish the dependence of the defect properties in binary intermetallics on the underlying structural and chemical composition. For more than 200 binary intermetallics comprising of AB, AB2 and AB3 structures, we computed the concentrations and formation enthalpies of vacancies and antisites in a small range of stoichiometries deviating from ideal stoichiometry. The calculated defect properties were datamined to gain predictive capabilities of defect properties as well as to classify the intermetallics for their suitability in high-T applications. Supported by the US DOE under Contract No. DEAC02-05CH11231 under the Materials Project Center grant (Award No. EDCBEE).

  10. Environmental Effects in Advanced Intermetallics

    SciTech Connect

    Liu, C.T.

    1998-11-24

    This paper provides a comprehensive review of environmental embrittlement in iron and nickel aluminizes. The embrittlement involves the interaction of these intermetallics with moisture in air and generation of atomic hydrogen, resulting in hydrogen-induced embrittlement at ambient temperatures. Environmental embrittlement promotes brittle grain-boundary fracture in Ni{sub 3}Al alloys but brittle cleavage fracture in Fe{sub 3}Al-FeAl alloys. The embrittlement strongly depends on strain rate, with tensile-ductility increase with increasing strain rate. It has been demonstrated that environmental embrittlement can be alleviated by alloying additions, surface modifications, and control of grain size and shape. Boron tends to segregate strongly to grain boundaries and is most effective in suppressing environmental embrittlement in Ni{sub 3}Al alloys. The mechanistic understanding of alloy effects and environmental embrittlement has led to the development of nickel and iron aluminide alloys with improved properties for structural use at elevated temperatures in hostile environments.

  11. Method of making sintered ductile intermetallic-bonded ceramic composites

    DOEpatents

    Plucknett, Kevin; Tiegs, Terry N.; Becher, Paul F.

    1999-01-01

    A method of making an intermetallic-bonded ceramic composite involves combining a particulate brittle intermetallic precursor with a particulate reactant metal and a particulate ceramic to form a mixture and heating the mixture in a non-oxidizing atmosphere at a sufficient temperature and for a sufficient time to react the brittle intermetallic precursor and the reactant metal to form a ductile intermetallic and sinter the mixture to form a ductile intermetallic-bonded ceramic composite.

  12. Method of making sintered ductile intermetallic-bonded ceramic composites

    DOEpatents

    Plucknett, K.; Tiegs, T.N.; Becher, P.F.

    1999-05-18

    A method of making an intermetallic-bonded ceramic composite involves combining a particulate brittle intermetallic precursor with a particulate reactant metal and a particulate ceramic to form a mixture and heating the mixture in a non-oxidizing atmosphere at a sufficient temperature and for a sufficient time to react the brittle intermetallic precursor and the reactant metal to form a ductile intermetallic and sinter the mixture to form a ductile intermetallic-bonded ceramic composite. 2 figs.

  13. Nuclear Magnetic Resonance in the Highly Anisotropic Rare EARTH-COBALT(5) Compounds.

    NASA Astrophysics Data System (ADS)

    Kunkel, Henry Peter

    The NMR spectra of magnetic materials containing domain walls and having a large anisotropy in the hyperfine field show two NMR peaks arising from a single site; one peak arising from nuclei located at the domain-wall-centre and the other peak arising from nuclei located at the domain -wall-edge. The identification of the origin of the observed peaks therefore gives a simple measurement of the total anisotropy in the hyperfine field. Techniques have been developed to identify the nature of the various peaks observed in the Co('59) NMR resonances in the RCo(,5) compounds. The modulation of the spin echo decay envelope by an external a.c. field has been observed. An enhancement of the external longitudinal modulating field resulting from the anisotropy in the hyperfine field has been identified. This is analogous to the enhancement of a transverse r.f. field by the isotropic hyperfine field which is characteristic of NMR in ferromagnetic materials. The observation of quadrupole splitting effects has been correlated to the rate of change of the hyperfine field in the domain wall as measured by the modulation experiment. The orbital contribution to the anisotropy in the hyperfine field consists of two contributions; one arising from the anisotropy in the crystal field and the other from an anisotropy in the spin-orbit interaction. A phenomenological model is presented which can consistently account for the data available on the anisotropy in the hyperfine field, the anisotropy in the magnetization and the magnetocrystalline anisotropy. The correlation between the anisotropy in the hyperfine field and the magnetocrystalline anisotropy represents an interesting new procedure for the study of the magnetocrystalline anisotropy and would therefore be of particular use in the fabrication of improved permanent magnetic materials.

  14. Investigations of intermetallic alloy hydriding mechanisms. Annual progress report, May 1 1979-April 30, 1980

    SciTech Connect

    Livesay, B.R.; Larsen, J.W.

    1980-05-01

    Investigations are being conducted on mechanisms involved with the hydrogen-metal interactions which control the absorption and desorption processes in intermetallic compounds. The status of the following investigations is reported: modeling of hydride formation; microbalance investigations; microstructure investigations; flexure experiments; resistivity experiments; and nuclear backscattering measurements. These investigations concern fundamental hydrogen interaction mechanisms involved in storage alloys.

  15. Intermetallic NaAu2 as a heterogeneous catalyst for low-temperature CO oxidation.

    PubMed

    Xiao, Chaoxian; Wang, Lin-Lin; Maligal-Ganesh, Raghu V; Smetana, Volodymyr; Walen, Holly; Thiel, Patricia A; Miller, Gordon J; Johnson, Duane D; Huang, Wenyu

    2013-07-01

    The enhanced stability and modified electronic structure of intermetallic compounds provide discovery of superior catalysts for chemical conversions with high activity, selectivity, and stability. We find that the intermetallic NaAu2 is an active catalyst for CO oxidation at low temperatures. From density functional theory calculations, a reaction mechanism is suggested to explain the observed low reaction barrier of CO oxidation by NaAu2, in which a CO molecule reacts directly with an adsorbed O2 to form an OOCO* intermediate. The presence of surface Na increases the binding energy of O2 and decreases the energy barrier of the transition states. PMID:23758405

  16. Rare earth metal rich magnesium compounds RE{sub 4}NiMg (RE=Y, Pr-Nd, Sm, Gd-Tm, Lu)-Synthesis, structure, and hydrogenation behavior

    SciTech Connect

    Tuncel, Selcan; Roquefere, Jean Gabriel; Stan, Cristina; Bobet, Jean-Louis Chevalier, Bernard Gaudin, Etienne; Hoffmann, Rolf-Dieter; Rodewald, Ute Ch; Poettgen, Rainer

    2009-02-15

    The rare earth metal rich compounds RE{sub 4}NiMg (RE=Y, Pr-Nd, Sm, Gd-Tm, Lu) were synthesized from the elements in sealed tantalum tubes in an induction furnace. All compounds were investigated by X-ray diffraction on powders and single crystals: Gd{sub 4}RhIn type, space group F4-bar 3m, Z=16, a=1367.6(2) pm for Y{sub 4}NiMg, a=1403.7(3) pm for Pr{sub 4}NiMg, a=1400.7(1) pm for Nd{sub 4}NiMg, a=1386.5(2) pm for Sm{sub 4}NiMg, a=1376.1(2) pm for Gd{sub 4}NiMg, a=1362.1(1) pm for Tb{sub 4}NiMg, a=1355.1(2) pm for Dy{sub 4}NiMg, a=1355.2(1) pm for Ho{sub 4}NiMg, a=1354.3(2) pm for Er{sub 4}NiMg, a=1342.9(3) pm for Tm{sub 4}NiMg, and a=1336.7(3) pm for Lu{sub 4}NiMg. The nickel atoms have trigonal prismatic rare earth coordination. These NiRE{sub 6} prisms are condensed via common edges to a three-dimensional network which leaves voids for Mg{sub 4} tetrahedra and the RE1 atoms which show only weak coordination to the nickel atoms. The single crystal data indicate two kinds of solid solutions. The RE1 positions reveal small RE1/Mg mixing and some compounds also show Ni/Mg mixing within the Mg{sub 4} tetrahedra. Y{sub 4}NiMg and Gd{sub 4}NiMg have been tested for hydrogenation. These compounds absorb up to eleven hydrogen atoms per formula unit under a hydrogen pressure of 1 MPa at room temperature. The structure of the metal atoms is maintained with only an increase of the lattice parameters ({delta}V/V{approx}22%) if the absorption is done at T<363 K as at higher temperature a decomposition into REH{sub 2}-REH{sub 3} hydrides occurred. Moreover, the hydrogenation affects drastically the magnetic properties of these intermetallics. For instance, Gd{sub 4}NiMg exhibits an antiferromagnetic behavior below T{sub N}=92 K whereas its hydride Gd{sub 4}NiMgH{sub 11} is paramagnetic down to 1.8 K. - Graphical abstract: The Mg{sub 4} and NiGd{sub 6} units in Gd{sub 4}NiMg and Gd{sub 4}NiMgH{sub x}.

  17. Wear Behavior and Mechanism of Fe-Al Intermetallic Coating Prepared by Hot-Dip Aluminizing and Diffusion

    NASA Astrophysics Data System (ADS)

    Zhang, Q. Y.; Zhou, Y.; Liu, J. Q.; Chen, K. M.; Mo, J. G.; Cui, X. H.; Wang, S. Q.

    2016-05-01

    A Fe-Al intermetallic compound coating was prepared on AISI H13 steel by hot-dip aluminizing and subsequent high-temperature diffusion. Dry sliding wear tests of the Fe-Al intermetallic coating were performed at 298 K to 873 K (25 °C to 600 °C). The wear behavior of the Fe-Al intermetallic coating was noticed to vary markedly with the temperature and load. At 298 K (25 °C), the wear rate rapidly increased with an increase of the load. As the temperature was elevated, the wear rate dramatically decreased except for the cases under 300 N at 473 K and 673 K (200 °C and 400 °C). The Fe-Al intermetallic coating possessed an excellent elevated-temperature wear performance, especially at 673 K to 873 K (400 °C to 600 °C), but worse room-temperature one, which were noticed to be attributed to the existence and inexistence of thin tribo-oxide layers, respectively. Such a thin tribo-oxide layer was considered to provide a protection for the intermetallic compound. When the tribo-oxide layer did not form at room temperature or the formed one was massively delaminated above the critical load at elevated temperatures, Fe-Al intermetallic coating possessed poor wear resistance.

  18. Rare earth elements and permanent magnets (invited)

    NASA Astrophysics Data System (ADS)

    Dent, Peter C.

    2012-04-01

    Rare earth (RE) magnets have become virtually indispensible in a wide variety of industries such as aerospace, automotive, electronics, medical, and military. RE elements are essential ingredients in these high performance magnets based on intermetallic compounds RECo5, RE2TM17 (TM: transition metal), and RE2TM14B. Rare earth magnets are known for their superior magnetic properties—high induction, and coercive force. These properties arise due to the extremely high magnetocrystalline anisotropy made possible by unique 3d-4f interactions between transition metals and rare earths. For more than 40 years, these magnets remain the number one choice in applications that require high magnetic fields in extreme operating conditions—high demagnetization forces and high temperature. EEC produces and specializes in RECo5 and RE2TM17 type sintered magnets. Samarium and gadolinium are key RE ingredients in the powder metallurgical magnet production processes which include melting, crushing, jet milling, pressing, sintering, and heat treating. The magnetic properties and applications of these magnets will be discussed. We will also briefly discuss the past, current, and future of the permanent magnet business. Currently, over 95% of all pure rare earth oxides are sourced from China, which currently controls the market. We will provide insights regarding current and potential new magnet technologies and designer choices, which may mitigate rare earth supply chain issues now and into the future.

  19. Exploratory Synthesis: The Fascinating and Diverse Chemistry of Polar Intermetallic Phases

    SciTech Connect

    Corbett, John D.

    2009-12-07

    Exploratory synthetic adventures regarding the inorganic chemistry of polar intermetallic phases have proven to be especially productive of novel compositions, new and unprecedented structures, and unusual bonding regimes. Reactions of diverse elements with widely different electronegativities allow the definition of two opposed classes of products: polycationic or polyanionic clusters or networks of metals paired with the corresponding monatomic anions or cations. These can be usefully viewed as intermetallic 'salts', redox products of simpler neutral intermetallic systems but with widely different factors governing their stabilities. Thus, combinations of rare-earth metals alone or with late transition metals form a novel variety of polymetal network structures with relatively isolated telluride (or halide) spacer anions. Similarly, extensions of traditional Zintl phases of the alkali or alkaline-earth metals from the later p elements to the earlier triels, Ga-Tl especially, yield many new and elegant polyanionic structures. The substitution or addition of still earlier p or late d metal components produces still electron-poorer and more condensed polar intermetallic phases with increasingly delocalized bonding, higher coordination numbers, and more unusual structures and bonding. These discoveries have also led to new approaches: electronic tuning via band calculations to generate new families of quasicrystals and their crystalline approximants with their characteristic structural regimes and regularities. Gold as a substituent generates particularly novel bonding in arrays of mixed metals or polygold anionic networks.

  20. In situ examination of moving crack tips in ordered intermetallics.

    SciTech Connect

    Heuer, J.; Lam, N. Q.; Okamoto, P. R.; Stubbins, J. F.

    1999-01-25

    Recent studies have shown that high stress concentrations at moving crack tips in the intermetallic compound NiTi can induce a crystalline-to-amorphous (C-A) transformation of the crack tip region. This stress-induced C-A transformation has a temperature dependence and crystallization behavior similar to those of ion irradiation-induced C-A transformation of NiTi. The present study examines if these similarities between stress- and irradiation-induced amorphization hold true for two other intermetallic compounds, CuTi and Ni{sub 3}Ti. In situ straining was performed in an intermediate-voltage transmission electron microscope. The presence or absence of an amorphous phase was determined by dark field imaging and selected area diffraction of crack tip regions. Crack tips in both CuTi and Ni{sub 3}Ti were found to remain crystalline upon fracture. The observed absence of stress-induced amorphization in Ni{sub 3}Ti is consistent with its known absence during irradiation, but the absence in CuTi differs from its known irradiation-induced amorphization behavior. Reasons for the similarity and difference are discussed.

  1. Dislocation sources in ordered intermetallics

    SciTech Connect

    Yoo, M.H.; Appel, F.; Wagner, R.; Mecking, H.

    1996-09-01

    An overview on the current understanding of dislocation sources and multiplication mechanisms is made for ordered intermetallic alloys of the L1{sub 2}, B2, and D0{sub 19} structures. In L1{sub 2} alloys, a large disparity of edge/screw segments in their relative mobility reduces the efficiency of a Frank-Read Type multiplication mechanism. In Fe-40%Al of the B2 structure, a variety of dislocation sources are available for <111> slip, including ones resulting from condensation of thermal vacancies. In NiAl with the relatively high APB energy, <100> dislocations may result from the dislocation decomposition reactions, the prismatic punching out from inclusion particles, and/or steps and coated layers of the surface. Internal interfaces often provide sites for dislocation multiplication, e.g., grain boundaries, sub-boundaries in Ni{sub 3}Ga, NiAl and Ti{sub 3}Al, and antiphase domain boundaries in Ti{sub 3}Al. As for the crack tip as a dislocation source, extended SISFs trailed by super-Shockley partials emanating form the cracks in Ni{sub 3}Al and Co{sub 3}Ti are discussed in view of a possible toughening mechanism.

  2. Advanced ordered intermetallic alloy deployment

    SciTech Connect

    Liu, C.T.; Maziasz, P.J.; Easton, D.S.

    1997-04-01

    The need for high-strength, high-temperature, and light-weight materials for structural applications has generated a great deal of interest in ordered intermetallic alloys, particularly in {gamma}-based titanium aluminides {gamma}-based TiAl alloys offer an attractive mix of low density ({approximately}4g/cm{sup 3}), good creep resistance, and high-temperature strength and oxidation resistance. For rotating or high-speed components. TiAl also has a high damping coefficient which minimizes vibrations and noise. These alloys generally contain two phases. {alpha}{sub 2} (DO{sub 19} structure) and {gamma} (L 1{sub 0}), at temperatures below 1120{degrees}C, the euticoid temperature. The mechanical properties of TiAl-based alloys are sensitive to both alloy compositions and microstructure. Depending on heat-treatment and thermomechanical processing, microstructures with near equiaxed {gamma}, a duplex structure (a mix of the {gamma} and {alpha}{sub 2} phases) can be developed in TiAl alloys containing 45 to 50 at. % Al. The major concern for structural use of TiAl alloys is their low ductility and poor fracture resistance at ambient temperatures. The purpose of this project is to improve the fracture toughness of TiAl-based alloys by controlling alloy composition, microstructure and thermomechanical treatment. This work is expected to lead to the development of TiAl alloys with significantly improved fracture toughness and tensile ductility for structural use.

  3. New intermetallic MIrP (M=Ti, Zr, Nb, Mo) and MgRuP compounds related with MoM'P (M'=Ni and Ru) superconductor

    NASA Astrophysics Data System (ADS)

    Kito, Hijiri; Iyo, Akira; Wada, Toshimi

    2011-01-01

    Using a cubic-anvil high-pressure apparatus, ternary iridium phosphides MIrP (M=Ti, Zr, Nb, Mo) and MgRuP have been prepared by reaction of stoichiometric amounts of each metal and phosphide powders at around 2 Gpa and above 1523 K for the first time. The structure of these compounds prepared at high-pressure has been characterized by X-ray powder diffraction. Diffraction lines of these compounds are assigned by the index of the Co2Si-type structure. The electrical resistivity and the d.c magnetic susceptibility of MIrP (M=Ti, Zr, Nb, Mo) have measured at low temperatures. Unfortunately, no superconducting transition for MIrP (M=Ti, Zr, Nb, Mo) and MgRuP are observed down to 2 K.

  4. Magnetic and thermal properties of RCu9In2 (R=La, Ce, Pr, Nd, Sm and Eu) compounds

    NASA Astrophysics Data System (ADS)

    Baran, S.; Przewoźnik, J.; Kalychak, Ya. M.; Tyvanchuk, Yu.; Szytuła, A.

    2016-07-01

    The RCu9In2 intermetallics with R=La, Ce, Pr, Nd, Sm, Eu have been synthesized and characterized with regards to their crystal structure as well as magnetic and thermal properties. The compounds have tetragonal structure of the YNi9In2-type (space group P4/mbm). Except for LaCu8.25In2.75, they exhibit localized magnetism due to the presence of magnetic moments on the respective trivalent rare-earth ions. The Nd-, Sm- and Eu- based compounds order antiferromagnetically below 4.6, 11.0 and 23.2 K, respectively.

  5. Process for synthesizing compounds from elemental powders and product

    DOEpatents

    Rabin, Barry H.; Wright, Richard N.

    1993-01-01

    A process for synthesizing intermetallic compounds from elemental powders. The elemental powders are initially combined in a ratio which approximates the stoichiometric composition of the intermetallic compound. The mixed powders are then formed into a compact which is heat treated at a controlled rate of heating such that an exothermic reaction between the elements is initiated. The heat treatment may be performed under controlled conditions ranging from a vacuum (pressureless sintering) to compression (hot pressing) to produce a desired densification of the intermetallic compound. In a preferred form of the invention, elemental powders of Fe and Al are combined to form aluminide compounds of Fe.sub.3 Al and FeAl.

  6. Spark plasma sintering of titanium aluminide intermetallics and its composites

    NASA Astrophysics Data System (ADS)

    Aldoshan, Abdelhakim Ahmed

    Titanium aluminide intermetallics are a distinct class of engineering materials having unique properties over conventional titanium alloys. gamma-TiAl compound possesses competitive physical and mechanical properties at elevated temperature applications compared to Ni-based superalloys. gamma-TiAl composite materials exhibit high melting point, low density, high strength and excellent corrosion resistance. Spark plasma sintering (SPS) is one of the powder metallurgy techniques where powder mixture undergoes simultaneous application of uniaxial pressure and pulsed direct current. Unlike other sintering techniques such as hot iso-static pressing and hot pressing, SPS compacts the materials in shorter time (< 10 min) with a lower temperature and leads to highly dense products. Reactive synthesis of titanium aluminide intermetallics is carried out using SPS. Reactive sintering takes place between liquid aluminum and solid titanium. In this work, reactive sintering through SPS was used to fabricate fully densified gamma-TiAl and titanium aluminide composites starting from elemental powders at different sintering temperatures. It was observed that sintering temperature played significant role in the densification of titanium aluminide composites. gamma-TiAl was the predominate phase at different temperatures. The effect of increasing sintering temperature on microhardness, microstructure, yield strength and wear behavior of titanium aluminide was studied. Addition of graphene nanoplatelets to titanium aluminide matrix resulted in change in microhardness. In Ti-Al-graphene composites, a noticeable decrease in coefficient of friction was observed due to the influence of self-lubrication caused by graphene.

  7. Elastic anisotropy, vibrational, and thermodynamic properties of U{sub 2}Ti intermetallic compound with AlB{sub 2}-type structure under high pressure up to 100 GPa

    SciTech Connect

    Yang, Jinwen; Gao, Tao; Liu, Benqiong; Sun, Guangai; Chen, Bo

    2015-03-28

    Structural, elastic anisotropy, dynamical, and thermodynamic properties of U{sub 2}Ti have been studied by employing density functional theory and density functional perturbative theory. The optimized lattice parameters a, c, unit volume V, bulk modulus B, and bond lengths d{sub U-U}, d{sub U-Ti} of U{sub 2}Ti are in favorable agreement with the available experimental data and other theoretical values. The elastic constants under pressure were obtained using “energy-strain” method. The polycrystalline modulus, Poisson's ratio, brittle/ductile characteristics, Debye temperature and the integration of elastic wave velocities over different directions, and hardness under pressure are also evaluated successfully. The anisotropy of the directional bulk modulus and the Young's modulus is systematically predicted for the first time. It turns out that U{sub 2}Ti should be stabilized mechanically up to 100 GPa, this compound just possesses slightly elastic anisotropy at zero pressure; however, the anisotropy becomes more and more significant with the increasing pressure. In particular, the phonon dispersion curves and phonon density of state under pressure are reported for the first time. The Raman and infrared-active phonon modes at Γ point are further assigned. Our results indicate that U{sub 2}Ti is also stable dynamically up to 100 GPa. Additionally, within the calculated phonon density of states, the thermodynamic properties are predicted.

  8. Microstructural evolution and intermetallic formation in Al-8wt% Si-0.8wt% Fe alloy due to grain refiner and modifier additions

    NASA Astrophysics Data System (ADS)

    Hassani, Amir; Ranjbar, Khalil; Sami, Sattar

    2012-08-01

    An alloy of Al-8wt% Si-0.8wt% Fe was cast in a metallic die, and its microstructural changes due to Ti-B refiner and Sr modifier additions were studied. Apart from usual refinement and modification of the microstructure, some mutual influences of the additives took place, and no mutual poisoning effects by these additives, in combined form, were observed. It was noticed that the dimensions of the iron-rich intermetallics were influenced by the additives causing them to become larger. The needle-shaped intermetallics that were obtained from refiner addition became thicker and longer when adding the modifier. It was also found that α-Al and eutectic silicon phases preferentially nucleate on different types of intermetallic compounds. The more iron content of the intermetallic compounds and the more changes in their dimensions occurred. Formation of the shrinkage porosities was also observed.

  9. Preparation and properties of the Ni-Al/Fe-Al intermetallics composite coating produced by plasma cladding

    NASA Astrophysics Data System (ADS)

    Zhang, Li-Min; Liu, Bang-Wu; Sun, Dong-Bai

    2011-12-01

    A novel approach to produce an intermetallic composite coating was put forward. The microstructure, microhardness, and dry-sliding wear behavior of the composite coating were investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectrum (EDS) analysis, microhardness test, and ball-on-disc wear experiment. XRD results indicate that some new phases FeAl, Fe0.23Ni0.77Al, and Ni3Al exit in the composite coating with the Al2O3 addition. SEM results show that the coating is bonded with carbon steel metallurgically and exhibits typical rapid directional solidification structures. The Cr7C3 carbide and intermetallic compounds co-reinforced composite coating has a high average hardness and exhibits an excellent wear resistance under dry-sliding wear test compared with the Cr7C3 carbide-reinforced composite coating. The formation mechanism of the intermetallic compounds was also investigated.

  10. Prebiotic Synthesis of Methionine and Other Sulfur-Containing Organic Compounds on the Primitive Earth: A Contemporary Reassessment Based on an Unpublished 1958 Stanley Miller Experiment

    NASA Technical Reports Server (NTRS)

    Parker, Eric T.; Cleaves, H. James; Callahan, Michael P.; Dworkin, Jason P.; Glavin, Daniel P.; Lazcano, Antonio

    2010-01-01

    Original extracts from an unpublished 1958 experiment conducted by the late Stanley L. Miller were recently found and analyzed using modern state-of-the-art analytical methods. The extracts were produced by the action of an electric discharge on a mixture of methane (CH4), hydrogen sulfide (H2S), ammonia (NH3), and carbon dioxide (CO2). Racemic methionine was farmed in significant yields, together with other sulfur-bearing organic compounds. The formation of methionine and other compounds from a model prebiotic atmosphere that contained H2S suggests that this type of synthesis is robust under reducing conditions, which may have existed either in the global primitive atmosphere or in localized volcanic environments on the early Earth. The presence of a wide array of sulfur-containing organic compounds produced by the decomposition of methionine and cysteine indicates that in addition to abiotic synthetic processes, degradation of organic compounds on the primordial Earth could have been important in diversifying the inventory of molecules of biochemical significance not readily formed from other abiotic reactions, or derived from extraterrestrial delivery.

  11. Trigonal Cu2-II-Sn-VI4 (II = Ba, Sr and VI = S, Se) quaternary compounds for earth-abundant photovoltaics.

    PubMed

    Hong, Feng; Lin, Wenjun; Meng, Weiwei; Yan, Yanfa

    2016-02-14

    We propose trigonal Cu2-II-Sn-VI4 (II = Ba, Sr and VI = S, Se) quaternary compounds for earth-abundant solar cell applications. Through density functional theory calculations, we show that these compounds exhibit similar electronic and optical properties to kesterite Cu2ZnSnS4 (CZTS): high optical absorption with band gaps suitable for efficient single-junction solar cell applications. However, the trigonal Cu2-II-Sn-VI4 compounds exhibit defect properties more suitable for photovoltaic applications than those of CZTS. In CZTS, the dominant defects are the deep acceptors, Cu substitutions on Zn sites, which cause non-radiative recombination and limit the open-circuit voltages of CZTS solar cells. On the contrary, the dominant defects in trigonal Cu2-II-Sn-VI4 are the shallow acceptors, Cu vacancies, similar to those in CuInSe2. Our results suggest that the trigonal Cu2-II-Sn-VI4 quaternary compounds could be promising candidates for efficient earth-abundant thin-film solar cell and photoeletrochemical water-splitting applications. PMID:26804024

  12. Development of intermetallic-hardened abrasion-resistant weld hardfacing alloys

    SciTech Connect

    School, M.R.

    1986-01-01

    Chromium and cobalt are strategic materials in the US and both are major constituents in many weld hardfacing alloys. Substitution for these materials or alternatives to their use was a primary direction of this investigation which was conducted in conjunction with the US Bureau of Mines. Minimization of the use of strategic materials was the criteria guiding the development of intermetallic-hardened abrasion resistant weld hardfacing materials. Other criteria were that the new alloy contain a hard intermetallic compound in an FCC matrix, and that these intermetallic compounds be stable at room temperature. A survey of ternary systems was made and the Fe-Mo-Ni system was selected to provide a basis for alloy development. Fe-Mo-Ni alloys synthesized by arc-melting and similar alloys made by welding possessed similar microstructures, a (Fe, Ni){sub 7}Mo{sub 6} intermetallic plus austenite eutectic in an austenitic matrix. These materials exhibited poor abrasive resistance. Silicon additions to the alloy promoted formation of a Laves phase FeMoSi intermetallic which helped increase the abrasive wear resistance. Through a series of alloy chemistry iterations a final composition of Fe-20Mo-15Ni-5Si was selected. Heat treatment of this alloy at 550 to 650 C caused second phase precipitation in the matrix and raised the hardness about 14 points HRC to 50 HRC. The alloy's wear rate, measured with the pin-on-drum abrasive wear test, was 6.3 to 6.5 mg/m. However this was twice the wear rate observed in commercial high-carbon high-chromium alloys. Based on examination of the alloy microstructures, their chemistry, and an analysis of the Fe-Mo-Si phase system; directions for further research are to increase the molybdenum and silicon content to produce a Fe-20Mo-10Ni-15Si composition.

  13. Surfaces of Intermetallics: Quasicrystals and Beyond

    SciTech Connect

    Yuen, Chad

    2012-01-01

    The goal of this work is to characterize surfaces of intermetallics, including quasicrystals. In this work, surface characterization is primarily focused on composition and structure using X-ray photoelectron spectroscopy (XPS) and scanning tunneling microscopy (STM) performed under ultrahigh vacuum (UHV) conditions.

  14. High-temperature ordered intermetallic alloys VII

    SciTech Connect

    Koch, C.C.; Liu, C.T.; Stoloff, N.S.; Wanner, A.

    1997-12-31

    This volume is divided into the following sections: (1) processing; (2) titanium aluminides; (3) creep and fatigue of titanium aluminides; (4) iron aluminides; (5) nickel aluminides; (6) refractory metal-based and other intermetallics; and (7) composites. Separate abstracts were prepared for most papers in this volume.

  15. Effects of intermetallic particles on the SCC initiation of zirconium alloys

    NASA Astrophysics Data System (ADS)

    Kubo, T.; Wakashima, Y.; Imahashi, H.; Nagai, M.

    1985-06-01

    In order to investigate effects of intermetallic particles on SCC initiation of zirconium alloys, tensile tests were conducted in an iodine atmosphere using zirconium plates with different amounts of impurities, and Zircaloy-2 plates. SCC susceptibility of zirconium increased significantly with its iron content. Even small amounts of iron could form the intermetallic compound ZrFe 2 whose particle size and number increased with iron content. In the case of Zircaloy-2, two different types of ternary compounds were detected, namely Zr(CrFe) 2 and Zr 2(NiFe). Metallographic examinations showed that the particles located at grain boundaries were important sites of SCC initiation in zirconium alloys. The initiation probability increased significantly with the amount of the particles, which supported the strong correlation between SCC susceptibility of zirconium and its iron content.

  16. Dissolution of iron intermetallics in Al-Si alloys through nonequilibrium heat treatment

    SciTech Connect

    Anantha Narayanan, L. |; Samuel, F.H.; Gruzleski, J.E.

    1995-08-01

    Conventional heat treatment techniques in Al-Si alloys to achieve optimum mechanical properties are limited to precipitation strengthening processes due to the presence of second-phase particles and spheroidization of silicon particles. The iron intermetallic compounds present in the microstructure of these alloys are reported to be stable, and they do not dissolve during conventional (equilibrium) heat treatments. The dissolution behavior of iron intermetallics on nonequilibrium heat treatment has been investigated by means of microstructure and mechanical property studies. The dissolution of iron intermetallics improves with increasing solution temperature. The addition of manganese to the alloy hinders the dissolution of iron intermetallics. Nonequilibrium heat treatment increases the strength properties of high iron alloys until a critical solution temperature is exceeded. Above this temperature, a large amount of liquid phase is formed as a result of interdendritic and grain boundary melting. The optimum solution treatment temperature for Al-6Si-3.5Cu-0.3Mg-1Fe alloys is found to be between 515 C and 520 C.

  17. Magnetic, resonance, and optical properties of Cu3Sm (SeO3)2O2Cl : A rare-earth francisite compound

    NASA Astrophysics Data System (ADS)

    Zakharov, K. V.; Zvereva, E. A.; Markina, M. M.; Stratan, M. I.; Kuznetsova, E. S.; Dunaev, S. F.; Berdonosov, P. S.; Dolgikh, V. A.; Olenev, A. V.; Klimin, S. A.; Mazaev, L. S.; Kashchenko, M. A.; Ahmed, Md. A.; Banerjee, A.; Bandyopadhyay, S.; Iqbal, A.; Rahaman, B.; Saha-Dasgupta, T.; Vasiliev, A. N.

    2016-08-01

    In this combined experimental and theoretical paper, we study the properties of Cu3Sm (SeO3)2O2Cl belonging to the francisite family of compounds, which are novel frustrated layered compounds. Cu3Sm (SeO3)2O2Cl is synthesized through a solid state reaction. Characterizations through measurements of magnetization, specific heat, X-band electron spin resonance, and rare-earth optical spectroscopy, establish that the compound orders antiferromagnetically at TN=35 K and undergoes a spin-reorientation phase transition at TC=8.5 K due to the interplay of anisotropies in transition metal and rare-earth subsystems. The ground state Kramers doublet of Sm is found to split only at T

  18. The μ3 model of acids and bases: extending the Lewis theory to intermetallics.

    PubMed

    Stacey, Timothy E; Fredrickson, Daniel C

    2012-04-01

    A central challenge in the design of new metallic materials is the elucidation of the chemical factors underlying the structures of intermetallic compounds. Analogies to molecular bonding phenomena, such as the Zintl concept, have proven very productive in approaching this goal. In this Article, we extend a foundational concept of molecular chemistry to intermetallics: the Lewis theory of acids and bases. The connection is developed through the method of moments, as applied to DFT-calibrated Hückel calculations. We begin by illustrating that the third and fourth moments (μ(3) and μ(4)) of the electronic density of states (DOS) distribution tune the properties of a pseudogap. μ(3) controls the balance of states above and below the DOS minimum, with μ(4) then determining the minimum's depth. In this way, μ(3) predicts an ideal occupancy for the DOS distribution. The μ(3)-ideal electron count is used to forge a link between the reactivity of transition metals toward intermetallic phase formation, and that of Lewis acids and bases toward adduct formation. This is accomplished through a moments-based definition of acidity which classifies systems that are electron-poor relative to the μ(3)-ideal as μ(3)-acidic, and those that are electron-rich as μ(3)-basic. The reaction of μ(3) acids and bases, whether in the formation of a Lewis acid/base adduct or an intermetallic phase, tends to neutralize the μ(3) acidity or basicity of the reactants. This μ(3)-neutralization is traced to the influence of electronegativity differences at heteroatomic contacts on the projected DOS curves of the atoms involved. The role of μ(3)-acid/base interactions in intermetallic phases is demonstrated through the examination of 23 binary phases forming between 3d metals, the stability range of the CsCl type, and structural trends within the Ti-Ni system. PMID:22420716

  19. Addressing Machining Issues for the Intermetallic Compound 60-NITINOL

    NASA Technical Reports Server (NTRS)

    Stanford, Malcolm K.; Wozniak, Walter A.; McCue, Terry R.

    2012-01-01

    60-NITINOL (60 wt.% Ni - 40 wt.% Ti) is being studied as a material for advanced aerospace components. Frequent wire breakage during electrical-discharge machining of this material was investigated. The studied material was fabricated from hot isostatically pressed 60-NITINOL powder obtained through a commercial source. Bulk chemical analysis of the material showed that the composition was nominal but had relatively high levels of certain impurities, including Al and O. It was later determined that Al2O3 particles had contaminated the material during the hot isostatic pressing procedure and that these particles were the most likely cause of the wire breakage. The results of this investigation highlight the importance of material cleanliness to its further implementation.

  20. Hydrogen sorption rate by intermetallic compounds suitable for tritium storage

    SciTech Connect

    Penzhorn, R.D.; Sirch, M.; Perevezentsev, A.N.; Borisenko, A.N.

    1995-10-01

    The kinetics of the sorption of molecular hydrogen by ZrCo and Zr{sub 0.8}Ti{sub 0.3}Mn{sub 1.9} was investigated as function of temperature at several constant pressures of hydrogen. A comparison between the isothermal hydrogen sorption rates by ZrCo, Zr{sub 0.8}Ti{sub 0.3}Mn{sub 1.9} and LaNi{sub 4.7}Al{sub 0.3} is given and reaction mechanisms are discussed. From fittings of the experimental results to well known gas/solid reaction rate laws it was concluded that the reaction mechanisms of the reaction with ZrCo is complex and dependent upon the prevailing reaction conditions. The hydrogen sorption rate by the powder of all three IMC`s was found to be second order in hydrogen pressure. 8 refs., 7 figs., 1 tab.

  1. Reduced workfunction intermetallic seed layers allow growth of porous n-GaN and low resistivity, ohmic electron transport.

    PubMed

    Bilousov, Oleksandr V; Carvajal, Joan J; Drouin, Dominique; Mateos, Xavier; Díaz, Francesc; Aguiló, Magdalena; O'Dwyer, Colm

    2012-12-01

    Porous GaN crystals have been successfully grown and electrically contacted simultaneously on Pt- and Au-coated silicon substrates as porous crystals and as porous layers. By the direct reaction of metallic Ga and NH(3) gas through chemical vapor deposition, intermetallic metal-Ga alloys form at the GaN-metal interface, allowing vapor-solid-solid seeding and subsequent growth of porous GaN. Current-voltage and capacitance-voltage measurements confirm that the intermetallic seed layers prevent interface oxidation and give a high-quality reduced workfunction contact that allows exceptionally low contact resistivities. Additionally, the simultaneous formation of a lower workfunction intermetallic permits ohmic electron transport to n-type GaN grown using high workfunction metals that best catalyze the formation of porous GaN layers and may be employed to seed and ohmically contact a range of III-N compounds and alloys for broadband absorption and emission. PMID:23167596

  2. Plasma spray forming metals, intermetallics, and composites

    NASA Astrophysics Data System (ADS)

    Sampath, Sanjay; Herman, Herbert

    1993-07-01

    Plasma spray processing is a droplet deposition method that combines the steps of melting, rapid solidification, and consolidation into a single step. The versatility of the technology enables the processing of freestanding bulk, near-net shapes of a wide range of alloys, intermetallics, ceramics, and composites, while still retaining the benefits of rapid solidification processing. In particular, it is possible to produce dense forms through vacuum plasma spraying.

  3. Arc Casting Intermetallic Alloy (Materials Preparation Center)

    SciTech Connect

    2010-01-01

    Arc casting of intermetallic (La-Ni-Sn) AB5 alloy used for metal hydride hydrogen storage. Upon solidification the Sn is partially rejected and increases in concentration in the remaining liquid. Upon completing solidification there is a great deal of internal stress in the ingot. As the ingot cools further the stress is relieved. This material was cast at the Ames Laboratorys Materials Preparation Center http://www.mpc.ameslab.gov

  4. A Study on the Formation of Intermetallics During the Heat Treatment of Explosively Welded Al-Ti Multilayers

    NASA Astrophysics Data System (ADS)

    Foadian, Farzad; Soltanieh, Mansour; Adeli, Mandana; Etminanbakhsh, Majid

    2014-04-01

    Metallic-intermetallic laminate composites are promising materials for many applications, namely, in the aerospace industry. Ti/TiAl3 laminates are one of the interesting laminate composites, which are mostly used in aerospace applications. In this work, commercially pure aluminum and titanium sheets were explosively joined. The multilayer samples were annealed between 1 and 260 hours at 903 K (630 °C) in ambient atmosphere, and the formation and growth of the intermetallic compound at the Ti/Al interface were monitored. Microstructural investigations were carried out using optical and scanning electron microscopes equipped with energy-dispersive spectroscopy and the X-ray diffraction technique. The microhardness profile of the layers was also determined. The thickness and type of Al-Ti intermetallics were determined. It was found that the only intermetallic phase observed in the interfaces was TiAl3. It was also shown that two mechanisms for TiAl3 growth exist: reaction and diffusion controlled. The growth exponent was equal to 0.94 for the reaction-controlled mechanism (first step) and 0.31 for the diffusion-controlled mechanism (second step). These values were in good agreement with theoretical values (1 and 0.5 for the first and second steps, respectively). Based on the results of this research, a kinetic model for the formation and growth of TiAl3 intermetallic phase was proposed.

  5. Tuning the Origin of Magnetic Relaxation by Substituting the 3d or Rare-Earth Ions into Three Isostructural Cyano-Bridged 3d-4f Heterodinuclear Compounds.

    PubMed

    Zhang, Yan; Guo, Zhen; Xie, Shuang; Li, Hui-Li; Zhu, Wen-Hua; Liu, Li; Dong, Xun-Qing; He, Wei-Xun; Ren, Jin-Chao; Liu, Ling-Zhi; Powell, Annie K

    2015-11-01

    Three isostructural cyano-bridged 3d-4f compounds, [YFe(CN)6(hep)2(H2O)4] (1), [DyFe(CN)6(hep)2(H2O)4] (2), and [DyCo(CN)6(hep)2(H2O)4] (3), were successfully assembled by site-targeted substitution of the 3d or rare-earth ions. All compounds have been structurally characterized to display slightly distorted pentagonal-bipyramidal local coordination geometry around the rare-earth ions. Magnetic analyses revealed negligible magnetic coupling in compound 1, antiferromagnetic intradimer interaction in 2, and weak ferromagnetic coupling through dipolar-dipolar interaction in 3. Under an applied direct-current (dc) field, 1 (Hdc = 2.5 kOe, τ0 = 1.3 × 10(-7) s, and Ueff/kB = 23 K) and 3 (Hdc = 2.0 kOe, τ0 = 7.1 × 10(-11) s, and Ueff/kB = 63 K) respectively indicated magnetic relaxation behavior based on a single [Fe(III)]LS ion and a Dy(III) ion; nevertheless, 2 (Hdc = 2.0 kOe, τ0 = 9.7 × 10(-8) s, and Ueff/kB = 23 K) appeared to be a single-molecule magnet based on a cyano-bridged DyFe dimer. Compound 1, which can be regarded as a single-ion magnet of the [Fe(III)]LS ion linked to a diamagnetic Y(III) ion in a cyano-bridged heterodimer, represents one of the rarely investigated examples based on a single Fe(III) ion explored in magnetic relaxation behavior. It demonstrated that the introduction of intradimer magnetic interaction of 2 through a cyano bridge between Dy(III) and [Fe(III)]LS ions negatively affects the energy barrier and χ″(T) peak temperature compared to 3. PMID:26473654

  6. Magneto-structural correlations in rare-earth cobalt pnictides

    NASA Astrophysics Data System (ADS)

    Thompson, Corey Mitchell

    Magnetic materials are used in many applications such as credit cards, hard drives, electric motors, sensors, etc. Although a vast range of magnetic solids is available for these purposes, our ability to improve their efficiency and discover new materials remains paramount to the sustainable progress and economic profitability in many technological areas. The search for magnetic solids with improved performance requires fundamental understanding of correlations between the structural, electronic, and magnetic properties of existing materials, as well as active exploratory synthesis that targets the development of new magnets. Some of the strongest permanent magnets, Nd 2Fe14B, SmCo5, and Sm2Co17, combine transition and rare-earth metals, benefiting from the strong exchange between the 4f and 3d magnetic sublattices. Although these materials have been studied in great detail, the development of novel magnets requires thorough investigation of other 3d-4 f intermetallics, in order to gain further insights into correlations between their crystal structures and magnetic properties. Among many types of intermetallic materials, ternary pnictides RCo 2Pn2 (R = La, Ce, Pr, Nd; Pn = P, As) are of interest because, despite their simple crystal structures, they contain two magnetic sublattices, exchange interactions between which may lead to rich and unprecedented magnetic behavior. Nevertheless, magnetism of these materials was studied only to a limited extent, especially as compared to the extensive studies of their silicide and germanide analogues. The ThCr2Si2 structure type, to which these ternary pnictides belong, is one of the most ubiquitous atomic arrangements encountered among intermetallic compounds. It accounts for over 1000 known intermetallics and has received increased attention due to the recently discovered FeAs-based superconductors. This dissertation is devoted to the investigation of

  7. Brushing up on the history of intermetallics in dentistry

    NASA Astrophysics Data System (ADS)

    Waterstrat, Richard M.

    1990-03-01

    Employing a silver-tin-mercury intermetallic to repair cavities may seem a little unusual, but intermetallics are quite common in dentistry, ranging from gold crowns to braces. Although the human mouth can be unfriendly territory for a brittle intermetallic alloy, dental amalgam has been around since 659 A.D., and its technology has been developed to the point where a filling can be expected to last 30 years or more.

  8. First-principles study of the binary intermetallics in the Au-Rb system

    NASA Astrophysics Data System (ADS)

    Benmechri, Achraf; Djaballah, Yassine; Amer, Ahmed Said; Belgacem-Bouzida, Aissa; Bouderba, Hichem

    2014-06-01

    First-principles calculations within density functional theory (DFT) with the projector augmented wave (PAW) technique were used to investigate the stabilities of intermetallics in the Au-Rb system at 0 K. Four intermetallics: Au7Rb3, Au3Rb2, Au5Rb and AuRb were investigated in their observed experimental structures. The Au2Rb compound, reported in the Au-Rb phase diagrams without specifying explicitly its structure, was also investigated by inspecting several hypothetical structures. A suspect compound (AuRb2) was also investigated. Results show that: (i) The Au3Rb2 and Au7Rb3 compounds, which were never reported in any Au-Rb phase diagram, are stable at 0 K. (ii) The Au2Rb compound is not a ground state for all the tested structures. (iii) Stability of the Au5Rb and AuRb compounds was confirmed. (iv) The new compound AuRb2, not yet reported experimentally, is found mechanically stable at 0 K.

  9. Second-order nonlinear optical Langmuir-Blodgett films based on a series of azo rare-earth coordination compounds

    SciTech Connect

    Gao, L.H.; Wang, K.Z.; Huang, C.H.

    1995-06-01

    A series of novel azo dyes composed of a lanthanide complex anion and an azo cation, in which strongly electron-donating (dihexadecylamino)phenyl and electron-accepting pyridinium groups are separated by an azo group, was designed as second-order nonlinear optical Langmuir-Blodgett (LB) film materials. The compounds are of good film-forming properties. The values of second-order molecular hyperpolarizability {beta} were determined to be (1.20-3.03) x 10{sup {minus}27} esu, comparable to the largest value known for azo LB materials. The compounds studied may be attactive in the application in future optical devices. 13 refs., 5 figs., 1 tab.

  10. Alkali metal, alkaline earth metal, and ammonium ion selectivities of dibenzo-16-crown-5 compounds with functional side arms in ion-selective electrodes

    SciTech Connect

    Ohki, Akira; Lu, J.P.; Huang, X.; Bartsch, R.A. )

    1994-12-01

    Potentiometric selectivities of 11 dibenzo-16-crown-5 compounds for alkali metal, alkaline earth metal, and ammonium ions have been determined in solvent polymeric membrane electrodes. The ionophores bear one or two pendent groups on the central carbon of the three-carbon bridge in the polyether ring. Side-arm variation includes OCH[sub 3], OCH[sub 2]CH[sub 2]OCH[sub 3], OCH[sub 2]CO[sub 2]C[sub 2]H[sub 5], OCH[sub 2]C(O)N(C[sub 2]H[sub 5])[sub 2], and OCH[sub 2]C(O)N(C[sub 5]H[sub 11])[sub 2] units. Attachment of a propyl group to the ring carbon that bears an extended, oxygen-containing side arm increases the selectivity for Na[sup +] relative to larger alkali metal and alkaline earth metal cations. For a given side arm, a linear relationship is obtained when the enhancement in Na[sup +] selectivity produced by attachment of a geminal propyl group is plotted against the diameter of the interference ion. Potentiometric responses of the dibenzo-16-crown-5 compounds are rationalized in terms of the crown ether ring size and the oxygen basicity, conformational positioning, and rigidity of the side arm. 22 refs., 3 figs., 2 tabs.

  11. A reliability study on tin based lead free micro joint including intermetallic and void evolution

    NASA Astrophysics Data System (ADS)

    Feyissa, Frezer Assefa

    In microelectronics soldering to Cu pad lead to formation of two intermetallic structures in the solder -pad interface. The growth of these layers is accompanied by microscopic voids that usually cause reliability concern in the industry. Therefore it is important to understand factors that contribute for the growth of IMC using various combination of reflow time, Sn thickness and aging temperature. Systematic study was conducted on Cu-Sn system to investigate the formation and growth of intermetallic compound (IMC) as well as voiding evolution for different solder thicknesses. The growth of the Cu6Sn5 IMC layer was found to be increasing as the Sn thicknesses increase after reflow while the Cu3Sn layer were decreasing under same conditions. Also after reflow and aging more voiding were shown to occur in the thin solder than thicker one.

  12. High-Performance Pd3Pb Intermetallic Catalyst for Electrochemical Oxygen Reduction.

    PubMed

    Cui, Zhiming; Chen, Hao; Zhao, Mengtian; DiSalvo, Francis J

    2016-04-13

    Extensive efforts to develop highly active and strongly durable electrocatalyst for oxygen reduction are motivated by a need for metal-air batteries and fuel cells. Here, we report a very promising catalyst prototype of structurally ordered Pd-based alloys, Pd3Pb intermetallic compound. Such structurally ordered Pd3Pb/C exhibits a significant increase in mass activity. More importantly, compared to the conventional Pt/C catalysts, ordered Pd3Pb/C is highly durable and exhibits a much longer cycle life and higher cell efficiency in Zn-air batteries. Interestingly, ordered Pd3Pb/C possesses very high methanol tolerance during electrochemical oxygen reduction, which make it an excellent methanol-tolerant cathode catalyst for alkaline polymer electrolyte membrane fuel cells. This study provides a promising route to optimize the synthesis of ordered Pd-based intermetallic catalysts for fuel cells and metal-air batteries. PMID:26848634

  13. Inelastic neutron scattering in valence fluctuation compounds

    SciTech Connect

    Jon M Lawrence

    2011-02-15

    The valence fluctuation compounds are rare earth intermetallics where hybridization of the nearly-localized 4f electrons with the conduction electrons leads to incorporation of the 4f's into the itinerant states. This hybridization slows down the conduction electrons and hence gives them a heavy effective mass, justifying application of the term 'heavy Fermion' (HF) to these materials. During the project period, we grew large single crystals of several such compounds and measured their properties using both standard thermodynamic probes and state-of-the-art inelastic neutron scattering. We obtained three main results. For the intermediate valence compounds CePd{sub 3} and YbAl{sub 3}, we showed that the scattering of neutrons by the fluctuations of the 4f magnetic moment does not have the momentum dependence expected for the itinerant heavy mass state; rather, the scattering is more typical of a localized spin fluctuation. We believe that incoherent scattering localizes the excitation. For the heavy Fermion compound Ce(Ni{sub 0.935}Pd{sub 0.065}){sub 2}Ge{sub 2}, which sits at a T = 0 critical point for transformation into an antiferromagnetic (AF) phase, we showed that the scattering from the AF fluctuations does not exhibit any of the divergences that are expected at a phase transition. We speculate that alloy disorder profoundly suppresses the growth of the fluctuating AF regions, leading to short range clusters rather than regions of infinite size. Finally, we explored the applicability of key concepts used to describe the behavior of rare earth heavy Fermions to uranium based HF compounds where the 5f electrons are itinerant as opposed to localized. We found that scaling laws relating the spin fluctuation energy measured in neutron scattering to the low temperature specific heat and susceptibility are valid for the uranium compounds, once corrections are made for AF fluctuations; however, the degeneracy of the high temperature moment is smaller than expected

  14. Deformation-Induced Amorphization of Copper-Titanium Intermetallics

    NASA Astrophysics Data System (ADS)

    Askenazy, Philip Douglas

    Two methods of inducing amorphization in Cu-Ti intermetallic compounds by mechanical means have been investigated. Ingots of compositions Cu_{35}Ti _{65} and Cu_ {33.3}Ti_{66.7} were rapidly quenched into ribbons. The microstructure consisted largely of microcrystals in an amorphous matrix, which were either quenched in or grown by annealing. The ribbons were cold-rolled, which reduced their effective thickness by a factor of about 8. The status of the intermetallic compound CuTi_2 was monitored by x-ray diffraction and transmission electron microscopy (TEM). The crystals were found to amorphize as rolling progressed. This behavior was not reproduced in polycrystalline samples that had no amorphous matrix present initially. The presence of the amorphous phase is thus necessary for amorphization of the crystal: it eliminates the need to nucleate the new glass, and it prevents the ribbon from disintegrating at high deformation stages. It may also change the deformation mechanism that occurs in the crystals, retarding the onset of amorphization. Diffuse scattering in close-packed directions is similar to that seen in electron irradiation experiments. It is postulated that the chemical disorder present in antiphase boundaries caused by deformation raises the free energy of the crystal higher than that of the amorphous phase. Ingots of the same compound were worn against each other in a custom-built wear apparatus. The design eliminates iron contamination of the wear sample and requires relatively small quantities of material. Alteration of the surface structure was monitored by plane-view and cross -sectional TEM. Larger subsurface crystals exhibit diffuse scattering, similar to that found in the rolled samples. A wide range of grain sizes was observed, due to the inhomogeneous nature of the wear process. An unusual phase was observed at the surface, consisting of a nanometer-scale mixture of aligned nanocrystalline regions and disordered areas. Some amorphous phase is

  15. Syntheses and characterization of energetic compounds constructed from alkaline earth metal cations (Sr and Ba) and 1,2-bis(tetrazol-5-yl)ethane

    SciTech Connect

    Xia Zhengqiang; Chen Sanping; Wei Qing; Qiao Chengfang

    2011-07-15

    Two new energetic compounds, [M(BTE)(H{sub 2}O){sub 5}]{sub n} (M=Sr(1), Ba(2)) [H{sub 2}BTE=1,2-bis(tetrazol-5-yl)ethane], have been hydrothermally synthesized and structurally characterized. Single-crystal X-ray diffraction analyses reveal that they are isomorphous and exhibit 2D (4,4) net framework, generated by 4-connected Sr{sub 2}(H{sub 2}O){sub 10}/Ba{sub 2}(H{sub 2}O){sub 10} SBUs linked up by two independent binding modes of H{sub 2}BTE, and the resulting 2D structure is interconnected by hydrogen-bond and strong face to face {pi}-{pi} stacking interactions between two tetrazole rings to lead to a 3D supramolecular architecture. DSC measurements show that they have significant catalytic effects on thermal decomposition of ammonium perchlorate. Moreover, the photoluminescence properties, thermogravimetric analyses, and flame colors of the as-prepared compounds are also investigated in this paper. - Graphical abstract: Two novel 2D isomorphous alkaline earth metal complexes were assembled by 4-connected Sr{sub 2}(H{sub 2}O){sub 10}/Ba{sub 2}(H{sub 2}O){sub 10} SBUs and two independent binding modes of H{sub 2}BTE ligands, and the catalytic performances toward thermal decomposition of ammonium perchlorate and photoluminescent properties of them were investigated. Highlights: > Two novel alkaline earth energetic coordination polymers have been prepared.{yields} Both structures are layered based on 4-connected Sr{sub 2}(H{sub 2}O){sub 10}/Ba{sub 2}(H{sub 2}O){sub 10} SBUs and two distinct H{sub 2}BTE coordination modes.{yields} The dehydrated products of the compounds possess good thermostability and significant catalytic effects on thermal decomposition of AP.

  16. Evolution, Interaction, and Intrinsic Properties of Dislocations in Intermetallics: Anisotropic 3D Dislocation Dynamics Approach

    SciTech Connect

    Qian Chen

    2008-08-18

    The generation, motion, and interaction of dislocations play key roles during the plastic deformation process of crystalline solids. 3D Dislocation Dynamics has been employed as a mesoscale simulation algorithm to investigate the collective and cooperative behavior of dislocations. Most current research on 3D Dislocation Dynamics is based on the solutions available in the framework of classical isotropic elasticity. However, due to some degree of elastic anisotropy in almost all crystalline solids, it is very necessary to extend 3D Dislocation Dynamics into anisotropic elasticity. In this study, first, the details of efficient and accurate incorporation of the fully anisotropic elasticity into 3D discrete Dislocation Dynamics by numerically evaluating the derivatives of Green's functions are described. Then the intrinsic properties of perfect dislocations, including their stability, their core properties and disassociation characteristics, in newly discovered rare earth-based intermetallics and in conventional intermetallics are investigated, within the framework of fully anisotropic elasticity supplemented with the atomistic information obtained from the ab initio calculations. Moreover, the evolution and interaction of dislocations in these intermetallics as well as the role of solute segregation are presented by utilizing fully anisotropic 3D dislocation dynamics. The results from this work clearly indicate the role and the importance of elastic anisotropy on the evolution of dislocation microstructures, the overall ductility and the hardening behavior in these systems.

  17. Effects of cerium substitution on magnetic properties of naturally layered TbMn6Sn6 compound

    NASA Astrophysics Data System (ADS)

    Chen, X. X.; Zhao, M.; Liu, G. Z.; Yao, J. L.; Gao, J.

    2016-04-01

    The Tb1‑xCexMn6Sn6 compounds with x = 0 ‑ 0.3 crystallize in the hexagonal HfFe6Ge6-type structure (space group P6/mmm). The cerium (Ce) substitution for Tb increases the magnetization while reduces the Curie and spin-orientation temperatures. The hard magnetic properties are enhanced by the Ce substitution, e.g., from a coercivity of ˜ 5.4 kOe for TbMn6Sn6 to ˜ 7.6 kOe for the Ce-substituted compounds with x = 0.2 at 5 K. The role of Ce substitution in the magnetocrystalline anisotropy is discussed based on the single-ion anisotropy model. The substitution of Ce for critical rare-earth atoms provides an opportunity of improving hard magnetic properties of the rare-earth-based intermetallics.

  18. Excitonic correlations in the intermetallic Fe2VAl

    NASA Astrophysics Data System (ADS)

    Weht, Ruben; Pickett, W. E.

    1998-09-01

    The intermetallic compound Fe2VAl looks nonmetallic in transport and strongly metallic in thermodynamic and photoemission data. It has in its band structure a highly differentiated set of valence and conduction bands leading to a semimetallic system with a very low density of carriers. The pseudogap itself is sensitive to the presence of Al states, but the resulting carriers have only minor Al character. The effects of generalized gradient corrections to the local density band structure are shown to be important, reducing the carrier density by a factor of 3. Spin-orbit coupling results in a redistribution of the holes among pockets at the Brillouin zone center. Doping of this nonmagnetic compound by 0.5 electrons per cell in a virtual crystal fashion results in a moment of 0.5μB and destroys the pseudogap. We assess the tendencies toward the formation of an excitonic condensate and toward an excitonic Wigner crystal and find both to be unlikely. We propose a model in which the observed properties result from excitonic correlations arising from two interpenetrating lattices of distinctive electrons (eg on V) and holes (t2g on Fe) of low density (one carrier of each sign per 350 formula units).

  19. Theoretical and experimental study of high-magnetic-field XMCD spectra at the L2,3 absorption edges of mixed-valence rare-earth compounds

    NASA Astrophysics Data System (ADS)

    Kotani, Akio; Matsuda, Yasuhiro H.; Nojiri, Hiroyuki

    2009-11-01

    X-ray magnetic circular dichroism(XMCD) spectra at the L2,3 edges of mixed-valence rare-earth compounds in high magnetic fields are studied both theoretically and experimentally. The theoretical study is based on a new framework proposed recently by Kotani. The Zeeman splitting of 4f states, the mixed-valence character of 4f states, and the 4f-5d exchange interaction are incorporated into a single impurity Anderson model. New XMCD experiments in high magnetic fields up to 40 T are carried out for the mixed-valence compounds EuNi2(Si0.18Ge0.82)2 and YbInCu4 by using a miniature pulsed magnet, which was developed recently by Matsuda et al. The XMCD data are taken at 5 K by transmission measurements for incident X-rays with ± helicities at BL39XU in SPring-8. After giving a survey on recent developments in the theory of XMCD spectra for mixed-valence Ce and Yb compounds, we calculate the XMCD spectra of YbInCu4 at the field-induced valence transition around 32 T by applying the recent theoretical framework and by newly introducing at 32 T a discontinuous change in the Yb 4f level and that in the hybridization strength between the Yb 4f and conduction electrons. The calculated results are compared with the experimental ones.

  20. R3Au(6+x)Al26T (R = Ca, Sr, Eu, Yb; T = early transition metal): a large family of compounds with a stuffed BaHg11 structure type grown from aluminum flux.

    PubMed

    Latturner, Susan E; Bilc, Daniel; Mahanti, S D; Kanatzidis, Mercouri G

    2009-02-16

    A collection of new quaternary intermetallic compounds with a cubic, stuffed BaHg(11) structure type has been synthesized by the combination of a divalent rare earth or alkaline earth metal R, an early transition metal T, and gold in an excess of molten aluminum. Structural characterization of these R(3)Au(6+x)Al(26)T compounds by powder and single crystal X-ray diffraction indicates that the unit cell varies with the radii of the early transition metal T and the rare earth/alkaline earth R as expected. The element T (where T = group 4, 5, 6, and 7 element) appears to be responsible for the stabilization of up to 43 different members of the R(3)Au(6+x)Al(26)T family of compounds. Varying amounts of disorder and trends in partial occupancies of the Au stuffed site--the site that is vacant in the parent compound BaHg(11)--are also indicated by the diffraction studies of this family of compounds. Magnetic susceptibility data reveals that the transition metal atoms in these materials do not possess local magnetic moments. For the magnetic rare earth containing materials, the europium compounds undergo a ferromagnetic transition at 10 K, and the ytterbium analogues show mixed valent behavior. Band structure calculations also support a mixed valent state for Yb in these compounds. PMID:19146424

  1. Magnetic properties and structural transitions of orthorhombic fluorite-related compounds Ln{sub 3}MO{sub 7} (Ln=rare earths, M=transition metals)

    SciTech Connect

    Wakeshima, Makoto; Hinatsu, Yukio

    2010-11-15

    Magnetic properties and structural transitions of ternary rare-earth transition-metal oxides Ln{sub 3}MO{sub 7} (Ln=rare earths, M=transition metals) were investigated. In this study, we prepared a series of molybdates Ln{sub 3}MoO{sub 7} (Ln=La-Gd). They crystallize in an orthorhombic superstructure of cubic fluorite with space group P2{sub 1}2{sub 1}2{sub 1}, in which Ln{sup 3+} ions occupy two different crystallographic sites (the 8-coordinated and 7-coordinated sites). All of these compounds show a phase transition from the space group P2{sub 1}2{sub 1}2{sub 1} to Pnma in the temperature range between 370 and 710 K. Their magnetic properties were characterized by magnetic susceptibility measurements from 1.8 to 400 K and specific heat measurements from 0.4 to 400 K. Gd{sub 3}MoO{sub 7} shows an antiferromagnetic transition at 1.9 K. Measurements of the specific heat for Sm{sub 3}MoO{sub 7} and the analysis of the magnetic specific heat indicate a 'two-step' antiferromagnetic transition due to the ordering of Sm magnetic moments in different crystallographic sites, i.e., with decreasing temperature, the antiferromagnetic ordering of the 7-coordinated Sm ions occur at 2.5 K, and then the 8-coordinated Sm ions order at 0.8 K. The results of Ln{sub 3}MoO{sub 7} were compared with the magnetic properties and structural transitions of Ln{sub 3}MO{sub 7} (M=Nb, Ru, Sb, Ta, Re, Os, or Ir). -- Graphical Abstract: Magnetic properties and structural transitions of ternary rare-earth transition-metal oxides Ln{sub 3}MO{sub 7} (Ln=rare earths, M=transition metals) were investigated. In this study, we prepared a series of molybdates Ln{sub 3}MoO{sub 7} (Ln=La{approx}Gd). These compounds show a phase transition from the space group P2{sub 1}2{sub 1}2{sub 1} to Pnma in the temperature range between 370 and 710 K. Their magnetic properties were characterized by magnetic susceptibility and specific heat measurements from 0.4 to 400 K. The results of Ln{sub 3}MoO{sub 7} were

  2. Genetic and chemical analyzes of transformations in compost compounds during biodegradation of oiled bleaching earth with waste sludge.

    PubMed

    Piotrowska-Cyplik, Agnieszka; Cyplik, Paweł; Marecik, Roman; Czarny, Jakub; Szymański, Andrzej; Wyrwas, Bogdan; Framski, Grzegorz; Chrzanowski, Lukasz; Materna, Katarzyna

    2012-06-01

    Composting of oiled bleaching earth with waste sludge and corn straw was carried out to investigate the ability of microorganisms to synthesize biosurfactants that might decrease the surface tension of composts. Analytical results and changes in the surface tension suggest that biodegradation of fatty by-products was the consequence of emulsifying properties of higher fatty acids. The surface tension for isolates from all composting phases was between 37 and 43 mN m(-1). No substances synthesized by microorganisms that might be able to decrease the surface tension were detected in composts. Tensammetric, TLC and HPLC-MS results and changes in surface tension suggest that biodegradation of fatty by-products results from the emulsifying properties of higher fatty acids. A decrease in fatty content from 144 to 6 mg g(-1) dry matter was obtained. PMID:22464418

  3. Intermetallics Characterization of Lead-Free Solder Joints under Isothermal Aging

    NASA Astrophysics Data System (ADS)

    Choubey, Anupam; Yu, Hao; Osterman, Michael; Pecht, Michael; Yun, Fu; Yonghong, Li; Ming, Xu

    2008-08-01

    Solder interconnect reliability is influenced by environmentally imposed loads, solder material properties, and the intermetallics formed within the solder and the metal surfaces to which the solder is bonded. Several lead-free metallurgies are being used for component terminal plating, board pad plating, and solder materials. These metallurgies react together and form intermetallic compounds (IMCs) that affect the metallurgical bond strength and the reliability of solder joint connections. This study evaluates the composition and extent of intermetallic growth in solder joints of ball grid array components for several printed circuit board pad finishes and solder materials. Intermetallic growth during solid state aging at 100°C and 125°C up to 1000 h for two solder alloys, Sn-3.5Ag and Sn-3.0Ag-0.5Cu, was investigated. For Sn-3.5Ag solder, the electroless nickel immersion gold (ENIG) pad finish was found to result in the lowest IMC thickness compared to immersion tin (ImSn), immersion silver (ImAg), and organic solderability preservative (OSP). Due to the brittle nature of the IMC, a lower IMC thickness is generally preferred for optimal solder joint reliability. A lower IMC thickness may make ENIG a desirable finish for long-life applications. Activation energies of IMC growth in solid-state aging were found to be 0.54 ± 0.1 eV for ENIG, 0.91 ± 0.12 eV for ImSn, and 1.03 ± 0.1 eV for ImAg. Cu3Sn and Cu6Sn5 IMCs were found between the solder and the copper pad on boards with the ImSn and ImAg pad finishes. Ternary (Cu,Ni)6Sn5 intermetallics were found for the ENIG pad finish on the board side. On the component side, a ternary IMC layer composed of Ni-Cu-Sn was found. Along with intermetallics, microvoids were observed at the interface between the copper pad and solder, which presents some concern if devices are subject to shock and vibration loading.

  4. Preparation, characterization, and second-harmonic generation of a Langmuir-Blodgett film based on a rare-earth coordination compound

    SciTech Connect

    Wang, K.Z.; Huang, C.H.; Xu, G.X.; Zhao, X.S.; Xie, X.M.; Wu, N.Z.; Xu, Y.; Liu, Y.Q.; Zhu, D.B.

    1994-11-01

    The rare-earth coordination compound (E)-N-hexadecyl-4-(2-(4-(dimethylamino)phenyl)-ethenyl)pyridinium tetrakis(1-phenyl-3-methyl-4-benzoyl-5-pyrazolonato)dysprosium(III) was synthesized. The LB films were prepared and characterized by UV-vis, IR, X-ray photoelectron spectroscopy, and low-angle X-ray diffraction. High-quality LB films up to 50 layers on the hydrophilic substrates of quartz, calcium fluoride, and glass were obtained. From the second-harmonic generation measurement, second-order molecular hyperpolarizability {beta} of the dysprosium complex was estimated to be about (6.6-9.3) x 10{sup {minus}28} esu. 14 refs., 6 figs., 1 tab.

  5. Nonstoichiometry of Al-Zr intermetallic phases

    SciTech Connect

    Radmilovic, V.; Thomas, G.

    1994-06-01

    Nonstoichiometry of metastable cubic {beta}{prime} and equilibrium tetragonal {beta} Al-Zr intermetallic phases of the nominal composition Al{sub 3}Zr in Al-rich alloys has been extensively studied. It is proposed that the ``dark contrast`` of {beta}{prime} core in {beta}{prime}/{sigma}{prime} complex precipitates, in Al-Li-Zr based alloys, is caused by incorporation of Al and Li atoms into the {beta}{prime} phase on Zr sublattice sites, forming nonstoichiometric Al-Zr intermetallic phases, rather than by Li partitioning only. {beta}{prime} particles contain very small amounts of Zr, approximately 5 at.%, much less than the stoichiometric 25 at.% in the Al{sub 3}Zr metastable phase. These particles are, according to simulation of high resolution images, of the Al{sub 3}(Al{sub 0.4}Li{sub 0.4}Zr{sub 0.2}) type. Nonstoichiometric particles of average composition Al{sub 4}Zr and Al{sub 6}Zr are observed also in the binary Al-Zr alloy, even after annealing for several hours at 600{degree}C.

  6. Cold Sprayed Intermetallic Thermal Barrier Coatings

    NASA Astrophysics Data System (ADS)

    Leshchinsky, Evgeny

    Conventional thermal barrier coating (TBC) systems consist of a duplex structure with a metallic bond coat and a ceramic heat-isolative topcoat. Several recent research activities are concentrated on the development of improved multilayer bond coat and TBC materials. This study represents an investigation performed for the aluminum based bond coats, especially those with reduced thermal conductivities. Using alternative TBC materials, such as metal alloys and intermetallics, their processing methods can be further optimized to achieve the best thermal physical parameters. One example is the ten-layer system in which cold sprayed aluminum based intermetallics are synthesized. These systems demonstrated improved heat insulation and thermal fatigue capabilities compared to conventional TBC. The microstructures and properties of the laminar coatings were characterized by SEM, EDS, XRD; micromechanical and durability tests were performed to define the structure and coating formation mechanisms. Application prospects for HCCI engines are discussed. Fuel energy can be utilized more efficiently with the concept of low heat rejection engines with applied TBC.

  7. Electronically- and crystal-structure-driven magnetic structures and physical properties of RScSb (R = rare earth) compounds. A neutron diffraction, magnetization and heat capacity study

    SciTech Connect

    Ritter, C; Dhar, S K; Kulkarni, R; Provino, A; Paudyal, Durga; Manfrinetti, Pietro; Gschneidner, Karl A

    2014-08-14

    The synthesis of the new equiatomic RScSb ( R = La-Nd, Sm, Gd-Tm, Lu, Y) compounds has been recently reported. These rare earth compounds crystallize in two different crystal structures, adopting the CeScSi-type ( I 4/ mmm) for the lighter R (La-Nd, Sm) and the CeFeSi-type (P4 /nmm) structure for the heavier R ( R = Gd-Tm, Lu, Y). Here we report the results of neutron diffraction, magnetization and heat capacity measurements on some of these compounds ( R = Ce, Pr, Nd, Gd and Tb). Band structure calculations have also been performed on CeScSb and GdScGe (CeScSi-type), and on GdScSb and TbScSb (CeFeSi-type) to compare and understand the exchange interactions in CeScSi and CeFeSi structure types. The neutron diffraction investigation shows that all five compounds order magnetically, with the highest transition temperature of 66 K in TbScSb and the lowest of about 9 K in CeScSb. The magnetic ground state is simple ferromagnetic (τ = [0 0 0]) in CeScSb, as well in NdScSb for 32 >T > 22 K. Below 22 K a second magnetic transition, with propagation vector τ = [¼ ¼ 0], appears in NdScSb. PrScSb has a magnetic structure within, determined by mostly ferromagnetic interactions and antiferromagnetic alignment of the Pr-sites connected through the I-centering ( τ = [1 0 0]). A cycloidal spiral structure with a temperature dependent propagation vector τ = [δ δ ½] is found in TbScSb. The results of magnetization and heat capacity lend support to the main conclusions derived from neutron diffraction. As inferred from a sharp peak in magnetization, GdScSb orders antiferromagnetically at 56 K. First principles calculations show lateral shift of spin split bands towards lower energy from the Fermi level as the CeScSi-type structure changes to the CeFeSi-type structure. This rigid shift may force the system to transform from exchange split ferromagnetic state to the antiferromagnetic state in RScSb compounds (as seen for example in GdScSb and TbScSb) and is proposed to

  8. Synthesis and densification of Ni{sub 3}(Si, Ti) intermetallics by hot isostatic pressing

    SciTech Connect

    Van Dyck, S.; Delaey, L.; Froyen, L.; Buekenhout, L.

    1996-12-31

    The production of complex parts from Ni{sub 3}(Si, Ti) intermetallic materials by reactive powder metallurgy offers significant advantages over more conventional processing techniques. The main problem associated with reactive powder metallurgy is controlling the exothermic reaction accompanying the synthesis of the intermetallic compound. The uncontrolled release of heat during the conversion of the reactants into nickel silicide leads to unacceptable deformation and melting of the part. The thermal evolution of a part during reactive synthesis of the intermetallic phase is described based on kinetic and heat transfer equations, giving the temperature and phase change as a function of the applied temperature cycle and the mass and size of the part under consideration. From this model, methods for controlling the exothermic reaction during synthesis are derived. When preparing nickel silicides by reactive powder metallurgy, the application of external pressure is required to eliminate porosity and to obtain good mechanical properties. The properties of materials produced by hot isostatic pressing, with different methods of reaction control, are compared to materials prepared from prealloyed powders. It is shown that by reactive HIP, materials can be obtained with a fracture strength exceeding 2,000 MPa.

  9. Marine and terrestrial sources of reactive volatile organic compounds and their impact on the tropospheric ozone chemistry of the earth

    NASA Astrophysics Data System (ADS)

    Riemer, Daniel David

    Two areas integral to the global cycle of tropospheric ozone were studied. The first segment of this investigation involved the study of marine ecosystems to define the sources of nonmethane hydrocarbons (NMHCs) in the surface ocean. This included laboratory and field investigations conducted to determine the function and importance of dissolved organic matter (DOM) in the abiotic photochemical production of nonmethane hydrocarbons (NMHCs) in surface seawater. Concurrently, phytoplankton were investigated as a biogenic source of NMHCs in the surface ocean. Low molecular weight alkenes, compounds observed in the greatest quantities in the surface ocean, are formed almost exclusively as a result of DOM-mediated photochemistry. Isoprene was found to be produced by all phytoplankton species investigated. The primary sink for NMHCs found in surface seawater was gas exchange. The second segment of this study focused on the prevalence of NMHCs and oxygenated volatile organic compounds (OVOCs) in the rural southeastern United States. To characterize the importance of NMHCs and OVOCs to the process of atmospheric reactivity and tropospheric ozone chemistry, mixing ratios for a number of NMHCs and OVOCs were determined. Isoprene and its primary oxidation products, methacrolein and methyl vinyl ketone, were observed to be the dominant hydroxyl radical (OH) sink in the rural atmosphere. Certain OVOCs, namely methanol, acetone and acetaldehyde-although not as important on a reactivity basis-were the most prevalent in terms of mass. Methanol was the dominant OVOC measured in the rural atmosphere and serves as an important source of formaldehyde in the rural atmosphere. On the basis of the mixing ratio patterns exhibited by many of the OVOCs present in the rural atmosphere, considerable biogenic sources are likely.

  10. On the standardization of crystal-field parameters and the multiple correlated fitting technique: Applications to rare-earth compounds

    NASA Astrophysics Data System (ADS)

    Rudowicz, C.; Chua, M.; Reid, M. F.

    2000-09-01

    This work investigates the crystal-field parameter (CFP) sets for rare-earth (RE) ions doped at orthorhombic and/or lower symmetry, i.e. monoclinic or triclinic sites. Two important questions are addressed: (1) How do you compare CFP sets reported by different authors when there can be as many as six numerically different equivalent sets? and (2) How do you distinguish between global and local minima in the multi-parameter fittings? To answer the first question we propose to adopt the standardization of CFP sets. The orthorhombic and/or monoclinic standardization has been carried out for several illustrative CFP sets, including the contributions from various mechanisms, for NdF 3, RE 2Te 4O 11, and RE 3+ in garnet materials. It is shown that adopting a well-defined standardization convention enables meaningful comparison of CFP sets taken from various sources. The analysis of literature data reveals also cases when the CF parameters may be misinterpreted due to the choice of a different representation in the multi-parameter fittings. To answer the second question we propose the multiple correlated fitting technique (MCFT). Using experimental data for Nd 3+ in YAG and LaF 3, MCFT is employed to probe for more reliable CFP sets.

  11. Zintl and intermetallic phases grown from calcium/lithium flux

    NASA Astrophysics Data System (ADS)

    Blankenship, Trevor

    Metal flux synthes is a useful alternative method to high temperature solid state synthesis; it allows easy diffusion of reactants at lower temperatures, and presents favorable conditions for crystal growth. A mixed flux of calcium and lithium in a 1:1 ratio was explored in this work; this mixture melts at 300°C and is an excellent solvent for main group elements and CaH 2. Reactions of p-block elements in a 1:1 Ca/Li flux have produced several new intermetallic and Zintl phases. Electronegative elements from groups 14 and 15 are reduced to anions in this flux, yielding charge-balanced products. More electropositive metals from group 13 are not fully reduced; the resulting products are complex intermetallics. The reactions of tin or lead and carbon in Ca/Li flux produced the analogous phases Ca11Tt3C8 (Tt = Sn, Pb) in the monoclinic C21/c space group (a = 13.2117(8) A, b =10.7029(7) A, c = 14.2493(9) A, beta = 105.650(1)° for the Sn analog). These compounds are carbide Zintl phases that includes the rare combination of C3 4- and C22- units as well as Sn4- or Pb4- anions. Ca/Li flux reactions of CaH2 and arsenic have produced the Zintl phases LiCa3As 2H in orthorhombic Pnma (a = 11.4064(7), b = 4.2702(3), c = 11.8762(8) A), and Ca 13As6C0.46N1.155H6.045in tetragonal P4/mbm (a = 15.7493(15), c = 9.1062(9) A). The complex stoichiometry of the latter phase was caused by incorporation of light element contaminants and was studied by neutron diffraction, showing mixing of anionic sites to achieve charge balance. Ca/Li flux reactions with group 13 metals have resulted in several new intermetallic phases. Reactions of indium and CaH2 in the Ca/Li flux (with or without boron) formed Ca53In13B4-x H23+x(2.4 < x < 4.0) in cubic space group Im-3 (a = 16.3608(6) A) which features metallic indium atoms and ionic hydride sites. The electronic properties of this "subhydride" were confirmed by 1H and 115In NMR spectroscopy. Attempts to replace boron with carbon yielded Ca12InC13-x

  12. Possibility of enhancement of the high-temperature strength and the heat resistance of a nickel aluminide-based structural intermetallic alloy

    NASA Astrophysics Data System (ADS)

    Bazyleva, O. A.; Shestakov, A. V.; Arginbaeva, E. G.; Turenko, E. Yu.

    2016-01-01

    The assimilation of a number of rare-earth metals (REM = praseodymium, neodymium, erbium) in a cast high-temperature nickel aluminide-based intermetallic alloy and the effect of REM alloying of the alloy on the critical temperatures, the high-temperature strength, and the heat resistance (time to failure) of the structural alloy are studied. It is shown that the heat resistance and the time to failure of the alloy at 1200°C can be increased by microalloying of the intermetallic alloy with REM.

  13. Photochemical studies in low Earth orbit for organic compounds related to small bodies, Titan and Mars. Current and future facilities.

    NASA Astrophysics Data System (ADS)

    Cottin, H.; Saiagh, K.; Nguyen, D.; Grand, N.; Bénilan, Y.; Cloix, M.; Coll, P.; Gazaux, M.-C.; Fray, N.; Khalaf, D.; Raulin, F.; Stalort, F.; Carrasco, N.; Szopa, C.; Chaput, D.; Bertrand, M.; Westall, F.; Mattioda, A.; Quinn, R.; Ricco, A.; Santos, O.; Baratta, G. A.; Strazzulla, G.; Palumbo, M. E.; Le Postollec, A.; Dobrijevic, M.; Coussot, G.; Vigier, F.; Vandenabeele-Trambouze, O.; Incerti, S.; Berger, T.

    2015-01-01

    The study of the evolution of organic matter subjected to space conditions, and more specifically to solar photons in the vacuum ultraviolet range (120-200 nm) has been undertaken in low Earth Orbit since the 90's, and implemented on various space platforms. The most recent exposure facilities are BIOPAN outside the Russian automatic capsules FOTON, and EXPOSE-E & -R (1&2) outside the International Space Station. They allow the photolysis of many different samples simultaneously, and provide us with valuable data about the formation and evolution of organic matter in the Solar System (meteorites, comets, Titan's atmosphere, the Martian surface...) and in the Interstellar Medium. They have been used by European teams in the recent past(ORGANIC on BIOPAN V-FOTON M2 and UVolution on BIOPAN VI-FOTON M3, PROCESS on EXPOSE-E, AMINO and ORGANICS on EXPOSE-R), and a new EXPOSE set is currently exposed outside the ISS (PSS on EXPOSE-R2). These existing tools are very valuable; however, they have significant limitations that limit their capabilities and scientific return. One of the most critical issues for current studies is the lack of any in-situ analysis of the evolution of the samples as a function of time. Only two measurements are available for the experiment: one before and one after the exposure. A significant step forward has been achieved with the O/OREOS NASA nanosatellite and the OREOcube ESA project with onboard UV-visible measurements. However, for organic samples, following the evolution of the samples would be more informative and provide greater insight with infrared measurements, which display specific patterns characteristic of major organic functionalities in the mid-infrared range (4000-1000 cm-1).

  14. A ship-in-a-bottle strategy to synthesize encapsulated intermetallic nanoparticle catalysts: Exemplified for furfural hydrogenation

    DOE PAGESBeta

    Maligal-Ganesh, Raghu V.; Xiao, Chaoxian; Goh, Tian Wei; Wang, Lin -Lin; Gustafson, Jeffrey; Pei, Yuchen; Qi, Zhiyuan; Johnson, Duane D.; Zhang, Shiran; Tao, Franklin; et al

    2016-01-28

    In this paper, intermetallic compounds are garnering increasing attention as efficient catalysts for improved selectivity in chemical processes. Here, using a ship-in-a-bottle strategy, we synthesize single-phase platinum-based intermetallic nanoparticles (NPs) protected by a mesoporous silica (mSiO2) shell by heterogeneous reduction and nucleation of Sn, Pb, or Zn in mSiO2-encapsulated Pt NPs. For selective hydrogenation of furfural to furfuryl alcohol, a dramatic increase in activity and selectivity is observed when intermetallic NPs catalysts are used in comparison to Pt@mSiO2. Among the intermetallic NPs, PtSn@mSiO2 exhibits the best performance, requiring only one-tenth of the quantity of Pt used in Pt@mSiO2 for similarmore » activity and near 100% selectivity to furfuryl alcohol. A high-temperature oxidation–reduction treatment easily reverses any carbon deposition-induced catalyst deactivation. X-ray photoelectron spectroscopy shows the importance of surface composition to the activity, whereas density functional theory calculations reveal that the enhanced selectivity on PtSn compared to Pt is due to the different furfural adsorption configurations on the two surfaces.« less

  15. Titanium aluminide intermetallic alloys with improved wear resistance

    DOEpatents

    Qu, Jun; Lin, Hua-Tay; Blau, Peter J.; Sikka, Vinod K.

    2014-07-08

    The invention is directed to a method for producing a titanium aluminide intermetallic alloy composition having an improved wear resistance, the method comprising heating a titanium aluminide intermetallic alloy material in an oxygen-containing environment at a temperature and for a time sufficient to produce a top oxide layer and underlying oxygen-diffused layer, followed by removal of the top oxide layer such that the oxygen-diffused layer is exposed. The invention is also directed to the resulting oxygen-diffused titanium aluminide intermetallic alloy, as well as mechanical components or devices containing the improved alloy composition.

  16. Magnetic properties and structural transitions of orthorhombic fluorite-related compounds Ln3MO 7 ( Ln=rare earths, M=transition metals)

    NASA Astrophysics Data System (ADS)

    Wakeshima, Makoto; Hinatsu, Yukio

    2010-11-01

    Magnetic properties and structural transitions of ternary rare-earth transition-metal oxides Ln3MO 7 ( Ln=rare earths, M=transition metals) were investigated. In this study, we prepared a series of molybdates Ln3MoO 7 ( Ln=La-Gd). They crystallize in an orthorhombic superstructure of cubic fluorite with space group P2 12 12 1, in which Ln3+ ions occupy two different crystallographic sites (the 8-coordinated and 7-coordinated sites). All of these compounds show a phase transition from the space group P2 12 12 1 to Pnma in the temperature range between 370 and 710 K. Their magnetic properties were characterized by magnetic susceptibility measurements from 1.8 to 400 K and specific heat measurements from 0.4 to 400 K. Gd 3MoO 7 shows an antiferromagnetic transition at 1.9 K. Measurements of the specific heat for Sm 3MoO 7 and the analysis of the magnetic specific heat indicate a "two-step" antiferromagnetic transition due to the ordering of Sm magnetic moments in different crystallographic sites, i.e., with decreasing temperature, the antiferromagnetic ordering of the 7-coordinated Sm ions occur at 2.5 K, and then the 8-coordinated Sm ions order at 0.8 K. The results of Ln3MoO 7 were compared with the magnetic properties and structural transitions of Ln3MO 7 ( M=Nb, Ru, Sb, Ta, Re, Os, or Ir).

  17. Modeling of Substitutional Site Preference in Ordered Intermetallic Alloys

    NASA Technical Reports Server (NTRS)

    Bozzolo, Guillermo; Noebe, Ronald D.; Honecy, Frank

    1998-01-01

    We investigate the site substitution scheme of specific alloying elements in ordered compounds and the dependence of site occupancy on compound stoichiometry, alloy concentration. This basic knowledge, and the interactions with other alloying additions are necessary in order to predict and understand the effect of various alloying schemes on the physical properties of a material, its response to various temperature treatments, and the resulting mechanical properties. Many theoretical methods can provide useful but limited insight in this area, since most techniques suffer from constraints in the type of elements and the crystallographic structures that can be modeled. With this in mind, the Bozzolo-Ferrante-Smith (BFS) method for alloys was designed to overcome these limitations, with the intent of providing an useful tool for the theoretical prediction of fundamental properties and structure of complex systems. After a brief description of the BFS method, its use for the determination of site substitution schemes for individual as well as collective alloying additions to intermetallic systems is described, including results for the concentration dependence of the lattice parameter. Focusing on B2 NiAl, FeAl and CoAl alloys, the energetics of Si, Ti, V, Cr, Fe, Co, Ni, Cu, Zr, Nb, Mo, Ru, Hf, Ta and W alloying additions are surveyed. The effect of single additions as well as the result of two simultaneous additions, discussing the interaction between additions and their influence on site preference schemes is considered. Finally, the BFS analysis is extended to ternary L1(sub 2) (Heusler phase) alloys. A comparison between experimental and theoretical results for the limited number of cases for which experimental data is available is also included.

  18. Ordering of atoms in 3d sublattice of the intermetallic quasibinary system Dy(Fe/sub 1-x/Mn/sub x/)/sub 2/

    SciTech Connect

    Ilyushin, A.S.; Kastro, D.A.; Makhmud, I.A.

    1986-12-01

    Methods of x-ray analysis and nuclear ..gamma..-resonance (Moessbauer effect) have been used to study the distribution of iron and manganese atoms in the intermetallic quaisbinary system Dy(Fe/sub 1-x/Mn/sub x/)/sub 2/, which is isostructural to the Laves phase C15. Ordering of atoms of transition metals has been found in 3d sublattice of intermetallic compounds Dy(Fe/sub 1-x/Mn/sub x/)/sub 2/ with the formation of triple superstructure having the stoichiometric composition Dy(Fe/sub 0 x 25/Mn/sub 0 x 75/)/sub 2/

  19. Multishell Intermetallic Onions by Symmetrical Configuration of Ordered Domains

    NASA Astrophysics Data System (ADS)

    Yu, R.; Chen, W.; Cheng, Z. Y.; Li, Y. D.; Zhu, J.

    2010-11-01

    Ordered domains are utilized to construct new nanostructures, i.e., multishell intermetallic onions, which are formed by symmetrical configuration of ordered domains. Through density-functional theory calculations, we have shown that the energy penalties for introducing antiphase boundaries into the nanoparticles are small in some alloy systems compared to typical surface energies, making it feasible to prepare intermetallic onions by tuning surface energies. The unique surface atomic arrangements would provide opportunities for developing novel materials like efficient catalysts.

  20. Nanocrystalline semiconductor doped rare earth oxide for the photocatalytic degradation studies on Acid Blue 113: A di-azo compound under UV slurry photoreactor.

    PubMed

    Suganya Josephine, G A; Mary Nisha, U; Meenakshi, G; Sivasamy, A

    2015-11-01

    Preventive measures for the control of environmental pollution and its remediation has received much interest in recent years due to the world-wide increase in the contamination of water bodies. Contributions of these harmful effluents are caused by the leather processing, pharmaceutical, cosmetic, textile, agricultural and other chemical industries. Nowadays, advanced oxidation processes considered to be better option for the complete destruction of organic contaminants in water and wastewater. Acid Blue 113 is a most widely used di-azo compound in leather, textile, dying and food industry as a color rending compound. In the present study, we have reported the photo catalytic degradation of Acid Blue 113 using a nanocrystalline semiconductor doped rare earth oxide as a photo catalyst under UV light irradiation. The photocatalyst was prepared by a simple precipitation technique and were characterized by XRD, FT-IR, UV-DRS and FE-SEM analysis. The experimental results proved that the prepared photo catalyst was nanocrystalline and highly active in the UV region. The UV-DRS results showed the band gap energy was 3.15eV for the prepared photo catalyst. The photodegradation efficiency was analyzed by various experimental parameters such as pH, catalyst dosage, variation of substrate concentration and effect of electrolyte addition. The photo degradation process followed a pseudo first order kinetics and was continuously monitored by UV-visible spectrophotometer. The experimental results proved the efficacy of the nanocrystalline zinc oxide doped dysprosium oxide which are highly active under UV light irradiations. It is also suggested that the prepared material would find wider applications in environmental remediation technologies to remove the carcinogenic and toxic moieties present in the industrial effluents. PMID:26025644

  1. Reactions of xenon with iron and nickel are predicted in the Earth's inner core.

    PubMed

    Zhu, Li; Liu, Hanyu; Pickard, Chris J; Zou, Guangtian; Ma, Yanming

    2014-07-01

    Studies of the Earth's atmosphere have shown that more than 90% of the expected amount of Xe is depleted, a finding often referred to as the 'missing Xe paradox'. Although several models for a Xe reservoir have been proposed, whether the missing Xe could be contained in the Earth's inner core has not yet been answered. The key to addressing this issue lies in the reactivity of Xe with Fe/Ni, the main constituents of the Earth's core. Here, we predict, through first-principles calculations and unbiased structure searching techniques, a chemical reaction of Xe with Fe/Ni at the temperatures and pressures found in the Earth's core. We find that, under these conditions, Xe and Fe/Ni can form intermetallic compounds, of which XeFe3 and XeNi3 are energetically the most stable. This shows that the Earth's inner core is a natural reservoir for Xe storage and provides a solution to the missing Xe paradox. PMID:24950336

  2. Rare earth-copper-magnesium compounds RECu 9Mg 2 ( RE=Y, La-Nd, Sm-Ho, Yb) with ordered CeNi 3-type structure

    NASA Astrophysics Data System (ADS)

    Solokha, P.; Pavlyuk, V.; Saccone, A.; De Negri, S.; Prochwicz, W.; Marciniak, B.; Różycka-Sokołowska, E.

    2006-10-01

    A series of ternary compounds RECu 9Mg 2 ( RE=Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Yb) have been synthesized via induction melting of elemental metal ingots followed by annealing at 400 °C for 4 weeks. Scanning electron microscopy (SEM) coupled with energy dispersive X-ray spectroscopy (EDXS) was used for examining microstructure and phase composition. These phases crystallize with an ordered version of the binary hexagonal structure type first reported for CeNi 3. The crystal structure was solved for TbCu 9Mg 2 from single crystal X-ray counter data (TbCu 9Mg 2-structure type, P6 3/mmc-space group, hP24-Pearson symbol, a=0.49886 (7) nm, c=1.61646 (3) nm, RF=0.0474 for 190 unique reflections). The Rietveld refinement of the X-ray powder diffraction patterns of RECu 9Mg 2 confirmed the same crystal structure for the reported rare earth metals. The unit cell volumes for RECu 9Mg 2 smoothly follow the lanthanide contraction. The existence of a RECu 9Mg 2 phase was excluded for RE=Er and Tm under the investigated experimental conditions.

  3. Crystal structures of three intermetallic phases in the Mo-Pt-Si system

    SciTech Connect

    Joubert, J.-M.; Tokaychuk, Ya.; Cerny, R.

    2010-01-15

    The crystal structures of three ternary Mo-Pt-Si intermetallic compounds have been determined ab initio from powder X-ray diffraction data. All three structures are representative of new structure types. Both the X (MoPt{sub 2}Si{sub 3}, Pmc2{sub 1}, oP12, a=3.48438(6), b=9.1511(2), c=5.48253(8) A) and Y (MoPt{sub 3}Si{sub 4}, Pnma, oP32, a=5.51210(9), b=3.49474(7), c=24.3090(4) A) phases derive from PtSi (FeAs type) structure while the Z phase (ideal composition Mo{sub 32}Pt{sub 20}Si{sub 16}, refined composition Mo{sub 29.9(2)}Pt{sub 21.0(3)}Si{sub 17.1(1)}, Cc, mC68, a=13.8868(3), b=8.0769(2), c=9.6110(2) A, beta=100.898(1){sup o}) present similarities with the group of Frank-Kasper phases. - Graphical abstract: The crystal structures of three ternary Mo-Pt-Si intermetallic compounds have been determined ab initio from powder X-ray diffraction data. The three structures represent new structure types.

  4. High temperature intermetallic binders for HVOF carbides

    SciTech Connect

    Shaw, K.G.; Gruninger, M.F.; Jarosinski, W.J.

    1994-12-31

    Gas turbines technology has a long history of employing the desirable high temperature physical attributes of ceramic-metallic (cermet) materials. The most commonly used coatings incorporate combinations of WC-Co and Cr{sub 3}C{sub 2}-NiCr, which have also been successfully utilized in other non-turbine coating applications. Increased turbine operating temperatures and other high temperature service conditions have made apparent the attractive notion of increasing the temperature capability and corrosion resistance of these coatings. In this study the intermetallic binder NiAl has been used to replace the cobalt and NiCr constituents of conventional WC and Cr{sub 3}C{sub 2} cermet powders. The composite carbide thermal spray powders were fabricated for use in the HVOF coating process. The structure of HVOF deposited NiAl-carbide coatings are compared directly to the more familiar WC-Co and Cr{sub 3}C{sub 2}-NiCr coatings using X-ray diffraction, back-scattered electron imaging (BEI) and electron dispersive spectroscopy (EDS). Hardness variations with temperature are reported and compared between the NiAl and Co/NiCr binders.

  5. Ground state searches in fcc intermetallics

    SciTech Connect

    Wolverton, C.; de Fontaine, D. ); Ceder, G. ); Dreysse, H. . Lab. de Physique du Solide)

    1991-12-01

    A cluster expansion is used to predict the fcc ground states, i.e., the stable phases at zero Kelvin as a function of composition, for alloy systems. The intermetallic structures are not assumed, but derived regorously by minimizing the configurational energy subject to linear constraints. This ground state search includes pair and multiplet interactions which spatially extend to fourth nearest neighbor. A large number of these concentration-independent interactions are computed by the method of direct configurational averaging using a linearized-muffin-tin orbital Hamiltonian cast into tight binding form (TB-LMTO). The interactions, derived without the use of any adjustable or experimentally obtained parameters, are compared to those calculated via the generalized perturbation method extention of the coherent potential approximation within the context of a KKR Hamiltonian (KKR-CPA-GPM). Agreement with the KKR-CPA-GPM results is quite excellent, as is the comparison of the ground state results with the fcc-based portions of the experimentally-determined phase diagrams under consideration.

  6. Thermal stress effects in intermetallic matrix composites

    NASA Technical Reports Server (NTRS)

    Wright, P. K.; Sensmeier, M. D.; Kupperman, D. S.; Wadley, H. N. G.

    1993-01-01

    Intermetallic matrix composites develop residual stresses from the large thermal expansion mismatch (delta-alpha) between the fibers and matrix. This work was undertaken to: establish improved techniques to measure these thermal stresses in IMC's; determine residual stresses in a variety of IMC systems by experiments and modeling; and, determine the effect of residual stresses on selected mechanical properties of an IMC. X ray diffraction (XRD), neutron diffraction (ND), synchrotron XRD (SXRD), and ultrasonics (US) techniques for measuring thermal stresses in IMC were examined and ND was selected as the most promising technique. ND was demonstrated on a variety of IMC systems encompassing Ti- and Ni-base matrices, SiC, W, and Al2O3 fibers, and different fiber fractions (Vf). Experimental results on these systems agreed with predictions of a concentric cylinder model. In SiC/Ti-base systems, little yielding was found and stresses were controlled primarily by delta-alpha and Vf. In Ni-base matrix systems, yield strength of the matrix and Vf controlled stress levels. The longitudinal residual stresses in SCS-6/Ti-24Al-llNb composite were modified by thermomechanical processing. Increasing residual stress decreased ultimate tensile strength in agreement with model predictions. Fiber pushout strength showed an unexpected inverse correlation with residual stress. In-plane shear yield strength showed no dependence on residual stress. Higher levels of residual tension led to higher fatigue crack growth rates, as suggested by matrix mean stress effects.

  7. Bulk and defect properties of ordered intermetallics

    SciTech Connect

    Fu, C.L.; Yoo, M.H.

    1993-12-31

    First-principles calculations based on the local-density-functional theory have been used to investigate the factors governing strength of ordered intermetallic alloys. Unlike Ni{sub 3}Al, calculated elastic constants and shear fault energies indicate anomalous yield strength behavior is not likely to occur in Ni{sub 3}Si. This suggests the inadequacy of cross-slip-pinning model to explain the strength anomaly in the L1{sub 2} structure. For strongly ordered NiAl, the defect structure is dominated by two types of defects -- monovacancies on the Ni sites and substitutional antisite defects on the Al sites. By contrast, for Ni{sub 3}Al, absence of structural vacancies and deviations from stoichiometry are accommodated by substitutional antisite defects on both sublattices. Intrinsic strengthening mechanisms in TiAl are discussed in terms of calculated elastic constants and shear fault energies. Because of reduced fault energies at the {gamma}/{alpha}{sub 2} interface, slip and twinning contribute significantly to high shear deformation of the lamellar structure.

  8. SCB ignition of pyrotechnics, thermites and intermetallics

    SciTech Connect

    Bickes, R.W. Jr.; Grubelich, M.C.

    1996-09-01

    We investigated ignition of pyrotechnics, metal-fuel/metal-oxide compositions (thermites), and exothermic alloy compositions (intermetallics) using a semiconductor bridge (SCB). It was shown that these materials could be ignited at low energy levels with an appropriately designed SCB, proper loading density, and good thermal isolation. Materials tested included Al/CuO, B/BaCrO{sub 4}, TiH{sub 1.65}/KClO{sub 4}, Ti/KClO{sub 4}, Zr/BaCrO{sub 4}, Zr/CuO, Zr/Fe{sub 2}O{sub 3}, Zr/KClO{sub 4}, and 100-mesh Al/Pd. Firing set was a capacitor discharge unit with charge capacitors ranging from 3 to 20,000 {mu}F at charge voltages 5-50 V. Devices functioned a few miliseconds after onset of current pulse at input energies as low as 3 mJ. We also report on a thermite torch design.

  9. RE(AuAl2)nAl2(AuxSi1-x)2: a new homologous series of quaternary intermetallics grown from aluminum flux.

    PubMed

    Latturner, Susan E; Kanatzidis, Mercouri G

    2008-03-17

    The combination of early rare earth metals (La- to Gd and Yb), gold, and silicon in molten aluminum results in the formation of intermetallic compounds with four related structures, forming a new homologous series: RE[AuAl2]nAl2(AuxSi(1-x))2, with x approximately 0.5 for most of the compound and n = 0, 1, 2, and 3. Because of the highly reducing nature of the Al flux, rare earth oxides instead of metals can also be used in these reactions. These compounds grow as large plate-like crystals and have tetragonal structure types that can be viewed as intergrowths of the BaAl4 structure and antifluorite-type AuAl2 layers. REAuAl2Si materials form with the BaAl4 structure type in space group I4/mmm (cell parameters for the La analogue are a = 4.322(2) A, c = 10.750(4) A, and Z = 2). REAu2Al4Si forms in a new ordered superstructure of the KCu4S3 structure type, with space group P4/nmm and cell parameters of the La analogue of a = 6.0973(6) A, c = 8.206(1) A, and Z = 2. REAu3Al6Si forms in a new I4/mmm symmetry structure type with cell parameters of a = 4.2733(7) A, c = 22.582(5) A, and Z = 2 for RE = Eu. The end member of the series, REAu4Al8Si, forms in space group P4/mmm with cell parameters for the Yb analogue of a = 4.2294(4) A, c = 14.422(2) A, and Z = 1. New intergrowth structures containing two different kinds of AuAl2 layers were also observed. The magnetic behavior of all these compounds is derived from the RE ions. Comparison of the susceptibility data for the europium compounds indicates a switch from 3-D magnetic interactions to 2-D interactions as the size of the AuAl2 layer increases. The Yb ions in YbAu(2.91)Al(6)Si(1.09) and YbAu(3.86)Al(8)Si(1.14) are divalent at high temperatures. PMID:18198865

  10. Process for synthesizing compounds from elemental powders and product

    DOEpatents

    Rabin, B.H.; Wright, R.N.

    1993-12-14

    A process for synthesizing intermetallic compounds from elemental powders is described. The elemental powders are initially combined in a ratio which approximates the stoichiometric composition of the intermetallic compound. The mixed powders are then formed into a compact which is heat treated at a controlled rate of heating such that an exothermic reaction between the elements is initiated. The heat treatment may be performed under controlled conditions ranging from a vacuum (pressureless sintering) to compression (hot pressing) to produce a desired densification of the intermetallic compound. In a preferred form of the invention, elemental powders of Fe and Al are combined to form aluminide compounds of Fe[sub 3] Al and FeAl. 25 figures.

  11. Intermetallic and ceramic matrix composites for 815 to 1370 C (1500 to 2500F) gas turbine engine applications

    SciTech Connect

    Stephens, J.R.

    1989-01-01

    Light weight and potential high temperature capability of intermetallic compounds, such as the aluminides, and structural ceramics, such as the carbides and nitrides, make these materials attractive for gas turbine engine applications. In terms of specific fuel consumption and specific thrust, revolutionary improvements over current technology are being sought by realizing the potential of these materials through their use as matrices combined with high strength, high temperature fibers. The U.S. along with other countries throughout the world have major research and development programs underway to characterize these composites materials; improve their reliability; identify and develop new processing techniques, new matrix compositions, and new fiber compositions; and to predict their life and failure mechanisms under engine operating conditions. The status is summarized of NASA's Advanced High Temperature Engine Materials Technology Program (HITEMP) and the potential benefits are described to be gained in 21st century transport aircraft by utilizing intermetallic and ceramic matrix composite materials.

  12. Intermetallic and ceramic matrix composites for 815 to 1370 C (1500 to 2500 F) gas turbine engine applications

    NASA Technical Reports Server (NTRS)

    Stephens, Joseph R.

    1989-01-01

    Light weight and potential high temperature capability of intermetallic compounds, such as the aluminides, and structural ceramics, such as the carbides and nitrides, make these materials attractive for gas turbine engine applications. In terms of specific fuel consumption and specific thrust, revolutionary improvements over current technology are being sought by realizing the potential of these materials through their use as matrices combined with high strength, high temperature fibers. The U.S. along with other countries throughout the world have major research and development programs underway to characterize these composites materials; improve their reliability; identify and develop new processing techniques, new matrix compositions, and new fiber compositions; and to predict their life and failure mechanisms under engine operating conditions. The status is summarized of NASA's Advanced High Temperature Engine Materials Technology Program (HITEMP) and the potential benefits are described to be gained in 21st century transport aircraft by utilizing intermetallic and ceramic matrix composite materials.

  13. Antiferromagnetic Kondo lattice in the layered compounds Re2NiGa9Ge2 (Re =Ce, Pr, Sm)

    NASA Astrophysics Data System (ADS)

    Zhu, Yanglin; Liu, Jinyu; Hu, Jin; Adams, Daniel; Spinu, Leonard; Mao, Zhiqiang

    Intermetallic compounds containing rare-earth/actinide elements with 4f/5f electrons have formed a special family of strongly correlated materials, i.e. heavy fermion systems. We have recently found a new layered rare earth intermetallic system showing moderate heavy fermion behavior: Re2NiGa9Ge2 (Re =Ce, Sm, Pr). The Re =Ce and Sm members were previously synthesized, while their electronic properties have not been reported. We have recently grown single crystals of Re2NiGa9Ge2 (Re =Ce, Sm, Pr) and characterized their electronic and magnetic properties. We find all these materials are antiferromagnetic, with TN = 2.5 K, 5 K, 3.4 K respectively for Re =Ce, Pr and Sm. Moreover, they also exhibit large values of electronic specific coefficient: γ ~ 101 mJ mol-Ce-1 K-2 for Re =Ce, 368 mJ mol-Pr-1 K-2 for Re =Pr, and 196.4 mJ mol-Sm-1 K-2 for Re =Sm, indicating enhanced Kondo effect and the presence of AFM Kondo lattice. Our findings suggest that Re2NiGa9Ge2 (Re =Ce, Pr, Sm) could be interesting candidate materials for exploring novel exotic properties of correlated electrons through external parameter tuning such as chemical substitution and pressure.

  14. Electronic structure, elasticity, bonding features and mechanical behaviour of zinc intermetallics: A DFT study

    NASA Astrophysics Data System (ADS)

    Fatima, Bushra; Acharya, Nikita; Sanyal, Sankar P.

    2016-05-01

    The structural stability, electronic structure, elastic and mechanical properties of TiZn and ZrZn intermetallics have been studied using ab-initio full potential linearized augmented plane wave (FP-LAPW) method within generalized gradient approximation for exchange and correlation potentials. The various structural parameters, such as lattice constant (a0), bulk modulus (B), and its pressure derivative (B') are analysed and compared. The investigation of elastic constants affirm that both TiZn and ZrZn are elastically stable in CsCl (B2 phase) structure. The electronic structures have been analysed quantitatively from the band structure which reveals the metallic nature of these compounds. To better illustrate the nature of bonding and charge transfer, we have also studied the Fermi surfaces. The three well known criterion of ductility namely Pugh's rule, Cauchy's pressure and Frantsevich rule elucidate the ductile nature of these compounds.

  15. Multiconfigurational nature of 5f orbitals in uranium and plutonium intermetallics

    PubMed Central

    Booth, C.H.; Jiang, Yu; Wang, D.L.; Mitchell, J.N.; Tobash, P.H.; Bauer, E.D.; Wall, M.A.; Allen, P.G.; Sokaras, D.; Nordlund, D.; Weng, T.-C.; Torrez, M.A.; Sarrao, J.L.

    2012-01-01

    Uranium and plutonium’s 5f electrons are tenuously poised between strongly bonding with ligand spd-states and residing close to the nucleus. The unusual properties of these elements and their compounds (e.g., the six different allotropes of elemental plutonium) are widely believed to depend on the related attributes of f-orbital occupancy and delocalization for which a quantitative measure is lacking. By employing resonant X-ray emission spectroscopy (RXES) and X-ray absorption near-edge structure (XANES) spectroscopy and making comparisons to specific heat measurements, we demonstrate the presence of multiconfigurational f-orbital states in the actinide elements U and Pu and in a wide range of uranium and plutonium intermetallic compounds. These results provide a robust experimental basis for a new framework toward understanding the strongly-correlated behavior of actinide materials. PMID:22706643

  16. Synthesis of cerium rich intermetallics using molten metal eutectics

    NASA Astrophysics Data System (ADS)

    Tucker, Patricia Christine

    Metal eutectic fluxes are useful for exploratory synthesis of new intermetallic phases. In this work the use of cerium/transition metal eutectics such as: Ce/Co, Ce/Ni, and Ce/Fe have yielded many new synthetically and magnetically complex phases. Structural units that were previously observed in phases grown in La/Ni eutectic reactions have also been observed in new structures and analogs grown from cerium/transition metal eutectics. These structural units include a main group element coordinated by 9 rare-earth atoms (such as the Al Ce9 clusters seen in Ce31.0(2)Fe11.8(5)Al6.5(6) B13C4), trigonal planar FeC3 units (also seen in Ce31.0(2)Fe11.8(5)Al6.5(6)B 13C4), iron clusters capped by light elements (Fe4C 6 frustrated tetrahedral in Ce21Fe8M7C 14, and larger Fe clusters in Ce33Fe14B25 C34). Variants of these building blocks were observed in Ce10Co2B7C16 with square Co units and chains of B and C connected to them, Fe2C8 units observed in Ce7Fe2C9, and FeC4 observed in Ce4FeGa0.85Al0.15C4 and Ce4FeAlC4. Two new phases were grown from Ce/Fe eutectic, Ce33Fe 14B25C34 and Ce33Fe13B 18C34 which exhibits very similar structures, but significantly different magnetic behavior. Structurally these two phases are similar. Both crystallize in the Im-3m space group, but differ by the centering of the Fe clusters. Ce33Fe14B25C34 contains Fe clusters centered by B atoms and Al doped on the Fe2 site. In Ce33Fe13B18C34, the Fe cluster is a perfect cuboctahedron. Ce33Fe14B25 C34 exhibits mixed valent behavior of cerium at 75K and no magnetic moment on iron, where-as Ce33Fe13B18C 34 exhibits tetravalent cerium and its iron clusters undergo a ferromagnetic transition at 180K. Another borocarbide, Ce10Co2B7C 16 was synthesized from Ce/Co eutectic flux. This structure features squares of Co surrounded by chains of C and B and a sea of cerium atoms. Temperature dependent magnetic susceptibility measurements at 1 Tesla were fit to a modified Curie-Weiss law and a moment per Ce was

  17. Phase stability in processing of high temperature intermetallic alloys

    SciTech Connect

    Perepezko, J.H.; Nunes, C.A.; Yi, S.H.; Thoma, D.J.

    1997-12-31

    In the development of high temperature intermetallics involving various aluminides, silicides and Laves phases, it has become evident that it is essential to consider the strong influence of materials processing throughout all stages. The underlying basis for alloy synthesis, processing and the assessment of thermal stability is established by the relevant phase equilibria, the characteristic diffusivities and the possible solidification reaction pathways. In almost all cases the microstructures of the most useful metallic alloys are multiphase assemblies in which the relative phase fractions, compositions and morphologies play key roles in optimizing the performance under high temperature conditions. The microstructure designs are usually tailored for strength, toughness, creep resistance and environmental stability and involve a balance of features derived from mixtures of a ductile phase and intermetallic phases. There is a clear experience that the level of materials processing can only be as sophisticated as the level of knowledge of the phase equilibria and the underlying kinetics. In many of the contemporary intermetallic alloys the phase stability must be considered in terms of multicomponent equilibria and non-stoichiometric intermetallic compositions. Recent developments in several important intermetallic alloy classes illustrate the guidance into alloy design and processing options provided by systematic studies of phase stability. 58 refs., 7 figs.

  18. New A2/3-xRh2O4 compounds with the CaFe2O4 structure where A is a rare earth or Bi.

    PubMed

    Mizoguchi, Hiroshi; Zakharov, L N; Ramirez, A P; Marshall, W J; Sleight, A W; Subramanian, M A

    2009-01-01

    New compounds of the type R(2/3-x)Rh(2)O(4) with the CaFe(2)O(4) structure have been prepared, where R is a rare earth. For crystals grown in a Bi/V/O flux, the rare earth was partially replaced by Bi. No evidence of ordering of the A cation vacancies is found, but the A cations are displaced from the ideal A cation site by about 0.24 A. Electrical conductivity measurements on crystals suggest that the materials are degenerate semiconductors with Seebeck measurements showing p-type behavior. This is consistent with our observation that x in R(2/3-x)Rh(2)O(4) ranges up to about 0.09. The compounds were also characterized by magnetic susceptibility and diffuse reflectance measurements. PMID:19049419

  19. Intermetallic alloy welding wires and method for fabricating the same

    DOEpatents

    Santella, M.L.; Sikka, V.K.

    1996-06-11

    Welding wires for welding together intermetallic alloys of nickel aluminides, nickel-iron aluminides, iron aluminides, or titanium aluminides, and preferably including additional alloying constituents are fabricated as two-component, clad structures in which one component contains the primary alloying constituent(s) except for aluminum and the other component contains the aluminum constituent. This two-component approach for fabricating the welding wire overcomes the difficulties associated with mechanically forming welding wires from intermetallic alloys which possess high strength and limited ductilities at elevated temperatures normally employed in conventional metal working processes. The composition of the clad welding wires is readily tailored so that the welding wire composition when melted will form an alloy defined by the weld deposit which substantially corresponds to the composition of the intermetallic alloy being joined. 4 figs.

  20. Intermetallic alloy welding wires and method for fabricating the same

    DOEpatents

    Santella, Michael L.; Sikka, Vinod K.

    1996-01-01

    Welding wires for welding together intermetallic alloys of nickel aluminides, nickel-iron aluminides, iron aluminides, or titanium aluminides, and preferably including additional alloying constituents are fabricated as two-component, clad structures in which one component contains the primary alloying constituent(s) except for aluminum and the other component contains the aluminum constituent. This two-component approach for fabricating the welding wire overcomes the difficulties associated with mechanically forming welding wires from intermetallic alloys which possess high strength and limited ductilities at elevated temperatures normally employed in conventional metal working processes. The composition of the clad welding wires is readily tailored so that the welding wire composition when melted will form an alloy defined by the weld deposit which substantially corresponds to the composition of the intermetallic alloy being joined.

  1. New rare-earth metal germanides with bismuth substitution. Synthesis, structural variations, and magnetism of the RE[Bi{sub x}Ge{sub 1-x}]{sub 2} (RE=Y, Pr, Nd, Sm, Gd-Tm, Lu) compounds

    SciTech Connect

    Zhang, Jiliang; Hmiel, Benjamin; Antonelli, Anthony; Tobash, Paul H.; Bobev, Svilen; Saha, Shanta; Kirshenbaum, Kevin; Greene, Richard L.; Paglione, Johnpierre

    2012-12-15

    Single-crystals of the novel rare-earth metal-bismuth digermanides with idealized formula RE[Bi{sub x}Ge{sub 1-x}]{sub 2} (RE=Y, Pr, Nd, Sm, Gd-Tm, Lu; x<0.16(1)) have been obtained using the Bi-flux technique. Their structures have been established by single-crystal X-ray diffraction; they can be divided into three classes, closely related to the ZrSi{sub 2} structure with the space group Cmcm (no. 63). The structural relationship and the variations with the type of the rare-earth metal have been explored and discussed. Temperature-dependent magnetization measurements on the single-crystals reveal magnetic behavior, which have been rationalized based on the mean-field theory. At cryogenic temperatures, the localized 4f electrons in most of the compounds exhibit antiferromagnetic ordering, mediated by the conduction electrons via Ruderman-Kittel-Kasuya-Yosida (RKKY) exchange interactions. - Graphical abstract: This paper details the synthesis and the structural characterization of an extended series of rare-earth metal-bismuth-germanides RE[Bi{sub x}Ge{sub 1-x}]{sub 2} (RE=Y, Pr-Sm, Gd-Tm, Lu). They crystallize with the same extended symmetry (space group Cmcm), but with three distinct structures, which are closely related. Magnetization measurements show low-temperature antiferromagnetic ordering. RE[Bi{sub x}Ge{sub 1-x}]{sub 2} are the first compounds between these elements. Highlights: Black-Right-Pointing-Pointer RE[Bi{sub x}Ge{sub 1-x}]{sub 2} (RE=rare-earth metal) are the first compounds of the respective elements. Black-Right-Pointing-Pointer Their structures are closely related. Black-Right-Pointing-Pointer Three structures can be distinguished based on the packing of the REGe{sub 6} triangular prisms. Black-Right-Pointing-Pointer All compounds show low-temperature antiferromagnetic ordering.

  2. Crystal Structure, Chemical Bonding and Magnetism Studies for Three Quinary Polar Intermetallic Compounds in the (Eu1−xCax)9In8(Ge1−ySny)8 (x = 0.66, y = 0.03) and the (Eu1−xCax)3In(Ge3−ySn1+y) (x = 0.66, 0.68; y = 0.13, 0.27) Phases

    PubMed Central

    Woo, Hyein; Jang, Eunyoung; Kim, Jin; Lee, Yunho; Kim, Jongsik; You, Tae-Soo

    2015-01-01

    Three quinary polar intermetallic compounds in the (Eu1−xCax)9In8(Ge1−ySny)8 (x = 0.66, y = 0.03) and the (Eu1−xCax)3In(Ge3-ySn1+y) (x = 0.66, 0.68; y = 0.13, 0.27) phases have been synthesized using the molten In-metal flux method, and the crystal structures are characterized by powder and single-crystal X-ray diffractions. Two orthorhombic structural types can be viewed as an assembly of polyanionic frameworks consisting of the In(Ge/Sn)4 tetrahedral chains, the bridging Ge2 dimers, either the annulene-like “12-membered rings” for the (Eu1−xCax)9In8(Ge1−ySny)8 series or the cis-trans Ge/Sn-chains for the (Eu1−xCax)3In(Ge3−ySn1+y) series, and several Eu/Ca-mixed cations. The most noticeable difference between two structural types is the amount and the location of the Sn-substitution for Ge: only a partial substitution (11%) occurs at the In(Ge/Sn)4 tetrahedron in the (Eu1−xCax)9In8(Ge1−ySny)8 series, whereas both a complete and a partial substitution (up to 27%) are observed, respectively, at the cis-trans Ge/Sn-chain and at the In(Ge/Sn)4 tetrahedron in the (Eu1−xCax)3In(Ge3−ySn1+y) series. A series of tight-binding linear muffin-tin orbital calculations is conducted to understand overall electronic structures and chemical bonding among components. Magnetic susceptibility measurement indicates a ferromagnetic ordering of Eu atoms below 5 K for Eu1.02(1)Ca1.98InGe2.87(1)Sn1.13. PMID:25913380

  3. Stress distribution in a continuously cast intermetallic strip

    NASA Astrophysics Data System (ADS)

    Roy, George; Wronski, Zbignew; Sahoo, Mahi; Kiff, Dave

    Results of a study on the determination of the residual stress state in a nickel aluminide intermetallic strip by the hole drilling method (HDM) are presented. Special correlation functions that relate the relaxed surface strain and the original stresses before drilling were developed. It is shown that the HDM may be used to determine residual stresses in anisotropic materials such as intermetallic strips. The results indicate that a complex stress field develops through the thickness and across the width of the strip. However, a suitable thermomechanical treatment may be applied to redistribute the stresses before aluminide strips can be used to make engineering components.

  4. Observations of a dynamical-to-kinematic diffraction transition in plastically deformed polycrystalline intermetallic YCu

    SciTech Connect

    Williams, Scott H.; Brown, Donald W.; Clausen, Bjorn; Russell, Alan; Gschneidner Jr., Karl A.

    2014-03-01

    Unlike most intermetallic compounds, polycrystalline YCu, a B2 (CsCl-type) intermetallic, is ductile at room temperature. The mechanisms for this behavior are not fully understood. In situ neutron diffraction was used to investigate whether a stress-induced phase transformation or twinning contribute to the ductility; however, neither mechanism was found to be active in YCu. Surprisingly, this study revealed that the intensities of the diffraction peaks increased after plastic deformation. It is thought that annealing the samples created nearly perfect crystallinity, and subsequent deformation reduced this high degree of lattice coherency, resulting in a modified mosaic structure that decreased or eliminated the extinction effect. Analysis of changes in diffraction peak intensity showed a region of primary plasticity that exhibits significant changes in diffraction behavior. Fully annealed samples initially contain diffracting volumes large enough to follow the dynamical theory of diffraction. When loaded beyond the yield point, dislocation motion disrupts the lattice perfection, and the diffracting volume is reduced to the point that diffraction follows the kinematic theory of diffraction. Since the sample preparation and deformation mechanisms present in this study are common in numerous material systems, this dynamical to kinematic diffraction transition should also be considered in other diffraction experiments. These measurements also suggest the possibility of a new method of investigating structural characteristics. (C) 2014 Published by Elsevier Ltd. on behalf of Acta Materialia Inc.

  5. Femtosecond laser ablation and nanoparticle formation in intermetallic NiAl

    NASA Astrophysics Data System (ADS)

    Jorgensen, David J.; Titus, Michael S.; Pollock, Tresa M.

    2015-10-01

    The ablation behavior of a stoichiometric intermetallic compound β-NiAl subjected to femtosecond laser pulsing in air has been investigated. The single-pulse ablation threshold for NiAl was determined to be 83 ± 4 mJ/cm2 and the transition to the high-fluence ablation regime occurred at 2.8 ± 0.3 J/cm2. Two sizes of nanoparticles consisting of Al, NiAl, Ni3Al and NiO were formed and ejected from the target during high-fluence ablation. Chemical analysis revealed that smaller nanoparticles (1-30 nm) tended to be rich in Al while larger nanoparticles (>100 nm) were lean in Al. Ablation in the low-fluence regime maintained this trend. Redeposited material and nanoparticles remaining on the surface after a single 3.7 J/cm2 pulse, one hundred 1.7 J/cm2 pulses, or one thousand 250 mJ/cm2 pulses were enriched in Al relative to the bulk target composition. Further, the surface of the irradiated high-fluence region was depleted in Al indicating that the fs laser ablation removal rate of the intermetallic constituents in this regime does not scale with the individual pure element ablation thresholds.

  6. Mixed-metal flux synthesis of quaternary RMn{sub 2} Tr{sub x} Zn{sub 20-} {sub x} compounds with Tr=Al, In

    SciTech Connect

    Benbow, Evan M. . E-mail: ebenbow@chem.fsu.edu; Latturner, Susan E. . E-mail: latturne@chem.fsu.edu

    2006-12-15

    Eighteen new intermetallic compounds RMn{sub 2} Tr{sub x} Zn{sub 20-} {sub x} (2earth metal; Tr=Al, In) were synthesized using low-melting mixtures of (Tr/Zn) as a solvent. Structural refinementng single-crystal X-ray diffraction data shows that the compounds are substituted variants of the cubic CeCr{sub 2}Al{sub 20}-type structure (Fd-3m, Z=8; unit cell parameters vary from a=14.1152(3)A for YbMn{sub 2}Al{sub 5.3}Zn{sub 14.7} to a=14.8125(4)A for SmMn{sub 2}In{sub 5.9}Zn{sub 14.1}). The Zn and Tr elements show site preferences in the indium compounds, but not in the aluminum analogs. The substitution of trielide element for zinc modifies the valence electron count of the compounds to allow for the incorporation of Mn into the structure. Magnetic susceptibility data show no evidence of magnetic ordering down to 3 K. - Graphical Abstract: Crystals of new intermetallic phases RMn{sub 2} Tr{sub x} Zn{sub 20-} {sub x} (Tr=Al or In; R=rare earth) were grown from Al/Zn or In/Zn flux mixtures. These compounds are quaternary variants of the CeCr{sub 2}Al{sub 20} structure type. This structure can be viewed as a packing of polyhedra, as shown.

  7. Quaternary borocarbides: Relatively high Tc intermetallic superconductors and magnetic superconductors

    NASA Astrophysics Data System (ADS)

    Mazumdar, Chandan; Nagarajan, R.

    2015-07-01

    Discovery of superconductivity in Y-Ni-B-C (Tc ∼ 13 K) gave rise to the class of quaternary rare earth transition metal borocarbide superconductors. Before the discovery of Fe-based arsenide superconductors, this was the only class of materials containing a magnetic element, viz., Ni, yet exhibiting Tcs > 5 K. Many members of this class have high Tc (>10 K). Tc of ∼23 K in Y-Pd-B-C system equaled the record Tc known then, for intermetallics. Another feature that sets this class apart, is the occurrence of the exotic phenomenon of coexistence of superconductivity and magnetism at temperatures >5 K. Availability of large and electronically 'clean' single crystals and large Ginzburg-Landau (G-L) parameter, κ, have enabled detailed investigation of nonlocal effects of superconductivity. Intermediate value of upper critical field Hc2, has enabled detailed investigation of superconductivity in this class, over the complete H-T plane. This has revealed details of anisotropy of superconductivity (e.g., a fourfold symmetry in the square a-b plane is found) and raised questions on the symmetry of order parameter. After a brief outline of the discovery, this article gives a summary of the materials and highlights of superconducting properties of this class of materials. Interesting results from studies, using various techniques, on YNi2B2C (Tc ∼ 15 K) and LuNi2B2C (Tc ∼ 16 K) are presented, including observation of unusual square vortex lattice and its structural transformation with H and T. With conduction electrons involved in the magnetic order of this class of superconductors, the interplay of superconductivity and magnetism is intimate in these magnetic superconductors. With Tc (∼11 K) > TN (∼6 K) in ErNi2B2C, Tc (∼8 K) = TN (∼8 K) in HoNi2B2C and Tc (∼6 K) < TN (∼11 K) in DyNi2B2C, and with other parameters being favorable as mentioned earlier, this class of magnetic superconductors have become ideal materials to investigate the coexistence

  8. Erosion behavior of Fe-Al intermetallic alloys

    SciTech Connect

    Kim, Y.S.; Song, J.H.; Chang, Y.W.

    1997-04-01

    The Fe-rich Fe-Al intermetallics have generated some interest, especially during the last decade, due to their excellent resistance for oxidation and sulfidation, high specific strength, and low material cost. The aluminide is therefore considered as one of the promising candidates for high-temperature structural materials in a corrosive atmosphere. Research effort has been focused mainly on process, development, and enhancement of room-temperature ductility together with the characterization of physical properties such as mechanical properties, oxidation, corrosion, and abrasive wear behavior. However, there have been only a few works reported to date in regard to the erosion characteristics of the alloy, one of the most important material property of this ordered intermetallic alloy for the use in a fossil-fuel plant. In this study, the solid-particle erosion behavior of the Fe-Al intermetallic alloys containing the various aluminum contents ranging from 25 to 30 at.% has been investigated to clarify the effect of aluminum content and different ordered structures, viz. DO{sub 3} and B2, on the erosion behavior. An attempt has been made to correlate the erosion behavior of these intermetallics to their mechanical properties by carrying out tensile tests together with SEM observation of the eroded surfaces.

  9. Electrocatalytic activity of ordered intermetallic phases for fuel cell applications.

    PubMed

    Casado-Rivera, Emerilis; Volpe, David J; Alden, Laif; Lind, Cora; Downie, Craig; Vázquez-Alvarez, Terannie; Angelo, Antonio C D; DiSalvo, Francis J; Abruña, Héctor D

    2004-03-31

    The electrocatalytic activities of a wide range of ordered intermetallic phases toward a variety of potential fuels have been studied, and results have been compared to those of a pure polycrystalline platinum (Pt(pc)) electrode. A significant number of the ordered intermetallic phases exhibited enhanced electrocatalytic activity when compared to that of Pt, in terms of both oxidation onset potential and current density. The PtBi, PtIn, and PtPb ordered intermetallic phases appeared to be the most promising electrocatalysts tested thus far for fuel cell applications. PtPb, in particular, showed an onset potential that was 100 mV less positive and a peak current density approximately 40 times higher than those observed for Pt in the case of methanol oxidation. The ability to control the geometric and electronic structures of the electrocatalytic material by using ordered intermetallic phases has been shown to be a promising direction of inquiry in the search for superior electrocatalysts for fuel cell applications. PMID:15038758

  10. Intermetallic Phase Formation in Explosively Welded Al/Cu Bimetals

    NASA Astrophysics Data System (ADS)

    Amani, H.; Soltanieh, M.

    2016-05-01

    Diffusion couples of aluminum and copper were fabricated by explosive welding process. The interface evolution caused by annealing at different temperatures and time durations was investigated by means of optical microscopy, scanning electron microscopy equipped with energy dispersive spectroscopy, and x-ray diffraction. Annealing in the temperature range of 573 K to 773 K (300 °C to 500 °C) up to 408 hours showed that four types of intermetallic layers have been formed at the interface, namely Al2Cu, AlCu, Al3Cu4, and Al4Cu9. Moreover, it was observed that iron trace in aluminum caused the formation of Fe-bearing intermetallics in Al, which is near the interface of the Al-Cu intermetallic layers. Finally, the activation energies for the growth of Al2Cu, AlCu + Al3Cu4, Al4Cu9, and the total intermetallic layer were calculated to be about 83.3, 112.8, 121.6, and 109.4 kJ/mol, respectively. Considering common welding methods (i.e., explosive welding, cold rolling, and friction welding), although there is a great difference in welding mechanism, it is found that the total activation energy is approximately the same.

  11. Intermetallic Phase Formation in Explosively Welded Al/Cu Bimetals

    NASA Astrophysics Data System (ADS)

    Amani, H.; Soltanieh, M.

    2016-08-01

    Diffusion couples of aluminum and copper were fabricated by explosive welding process. The interface evolution caused by annealing at different temperatures and time durations was investigated by means of optical microscopy, scanning electron microscopy equipped with energy dispersive spectroscopy, and x-ray diffraction. Annealing in the temperature range of 573 K to 773 K (300 °C to 500 °C) up to 408 hours showed that four types of intermetallic layers have been formed at the interface, namely Al2Cu, AlCu, Al3Cu4, and Al4Cu9. Moreover, it was observed that iron trace in aluminum caused the formation of Fe-bearing intermetallics in Al, which is near the interface of the Al-Cu intermetallic layers. Finally, the activation energies for the growth of Al2Cu, AlCu + Al3Cu4, Al4Cu9, and the total intermetallic layer were calculated to be about 83.3, 112.8, 121.6, and 109.4 kJ/mol, respectively. Considering common welding methods ( i.e., explosive welding, cold rolling, and friction welding), although there is a great difference in welding mechanism, it is found that the total activation energy is approximately the same.

  12. Oxidation of high-temperature intermetallics; Proceedings of the Workshop, Cleveland, OH, Sept. 22, 23, 1988

    NASA Technical Reports Server (NTRS)

    Grobstein, Toni (Editor); Doychak, Joseph (Editor)

    1989-01-01

    The present conference on the high-temperature oxidation behavior of aerospace structures-applicable intermetallic compounds discusses the influence of reactive-element additions on the oxidation of Ni3Al base alloys, the effect of Ni3Al oxidation below 850 C on fracture behavior, the oxidation of FeAl + Hf, Zr, and B, the synergistic effect of Al and Si on the oxidation resistance of Fe alloys, and pack cementation coatings of Cr-Al on Fe, Ni, and Co alloys. Also discussed are the formation of alumina on Nb- and Ti-base alloys, the oxidation behavior of titanium aluminide alloys, silicide coatings for refractory metals, the oxidation of chromium disilicide, and the oxidation behavior of nickel beryllides.

  13. Pressure tuning of competing magnetic interactions in intermetallic CeFe2

    SciTech Connect

    Wang, Jiyang; Feng, Yejun; Jaramillo, R.; van Wezel, Jasper; Canfield, Paul C.; Rosenbaum, T.F.

    2012-07-20

    We use high-pressure magnetic x-ray diffraction and numerical simulation to determine the low-temperature magnetic phase diagram of stoichiometric CeFe2. Near 1.5 GPa we find a transition from ferromagnetism to antiferromagnetism, accompanied by a rhombohedral distortion of the cubic Laves crystal lattice. By comparing pressure and chemical substitution we find that the phase transition is controlled by a shift of magnetic frustration from the Ce-Ce to the Fe-Fe sublattice. Notably the dominant Ce-Fe magnetic interaction, which sets the temperature scale for the onset of long-range order, remains satisfied throughout the phase diagram but does not determine the magnetic ground state. Our results illustrate the complexity of a system with multiple competing magnetic energy scales and lead to a general model for magnetism in cubic Laves phase intermetallic compounds.

  14. Advances in processing of NiAl intermetallic alloys and composites for high temperature aerospace applications

    NASA Astrophysics Data System (ADS)

    Bochenek, Kamil; Basista, Michal

    2015-11-01

    Over the last few decades intermetallic compounds such as NiAl have been considered as potential high temperature structural materials for aerospace industry. A large number of investigations have been reported describing complex fabrication routes, introducing various reinforcing/alloying elements along with theoretical analyses. These research works were mainly focused on the overcoming of main disadvantage of nickel aluminides that still restricts their application range, i.e. brittleness at room temperature. In this paper we present an overview of research on NiAl processing and indicate methods that are promising in solving the low fracture toughness issue at room temperature. Other material properties relevant for high temperature applications are also addressed. The analysis is primarily done from the perspective of NiAl application in aero engines in temperature regimes from room up to the operating temperature (over 1150 °C) of turbine blades.

  15. Comparative NMR study of copper-based intermetallics with ZrCuSiAs-type structure

    NASA Astrophysics Data System (ADS)

    Lue, C. S.; ChangJen, W. J.; Su, T. H.

    2010-07-01

    The electronic characteristics of ZrCuGe2, ZrCuSi2, and HfCuSi2 are systematically investigated using C63u NMR spectroscopy. The quadrupole splittings, Knight shifts, and spin-lattice relaxation times on each individual compound have been identified. We found that the observed electric field gradient is consistent with the covalent bonding nature within the Cu atomic layers. The Knight shifts together with relaxation rates provide a measure of Cu d partial Fermi-level density of states, Nd(EF). Universally small Nd(EF) was found in all studied materials, suggests that the Cu d states are well below the Fermi energy and therefore the characteristic electronic structure near EF is primarily of sp type. We further pointed out that the low Nd(EF) value is an important factor for the lack of superconductivity in these Cu-based intermetallics within the ZrCuSiAs-type structure.

  16. Complex antiferromagnetic structure in the intermediate-valence intermetallic Ce2RuZn4

    NASA Astrophysics Data System (ADS)

    Hartwig, Steffen; Prokeš, Karel; Hansen, Thomas; Ritter, Clemens; Gerke, Birgit; Pöttgen, Rainer; Mydosh, J. A.; Förster, Tobias

    2015-07-01

    Neutron powder diffraction experiments were performed on the intermediate-valence Ce2RuZn4 intermetallic compound and combined with magnetic bulk measurements including high magnetic field experiments up to 58 T. Previous theoretical studies suggest that only one (here Ce1) out of two inequivalent Ce sites is magnetically active. Ce2RuZn4 orders antiferromagnetically at TN=2.3 K . The magnetic structure is characterized by an incommensurate propagation vector qm=(0.384 ,0.384 ,1/2 ). Assuming that the Ce2 site does not carry any substantial moment, Ce1 magnetic moments are confined to the (110)-type planes and transversely modulated with an amplitude of 1.77 (3 )μB.

  17. Numerical simulations of interfacial debonding in ductile-phase reinforced intermetallic matrix composites

    SciTech Connect

    Henshall, G.A.; Zywicz, E.; Strum, M.J.

    1993-08-10

    The fracture toughness of brittle intermetallic compounds can be improved by ductile-phase reinforcements. Effectiveness of the ductile phase in bridging cracks, and therefore increasing, the composite toughness, is known qualitatively to depend upon the extent of debonding, between the two phases. Numerical crack-growth simulations are used here to provide semi-quantitative predictions of the influence of interfacial debonding on the macroscopic stress-displacement behavior and, hence, the fracture toughness of an idealized Pb/glass composite. The interfacial toughness required to cause debonding, characterized by a constant critical energy release rate, is varied parametrically. As expected, higher interfacial toughness results in less interphase debonding, higher composite strength, and greater ductile-phase constraint. Consequently, the increase in ductile-phase triaxiality can potentially accelerate internal void formation and growth or facilitate cleavage fracture, either of which would likely decrease the toughness of the composite.

  18. Electronic and optical properties of RESn{sub 3} (RE=Pr & Nd) intermetallics: A first principles study

    SciTech Connect

    Pagare, G.; Abraham, Jisha A.; Sanyal, S. P.

    2015-06-24

    A theoretical study of structural, electronic and optical properties of RESn{sub 3} (RE = Pr & Nd) intermetallics have been investigated systematically using first principles density functional theory. The calculations are carried out within the PBE-GGA and LSDA for the exchange correlation potential. The ground state properties such as lattice parameter (a{sub 0}), bulk modulus (B) and its pressure derivative (B′) are calculated and the calculated lattice parameters show well agreement with the experimental results. We first time predict elastic constants for these compounds. From energy dispersion curves, it is found that these compounds are metallic in nature. The linear optical response of these compounds are also studied and the higher value of static dielectric constant shows the possibility to use them as good dielectric materials.

  19. Superconductivity by rare earth doping in the 1038-type compounds (Ca1-xREx) 10(FeAs)10(Pt3As8) with RE=Y, La-Nd, Sm-Lu

    NASA Astrophysics Data System (ADS)

    Stürzer, Tobias; Derondeau, Gerald; Bertschler, Eva-Maria; Johrendt, Dirk

    2015-01-01

    We report superconductivity in polycrystalline samples of the 1038-type compounds (Ca1-xREx) 10(FeAs)10(Pt3As8) up to Tc=35 K with RE=Y, La-Nd, Sm, Gd-Lu. The critical temperatures are nearly independent of the trivalent rare earth element used, yielding a common Tc(xRE) phase diagram for electron doping in all these systems. The absence of superconductivity in Eu2+ doped samples, as well as the close resemblance of (Ca1-xREx) 10(FeAs)10(Pt3As8) to the 1048 compound substantiate that the electron doping scenario in the RE-1038 and 1048 phases is analogous to other iron-based superconductors with simpler crystal structures.

  20. Discontinuously reinforced intermetallic matrix composites via XD synthesis. [exothermal dispersion

    NASA Technical Reports Server (NTRS)

    Kumar, K. S.; Whittenberger, J. D.

    1992-01-01

    A review is given of recent results obtained for discontinuously reinforced intermetallic matrix composites produced using the XD process. Intermetallic matrices investigated include NiAl, multiphase NiAl + Ni2AlTi, CoAl, near-gamma titanium aluminides, and Ll2 trialuminides containing minor amounts of second phase. Such mechanical properties as low and high temperature strength, compressive and tensile creep, elastic modulus, ambient ductility, and fracture toughness are discussed as functions of reinforcement size, shape, and volume fraction. Microstructures before and after deformation are examined and correlated with measured properties. An observation of interest in many of the systems examined is 'dispersion weakening' at high temperatures and high strain rates. This behavior is not specific to the XD process; rather similar observations have been reported in other discontinuous composites. Proposed mechanisms for this behavior are presented.

  1. Theoretical energy release of thermites, intermetallics, and combustible metals

    SciTech Connect

    Fischer, S.H.; Grubelich, M.C.

    1998-06-01

    Thermite (metal oxide) mixtures, intermetallic reactants, and metal fuels have long been used in pyrotechnic applications. Advantages of these systems typically include high energy density, impact insensitivity, high combustion temperature, and a wide range of gas production. They generally exhibit high temperature stability, and possess insensitive ignition properties. In this paper, the authors review the applications, benefits, and characteristics of thermite mixtures, intermetallic reactants, and metal fuels. Calculated values for reactant density, heat of reaction (per unit mass and per unit volume), and reaction temperature (without and with consideration of phase changes and the variation of specific heat values) are tabulated. These data are ranked in several ways, according to density, heat of reaction, reaction temperature, and gas production.

  2. An intermetallic forming steel under radiation for nuclear applications

    NASA Astrophysics Data System (ADS)

    Hofer, C.; Stergar, E.; Maloy, S. A.; Wang, Y. Q.; Hosemann, P.

    2015-03-01

    In this work we investigated the formation and stability of intermetallics formed in a maraging steel PH 13-8 Mo under proton radiation up to 2 dpa utilizing nanoindentation, microcompression testing and atom probe tomography. A comprehensive discussion analyzing the findings utilizing rate theory is introduced, comparing the aging process to radiation induced diffusion. New findings of radiation induced segregation of undersize solute atoms (Si) towards the precipitates are considered.

  3. Cluster expansion of fcc Pd-V intermetallics

    SciTech Connect

    de Fontaine, D.; Wolverton, C.; Ceder, G. ); Dreysse, H. . Lab. de Physique du Solide)

    1991-06-01

    A cluster expansion is used to compute fcc ground states from first principles for the Pd-V system. Intermetallic structures are not assumed but derived rigorously by minimizing the configurational energy subject to linear constraints. A large number of concentration-independent interactions are calculated by the method of direct configurational averaging. Agreement with the fcc-based portion of the experimentally-determined Pd-V phase diagram is quite satisfactory. 25 refs., 2 figs.

  4. Superplastic ceramics and intermetallics and their potential applications

    SciTech Connect

    Wadsworth, J.; Nieh, T.G.

    1994-11-01

    Recent advances in the basic understanding of superplasticity and superplastic forming of ceramics and intermetallics are reviewed. Fine-grained superplastic ceramics, including yttria-stabilized tetragonal zirconia polycrystal, Y- or MgO-doped Al{sub 2}O{sub 3} Hydroxyapatite, {beta}-spodumene glass ceramics, Al{sub 2}0{sub 3}-YTZP two-phase composites, SiC-Si{sub 3}N{sub 4} and Fe-Fe{sub 3}C composites, are discussed. Superplasticity in the nickel-base (e.g., Ni{sub 3}Al and Ni{sub 3}Si) and titanium-base intermetallics (TiAl and T1{sub 3}Al), is described. Deformation mechanisms as well as microstructural requirements and effects such as grain size, grain growth, and grain-boundary phases, on the superplastic deformation behavior am addressed. Factors that control the superplastic tensile elongation of ceramics are discussed. Superplastic forming, and particularly biaxial gas-pressure forming, of several ceramics and intermetallics are presented with comments on the likelihood of commercial application.

  5. Superconductivity up to 114 K in the Bi-Al-Ca-Sr-Cu-O compound system without rare-earth elements

    NASA Technical Reports Server (NTRS)

    Chu, C. W.; Bechtold, J.; Gao, L.; Hor, P. H.; Huang, Z. J.

    1988-01-01

    Stable superconductivity up to 114 K has been reproducibly detected in Bi-Al-Ca-Sr-Cu-O multiphase systems without any rare-earth elements. Pressure has only a slight positive effect on T(c). These observations provide an extra material base for the study of the mechanism of high-temperature superconductivity and also the prospect of reduced material cost for future applications of superconductivity.

  6. Magnetic phase transitions in Y1-xTbxMn6Sn6, La1-xSmxMn2Si2, Lu2(Fe1-xMnx)17, and La(Fe0.88SixAl0.12-x)13 intermetallic compounds

    NASA Astrophysics Data System (ADS)

    Mushnikov, N. V.; Kuchin, A. G.; Gerasimov, E. G.; Terentev, P. B.; Gaviko, V. S.; Serikov, V. V.; Kleinerman, N. M.; Vershinin, A. V.

    2015-06-01

    Magnetic properties have been measured for the Y1-xTbxMn6Sn6, La1-xSmxMn2Si2, Lu2(Fe1-xMnx)17, and La(Fe0.88SixAl0.12-x)13 systems which show up transitions from antiferromagnetic to ferromagnetic state upon changing concentration of the constituents or application of magnetic field. We determined the concentrations and temperatures of the magnetic phase transitions and plotted magnetic phase diagrams. Near a critical concentration, the AF-F transition can be realized in low magnetic fields, which makes these compounds attractive for magnetothermal applications. Using the data of the magnetization measurement, we determined the isothermal magnetic entropy change in a wide temperature range. All the studied systems have a layered magnetic structure with the positive intralayer exchange interaction and the interlayer exchange integrals of different signs depending on the composition and temperature. For the compounds La(Fe0.88SixAl0.12-x)13 with the cubic crystal structure, the origin of formation of a layered magnetic structure is discussed based on the data of Mössbauer studies which revealed a difference in the local surrounding of resonant atoms in the compounds with different magnetic orders.

  7. Lightweight Intermetallics with Laves Structures as Potential Hydrogen Storage Materials

    NASA Astrophysics Data System (ADS)

    Billet, Beau Austin

    Hydrogen storage was identified by the US Department of Energy as a "grand challenge" for the implementation of hydrogen-powered fuel cell vehicles for reduced CO2 emissions from transportation vehicles. None of the hydrogen storage options currently developed can satisfy the high gravimetric, volumetric and system design requirements. Intermetallic compounds with Laves structures in the formula of AB2 have long been known to store hydrogen in their interstitial sites to serve as reversible hydrogen storage materials (A and B are metallic elements). They have the potential to be hydrided to a maximum of ~ AB2H6 due to the impeding H-H interactions at neighboring interstitial sites. To achieve the highest weight percent of hydrogen storage in AB2H6, the lowest combined atomic weight of AB2 is required. The CaLi2 compound is the lightest known Laves phase, but it could not maintain its Laves structure when it was hydrided. Existing work of Akiba's group showed that a ternary Laves phase CaLi1.8Mg0.2 could be hydrided to form a hydrogenated Laves phase, but the absorbed hydrogen could not be released for reversible storage. Substitutions (Ca,X)Li1.8Mg0.2 are explored in the present study to see whether heavier elements [X = Sr, Ba and Ce] in small quantities can make the lightweight Laves compounds reversibly store hydrogen. Induction melting was successful in obtaining the desired Laves phases. The base system, CaLi1.8Mg0.2, formed a single phase, consistent with the literature result. Both Ca0.9Ba0.1Li 1.8Mg0.2 and Ca0.9Ce0.1Li1.8Mg 0.2 also formed a single-phase C14 Laves, whereas both Ca0.9Sr 0.1Li1.8Mg0.2 and Ca0.8Sr0.2Li 1.8Mg0.2 formed two seperature Laves phases with the same crystal structure, indicating a phase separation. The Ca0.8Ba 0.2Li1.8Mg0.2 composition completely lost the Laves-phase structure, forming CaLi2, CaMg2, BaLi 4 and Ca. All compounds tested at temperatures from 25 °C to 150 °C show the characteristic "plateau" behavior in the pressure

  8. {sup 57}Fe Moessbauer and x-ray magnetic circular dichroism study of magnetic compensation of the rare-earth sublattice in Nd{sub 2-x}Ho{sub x}Fe{sub 14}B compounds

    SciTech Connect

    Chaboy, J.; Piquer, C.; Plugaru, N.; Bartolome, F.; Laguna-Marco, M. A.

    2007-10-01

    We present here a study of the magnetic properties of the Nd{sub 2-x}Ho{sub x}Fe{sub 14}B series. The macroscopic properties of these compounds evolve continuously from those of Nd{sub 2}Fe{sub 14}B to those of Ho{sub 2}Fe{sub 14}B as Ho gradually replaces Nd. The system shows a compensation of the rare-earth sublattice magnetization for a critical concentration, x{sub c}=0.55, that is reflected into the anomalous behavior of both macroscopic and microscopic magnetic probes. The combined analysis of magnetization, {sup 57}Fe Moessbauer spectroscopy and Fe K-edge x-ray magnetic circular dichroism (XMCD) measurements suggests that the origin of the anomalous magnetic behavior found at x{sub c}=0.55 is mainly due to the Ho sublattice. Moreover, the analysis of the Fe K-edge XMCD signals reveal the presence of a rare-earth contribution, reflecting the coupling of the rare-earth and Fe magnetic moments, which can lead to the possibility of disentangling the magnetic behavior of both Fe and R atoms using a single absorption edge.

  9. Generality of the 18-n Rule: Intermetallic Structural Chemistry Explained through Isolobal Analogies to Transition Metal Complexes.

    PubMed

    Yannello, Vincent J; Fredrickson, Daniel C

    2015-12-01

    Intermetallic phases exhibit a vast structural diversity in which electron count is known to be one controlling factor. However, chemical bonding theory has yet to establish how electron counts and structure are interrelated for the majority of these compounds. Recently, a simple bonding picture for transition metal (T)-main group (E) intermetallics has begun to take shape based on isolobal analogies to molecular T complexes. This bonding picture is summarized in the 18-n rule: each T atom in a T-E intermetallic phase will need 18-n electrons to achieve a closed-shell 18-electron configuration, where n is the number of electron pairs it shares with other T atoms in multicenter interactions isolobal to T-T bonds. In this Article, we illustrate the generality of this rule with a survey over a wide range of T-E phases. First, we illustrate how three structural progressions with changing electron counts can be accounted for, both geometrically and electronically, with the 18-n rule: (1) the transition between the fluorite and complex β-FeSi2 types for TSi2 phases; (2) the sequence from the marcasite type to the arsenopyrite type and back to the marcasite type for TSb2 compounds; and (3) the evolution from the AuCu3 type to the ZrAl3 and TiAl3 types for TAl3 phases. We then turn to a broader survey of the applicability of the 18-n rule through a study of the following 34 binary structure types: PtHg4, CaF2 (fluorite), Fe3C, CoGa3, Co2Al5, Ru2B3, β-FeSi2, NiAs, Ni2Al3, Rh4Si5, CrSi2, Ir3Ga5, Mo3Al8, MnP, TiSi2, Ru2Sn3, TiAl3, MoSi2, CoSn, ZrAl3, CsCl, FeSi, AuCu3, ZrSi2, Mn2Hg5, FeS2 (oP6, marcasite), CoAs3 (skutterudite), PdSn2, CoSb2, Ir3Ge7, CuAl2, Re3Ge7, CrP2, and Mg2Ni. Through these analyses, the 18-n rule is established as a framework for interpreting the stability of 341 intermetallic phases and anticipating their properties. PMID:26581113

  10. Syntheses and characterization of energetic compounds constructed from alkaline earth metal cations (Sr and Ba) and 1,2-bis(tetrazol-5-yl)ethane

    NASA Astrophysics Data System (ADS)

    Xia, Zhengqiang; Chen, Sanping; Wei, Qing; Qiao, Chengfang

    2011-07-01

    Two new energetic compounds, [ M(BTE)(H 2O) 5] n ( M=Sr(1), Ba(2)) [H 2BTE=1,2-bis(tetrazol-5-yl)ethane], have been hydrothermally synthesized and structurally characterized. Single-crystal X-ray diffraction analyses reveal that they are isomorphous and exhibit 2D (4,4) net framework, generated by 4-connected Sr 2(H 2O) 10/Ba 2(H 2O) 10 SBUs linked up by two independent binding modes of H 2BTE, and the resulting 2D structure is interconnected by hydrogen-bond and strong face to face π- π stacking interactions between two tetrazole rings to lead to a 3D supramolecular architecture. DSC measurements show that they have significant catalytic effects on thermal decomposition of ammonium perchlorate. Moreover, the photoluminescence properties, thermogravimetric analyses, and flame colors of the as-prepared compounds are also investigated in this paper.

  11. Solid/gas heterogeneous chemistry of organic compounds related to comets, Titan and Mars, through experiments in the laboratory and in Earth orbit

    NASA Astrophysics Data System (ADS)

    Cottin, H.; Amino/Process Team

    Solar UV radiation is a major source of energy to initiate chemical evolution towards complex organic structures but it can also photodissociate the most elaborate molecules Thus Solar UV can erase the organic traces of past life on the surface of planets like Mars or it can influence the production of extended sources in comets AMINO PROCESS and UV-olution are three experiments selected to be flown on the EXPOSE facility on the International Space Station or on the BIOPAN facility during the next FOTON M3 space capsule mission The goal of our experiments is to improve our knowledge of the chemical nature and evolution of organic molecules involved in extraterrestrial environments with astrobiological implications Similar experiments implemented in space so far were carried out in vented cells exposed to solar UVs For the first time sealed exposition cells will be used which will allow us to study chemical evolution in the gaseous phase as well as heterogeneous processes degradation of solid compounds and release of gaseous fragments Three kinds of experiments will be carried out The first ones deal with comets and are related to the Rosetta mission the second ones deal with Titan and are related to the Cassini-Huygens mission while the third ones are related to the search for life-related organic compounds on Mars Concerning comets we plan to study the photodegradation of high molecular weight organic compounds which might be responsible for the wide range of organics polyoxymethylene hexamethylenetetramine HCN polymers and carbon suboxide

  12. UVolution and PROCESS: compared photochemistry in low Earth orbit and in the laboratory of prebiotic organic compounds related to small bodies

    NASA Astrophysics Data System (ADS)

    Cottin, Hervé; Guan, Yuan Yong; Macari, Frederique; Jerome, Murielle; Philippon, Carole; Cloix, Megane; Coll, Patrice; Fray, Nicolas; Szopa, Cyril; Raulin, Francois

    UVolution is an experiment which has been selected by ESA to be flown during 12 days in September 2007, in low Earth orbit on a BIOPAN module outside the Russian space capsule FOTON M3, before being brought back to Earth. PROCESS, is a similar experiment which has been exposed outside the International Space Station during 18 months in 2008-2009. With these experiments, more than 100 organic samples, among them some chosen for their relevance to astrochemistry and astrobiology questions related to comets and meteorites (glycine, ade-nine, guanine, xanthine, hypoxanthine, urea, HCN and C3O2 polymer), were exposed to the space environment. The main goal of this experiment was to study the influence of the solar vacuum Ultra Violet flux (λ<190 nm), which is difficult to reproduce in the laboratory. The re-sults derived from space exposures (photodissociation rates) have been compared to laboratory simulations using a microwave powered H2/He UV lamp as an energy source. We will present, compare and discuss the space and laboratory set of values, and discuss the implication of these measurements in the frame of the studies of the organic content of the small bodies of the Solar System.

  13. FP-LAPW study of structural, electronic, elastic, mechanical and thermal properties of AlFe intermetallic

    NASA Astrophysics Data System (ADS)

    Jain, Ekta; Pagare, Gitanjali; Sanyal, S. P.

    2016-05-01

    The structural, electronic, elastic, mechanical and thermal properties of AlFe intermetallic compound in B2-type (CsCl) structure have been investigated using first-principles calculations. The exchange-correlation term was treated within generalized gradient approximation. Ground state properties i.e. lattice constants (a0), bulk modulus (B) and first-order pressure derivative of bulk modulus (B') are presented. The density of states are derived which show the metallic character of present compound. Our results for C11, C12 and C44 agree well with previous theoretical data. Using Pugh's criteria (B/GH < 1.75), brittle character of AlFe is satisfied. In addition shear modulus (GH), Young's modulus (E), sound wave velocities and Debye temperature (θD) have also been estimated.

  14. First-principles investigations on vibrational, thermodynamic, mechanical properties and thermal conductivity of L12 Al3X (X = Sc, Er, Tm, Yb) intermetallics

    NASA Astrophysics Data System (ADS)

    Zhang, Xudong; Jiang, Wei

    2015-06-01

    The lattice dynamics, thermodynamic, mechanical properties and thermal conductivity of L12 Al3X (X = Sc, Er, Tm, Yb) intermetallics have been investigated from first-principles calculations by means of using the VASP code. Our results agree well with the previous experiments and calculations. The phonon dispersion curves and the density of phonon states have been calculated by means of using the PHONONPY code and compared with the experimental results. The four compounds stay dynamically stable in the L12 structure. We also calculated the thermodynamics properties and give the relationships between thermal parameters and temperature. The elastic constants of the considered compounds are satisfied with mechanical stability criteria. The related mechanical parameters predict that Al3Sc has higher hardness than the other three compounds, and four compounds all posses a brittle nature. The mechanical anisotropy is predicted by anisotropic constants AU and AZ. The results show that the four compounds are all elastically isotropic. We also calculated the thermal conductivity by means of the Clarke’s model and Cahill’s model and found that the thermal conductivity of the four intermetallics follows the order: Al3Sc > Al3Er > Al3Tm > Al3Yb.

  15. Synthesis and characterization of A-site deficient rare-earth doped BaZr xTi 1- xO 3 perovskite-type compounds

    NASA Astrophysics Data System (ADS)

    Ostos, C.; Mestres, L.; Martínez-Sarrión, M. L.; García, J. E.; Albareda, A.; Perez, R.

    2009-05-01

    A-site deficient rare-earth doped BaZr xTi 1- xO 3 (BZT) ceramics were prepared from a soft-chemistry route and by solid-state reaction (SSR). Perovskite-like single-phase diagrams for the BaTiO 3-La 2/3TiO 3-BaZrO 3 system were constructed for each method of synthesis. Infrared spectroscopy on (Ba 1- yLa 2 y/3 )Zr xTi 1- xO 3 solid solution revealed a dramatic stress on the M-O (M = Ti, Zr) bonds due to the combined effect of A-site vacancies and the lower ionic radius of La 3+ than that of Ba 2+. A relationship between the M-O stretching vibration ( υ) and the tolerance factor ( t) was determined. (Ba 1- yLn 2 y/3 )Zr 0.09Ti 0.91O 3 (Ln = La, Pr, Nd) samples synthesized by SSR were selected for detailed studies. X-ray diffraction data were refined by the Rietveld method. Scanning electron microscopy on sintered compacts detected abnormal crystal growth and grain sizes in the range of about 1 μm up to 10 μm when the dopant concentration is 6.7 at. %. Impedance measurements exhibited that ferroelectric to paraelectric phase-transition temperature shifted to lower values as increasing rare-earth content. (Ba 1- yLn 2 y/3 )Zr 0.09Ti 0.91O 3 system showed a diffuse phase transition with a relaxor-like ferroelectric behaviour. Furthermore, the dielectric constant was enhanced with respect to non-doped BZT system.

  16. Development of intermetallic coatings for fusion power applications

    SciTech Connect

    Park, J.H.; Domenico, T.; Dragel, G.; Clark, R.

    1994-03-01

    In the design of liquid-metal cooling systems, corrosion resistance of structural materials and magnetohydrodynamic (MHD) force and its subsequent influence on thermal hydraulics and corrosion are major concerns. The objective of this study is to develop stable corrosion-resistant electrical insulator coatings at the liquid-metal/structural-material interface, with emphasis on electrically insulating coatings that prevent adverse MHD-generated currents from passing through the structural walls. Vanadium and V-base alloys are potential materials for structural applications in a fusion reactor. Insulator coatings inside the tubing are required when the system is cooled by liquid metals. Various intermetallic films were produced on V, V-t, and V-20 Ti, V-5Cr-t and V-15Cr-t, and Ti, and Types 304 and 316 stainless steel. The intermetallic layers were developed by exposure of the materials to liquid lithium of 3--5 at.% and containing dissolved metallic solutes at temperatures of 416--880{degrees}C. Subsequently, electrical insulator coatings were produced by reaction of the reactive layers with dissolved nitrogen in liquid lithium or by air oxidation under controlled conditions at 600--1000{degrees}C. These reactions converted the intermetallic layers to electrically insulating oxide/nitride or oxy-nitride layers. This coating method could be applied to a commercial product. The liquid metal can be used over and over because only the solutes are consumed within the liquid metal. The technique can be applied to various shapes because the coating is formed by liquid-phase reaction. This paper will discuss initial results on the nature of the coatings and their in-situ electrical resistivity characteristics in liquid lithium at high temperatures.

  17. Life on Earth: From Chemicals in Space?

    ERIC Educational Resources Information Center

    Chemical and Engineering News, 1973

    1973-01-01

    Discusses experimental evidence for the existence of organic material in the solar system prior to the earth's formation. Indicates that the earth could have received much of its organic compounds from meteors falling on its primitive surface. (CC)

  18. Exo-Melt{trademark} process for intermetallic powders

    SciTech Connect

    Sikka, V.K.; Deevi, S.C.

    1996-06-01

    The methods of powder production for intermetallics are reviewed. An innovative method known as Exo-Melt{trademark} is described for producing molten aluminides for gas- and water-atomization processes that require a molten metal stream. The Exo-Melt{trademark} process is based on the effective utilization of the heats of formation of aluminides from their constituent elements. The Exo-Melt{trademark} process principles are discussed along with a description of a furnace-loading sequence that uses the principles for practical applications. The benefits of the Exo-Melt{trademark} process are compared with the problems associated with the conventional melting process.

  19. Study of Intermetallic Nanostructures for Light-Water Reactors

    SciTech Connect

    Jensen, Niels Grobech; Asta, Mark D.; Hosemann, Peter; Maloy, Stuart

    2015-09-30

    High temperature mechanical measurements were conducted to study the effect of the dynamic precipitation process of PH 13-8 Mo maraging steel. Yield stress, ultimate tensile strength, total elongation, hardness, strain rate sensitivity and activation volume were evaluated as a function of the temperature. The dynamic changes in the mechanical properties at different temperatures were evaluated and a balance between precipitation hardening and annealed softening is discussed. A comparison between hardness and yield stress and ultimate tensile strength over a temperature range from 300 to 600 °C is made. The behavior of the strain rate sensitivity was correlated with the intermetallic precipitates formed during the experiments.

  20. A survey of combustible metals, thermites, and intermetallics for pyrotechnic applications

    SciTech Connect

    Fischer, S.H.; Grubelich, M.C.

    1996-08-01

    Thermite mixtures, intermetallic reactants, and metal fuels have long been used in pyrotechnics. Advantages include high energy density, impact insensitivity, high combustion temperature, and a wide range of gas production. They generally exhibit high temperature stability and possess insensitive ignition properties. This paper reviews the applications, benefits, and characteristics of thermite mixtures, intermetallic reactants, and metal fuels. 50 refs, tables.

  1. Evidence of conduction-electron shielding of the crystal electric field of Tb sub x Gd sub 1 minus x Al sub 2 intermetallics

    SciTech Connect

    del Moral, A.; Joven, E. Instituto de Ciencio de Materiales de Aragon, Universidad de Zaragoza, Consejo Superior de Investigaciones Cientificas, Zaragoza )

    1990-12-01

    A comparison of the values obtained for the {ital B}{sub 4} crystal-electric-field (CEF) parameter in the series of cubic intermetallics Tb{sub {ital x}}Gd{sub 1{minus}{ital x}}Al{sub 2} with a model which predicts a dependence of {ital B}{sub 4} on the density of states with {ital d} character at the Fermi level, allows us to demonstrate directly the shielding effect of the conduction electrons on the CEF produced by the lattice of tripositive rare-earth and Al ions.

  2. Transport and magnetic properties of RTX and related compounds

    NASA Astrophysics Data System (ADS)

    Goruganti, Venkateshwarlu

    Physical properties of RTX compounds (R = Rare earth, T = Transition metal and X = main group element from B, C or N group) compounds have been studied by means of electrical resistivity, heat capacity, dc magnetization and NMR. Searching for new magnetic materials is always an interesting topic from both a technological and basic research prospective; it is even more interesting when unusual magnetic phases are observed. Ternary intermetallic plumbides are interesting because of their unconventional magnetic ordering and variety of multiple magnetic transitions. Crystalline electric fields (CEF) also strongly effect the magnetic properties of these intermetallics. To understand the phase transitions, CEF effects, and magnetic interactions, a systematic study of the RNiPb, R 2Ni2Pb, R5NiPb3 and RCuGe systems were conducted. Among the results for NdNiPb a single antiferromagnetic transition was found at 3.5K, while the superconductivity found in some ingots of this material was shown not to correspond to a bulk behavior for this phase. Nd2Ni 2Pb was shown to have a canted zero field magnetic structure with a low temperature metamagnetic transition 3 T. In NdCuGe, a 3K AF transition was found along with a corresponding magnon contribution to the specific heat and magnetic and thermodynamic behavior from which the detailed CEF configuration was obtained. In a series of measurements on recently-synthesized R 5NiPb3 (R=Ce, Nd, Gd), for Ce5NiPb 3 a transition at 48 K was found, which was confirmed to be ferromagnetic character from field dependent heat capacity and Curie-Weiss susceptibility. Nd5NiPb3 exhibits two transitions, an antiferromagnetic transition at 42 K and an apparently weak ferromagnetic canting transition at 8 K. For Gd5NiPb3, a ferro- or ferrimagnetic transition was found at 68 K. For the Ce and Nd materials metamagnetism was also observed at low temperatures. In addition, very large metallic type gamma terms were found in the specific heat, as well as a

  3. Electronic packing frustration in complex intermetallic structures: the role of chemical pressure in Ca2Ag7.

    PubMed

    Fredrickson, Daniel C

    2011-07-01

    The assignment of distinct roles to electronics and sterics has a long history in our rationalization of chemical phenomena. Exploratory synthesis in the field of intermetallic compounds challenges this dichotomy with a growing list of phases whose structural chemistry points to an interplay between atomic size effects and orbital interactions. In this paper, we begin with a simple model for how this interdependence may arise in the dense atomic packing of intermetallics: correlations between interatomic distances lead to the inability of a phase to optimize bonds without simultaneously shortening electronically under-supported contacts, a conflict we term electronic packing frustration (EPF). An anticipated consequence of this frustration is the emergence of chemical pressures (CPs) acting on the affected atoms. We develop a theoretical method based on DFT-calibrated μ(2)-Hückel calculations for probing these CP effects. Applying this method to the Ca(2)Ag(7) structure, a variant of the CaCu(5) type with defect planes, reveals its formation is EPF-driven. The defect planes resolve severe CPs surrounding the Ca atoms in a hypothetical CaCu(5)-type CaAg(5) phase. CP analysis also points to a rationale for these results in terms of a CP analogue of the pressure-distance paradox and predicts that the impetus for defect plane insertion is tunable via variations in the electron count. PMID:21619054

  4. Theoretical Energy Release of Thermites, Intermetallics, and Combustible Metals

    SciTech Connect

    Fischer, S.H.; Grubelich, M.C.

    1999-05-14

    Thermite mixtures, intermetallic reactants, and metal fuels have long been used in pyrotechnic applications. Advantages of these systems typically include high energy density, high combustion temperature, and a wide range of gas production. They generally exhibit high temperature stability and possess insensitive ignition properties. For the specific applications of humanitarian demining and disposal of unexploded ordnance, these pyrotechnic formulations offer additional benefits. The combination of high thermal input with low brisance can be used to neutralize the energetic materials in mines and other ordnance without the "explosive" high-blast-pressure events that can cause extensive collateral damage to personnel, facilities, and the environment. In this paper, we review the applications, benefits, and characteristics of thermite mixtures, intermetallic reactants, and metal fuels. Calculated values for reactant density, heat of reaction (per unit mass and per unit volume), and reaction temperature (without and with consideration of phase changes and the variation of specific heat values) are tabulated. These data are ranked in several ways, according to density, heat of reaction, reaction temperature, and gas production.

  5. Intermetallic and titanium matrix composite materials for hypersonic applications

    SciTech Connect

    Berton, B.; Surdon, G.; Colin, C. |

    1995-09-01

    As part of the French Program of Research and Technology for Advanced Hypersonic Propulsion (PREPHA) which was launched in 1992 between Aerospatiale, Dassault Aviation, ONERA, SNECMA and SEP, an important work is specially devoted to the development of titanium and intermetallic composite materials for large airframe structures. At Dassault Aviation, starting from a long experience in Superplastic Forming - Diffusion Bonding (SPF-DB) of titanium parts, the effort is brought on the manufacturing and characterization of composites made from Timet beta 21S or IMI 834 foils and Textron SCS6 fiber fabrics. At `Aersopatiale Espace & Defence`, associated since a long time about intermetallic composite materials with university research laboratories, the principal effort is brought on plasma technology to develop the gamma titanium aluminide TiAl matrix composite reinforced by protected silicon carbide fibers (BP SM 1240 or TEXTRON SCS6). The objective, is to achieve, after 3 years of time, to elaborate a medium size integrally stiffened panel (300 x 600 sq mm).

  6. SURFACE MODIFICATION OF ZIRCALOY-4 SUBSTRATES WITH NICKEL ZIRCONIUM INTERMETALLICS

    SciTech Connect

    Luscher, Walter G.; Gilbert, Edgar R.; Pitman, Stan G.; Love, Edward F.

    2013-02-01

    Surfaces of Zircaloy-4 (Zr-4) substrates were modified with nickel-zirconium (NiZr) intermetallics to tailor oxidation performance for specialized applications. Surface modification was achieved by electroplating Zr-4 substrates with nickel (Ni) and then performing thermal treatments to fully react the Ni plating with the substrates, which resulted in a coating of NiZr intermetallics on the substrate surfaces. Both plating thickness and thermal treatment were evaluated to determine the effects of these fabrication parameters on oxidation performance and to identify an optimal surface modification process. Isothermal oxidation tests were performed on surface-modified materials at 290°, 330°, and 370°C under a constant partial pressure of oxidant (i.e., 1 kPa D2O in dry Ar at 101 kPa) for 64 days. Test results revealed an enhanced, transient oxidation rate that decreased asymptotically toward the rate of the Zr-4 substrate. Oxidation kinetics were analyzed from isothermal weight gain data, which were correlated with microstructure, hydrogen pickup, strength, and hardness.

  7. Biosignatures of early earths

    NASA Technical Reports Server (NTRS)

    Pilcher, Carl B.

    2003-01-01

    A major goal of NASA's Origins Program is to find habitable planets around other stars and determine which might harbor life. Determining whether or not an extrasolar planet harbors life requires an understanding of what spectral features (i.e., biosignatures) might result from life's presence. Consideration of potential biosignatures has tended to focus on spectral features of gases in Earth's modern atmosphere, particularly ozone, the photolytic product of biogenically produced molecular oxygen. But life existed on Earth for about 1(1/2) billion years before the buildup of atmospheric oxygen. Inferred characteristics of Earth's earliest biosphere and studies of modern microbial ecosystems that share some of those characteristics suggest that organosulfur compounds, particularly methanethiol (CH(3)SH, the sulfur analog of methanol), may have been biogenic products on early Earth. Similar production could take place on extrasolar Earth-like planets whose biota share functional chemical characteristics with Earth life. Since methanethiol and related organosulfur compounds (as well as carbon dioxide) absorb at wavelengths near or overlapping the 9.6-microm band of ozone, there is potential ambiguity in interpreting a feature around this wavelength in an extrasolar planet spectrum.

  8. Biosignatures of Early Earths

    NASA Astrophysics Data System (ADS)

    Pilcher, Carl B.

    2003-11-01

    A major goal of NASA's Origins Program is to find habitable planets around other stars and determine which might harbor life. Determining whether or not an extrasolar planet harbors life requires an understanding of what spectral features (i.e., biosignatures) might result from life's presence. Consideration of potential biosignatures has tended to focus on spectral features of gases in Earth's modern atmosphere, particularly ozone, the photolytic product of biogenically produced molecular oxygen. But life existed on Earth for about 1½ billion years before the buildup of atmospheric oxygen. Inferred characteristics of Earth's earliest biosphere and studies of modern microbial ecosystems that share some of those characteristics suggest that organosulfur compounds, particularly methanethiol (CH3SH, the sulfur analog of methanol), may have been biogenic products on early Earth. Similar production could take place on extrasolar Earth-like planets whose biota share functional chemical characteristics with Earth life. Since methanethiol and related organosulfur compounds (as well as carbon dioxide) absorb at wavelengths near or overlapping the 9.6-μm band of ozone, there is potential ambiguity in interpreting a feature around this wavelength in an extrasolar planet spectrum.

  9. Magnetoelastic properties of substituted Er1-xGdxMn6Sn6 intermetallic system

    NASA Astrophysics Data System (ADS)

    Tabatabai Yazdi, Sh.; Tajabor, N.; Roknabadi, M. Rezaee; Behdani, M.; Pourarian, F.

    2014-06-01

    The forced magnetostriction of polycrystalline samples of Er1-xGdxMn6Sn6 (0≤x≤1) intermetallics with hexagonal HfFe6Ge6-type structure is investigated in the temperature range of 77-480 K. Gd substitution has a significant effect on interatomic distances and especially on inter-sublattice R-Mn couplings. The replacement of Er by Gd results in increasing the ordering temperature followed by reinforcement of the R-Mn coupling, as well as decreasing the magnetostriction values owing to the S-state character of Gd3+ ions. The results show that the contribution of Er sublattice to anisotropic magnetoelastic effects is positive, while that of Gd and Mn is negative. All the examined samples exhibit considerable magnetovolume anomalies at the ordering temperature (TC=338, 381, 412 and 434 K for the samples with x=0, 0.2, 0.6 and 1.0, respectively). While the unsubstituted sample exhibits metamagnetic transitions, Gd-contained compounds do not show this behavior, owing to the strong Gd-Mn coupling. The experimental results obtained are discussed in the framework of the two-magnetic sublattice by bearing in mind the lattice parameter dependence of the interlayer Mn-Mn exchange interaction in these layered compounds. From the temperature dependence of magnetostriction values and considering the magnetostriction equation for a hexagonal structure, we attempt to determine the signs of some of the magnetostriction constants for these compounds and the influence of Gd substitution on them.

  10. Earth Resources

    ERIC Educational Resources Information Center

    Brewer, Tom

    1970-01-01

    Reviews some of the more concerted, large-scale efforts in the earth resources areas" in order to help the computer community obtain insights into the activities it can jointly particpate in withthe earth resources community." (Author)

  11. Characterization of ceramics and intermetallics fabricated by self-propagating high-temperature synthesis

    NASA Technical Reports Server (NTRS)

    Hurst, Janet B.

    1989-01-01

    Three efforts aimed at investigating the process of self-propagating high temperature synthesis (SHS) for the fabrication of structural ceramics and intermetallics are summarized. Of special interest was the influence of processing variables such as exothermic dopants, gravity, and green state morphology in materials produced by SHS. In the first effort directed toward the fabrication of SiC, exothermic dopants of yttrium and zirconium were added to SiO2 or SiO2 + NiO plus carbon powder mix and processed by SHS. This approach was unsuccessful since it did not produce the desired product of crystalline SiC. In the second effort, the influence of gravity was investigated by examining Ni-Al microstructures which were produced by SHS combustion waves traveling with and opposite the gravity direction. Although final composition and total porosities of the combusted Ni-Al compounds were found to be gravity independent, larger pores were created in those specimens which were combusted opposite to the gravity force direction. Finally, it was found that green microstructure has a significant effect on the appearance of the combusted piece. Severe pressing laminations were observed to arrest the combustion front for TiC samples.

  12. Innovative processing to produce advanced intermetallic materials. Phase 1 final report

    SciTech Connect

    Loutfy, R.O.

    1989-09-01

    The program demonstrates the technical feasibility of synthesizing submicron titanium aluminide in a thermal rf plasma. Micron and submicron spherical titanium aluminide particles are produced in argon, hydrogen, and argon/hydrogen plasmas from the reaction of TiCl4(g), and Al(g). The ratio of Ti and Al is varied to produce the compounds Ti3Al, TiAl, and TiAl3. Microalloying with boron and macroalloying with niobium is demonstrated. Ti3Al whiskers can be produced, as well as other intermetallics of niobium aluminide, nickel aluminide, and molybdenum disilicide in the plasma synthesis process. Since submicron particles are produced, they have a high surface area and are sensitive to oxidation if not treated with a fugitive protective coating or utilized in a nonoxidizing atmosphere. Ti3Al particles are consolidated and utilized as a matrix for TiC and AlN composites. The submicron AlTi3 has significantly higher strength at room temperature than reported for commercial Ti3Al-11Nb alloy and useable strength is maintained up to 1000 C. The elongation is about the same as for commercial material because of possible oxide contamination in powder handling. However, dimpling and nacking is evident in the fracture surface, which suggests true room temperature ductility. Titanium aluminides have the potential to replace superalloys and become the dominant material for aerospace engines, air frames and skins for hypersonic vehicles.

  13. Optimized Cu-Sn Wafer-Level Bonding Using Intermetallic Phase Characterization

    NASA Astrophysics Data System (ADS)

    Luu, Thi-Thuy; Duan, Ani; Aasmundtveit, Knut E.; Hoivik, Nils

    2013-12-01

    The objective of this study is to optimize the Cu/Sn solid-liquid interdiffusion process for wafer-level bonding applications. To optimize the temperature profile of the bonding process, the formation of intermetallic compounds (IMCs) which takes place during the bonding process needs to be well understood and characterized. In this study, a simulation model for the development of IMCs and the unreacted remaining Sn thickness as a function of the bonding temperature profile was developed. With this accurate simulation model, we are able to predict the parameters which are critical for bonding process optimization. The initial characterization focuses on a kinetics model of the Cu3Sn thickness growth and the amount of Sn thickness that reacts with Cu to form IMCs. As-plated Cu/Sn samples were annealed using different temperatures (150°C to 300°C) and durations (0 min to 320 min). The kinetics model is then extracted from the measured thickness of IMCs of the annealed samples.

  14. Physical properties and electronic structure of La3Co and La3Ni intermetallic superconductors

    NASA Astrophysics Data System (ADS)

    Strychalska, J.; Roman, M.; Sobczak, Z.; Wiendlocha, B.; Winiarski, M. J.; Ronning, F.; Klimczuk, T.

    2016-09-01

    La3Co and La3Ni are reported superconductors with transition temperatures of 4.5 and 6 K, respectively. Here, we reinvestigate the physical properties of these two intermetallic compounds with magnetic susceptibility χ, specific heat Cp and electrical resistivity ρ measurements down to 1.9 K. Although bulk superconductivity is confirmed in La3Co, as observed previously, only a trace of it is found in La3Ni, indicating that the superconductivity in La3Ni originates from an impurity phase. Superconducting state parameters for La3Co, including lower and upper critical fields and the superconducting gap, are estimated. Results of the theoretical calculations of the electronic structure for both materials are also presented, and comparison of the Fermi level location in La3Co versus La3Ni explains its larger superconducting Tc. A major discrepancy between band structure calculations and the experimentally measured Sommerfeld coefficient is found. The measured electronic density of states is about 2.5 times larger than the theoretical value for La3Co. This effect cannot be explained by the electron-phonon interaction alone. Renormalization of γ, as well as an ∼T2 behavior of the resistivity, suggests the presence of spin fluctuations in both systems.

  15. Incorporation of Interfacial Intermetallic Morphology in Fracture Mechanism Map for Sn-Ag-Cu Solder Joints

    NASA Astrophysics Data System (ADS)

    Huang, Z.; Kumar, P.; Dutta, I.; Sidhu, R.; Renavikar, M.; Mahajan, R.

    2014-01-01

    A fracture mechanism map (FMM) is a powerful tool which correlates the fracture behavior of a material to its microstructural characteristics in an explicit and convenient way. In the FMM for solder joints, an effective thickness of the interfacial intermetallic compound (IMC) layer ( t eff) and the solder yield strength ( σ ys,eff) are used as abscissa and ordinate axes, respectively, as these two predominantly affect the fracture behavior of solder joints. Earlier, a definition of t eff, based on the uniform thickness of IMC ( t u) and the average height of the IMC scallops ( t s), was proposed and shown to aptly explain the fracture behavior of solder joints on Cu. This paper presents a more general definition of t eff that is more widely applicable to a range of metallizations, including Cu and electroless nickel immersion gold (ENIG). Using this new definition of t eff, mode I FMM for SAC387/Cu joints has been updated and its validity was confirmed. A preliminary FMM for SAC387/Cu joints with ENIG metallization is also presented.

  16. Intermetallic Formation at Interface of Al/Cu Clad Fabricated by Hydrostatic Extrusion and Its Properties.

    PubMed

    Lee, Jongbeom; Jeong, Haguk

    2015-11-01

    Al/Cu clad composed of Al core and Cu sheath has been produced by hydrostatic extrusion at 523 K, at an extrusion rate of 27. The prepared specimen was post-annealed at temperatures of 673 K and 773 K for various time durations, and the effect of annealing conditions have been analyzed. The hardness at the interface between Al and Cu matrix of the Al/Cu bimetal clad increases because of annealing. Results indicate that the hardness is more sensitive to annealing temperature than the annealing time. Three kinds of intermetallic compounds (IMC), namely, CuAl, Cu3Al2, and CuAl2, are formed at the Al-Cu interface, upon annealing at 673 K. On the other hand, four kinds of IMCs, namely, Cu4Al3, CuAl, Cu3Al2, CuAl2, are formed at the annealing temperature of 773 K. The growth of each IMC follows the parabolic law as a function of annealing times at certain annealing temperature. The growth rate of each IMC is limited to its interdiffusion rate constant. The IMC Cu4Al3 appears upon annealing at 773 K, and not during annealing at 673 K, because of the higher value of activation energy associated with its formation, when compared to other IMCs. PMID:26726557

  17. Joining of Ni-TiC FGM and Ni-Al Intermetallics by Centrifugal Combustion Synthesis

    NASA Astrophysics Data System (ADS)

    Ohmi, Tatsuya; Mizuma, Kiminori; Matsuura, Kiyotaka; Iguchi, Manabu

    2008-02-01

    A centrifugal combustion synthesis (CCS) process has been investigated to join a Ni-Al intermetallic compound and a Ni-TiC cermet. The cermet, a tubular graphite mold, and a green compact of reactants consisting of Al, Ni and NiO were set in a centrifugal caster. When the combustion synthesis reaction was induced in the centrifugal force field, a synthesized molten Ni-Al alloy flowed into the graphite mold and joined to the cermet. The soundness of the joint interface depended on the volume percentage of TiC phase in the cermet. A lot of defects were formed near the interface between the Ni-TiC cermet and the cast Ni-Al alloy when the volume percentage of TiC was 50% or higher. For this kind of cermet system, using a functionally graded cermet such as Ni-10 vol.%TiC/Ni-25 vol.%TiC/Ni-50 vol.%TiC overcame this difficulty. The four-point bending strength of the joined specimen consisting of the three-layered FGM cermet and cast Ni-29 mol%Al alloy was 1010 MPa which is close to the result for a Ni-29 mol%Al alloy specimen.

  18. Synthesis, Structure and bonding Analysis of the Polar Intermetallic Phase Ca2Pt2Cd

    SciTech Connect

    Samal, Saroj L.; Corbett, John D.

    2012-08-14

    The polar intermetallic phase Ca2Pt2Cd was discovered during explorations of the Ca-Pt-Cd system. The compound was synthesized by high temperature reactions, and its structure refined by single-crystal X-ray diffraction as orthorhombic, Immm, a = 4.4514(5), b = 5.8415(6), c = 8.5976(9) Å, Z = 2. The structure formally contains infinite, planar networks of [Pt2Cd]4– along the ab plane, which can be described as tessellation of six and four-member rings of the anions, with cations stuffed between the anion layers. The infinite condensed platinum chains show a substantial long–short distortion of 0.52 Å, an appreciable difference between Ca2Pt2Cd (26 valence electrons) and the isotypic but regular Ca2Cu2Ga (29 VE). The relatively large cation proportion diminishes the usual dominance of polar (Pt–Cd) and 5d–5d (Pt–Pt) contributions to the total Hamilton populations.

  19. Disturbing the dimers: Electron and hole doping in the intermetallic insulator FeGa3

    NASA Astrophysics Data System (ADS)

    Botana, Antia S.; Quan, Yundi; Pickett, Warren E.

    2015-10-01

    Insulating FeGa3 poses peculiar puzzles beyond the occurrence of an electronic gap in an intermetallic compound. This Fe-based material has a very distinctive structural characteristic with the Fe atoms occurring in dimers. The insulating gap can be described comparably well in either the weakly correlated limit or the strongly correlated limit within density functional theory viewpoints, where the latter corresponds to singlet formation on the Fe2 dimers. Though most of the calculated occupied Wannier functions are an admixture of Fe 3 d and Ga 4 s or 4 p states, there is a single bonding-type Wannier function per spin centered on each Fe2 dimer. Density functional theory methods have been applied to follow the evolution of the magnetic properties and electronic spectrum with doping, where unusual behavior is observed experimentally. Both electron and hole doping are considered, by Ge and Zn on the Ga site, and by Co and Mn on the Fe site, the latter introducing direct disturbance of the Fe2 dimer. Results from weakly and strongly correlated pictures are compared. Regardless of the method, magnetism including itinerant phases appears readily with doping. The correlated picture suggests that in the low doping limit Mn (for Fe) produces an in-gap hole state, while Co (for Fe) introduces a localized electronic gap state.

  20. Joining of Ni-TiC FGM and Ni-Al Intermetallics by Centrifugal Combustion Synthesis

    SciTech Connect

    Ohmi, Tatsuya; Matsuura, Kiyotaka; Iguchi, Manabu; Mizuma, Kiminori

    2008-02-15

    A centrifugal combustion synthesis (CCS) process has been investigated to join a Ni-Al intermetallic compound and a Ni-TiC cermet. The cermet, a tubular graphite mold, and a green compact of reactants consisting of Al, Ni and NiO were set in a centrifugal caster. When the combustion synthesis reaction was induced in the centrifugal force field, a synthesized molten Ni-Al alloy flowed into the graphite mold and joined to the cermet. The soundness of the joint interface depended on the volume percentage of TiC phase in the cermet. A lot of defects were formed near the interface between the Ni-TiC cermet and the cast Ni-Al alloy when the volume percentage of TiC was 50% or higher. For this kind of cermet system, using a functionally graded cermet such as Ni-10 vol.%TiC/Ni-25 vol.%TiC/Ni-50 vol.%TiC overcame this difficulty. The four-point bending strength of the joined specimen consisting of the three-layered FGM cermet and cast Ni-29 mol%Al alloy was 1010 MPa which is close to the result for a Ni-29 mol%Al alloy specimen.

  1. Influence of Al grain boundaries segregations and La-doping on embrittlement of intermetallic NiAl

    NASA Astrophysics Data System (ADS)

    Kovalev, Anatoly I.; Wainstein, Dmitry L.; Rashkovskiy, Alexander Yu.

    2015-11-01

    The microscopic nature of intergranular fracture of NiAl was experimentally investigated by the set of electron spectroscopy techniques. The paper demonstrates that embrittlement of NiAl intermetallic compound is caused by ordering of atomic structure that leads to formation of structural aluminum segregations at grain boundaries (GB). Such segregations contain high number of brittle covalent interatomic bonds. The alloying by La increases the ductility of material avoiding Al GB enrichment and disordering GB atomic structure. The influence of La alloying on NiAl mechanical properties was investigated. GB chemical composition, atomic and electronic structure transformations after La doping were investigated by AES, XPS and EELFS techniques. To qualify the interatomic bonds metallicity the Fermi level (EF) position and electrons density (neff) in conduction band were determined in both undoped and doped NiAl. Basing on experimental results the physical model of GB brittleness formation was proposed.

  2. Formation of intermetallics at the interface of explosively welded Ni-Al multilayered composites during annealing

    NASA Astrophysics Data System (ADS)

    Ogneva, T. S.; Lazurenko, D. V.; Bataev, I. A.; Mali, V. I.; Esikov, M. A.; Bataev, A. A.

    2016-04-01

    The Ni-Al multilayer composite was fabricated using explosive welding. The zones of mixing of Ni and Al are observed at the composite interfaces after the welding. The composition of these zones is inhomogeneous. Continuous homogeneous intermetallic layers are formed at the interface after heat treatment at 620 °C during 5 h These intermetallic layers consist of NiAl3 and Ni2Al3 phases. The presence of mixed zones significantly accelerates the growth rate of intermetallic phases at the initial stages of heating.

  3. Metal- and intermetallic-matrix composites for aerospace propulsion and power systems

    NASA Technical Reports Server (NTRS)

    Doychak, J.

    1992-01-01

    The requirements for high specific strength refractory materials of prospective military, civil, and space propulsion systems are presently addressed in the context of emerging capabilities in metal- and intermetallic-matrix composites. The candidate systems encompass composite matrix compositions of superalloy, Nb-Zr refractory alloy, Cu-base, and Ti-base alloy types, as well as such intermetallics as TiAl, Ti3Al, NiAl, and MoSi2. The brittleness of intermetallic matrices remains a major consideration, as does their general difficulty of fabrication.

  4. Elementary diffusion jump of iron atoms in intermetallic phases studied by Moessbauer spectroscopy; 1: Fe-Al close to equiatomic stoichiometry

    SciTech Connect

    Vogl, G.; Sepiol, B. . Inst. fuer Festkoerperphysik)

    1994-09-01

    The authors have studied the quasielastic broadening of the [sup 57]Fe Moessbauer resonance in the intermetallic compound FeAl in order to determine the diffusion jump mechanism of the Fe atoms. From the angular dependence of the line broadening relative to an oriented single crystal they deduce that the Fe atoms jump effectively to different neighbor sites on the Fe sublattice. The jump is, however, not a direct one, but rather a combination of a jump into a nearest neighbor vacancy--leading to short-time occupation of an antistructure site on the Al sublattice--and a jump into a vacancy back on the Fe sublattice.

  5. Plastic deformation of ordered intermetallic alloys: Fundamental aspects

    SciTech Connect

    Yoo, M.H.

    1994-10-01

    Fundamental aspects of plastic deformation in ordered intermetallic alloys are reviewed by directly comparing the temperature-dependent yield stresses of Ni{sub 3}Al and Ni{sub 3}Si (the L1{sub 2} structure), NiAl and FeAl (the B2 structure), and TiAl and Ti{sub 3}Al (non-cubic L1{sub 0} and D0{sub 19} structures, respectively). While the yield strength anomaly observed in Ni{sub 3}Al is consistent with the prevailing dislocation models, that found in stoichiometric Ni{sub 3}Si is not. The strong plastic anisotropy observed in NiAl stems from the high antiphase boundary energy, and that found in two-phase {gamma}-TiAl/{alpha}{sub 2}-Ti{sub 3}Al is due to the exceptionally high compressive yield strength along the c-axis of Ti{sub 3}Al.

  6. The oxidation of Ni-rich Ni-Al intermetallics

    NASA Technical Reports Server (NTRS)

    Doychak, J.; Smialek, J. L.; Barrett, C. A.

    1989-01-01

    The oxidation of Ni-Al intermetallic alloys in the beta-NiAl phase field and in the two phase beta-NiAl/gamma'-Ni3Al phase field has been studied between 1000 and 1400 C. The stoichiometric beta-NiAl alloy doped with Zr was superior to other alloy compositions under cyclic and isothermal oxidation. The isothermal growth rates did not increase monotonically as the alloy Al content was decreased. The characteristically ridged alpha-Al203 scale morphology, consisting of cells of thin, textured oxide with thick growth ridges at cell boundaries, forms on oxidized beta-NiAl alloys. The correlation of scale features with isothermal growth rates indicates a predominant grain boundary diffusion growth mechanism. The 1200 C cyclic oxidation resistance decreases near the lower end of the beta-NiAl phase field.

  7. The oxidation of Ni-rich Ni-Al intermetallics

    NASA Technical Reports Server (NTRS)

    Doychak, Joseph; Smialek, James L.; Barrett, Charles A.

    1988-01-01

    The oxidation of Ni-Al intermetallic alloys in the beta-NiAl phase field and in the two phase beta-NiAl/gamma'-Ni3Al phase field has been studied between 1000 and 1400 C. The stoichiometric beta-NiAl alloy doped with Zr was superior to other alloy compositions under cyclic and isothermal oxidation. The isothermal growth rates did not increase monotonically as the alloy Al content was decreased. The characteristically ridged alpha-Al2O3 scale morphology, consisting of cells of thin, textured oxide with thick growth ridges at cell boundaries, forms on oxidized beta-NiAl alloys. The correlation of scale features with isothermal growth rates indicates a predominant grain boundary diffusion growth mechanism. The 1200 C cyclic oxidation resistance decreases near the lower end of the beta-NiAl phase field.

  8. Overview of the development of FeAl intermetallic alloys

    SciTech Connect

    Maziasz, P.J.; Liu, C.T.; Goodwin, G.M.

    1995-09-01

    B2-phase FeAl ordered intermetallic alloys based on an Fe-36 at.% Al composition are being developed to optimize a combination of properties that includes high-temperature strength, room-temperature ductility, and weldability. Microalloying with boron and proper processing are very important for FeAl properties optimization. These alloys also have the good to outstanding resistance to oxidation, sulfidation, and corrosion in molten salts or chlorides at elevated temperatures, characteristic of FeAl with 30--40 at.% Al. Ingot- and powder-metallurgy (IM and PM, respectively) processing both produce good properties, including strength above 400 MPa up to about 750 C. Technology development to produce FeAl components for industry testing is in progress. In parallel, weld-overlay cladding and powder coating technologies are also being developed to take immediate advantage of the high-temperature corrosion/oxidation and erosion/wear resistance of FeAl.

  9. Compton Profile Study of Intermetallic Ti{sub 3}Al

    SciTech Connect

    Vyas, V.; Sharma, G.; Mishra, M. C.; Sharma, B. K.; Joshi, K. B.

    2011-10-20

    The Compton scattering measurement on intermetallic alloy Ti{sub 3}Al is reported in this work. The measurement is made using 59.54 keV gamma-rays from Am{sup 241} source. Theoretical calculation of Compton profile is also performed employing CRYSTAL code within the framework of density functional theory to compare with the measurement. The theoretical profile of the alloy is also synthesized following the superposition model taking the published Compton profiles of elemental solids from the APW method. The experimental study of charge transfer in the alloys has also been done by performing the experimental Compton profile measurements on Ti and Al following the superposition model and charge transfer from Al to Ti is clearly seen on the alloy formation.

  10. Intermetallic strengthened alumina-forming austenitic steels for energy applications

    NASA Astrophysics Data System (ADS)

    Hu, Bin

    In order to achieve energy conversion efficiencies of >50 % for steam turbines/boilers in power generation systems, materials required are strong, corrosion-resistant at high temperatures (>700°C), and economically viable. Austenitic steels strengthened with Laves phase and Ni3Al precipitates, and alloyed with aluminum to improve oxidation resistance, are potential candidate materials for these applications. The creep resistance of these alloys is significantly improved through intermetallic strengthening (Laves-Fe 2Nb + L12-Ni3Al precipitates) without harmful effects on oxidation resistance. This research starts with microstructural and microchemical analyses of these intermetallic strengthened alumina-forming austenitic steels in a scanning electron microscope. The microchemistry of precipitates, as determined by energy-dispersive x-ray spectroscopy and transmission electron microscope, is also studied. Different thermo-mechanical treatments were carried out to these stainless steels in an attempt to further improve their mechanical properties. The microstructural and microchemical analyses were again performed after the thermo-mechanical processing. Synchrotron X-ray diffraction was used to measure the lattice parameters of these steels after different thermo-mechanical treatments. Tensile tests at both room and elevated temperatures were performed to study mechanical behaviors of this novel alloy system; the deformation mechanisms were studied by strain rate jump tests at elevated temperatures. Failure analysis and post-mortem TEM analysis were performed to study the creep failure mechanisms of these alumina-forming austenitic steels after creep tests. Experiments were carried out to study the effects of boron and carbon additions in the aged alumina-forming austenitic steels.

  11. Thermal stability of sputtered intermetallic Al-Au coatings

    SciTech Connect

    Moser, M.; Mayrhofer, P. H.; Ross, I. M.; Rainforth, W. M.

    2007-09-15

    Recently, the authors have shown that single-phase Al{sub 2}Au coatings, prepared by unbalanced magnetron sputtering, exhibit a dense columnar structure and highest hardness and indentation moduli of 8 and 144 GPa, respectively, within the Al-Au films investigated. This study focuses on the thermal stability of Al{sub 2}Au with respect to films containing more Al and Au having Al/Au at. % ratios of 4.32 and 1.85, respectively. Single-phase Al{sub 2}Au has the highest onset temperature for recovery of 475 deg. C and recrystallization of 575 deg. C. Upon annealing Au- and Al-rich films, their stresses deviate from the linear thermoelastic behavior at temperatures (T) above 200 and 450 deg. C, respectively, due to pores and metallic phases present. Metastable Au within the as-deposited Au-rich film is consumed by the growing intermetallic AlAu and AlAu{sub 2} phases at T{>=}450 deg. C, which themselves melt at {approx}625 deg. C. Due to nanometer scale segregations of Al, encapsulated by Al{sub 2}Au in Al-rich coatings, their melting point is reduced by {approx}85 deg. C to 575 deg. C. Dynamic thermal analyses up to 1100 deg. C in synthetic air reveal the single-phase Al{sub 2}Au films with a superior thermal stability and only negligible oxidation. At 750 deg. C, the mass gain is {approx}1.5 mg/cm{sup 2} after 50 h isothermal exposure. Based on the investigations, the authors can conclude that single-phase intermetallic Al{sub 2}Au films have a high potential for oxidation protection of sensitive materials.

  12. Rapid Microwave Preparation of Thermoelectric TiNiSn and TiCoSb Half-Heusler Compounds

    SciTech Connect

    Birkel, Christina S.; Zeier, Wolfgang G.; Douglas, Jason E.; Lettiere, Bethany R.; Mills, Carolyn E.; Seward, Gareth; Birkel, Alexander; Snedaker, Matthew L.; Zhang, Yichi; Snyder, G. Jeffrey; Pollock, Tresa M.; Seshadri, Ram; Stucky, Galen D.

    2012-10-25

    The 18-electron ternary intermetallic systems TiNiSn and TiCoSb are promising for applications as high-temperature thermoelectrics and comprise earth-abundant, and relatively nontoxic elements. Heusler and half-Heusler compounds are usually prepared by conventional solid state methods involving arc-melting and annealing at high temperatures for an extended period of time. Here, we report an energy-saving preparation route using a domestic microwave oven, reducing the reaction time significantly from more than a week to one minute. A microwave susceptor material rapidly heats the elemental starting materials inside an evacuated quartz tube resulting in near single phase compounds. The initial preparation is followed by a densification step involving hot-pressing, which reduces the amount of secondary phases, as verified by synchrotron X-ray diffraction, leading to the desired half-Heusler compounds, demonstrating that hot-pressing should be treated as part of the preparative process. For TiNiSn, high thermoelectric power factors of 2 mW/mK{sup 2} at temperatures in the 700 to 800 K range, and zT values of around 0.4 are found, with the microwave-prepared sample displaying somewhat superior properties to conventionally prepared half-Heuslers due to lower thermal conductivity. The TiCoSb sample shows a lower thermoelectric figure of merit when prepared using microwave methods because of a metallic second phase.

  13. Ab Initio Study of Binary and Ternary Nb3(X,Y) A15 Intermetallic Phases (X,Y = Al, Ge, Si, Sn)

    NASA Astrophysics Data System (ADS)

    Papadimitriou, Ioannis; Utton, Claire; Scott, Andrew; Tsakiropoulos, Panos

    2015-02-01

    Elastic and thermodynamic properties of binary and ternary A15 phases containing Al, Ge, Si, and Sn were studied using the first-principles pseudopotential plane-wave method based on density functional theory. The temperature dependence of the enthalpy of formation for the A15 intermetallics is reported using the quasiharmonic approximation. Elastic properties of the studied compounds were calculated at T = 0 K and were in agreement with the measured values reported in the literature. The elastic properties and thermodynamic data for the metastable A15-Nb3Si are reported for the first time. The Nb3Si has the highest bulk, shear, and Young's modulus values and is predicted to be less ductile than the other three binary A15 intermetallics. The calculations suggest (i) that Al and Sn have a positive effect on the ductility of the A15 compounds of this study, (ii) that Ge as a ternary addition has a ductilizing effect only in the A15-Nb3Si, and (iii) that Si as a ternary addition has a negative effect on the ductility of all the A15 compounds of the present study. The linear thermal expansion coefficients of the Nb, Al, the A15 Nb3Al, Nb3Ge, Nb3Sn, and Nb3Si (A15) phases are reported. The Sn and Al additions in the Nb3Si stabilize the A15 structure, while the Ge addition has the opposite effect, stabilizing the tP32 Nb3Si.

  14. Liquid-phase syntheses and material properties of two-dimensional nanocrystals of rare earth-selenium compound containing planar Se layers: RESe2 nanosheets and RE4O4Se3 nanoplates.

    PubMed

    Gu, Jun; Zhao, Ze-Qiong; Ding, Yi; Chen, Hong-Liang; Zhang, Ya-Wen; Yan, Chun-Hua

    2013-06-01

    Synthesis of diverse two-dimensional nanostructures with unique material properties is of current interest and multidisciplinary importance but remains a challenge for trivalent rare earth (RE)-selenium (Se) compounds because of the weak affinity between hard rare earth cations and soft selenium anions. In this article, for the first time, we report a mild solution approach toward a series of two-dimensional trivalent RE-selenium compound nanocrystals, namely RESe2 nanosheets (RE = La to Nd, for EuSe2, nanobars were obtained) and RE4O4Se3 nanoplates (RE = Nd, Sm, Gd to Ho), under a high chemical potential of selenium obtained by activating SeO2 powder with oleylamine in high boiling point organic solvents. Both kinds of nanocrystals contain Se with -1 valence in planar Se layers, allowing for a great variability in their crystal structures. Satellite diffraction peaks were observed in the electron diffraction pattern of LaSe2 nanosheets, indicating the presence of Peierls distortion in the Se layers. In the RE4O4Se3 nanoplates, the interaction between Se(2-) ions and [Se-Se](2-) dumbbells in the Se layers increases when the radii of the RE(3+) ions decrease along the lanthanide series, resulting in a narrower optical band gap (from 1.96 to 1.73 eV). The LaSe2 nanosheet films fabricated by drop-casting exhibited good electrical conductivity at room temperature (about 1 Ω·cm(-1)). Further, the RE4O4Se3 nanoplates showed very high light extinction capacity in the visible region (extinction coefficient μi: 4.4 × 10(5) cm(-1) for Nd4O4Se3, and 3.1 × 10(5) cm(-1) for Gd4O4Se3), comparable to that (5 × 10(5) cm(-1)) of CuInS2 commonly used in solar cells. PMID:23672182

  15. Synthesis, crystal structure and properties of Mg3B36Si9C and related rare earth compounds RE3-xB36Si9C (RE=Y, Gd-Lu)

    NASA Astrophysics Data System (ADS)

    Ludwig, Thilo; Pediaditakis, Alexis; Sagawe, Vanessa; Hillebrecht, Harald

    2013-08-01

    We report on the synthesis and characterisation of Mg3B36Si9C. Black single crystals of hexagonal shape were yielded from the elements at 1600 °C in h-BN crucibles welded in Ta ampoules. The crystal structure (space group R3barm, a=10.0793(13) Å, c=16.372(3) Å, 660 refl., 51 param., R1(F)=0.019; wR2(F2)=0.051) is characterized by a Kagome-net of B12 icosahedra, ethane like Si8-units and disordered SiC-dumbbells. Vibrational spectra show typical features of boron-rich borides and Zintl phases. Mg3B36Si9C is stable against HF/HNO3 and conc. NaOH. The micro-hardness is 17.0 GPa (Vickers) and 14.5 GPa (Knoop), respectively. According to simple electron counting rules Mg3B36Si9C is an electron precise compound. Band structure calculations reveal a band gap of 1.0 eV in agreement to the black colour. Interatomic distances obtained from the refinement of X-ray data are biased and falsified by the disorder of the SiC-dumbbell. The most evident structural parameters were obtained by relaxation calculation. Composition and carbon content were confirmed by WDX measurements. The small but significant carbon content is necessary by structural reasons and frequently caused by contaminations. The rare earth compounds RE3-xB36Si9C (RE=Y, Dy-Lu) are isotypic. Single crystals were grown from a silicon melt and their structures refined. The partial occupation of the RE-sites fits to the requirements of an electron-precise composition. According to the displacement parameters a relaxation should be applied to obtain correct structural parameters.

  16. Ternary rare earth-lanthanide sulfides

    DOEpatents

    Takeshita, Takuo; Gschneidner JR., Karl A.; Beaudry, Bernard J.

    1987-01-06

    A new ternary rare earth sulfur compound having the formula: where M is a rare earth element selected from the group europium, samarium and ytterbium and x=0.15 to 0.8. The compound has good high-temperature thermoelectric properties and exhibits long-term structural stability up to 1000.degree. C.

  17. The role of ALCHEMI in understanding the properties of ordered intermetallic alloys

    SciTech Connect

    Anderson, I.M.

    1998-11-01

    After one and one-half decades of development, ALCHEMI is approaching the status of an established analytical technique. Many of the problems that have plagued ALCHEMI, especially for the analysis of ordered intermetallic alloys, are now well understood, and accurate site-distributions can be extracted from a variety of intermetallic alloys. This paper begins with an overview of the factors that can lead to large systematic errors or gross misinterpretations of ALCHEMI data, with illustrations from a variety of ordered intermetallic alloys. The paper concludes with a discussion of ALCHEMI in the broader context of understanding the properties of ordered intermetallic alloys. The results of systematic studies are used to illustrate the role of ALCHEMI in determining the competing effects of thermodynamic and kinetic factors during alloy processing and the correlation of alloy properties with the atomic site distributions on which the properties ultimately depend.

  18. Discover Earth

    NASA Technical Reports Server (NTRS)

    Steele, Colleen

    1998-01-01

    Discover Earth is a NASA-sponsored project for teachers of grades 5-12, designed to: (1) enhance understanding of the Earth as an integrated system; (2) enhance the interdisciplinary approach to science instruction; and (3) provide classroom materials that focus on those goals. Discover Earth is conducted by the Institute for Global Environmental Strategies in collaboration with Dr. Eric Barron, Director, Earth System Science Center, The Pennsylvania State University; and Dr. Robert Hudson, Chair, the Department of Meteorology, University of Maryland at College Park. The enclosed materials: (1) represent only part of the Discover Earth materials; (2) were developed by classroom teachers who are participating in the Discover Earth project; (3) utilize an investigative approach and on-line data; and (4) can be effectively adjusted to classrooms with greater/without technology access. The Discover Earth classroom materials focus on the Earth system and key issues of global climate change including topics such as the greenhouse effect, clouds and Earth's radiation balance, surface hydrology and land cover, and volcanoes and climate change. All the materials developed to date are available on line at (http://www.strategies.org) You are encouraged to submit comments and recommendations about these materials to the Discover Earth project manager, contact information is listed below. You are welcome to duplicate all these materials.

  19. Mixed-metal flux synthesis of quaternary RMn 2Tr xZn 20-x compounds with Tr=Al, In

    NASA Astrophysics Data System (ADS)

    Benbow, Evan M.; Latturner, Susan E.

    2006-12-01

    Eighteen new intermetallic compounds RMn 2Tr xZn 20-x (2< x<7; R=rare-earth metal; Tr=Al, In) were synthesized using low-melting mixtures of ( Tr/Zn) as a solvent. Structural refinement using single-crystal X-ray diffraction data shows that the compounds are substituted variants of the cubic CeCr 2Al 20-type structure ( Fd-3 m, Z=8; unit cell parameters vary from a=14.1152(3)Å for YbMn 2Al 5.3Zn 14.7 to a=14.8125(4)Å for SmMn 2In 5.9Zn 14.1). The Zn and Tr elements show site preferences in the indium compounds, but not in the aluminum analogs. The substitution of trielide element for zinc modifies the valence electron count of the compounds to allow for the incorporation of Mn into the structure. Magnetic susceptibility data show no evidence of magnetic ordering down to 3 K.

  20. Exchange interactions in the intermetallic compounds GdCo 4-xNi xAl

    NASA Astrophysics Data System (ADS)

    Prasongkit, J.; Tang, I. M.

    2004-12-01

    The two sub-lattice model is modified to take into account the presence of two types of transition metal ions in GdCo4-xNixAl. An expression for magnetization is obtained and is used to fit the experimental results of Burzo and Pop (J. Magn. Magn. Mater. 196-97 (1999) 768)). From the values of the molecular field coefficients nij (i, j=Gd, Co or Ni), the values of the exchange interactions JGdGd, JGdCo, JGdNi, JCoCo, JCoNi and JNiNi were found. It is seen that three of them, JGdGd, JNiNi and JGdNi, exhibit clear exponential decreases as the Ni content increases; one of them, JCoCo, exhibits a clear exponential increase. The other two exchange interactions, JGdCo (JCoNi), appear to exhibit a parabolic (inverted parabolic) dependence on the Ni content.

  1. Crystallographic features of the structure of a martensite packet of the NiMn intermetallic compound

    NASA Astrophysics Data System (ADS)

    Khlebnikova, Yu. V.; Egorova, L. Yu.; Rodionov, D. P.; Belosludtseva, E. S.; Kazantsev, V. A.

    2016-06-01

    Optical microscopy, scanning electron microscopy, and X-ray diffraction are used to show that a pseudosingle crystal forms upon cooling of an alloy Ni49Mn51 single crystal below the temperature of the β→θ (bcc → fct) transformation. At room temperature, this pseudosingle crystal has the structure of tetragonal L10 martensite with parameters a = 0.3732 nm and c = 0.3537 nm and a tetragonality c/ a = 0.94775. The temperatures of the forward and reverse B2 → L10 transformations are determined. The crystallographic features of martensite packet formation are analyzed. As shown by EBSD, neighboring martensite packets always have three kinds of tetragonal martensite plates, which are in a twin position and have different tetragonality axis directions. Repeated heating and quenching of the pseudosingle crystal result in recrystallization with the formation of coarse grains. The packet structure of the tetragonal martensite is retained in this case, and the sizes of the packets formed within a grain decrease by a factor of 2-3 as compared to the initial pseudosingle crystal.

  2. A Sodium-Containing Quasicrystal: Using Gold To Enhance Sodium's Covalency in Intermetallic Compounds

    SciTech Connect

    Smetana, Volodymyr; Lin, Qisheng; Pratt, Daniel K.; Kreyssig, Andreas; Ramazanoglu, Mehmet; Corbett, John D.; Goldman, Alan I.; Miller, Gordon J.

    2013-09-26

    Gold macht stabil: Na13Au12Ga15, ein natriumhaltiges thermodynamisch stabiles quasikristallines Material, wurde bei einer systematischen Studie des polaren Na-Au-Ga-Intermetallsystems entdeckt. Sein Elektron/Atom-Verhältnis von 1.75 ist für Bergman-Ikosaederphasen extrem klein, doch der substanzielle Au-Anteil sorgt für eine Hume-Rothery-Stabilisierung und neuartige polar-kovalente Na-Au-Wechselwirkungen.

  3. Point defect behavior in B2-type intermetallic compound FeAl

    SciTech Connect

    Haraguchi, T.; Kogachi, M.

    1999-07-01

    Point defect behavior in B2-type FeAl alloys is investigated from a thermodynamic point of view, based on the Bragg-Williams method. The model is developed by taking new defect formation mechanisms, random vacancy distribution (RVD), and antisite atom recovering (ASAR), into consideration, which were proposed based on the current findings in in situ neutron and X-ray diffraction studies for the B2 FeAl. The condition for appearance of the RVD and ASAR states is given. Application of this model to B2 FeAl alloys shows that the RVD-like behavior is reproduced in the Fe-rich composition region and also a rapid increase in vacancy concentration observed in the Al-rich region can be interpreted by the ASAR process by antisite Al atoms.

  4. Analysis of chill-cast NiAl intermetallic compound with copper additions

    NASA Astrophysics Data System (ADS)

    Colin, J.; Gonzalez, C.; Herrera, R.; Juarez-Islas, J. A.

    2002-10-01

    This study carried out a characterization of chill-cast NiAl alloys with copper additions, which were added to NiAl, such that the resulting alloy composition occurred in the β-field of the ternary NiAlCu phase diagram. The alloys were vacuum induction melted and casted in copper chill molds to produce ingots 0.002 m thick, 0.020 m wide, and 0.050 m long. X-ray diffractometry (XRD) and transmission electron microscopy (TEM) performed in chill-cast ingots identified mainly the presence of the β-(Ni,Cu)Al phase. As-cast ingots showed essentially no ductility at room temperature except for the Ni50Al40Cu10 alloy, which showed 1.79% of elongation at room temperature. Ingots with this alloy composition were then heat treated under a high-purity argon atmosphere at 550 °C (24 h) and cooled either in the furnace or in air, until room temperature was reached. β-(Ni,Cu)Al and γ'(Ni,Cu)3Al were present in specimens cooled in the furnace and β-(Ni,Cu)Al, γ'(Ni,Cu)3Al plus martensite-(Ni,Cu)Al were present in specimens cooled in air. Thermogravimetric analysis indicated that martensite transformation was the result of a solid-state reaction with M s ˜ 470 and M f ˜ 430 °C. Tensile tests performed on bulk heat-treated ingots showed room-temperature ductility between 3 and 6%, depending on the cooling media.

  5. Processing Issues for Preliminary Melts of the Intermetallic Compound 60-NITINOL

    NASA Technical Reports Server (NTRS)

    Stanford, Malcolm K.; Thomas, Fransua; DellaCorte, Christopher

    2012-01-01

    The effect of various high temperature heat treatments and cooling rates on the hardness of cast 60-NITINOL (60wt%Ni- 40wt%Ti) was studied. The hardness ranged from approximately 33 HRC for annealed specimens to 63 HRC for water quenched specimens. Aging did not have a further effect on the hardness of the heat-treated and quenched material. The issue of material contamination and its possible effect on quench cracking during heat treatment above 1000 C was explored. The Charpy impact energy of the material was found to be relatively low (ranging from 0.4 to 1.0 J) and comparable to that of cast magnesium. Selection of service environments and applications for this material based on these findings should consider the processing route by which it was produced.

  6. Fabrication and corrosion resistance of HVOF-sprayed Ni2Si intermetallic compound

    NASA Astrophysics Data System (ADS)

    Verdian, M. M.; Raeissi, K.; Salehi, M.

    2013-05-01

    In this study, Ni2Si powders were deposited onto 420 stainless steel substrate using high velocity oxy-fuel (HVOF) process. The coatings were characterized by X-ray diffractometery, optical and scanning electron microscopy and microhardness measurements. Tafel polarization tests and electrochemical impedance spectroscopy (EIS) measurements were employed to study corrosion performance of the coatings in 70% H2SO4 media at room temperature. Here, a dense sintered Ni2Si was used as reference material. The results showed the phase composition of HVOF coating is similar to that of feedstock powders. The corrosion rate of HVOF Ni2Si coatings was much lower than that of 420 stainless steel substrate but slightly higher than that of bulk Ni2Si. Further investigation showed that both thermally sprayed and sintered (reference) Ni2Si alloys exhibited similar anodic polarization behavior including a narrow active section followed by a wide passive region.

  7. Modeling of crack tip dislocation emission in B2 intermetallic alloys

    NASA Astrophysics Data System (ADS)

    Bartholomeusz, Michael F.; Wert, John A.

    1992-04-01

    A model has been previously proposed to describe the energy associated with emission of dissociated superlattice dislocations from crack tips in ordered intermetallic alloys. In the present paper, the model is applied to several B2 intermetallic alloys. The results of the analysis reveal a correlation between the range of slip system orientations for which emission of a dislocation from a crack tip is energetically favorable and the macroscopic fracture mode of the alloy.

  8. Rare earths, the lanthanides, yttrium and scandium

    USGS Publications Warehouse

    Hedrick, J.B.

    2006-01-01

    In 2005, rare earths were not mined in the United States. The major supplier, Molycorp, continued to maintain a large stockpile of rare-earth concentrates and compounds. Consumption decreased of refined rare-earth products. The United States remained a major importer and exporter of rare earths in 2005. During the same period, yttrium was not mined or refined in the US. Hence, supply of yttrium compounds for refined yttrium products came from China, France and Japan. Scandium was not also mined. World production was primarily in China, Russia and Ukraine. Demand for rare earths in 2006 is expected to be closely tied to economic conditions in the US.

  9. Superconducting compounds and alloys research

    NASA Technical Reports Server (NTRS)

    Otto, G.

    1975-01-01

    Resistivity measurements as a function of temperature were performed on alloys of the binary material system In sub(1-x) Bi sub x for x varying between 0 and 1. It was found that for all single-phase alloys (the pure elements, alpha-In, and the three intermetallic compounds) at temperatures sufficiently above the Debye-temperature, the resistivity p can be expressed as p = a sub o T(n), where a sub o and n are composition-dependent constants. The same exponential relationship can also be applied for the sub-system In-In2Bi, when the two phases are in compositional equilibrium. Superconductivity measurements on single and two-phase alloys can be explained with respect to the phase diagram. There occur three superconducting phases (alpha-In, In2Bi, and In5Bi3) with different transition temperatures in the alloying system. The magnitude of the transition temperatures for the various intermetallic phases of In-Bi is such that the disappearance or occurrence of a phase in two component alloys can be demonstrated easily by means of superconductivity measurements.

  10. Rainbow Earth.

    ERIC Educational Resources Information Center

    Arizona State Dept. of Library and Archives, Phoenix.

    The environment is a great concern in the 1990s, and everyone needs to work at maintaining our planet. The 1992 Arizona State Library Reading Program, "Rainbow Earth," provides children with many techniques they can use to help the Earth. This reading program guide provides information on the following: goals, objectives, and evaluation; getting…

  11. Earth Wisdom.

    ERIC Educational Resources Information Center

    Van Matre, Steve

    1985-01-01

    In our human-centered ignorance and arrogance we are rapidly destroying the earth. We must start helping people understand the big picture of ecological concepts. What these concepts mean for our own lives and how we must begin to change our lifestyles in order to live more harmoniously with the earth. (JHZ)

  12. Earth tides

    SciTech Connect

    Harrison, J.C.

    1984-01-01

    Nineteen papers on gravity, tilt, and strain tides are compiled into this volume. Detailed chapters cover the calculation of the tidal forces and of the Earth's response to them, as well as actual observations of earth tides. Partial Contents: On Earth tides. The tidal forces: Tidal Forces. New Computations of the Tide-Generating Potential. Corrected Tables of Tidal Harmonics. The Theory of Tidal Deformations. Body Tides on an Elliptical, Rotating, Elastic and Oceanless Earth, Deformation of the Earth by Surface Loads. Gravimetric Tidal Loading Computed from Integrated Green's Functions. Tidal Friction in the Solid Earth. Loading Tides Versus Body Tides. Lunar Tidal Acceleration from Earth Satellite Orbit Analysis. Observations: gravity. Tidal Gravity in Britain: Tidal Loading and the Spatial Distribution of the Marine Tide. Tidal Loading along a Profile Europe-East Africa-South Asia-Australia and the Pacific Ocean. Detailed Gravity-Tide Spectrum between One and Four Cycles per Day. Observations: tilt and strain. Cavity and Topographic Effects in Tilt and Strain Measurement. Observations of Local Elastic Effects on Earth Tide Tilts and Strains.

  13. Effect of Y2O3 and TiC Reinforcement Particles on Intermetallic Formation and Hardness of Al6061 Composites via Mechanical Alloying and Sintering

    NASA Astrophysics Data System (ADS)

    Chen, Chun-Liang; Lin, Chen-Han

    2015-08-01

    Al6061-based composites reinforced with 2 wt pctY2O3 and 2 wt pctTiC particles produced by mechanical alloying were investigated. The reinforced particles play important roles in the microstructural development and in determining the properties of the alloys. High-energy ball milling can facilitate a solid-state reaction between reinforced particles and the Al matrix, and the reaction kinetics of atomic diffusion can be accelerated enormously by subsequent sintering processing. As a result, complex intermetallic compounds and oxide particles can be formed in the alloy. In this study, the effect of reinforcement on phase formation and mechanical properties of Al6061-based composites has been examined. The results suggest that nano-Y2O3 particles can act as nucleation sites to facilitate formation of Al-Si-Y-O-based oxide particles. The addition of TiC particles can effectively refine the grain structure and encourage formation of iron-rich intermetallic compounds. Nanoindentation was used to understand the local variations in mechanical properties of the Al6061-based composites.

  14. Syntheses, structures, and properties of the bis(cyclopentadienyl) rare-earth imidodiphosphinochalocogenido compounds Cp2Ln[N(QPPh2)2] (Ln = La, Gd, Er, or Yb for Q = Se; Ln = Yb for Q = S).

    PubMed

    Pernin, C G; Ibers, J A

    2000-03-20

    The compounds Cp2Ln[N(QPPh2)2] (Ln = La (1), Gd (2), Er (3), or Yb (4) for Q = Se, Ln = Yb (5) for Q = S) have been synthesized from the corresponding rare-earth tris(cyclopentadienyl) compound and H[N(QPPh2)2]. The structures of compounds 1, 2, 3, and 5, as determined by X-ray crystallography, consist of a Cp2Ln fragment, coordinated eta 3 through two chalcogen atoms and an N atom of the imidodiphosphinochalcogenido ligand [N(QPPh2)2]-. In compound 4, the Cp2Yb moiety is coordinated eta 2 through the two Se atoms of the [N(SePPh2)2]-ligand. 31P and 77Se (for 1) NMR spectroscopies lend insight into the solution nature of these species. Crystal data: 1, C34H30LaNP2Se2, triclinic, P1, a = 9.7959(10) A, b = 12.4134(13) A, c = 13.9077(14) A, alpha = 88.106(2) degrees, beta = 88.327(2) degrees, gamma = 68.481(2) degrees, V = 1572.2(3) A3, T = 153 K, Z = 2, and R1(F) = 0.0257 for the 5947 reflections with I > .2 sigma(I); 2, C34H30GdNP2Se2, triclinic, P1, a = 9.7130(14) A, b = 12.2659(17) A, c = 13.953(2) A, alpha = 88.062(2) degrees, beta = 87.613(2) degrees, gamma = 69.041(2) degrees, V = 1550.7(4) A3, T = 153 K, Z = 2, and R1(F) = 0.0323 for the 5064 reflections with I > 2 sigma(I); 3, C34H30ErNP2Se2, triclinic, P1, a = 9.704(2) A, b = 12.222(3) A, c = 13.980(4) A, alpha = 88.230(4) degrees, beta = 87.487(4) degees, gamma = 69.107(4) degrees, V = 1547.4(7) A3, T = 153 K, Z = 2, and R1(F) = 0.0278 for the 6377 reflections with I > 2 sigma(I); 4, C34H30NP2Se2Yb.C4H8O, triclinic, P1, a = 12.087(4) A, b = 12.429(4) A, c = 23.990(7) A, alpha = 89.406(5) degrees, beta = 86.368(5) degrees, gamma = 81.664(5) degrees, V = 3558.8(18) A3, T = 153 K, Z = 4, and R1(F) = 0.0321 for the 11,883 reflections with I > 2 sigma(I); and 5, C34H30NP2S2Yb, monoclinic, P21/n, a = 13.8799(18) A, b = 12.6747(16) A, c = 17.180(2) A, beta = 91.102(3) degrees, V = 3021.8(7) A3, T = 153 K, Z = 4, and R1(F) = 0.0218 for the 6698 reflections with I > 2 sigma(I). PMID:12526413

  15. Determination of site-occupancies in aluminide intermetallics by ALCHEMI

    SciTech Connect

    Anderson, I.M.; Bentley, J.; Duncan, A.J.

    1995-04-01

    The site-distributions of Fe in four B2-ordered NiAl-based alloys with Fe concentrations of 10%, 2%, and 0.5% have been determined by ALCHEMI (atom-location by channeling-enhanced microanalysis). Site-distributions have been extracted with standard errors between {approximately} 1.5% (10% Fe concentration) and {approximately} 6% (0.5% Fe concentration). The results show that Fe has no strong site-preference in NiAl and tends to reside on the site of the stoichiometrically deficient host element. An improved ALCHEMI analysis procedure is outlined. The analysis explicitly addresses the phenomenon of ionization delocalization, which previously complicated the determination of site-distributions in aluminide intermetallics, leading to inaccurate and oftentimes nonphysical results. The improved ALCHEMI analysis also addresses the presence of anti-site defects. The data acquisition conditions have been optimized to minimize the sources of statistical and systematic error. This optimized procedure should be suitable for all analyses of B2-ordered alloys. Several analyses at different channeling orientations show that the extracted site-occupancies are robust as long as the data are acquired at orientations that are remote from any major pole of the crystal.

  16. Processing and properties of molybdenum silicide intermetallics containing boron

    SciTech Connect

    Schneibel, J.H.; Liu, C.T.; Heatherly, L.; Wright, J.L.; Carmichael, C.A.

    1997-08-01

    Molybdenum-silicon-boron intermetallics with the composition Mo-10.5 Si-1.1 B, wt% (Mo-26.7 Si-7.3 B, at. %) were fabricated by several processing techniques. Powder processing (PM) resulted in macrocrack-free material containing no or only few microcracks. The PM materials contained quasi-equilibrium pores and large concentrations of oxygen. Average room temperature flexure strengths of 270 MPa were obtained. At 1,200 C in air, flexure strengths as high as 600 MPa were observed. These high values are attributed to crack healing and incipient plasticity. Ingot metallurgy (IM) materials contained much less oxygen than their PM counterparts. Depending on the cooling rate during solidification, they developed either mostly macrocracks or mostly microcracks. Due to the high flaw densities, the room temperature flexure strengths were only of the order of 100 MPa. However, the flexure strengths at 1,200 C were up to 3 times higher than those at room temperature. Again, this is attributed to crack healing and incipient plasticity. The IM materials will require secondary processing to develop their full potential. A preliminary examination of secondary processing routes included isothermal forging and hot extrusion.

  17. Thermal stress effects in intermetallic matrix composites. Final report

    SciTech Connect

    Wright, P.K.; Sensmeier, M.D.; Kupperman, D.S.; Wadley, H.N.G.

    1993-09-01

    Intermetallic matrix composites develop residual stresses from the large thermal expansion mismatch (delta-alpha) between the fibers and matrix. This work was undertaken to: establish improved techniques to measure these thermal stresses in IMC's; determine residual stresses in a variety of IMC systems by experiments and modeling; and, determine the effect of residual stresses on selected mechanical properties of an IMC. X ray diffraction (XRD), neutron diffraction (ND), synchrotron XRD (SXRD), and ultrasonics (US) techniques for measuring thermal stresses in IMC were examined and ND was selected as the most promising technique. ND was demonstrated on a variety of IMC systems encompassing Ti- and Ni-base matrices, SiC, W, and Al2O3 fibers, and different fiber fractions (Vf). Experimental results on these systems agreed with predictions of a concentric cylinder model. In SiC/Ti-base systems, little yielding was found and stresses were controlled primarily by delta-alpha and Vf. In Ni-base matrix systems, yield strength of the matrix and Vf controlled stress levels. The longitudinal residual stresses in SCS-6/Ti-24Al-llNb composite were modified by thermomechanical processing. Increasing residual stress decreased ultimate tensile strength in agreement with model predictions. Fiber pushout strength showed an unexpected inverse correlation with residual stress. In-plane shear yield strength showed no dependence on residual stress. Higher levels of residual tension led to higher fatigue crack growth rates, as suggested by matrix mean stress effects.

  18. Processing and properties of molybdenum silicide intermetallics containing boron

    SciTech Connect

    Schneibel, J.H.; Liu, C.T.; Heatherly, L. Jr.; Carmichael, C.A.

    1998-11-01

    The processing and mechanical properties of Mo-Si-B intermetallic alloys with compositions Mo-26.7Si-7.3B and Mo-12Si-8.5B (at.%) were investigated. The first alloy consisted of the phases Mo{sub 3}Si, Mo{sub 5}Si{sub 3} (T1) and Mo{sub 5}SiB{sub 2} (T2). Attempts to extrude castings of this alloy at 1700 or 1800 C were not successful. Hot isostatic pressing of elemental powders was more promising and room temperature flexure strengths on the order of 200 MPa were reached. The second alloy with the composition Mo-12Si-8.5B could be readily cast and consisted of {alpha}-Mo inclusion in a brittle matrix of Mo{sub 3}Si and T2. A heat treatment of 1 day at 1600C in vacuum improved the room temperature strength and fracture toughness. Values on the order of 500 MPa and 10 MPa m{sup 1/2}, respectively, were obtained. Consistent with ductile phase toughening, limited plastic deformation as well as debonding of the {alpha}-Mo inclusions were seen on fracture surfaces.

  19. Molecular assembly and organic film growth on complex intermetallic surfaces

    NASA Astrophysics Data System (ADS)

    Al-Mahboob, Abdullah; Sharma, Hem Raj; Sadowski, Jerzy T.; Ledieu, Julian; Fournée, Vincent; McGrath, Ronan

    We extensively studied the role of molecular symmetry and symmetry/structures of wide ranges of substrate-surfaces from non-periodic to periodic to quasi-crystalline in nucleation, growth and phase transition in films made of organic molecular materials. Recently, most interest in quasicrystals is due to the generalization of aperiodic ordering to several classes of systems. Compared to periodic materials, these provide a closer approximation to an isotropic first Brillouin zone, which is of great importance to the design of new functional materials. Here, we present results obtained from our ongoing study of interface mediated molecular assembly extended on complex intermetallic surfaces with specific examples of C60 and Zn-phthalocyanine on quasicrystalline and approximant surfaces. We employed in-situ real-time low-energy electron microscopy (LEEM) for investigation of the processes in assembly and film growth and post-growth STM study and DFT calculations to understand structural details and growth mechanism. Research were carried out in part at the Center for Functional Nanomaterials, Brookhaven National Lab, USA; partly at Institut Jean Lamour, Université de Lorraine, France; and partly at the Surface Science Research Centre, University of Liverpool, UK.

  20. Discover Earth

    NASA Technical Reports Server (NTRS)

    1997-01-01

    Discover Earth is a NASA-funded project for teachers of grades 5-12 who want to expand their knowledge of the Earth system, and prepare to become master teachers who promote Earth system science in their own schools, counties, and throughout their state. Participants from the following states are invited to apply: Connecticut, Delaware, Maine, Maryland, Massachusetts, New Hampshire, New Jersey, New York, Pennsylvania, Rhode Island, Vermont, and Washington, DC. Teachers selected for the project participate in a two-week summer workshop conducted at the University of Maryland, College Park; develop classroom-ready materials during the workshop for broad dissemination; conduct a minimum of two peer training activities during the coming school year; and participate in other enrichment/education opportunities as available and desired. Discover Earth is a team effort that utilizes expertise from a range of contributors, and balances science content with hands-on classroom applications.