Intermetallic Solid Solutions Research Articles

Developing contacting solutions for n-type Mg3Sb1.5Bi0.5 based thermoelectric materials

n-type Mg3Sb1.5Bi0.5 intermetallic solid solution is a promising thermoelectric (TE) material for medium temperature range (room temperature to 450⁰ C) applications due to its high figure of Merit (peak zT value of 1.5-1.7) and cost-effective constituent elements. Extensive research on materials development has been carried out on this material system but there are limited reports related to its contacting. In this work, a detailed study of the contacting in Mg3.0+ySb1.49Bi0.49Te0.02(y=0.3) has been carried out using both single layer and multilayer approaches. For single layer contacting studies, the contact metal (Ni/Fe) is directly in contact with TE material while in case of the multilayer contacting process, the TE material powder is sandwiched between two layers (with different functionalities). The top layer is a metal foil (Cu/Ni) and is followed by a composite layer consisting of a mixture of TE material and Ni powder. Compaction in both cases is carried out by simultaneous application of temperature and pressure using the mono-block sintering process. It is observed that the electrical contact resistance (Rc) values for all cases lie in the range of 30-50μΩcm2. However, a marked difference in the microstructure and nature of bonding is observed between the various contacting approaches. For single layer contacting, Fe is observed to form an abrupt interface with absence of any reactive phases at the interface. However, Ni results in the formation of various intermetallic phases and a diffuse interface. For both Fe and Ni, cracks or delamination are observed at the interface. The multilayer contacting studies result in well bonded and crack-free interface for all the studied compositions. Various intermetallic phases have been identified from an elemental analysis of the interface region. Further, no diffusion of the metal layers is observed into the thermoelectric matrix.

Chemical Vapor Deposition of an Iridium Phase on Hafnium Carbide and Tantalum Carbide

Nanocrystalline iridium coatings on hafnium carbide and tantalum carbide substrates are prepared by chemical vapor deposition (MOCVD) at 600°С. Subsequent high-temperature treatment at 1100°С gives rise to chemical reactions between iridium and hafnium carbide or tantalum carbide to yield nanosized substitutional intermetallic solid solutions MIr3 – x and evolve free carbon. The occurrence of intermetallic interaction is proved by X-ray photoelectron (XPS) spectroscopy.

Structural transition and antiferromagnetic ordering in the solid solution CePd1−x Au x Al (x = 0.1–0.9)

Abstract The intermetallic solid solution CePd1−x Au x Al (x = 0.1–0.9) has been synthesized from the elements by arc-melting and subsequent annealing in induction followed by tube furnaces. The samples were characterized using the Guinier powder diffraction technique and the structures of the nominal compositions CeAuAl and CePd0.2Au0.8Al were refined from single crystal X-ray diffractometer data. For small values of x = 0.1–0.3, the compounds crystallize in the hexagonal ZrNiAl-type structure (space group P 6 ‾ $‾{6}$ 2m), while for x = 0.5–0.9 the orthorhombic TiNiSi-type structure (space group Pnma) was observed. In both structure types, the transition metal and aluminum atoms form a complex polyanionic network with the cerium atoms filling the respective cavities. The transition metal atoms are in both cases surrounded in the shape of a tri-capped trigonal prism, the connectivity of these units, however, is different. Temperature-dependent magnetic susceptibility measurements of all compounds indicated a stable trivalent oxidation state for the cerium atoms along with antiferromagnetic ordering around T N ∼ 3 K.

Hardness of promising intermetallics obtained by the solid-state reaction of refractory carbides with iridium

Solid-state reactions of refractory carbides MC (M = Hf, Ta, W) with iridium powder at 1600 °C result in the formation of the corresponding MIr3±x intermetallic solid solution. Vickers microhardness tests of MIr3 intermetallics were performed using the load of 10 gf (HV0.01), and the local elemental composition was determined by energy dispersive spectroscopy (EDS) for each indentation area. The results of indentation tests showed that MIr3 intermetallics are much harder than pure Hf, Ta, W, or Ir (top-hardness metals), with the hardness 900–1400 HV0.01. The hardness value is affected by the real elemental composition of MIr3±x solid solution. Free carbon released during the interaction of metal carbide with iridium can contribute to the microhardness values.

Crystal structure and magnetic properties of intermetallic semiconductor FeGa3 lightly doped by Co and Ni

We have explored the crystal structure and magnetic properties of two intermetallic solid solutions of the IrIn3 structure type. Although Fe0.95Co0.05Ga3 and Fe0.975Ni0.025Ga3 are isomorphous and possess exactly the same concentration of valence electrons, they display noticeable differences in their crystal structure associated with a different nature of the FeCo and FeNi dumbbells. The former contains an odd number of electrons compared to an even number of the latter dumbbell. Responding to localized spins of the FeCo dumbbells, the 69Ga NQR relaxation rate in Fe0.95Co0.05Ga3 is governed by temperature independent spin-lattice relaxation typical for diluted paramagnetic centers at low temperatures. In Fe0.975Ni0.025Ga3 with zero magnetic moment of the dumbbells the 69Ga spin-lattice relaxation rate is strongly reduced and in-gap states in the energy gap show up as a broad maximum near 70 K.

RE16AuxAl13-x with RE = La-Nd, Sm (x≤ 3.37): synthesis, crystal structure and physical properties of an intermetallic solid solution with barrelane analogue units.

During phase analytical investigations in the rare-earth element rich side of the ternary system cerium-gold-aluminum, the new ternary rare-earth (RE) gold aluminides with a composition of RE16AuxAl13-x (RE = La-Nd, Sm, x≤ 3.37) have been synthesized first by reactive eutectics of RE/Au with Al. Single crystals of high quality can be obtained by this method. The title compounds can be selectively prepared by annealing arc-melted beads of appropriate composition below the peritectic point of the respective system. Like prototypic La16Al13, the representatives of the solid solution RE16AuxAl13-x (RE = La-Nd, Sm; x≤ 3.37) crystallize in the hexagonal crystal system (space group P6[combining macron]2m, a = 916.6-890.4 pm, c = 1122.4-1090.1 pm) with one formula unit per unit cell. Single crystal investigations revealed Au/Al mixing on three of the four crystallographic aluminum sites. These sites form an empty (Au/Al)11 barrelane analogous unit, coordinated solely by the respective rare-earth atoms. In addition one independent Al site with a fivefold capped trigonal prismatic arrangement, a so called Edshammar polyhedron, exists. Magnetic measurements of Ce16Au3Al10 revealed two antiferromagnetic transitions with Neél-temperatures of 7.7(1) and 2.7(1) K and a magnetic moment of μeff = 2.48(1) μB, Pr16Au3Al10 shows ferromagentic ordering with a Curie-temperature of 19.8(1) K and a magnetic moment of μeff = 3.58(1) μB.

Synthesis, crystal stability, and electrical behaviors of La0.7Sr0.3Cr0.4Mn0.6O3−δ–XCu0.75Ni0.25 for its possible application as SOFC anode

La0.7Sr0.3Cr0.4Mn0.6O3−δ (perovskite-type) nanocomposites impregnated with XCu0.75Ni0.25 have been synthesized by sol–gel method. Crystal structure of LSCM–Cu0.75Ni0.25 composites were refined by the Rietveld method. Crystal symmetry of CuO and NiO nanoparticles have monoclinic $$ C12/c $$ and cubic $$ Fm\bar{3}m $$ symmetry, respectively, but after sintering at 1,200 °C and reducing the temperature to 600 °C, it’s transformed into a new Cu0.75Ni0.25 intermetallic solid solution without secondary phase. We have detected a cationic inter-diffusion in Cu ↔ Ni interphase crystals during this reduction process; however, when sintering time exceeds 2 h at 1,200 °C this reaction mechanism is interrupted by a sublimation phenomenon; which causes Cu2O cubic structure segregation from monoclinic CuO structure. This leads to Cu precipitation from the Cu1−x Ni x solid solution. Cu0.75Ni0.25 inhibits the LSCM perovskite-type grain growth (t ≈ 220 nm). Electrical conductivity indicates the presence of semiconductor and metallic-type behaviors with a maximum electrical conductivity (800 °C) >4.5 (log σ, Sm cm−1). When Cu0.75Ni0.25 concentration was 25 and 35 %, semiconductor behavior were dominated. Thermal expansion coefficients showed a linear dependence inversely proportional to Cu0.75Ni0.25 concentration. Electrical conductivity, Rietveld analysis, Porosity, TEC, and E a behaviors lead to the conclusion that the anodes between 25 and 35 % (Cu0.75Ni0.25) are closer to applications at SOFC.

Intermetallic solid solution Fe1−xCoxGa3: Synthesis, structure, NQR study and electronic band structure calculations

Unlimited solid solution Fe1−xCoxGa3 was prepared from Ga flux. Its crystal structure was refined for Fe0.5Co0.5Ga3 (P42/mnm, a=6.2436(9), c=6.4654(13), Z=4) and showed no ordering of the metal atoms. A combination of the electronic band structure calculations within the density functional theory (DFT) approach and 69,71Ga nuclear quadrupole resonance (NQR) spectroscopy clearly shows that the Fe–Fe and Co–Co dumbbells are preferred to the Fe–Co dumbbells in the crystals structure. The band structure features a band gap of about 0.4eV, with the Fermi level crossing peaks of a substantial density of electronic states above the gap for x>0. The solid solution is metallic for x>0.025. The study of the nuclear spin–lattice relaxation shows that the rate of the relaxation, 1/T1, is very sensitive to the Co concentration and correlates well with the square of the density of states at the Fermi level, N2(EF).

Multi-scaled polymer-based composite materials synthesized by mechanical alloying

Multi-scaled composite materials are of great importance, because they exhibit higher mechanical properties than those attained using conventional fillers or polymer blends. In this work, multi-scaled composite materials based on ultra-high-molecular weight polyethylene (UHMWPE), quasicrystals, polyimide and bronze are investigated for use in the moving parts of machines, gears, bearings, and sliding elements. The main object is to investigate the process of fabricating such composite materials, and to check if these materials are reproducible and reliable to an industrial extent. The specimens were prepared using a high-energy planetary mill. When milled with bronze, the quasicrystalline phase was dissolved into an intermetallic solid solution; milling with polymers showed to conserve the quasicrystalline phase, whereas the crystallization of UHMWPE was achieved during the milling process. Tribological study of consolidated samples showed an increase in the wear resistance for the bronze-containing composite materials. In comparison with pure UHMWPE, the polyimide-based specimen exhibited higher strength and hardness. This work has demonstrated the possibility of producing composite materials with acceptable and reliable properties using the mechanical alloying technology.

Kinetics of antiphase domain boundaries during an L12order-disorder phase transformation: A Monte Carlo simulation

Abstract The formation of the L12 phase in an A3B intermetallic solid solution has been investigated by Monte Carlo simulation. The ordering is modelled with a simple atomic exchange mechanism based on a fcc Ising model with appropriate values for the pairwise atomic interactions. It is shown that the ordering kinetics occurs on two time scales: nucleation and growth of ordered domains and the annealing of antiphase boundaries between the domains. The model is applied to the L12 ordered Ni3Al phase under various irradiation conditions. It is demonstrated that the migration and annihilation of antiphase boundaries largely determine the time evolution of the L12 phase.

Evidence for biquadratic exchange interactions in GdAg1_xZnx

Copyright (c) 1997 Elsevier Science B.V. All rights reserved. We have re-examined the magnetic-phase diagram of GdAg 1−x Zn x , an intermetallic solid solution of a ferromagnet (GdZn) and an antiferromagnet (GdAg). Samples of the intermediate composition range 0.48<x<0.59 show new magnetic-ordering phenomena and all exhibit nearly the same phase diagram at the application of a magnetic field. These phase diagrams comprise two ferrimagnetic phases with ground-state magnetization values of m≃(1)/(3) and m≃(2)/(3) and one uncommon high-temperature phase which is nearly ferromagnetic but which has a finite susceptibility and therefore no spontaneous magnetization. All ordered phases seem to coexist at one multicritical point. It is argued that the observed variety of magnetic phases is due to biquadratic exchange interactions which remain as the only active ones in a situation where the ferromagnetic and antiferromagnetic bilinear interactions compensate each other. The easiest method to identify biquadratic interactions is the Curie−Weiss law of the cubic susceptibility χ 3 . However, in metallic systems the Curie−Weiss temperature regime of χ 3 is not nearly reached even at five times the ordering temperature, thus preventing the evaluation of t 3 which provides a measure for the strength of the biquadratic interaction in insulating systems. This shows that there are much stronger and strongly temperature-dependent individual biquadratic interaction processes of either sign than one might assume according to the macroscopically observed average interaction. Although the existence of the new magnetically ordered states is confirmed with magnetization, dilatometric and specific heat measurements, no corresponding neutron-diffraction intensities are observed in zero-magnetic field which points to strongly fluctuating or non-collinear magnetic structures. Since the outlined observations fall into a composition and temperature range in this random magnetic-bond system where magnetic non-equilibrium phenomena become visible, special precautions are necessary to obtain the low-temperature equilibrium magnetization curves.

Study of palladium–analyte binary system in the graphite furnace by surface analytical techniques

The mechanisms of the stabilization of Pb, Zn and As by a palladium modifier were investigated by scanning electron microscopy, X-ray diffraction spectrometry and X-ray photoelectron spectrometry. All three elements were found to form an intermetallic solid solution with excess of Pd. The concentration ratio of Pd to analyte varies with the surface depth of Pd–analyte species. Chemical shifts measured in the binding energy of Pd and analyte are insignificant. The monophase of the Pd lattice in which some Pd atoms are displaced by the analyte atoms has been identified as being dominant. It is suggested that the reduced Pd and analyte form a stable intermetallic solid solution during the ashing stage and the analyte atoms remain in the Pd lattice until the temperature is high enough to break down the lattice.

Magnetic phase diagram of GdAg1− xZnx

The magnetic phase diagram of GdAg 1− x Zn x , an intermetallic solid solution of an antiferromagnet ( GdAg: T N = 136 K) and a ferromagnet ( GdZn: T C = 269 K), has been elaborated from magnetization measurements. The antiferromagnetic phase boundary T N( x) first passes a broad maximum meeting the ferromagnetic phase boundary T C( x) at x 1 = 0.575 and T 1 = 72 K, where four phases coexist. On approaching ( x 1, T 1) along T N( x) the magnetization phenomena vanish. At x 1 the phase transition still has ferromagnetic appearance but proceeds into a state without spontaneous magnetic moment. Two different ferromagnetic phases (F 1, F 2) and one ferrimagnetic phase (F 3) occur in the composition intervals 0.69 < x 1 <1, and 0.61 < x 2 < 0.69 and 0.51 < x 3 < 0.61. All phase transitions seem to be of second order except th e F 1− F 2 one at x = 0.69 which is of first order. This phase line meets the paramagnetic to ferromagnetic phase boundary T C( x) in a multicritical point with the coordinates x m = 0.69, T m = 123 K. Six further mixed magnetic phases, M 1, 2, ..., 6, are observed between x = 0.33 and 0.6 below the antiferromagnetic branch and exhibit irreversible thermodynamic properties, such as hysteresis, below about 40 K. Assuming local magnetic interactions only between nearest and next-nearest Gd neighbours, the T N( x) and T C( x) phase boundaries can be described fairly well by a simple model calculation using different exchange parameters for a few relevant distributions of Ag and Zn atoms.

Intermetallic compounds?A new base for heat-resisting materials

1. Intermetallic compounds form a special class of inorganic compounds which is promising as a source of heat-resisting materials. They have many properties which are characteristic of metals—mechanical, physical, chemical, and others. 2. Intermetallic compounds have higher melting points than their constituents, higher strength, and retain their heat resistance up to higher temperatures than metals and their solid solutions. 3. Many intermetallic compounds have a high thermal stability and resistance to corrosive media, and can therefore be used as protective coatings for metals and alloys easily oxidized on heating. 4. Intermetallic compounds can interact between themselves. The principles of the formation of intermetallic solid solutions and compounds of complex composition have been determined. 5. The variation of the properties with the composition follows Kurnakov's rules, but the properties of intermetallic compounds may be tens of times higher than those of solid solutions of metals. 6. Certain intermetallic compounds have ductile properties permitting hot and even cold working. These include Ni3Ti, NiTi, Ti3Al, TiAg, etc. 7. With different compositions of precipitation-hardening alloys based on intermetallic solid solutions, a considerable increase in the strength and heat resistance of these materials is possible. 8. Intermetallic compounds and alloys based on them can be used for creating heat-resisting, thermally stable materials. New alloys based on Ni3Al and Ti3Al are very promising.

An investigation of the aluminium-rich alloys in the aluminium-samarium-uranium and aluminium-dysprosium-uranium ternary systems: II. The aluminium-rich alloys in the Al-Dy-U ternary system

As in the ease of U/Al/Sm system discussed in the preceding paper, an isothermal section at 600° C of the aluminium-rich corner of the Al/U/Dy system, freezing sequence of some ternary alloys and the fabrication characteristics of Al/U/Dy alloys in the Al/24% U region were investigated. Micrographie and X-ray methods, thermal and microprobe analysis were used in this investigation. One ternary intermetallic compound was identified as U 2Dy 3Al 15. A pseudobinary system DyAl 2-UAl 2 (cubic C 15 MgCu 2 type) was found. The phase boundaries of the single-, two- and three-phase alloys were determined; a region of insolubility in the liquid and solid state was delineated. Three intermetallic compounds were found to be in equilibrium with the aluminium-rich solid solution. The existence of three intermetallic solid solutions (Dy, U)Al 4, (Dy, U)Al 3and (Dy, U)Al 2 was established.

The molecular constitution of certain intermetallic solid solutions at temperatures below that of the eutectic examined thermodynamically

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