Quasi-binary Alloys Research Articles

Liquid–liquid phase equilibrium in ternary immiscible In–Tl–Te melts

The shear viscosity measurements were performed for a liquid immiscible ternary system In–Tl–Te in a temperature range from the monotectic to about 1130 K using an oscillating-cup viscometer. The In x Tl 80− x Te 20 (0 ≤ x ≤ 80 at.%) melts may be considered as a set of quasibinary (In/Tl)Te alloys of almost critical compositions. Variation of the In/Tl ratio at a constant Te content changes properties of coexisting liquids and affects the binodal temperature. Critical parameters describing peculiarities of viscosity near the critical point (CP) are evaluated. A new analysis technique based on the dynamic theory of phase transitions for viscosity behavior near to the CP is proposed. The results are compared with available data for immiscible dielectric solutions.

The miscibility gap in cadmium, mercury and zinc telluride systems: Theoretical description

Miscibility gap locations in the CdTe–ZnTe and HgTe–ZnTe systems are calculated yielding the critical parameters ( T c / K , x c (second compound)) (407, 0.38) and (558, 0.33), respectively. The obtained functions allow us to predict the location of the miscibility gap in the CdTe–HgTe–ZnTe system based on the Kohler and Redlich–Kister–Muggianu procedures. Ternary phase diagrams for the Hg–Cd–Te, Cd–Zn–Te and Hg–Zn–Te systems in the subsolidus region are also estimated based on known thermodynamic properties of the binary systems and our results for the quasi-binary alloys in the paper.

Spinodal decomposition range of alloy with wurtzite structure

Spinodal decomposition ranges of quasibinary alloys with the wurtzite structure are described considering the coherency strain energy. The alloys are represented as quasibinary regular solutions that are externally unstrained. Spinodal decomposition should occur in planes with the orientation depending on lattice parameters and elastic coefficients of constituent compounds. The coherency strain energy eliminates spinodal decomposition in InxGa1–xN and InxB1–xN in total composition range at all temperatures of interest. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

The effect of hydrogen on the shear modulus of quasibinary alloys of the TiNi-TiCu system

Hydrogen saturation of amorphous quasibinary alloys of the TiNi-TiCu system is accompanied by a catastrophic decrease in their shear moduli. The effect is not related to the formation of new phases or structural components during hydrogenation.

The Ti–TiNi–TiOs system

The TiNi–TiOs vertical section formed by the equiatomic phases of the Ti–Ni and Ti–Os binary systems was constructed by the method of thermodynamic calculation, using the principle of equalities between chemical potentials of the components in coexisting phases, experimental data for the quasibinary section alloys and thermodynamic data for the TiNi and TiOs phases. A good agreement observed between the calculated and the experimental results indicates that the adopted thermodynamic model is a reasonable approximation. The set of parameters derived from the optimization is thus recommended for use in future studies.

Effects of Excess Mg and Si on the Isothermal Ageing Behaviours in the Al-Mg<SUB>2</SUB>Si Alloys

The effects of excess Mg and Si contents on the isothermal ageing processes of Al-Mg2Si alloys have been investigated by means of transmission electron microscopy and the following results were obtained. After the formation of β′′ needles inducing large age hardening, cuboid β particles precipitate in both the excess Mg and the quasi-binary alloys, but fine Si particles nucleate in the excess Si alloys. In the quasi-binary alloy, the following reaction is the precipitation of β′ rods and then β plates form. In the excess Si alloys, various rodlike precipitates form after the precipitation of β′′ needles and Si particles in the sequence: Type-A rods→Type-B rods→β′ rods. This precipitation sequence can be understood by considering the chemical compositions of them determined by Matsuda et al.

Kondo effect inCexLa1−xCu2.05Si2intermetallics

The magnetic susceptibility and susceptibility anisotropy of the quasibinary alloy system ${\mathrm{Ce}}_{x}{\mathrm{La}}_{1\ensuremath{-}x}{\mathrm{Cu}}_{2.05}{\mathrm{Si}}_{2}$ have been studied for low concentration of Ce ions. The single-ion description is found to be valid for $x<~0.09.$ The experimental results are discussed in terms of the degenerate Coqblin-Schrieffer model with a crystalline electric field splitting \ensuremath{\Delta}\ensuremath{\simeq}330 K. The properties of the model, obtained by combining the lowest-order scaling and the perturbation theory, provide a satisfactory description of the experimental data down to 30 K. The experimental results between 20 K and 2 K are explained by the exact solution of the Kondo model for an effective doublet.

Investigation on self-aligned HgTe nano-crystals induced by controlled precipitation in PbTe–HgTe quasi-binary compound semiconductor alloys

The present paper reports the results of the controlled precipitation for the HgTe nano-crystals in the PbTe semiconductor matrix and demonstrates its effectiveness in producing well-organized and crystallographically aligned semiconductor nano-crystals. Following the same procedure used in metallic alloys, the semiconductor alloys are treated at 600°C for 48 h, quenched and aged up to 400 h at 300°C and 400°C to induce homogeneous nucleation and growth of HgTe precipitates. Examination of the resulting precipitates using transmission electron microscopy (TEM) reveals that the coherent HgTe precipitates form as thin disks along the {1 0 0} habit planes of PbTe matrix. It is also found that the precipitate undergoes a gradual shape change without any noticeable coarsening, from a disk to a cube, as the aging time increases. The microstructure after full aging is found to contain almost equal sized HgTe cubes, roughly 7 nm, that maintain coherency with {1 0 0} planes of the matrix. These results combined with the extreme dimension of the precipitates and the simplicity of the formation process leads to a belief that controlled precipitation can be an effective method in preparing a desirable quantum-dot microstructure.

Crystallization of the A IIIxB III1 −xC V alloys from the supercooled liquid solutions

The initial stage crystallization of the A x IIIB 1− x IIIC V quasibinary alloys from the supercooled dilute liquid solutions is considered. Nonequilibrium crystallization is presented by the minimum condition of the Helmholtz free energy. A model of the regular solutions is used for the description of the liquid and solid phases. The compositional dependencies of the Ga x Al 1 −x As and In x Ga 1 −x P alloys on temperature and supercooling of the liquid solutions are demonstrated. The affinities of the formation reactions of binary compounds constituting the A x IIIB 1− x IIIC V alloys are equal one another. Ratios between the affinities and temperature in the energy units are substantially smaller than unity for all considered growth processes.

Precipitation sequence in a SiC/Al-Mg2Si alloy composite material

The precipitation sequence of an Al-1.0mass%Mg2Si composite material having 8 vol.% SiC particles was investigated by Vickers micro hardness and specific electrical resistivity measurements, and by TEM observation. The formation of GP zones was suppressed in the composite material and its age-hardenability was reduced. Distribution of precipitates in the composite material was coarser and their size was larger than that in the Al-1.0mass%Mg2Si alloy (base alloy). Some types of precipitates in the composite material were not similar to those found in the base alloy but were similar to those in an Al-1.0mass%Mg2Si alloys with excess silicon (the excess Si alloy). Especially, the metastable phases in the composite material aged at 473 K belonged to the type-A, type-B and type-C precipitates, which are typical metastable phases in the excess Si alloy, instead of the β′ phase that is a typical metastable phase in quasi-binary Al-Mg2Si alloys. The dislocations had little effect on the aging process of this composite material, because of the small number of dislocations introduced by the quenching after solution treatment.

Band gap and lattice constant of GaxIn1−xAsySb1−y

The energy band gap and lattice constant of the quaternary alloy GaxIn1−xAsySb1−y were determined over the entire composition space (x, y) using a correlated function expansion (CFE) technique to interpolate from observed ternary compound data. Considerable anomalous band gap behavior (i.e., deep bowing) was found, which produced band gap minima as a function of composition. This deep bowing effect was experimentally observed in a quasibinary alloy (GaSb)1−z(InAs)z at low values of z. In addition, the CFE lattice matching relations of the alloy grown on GaSb and InAs were obtained as a function of composition, and the corresponding band gaps were estimated. The CFE estimates were in good agreement with existing experimental data.

The shift of the growth interface during the Bridgman process due to the solute redistribution

The mathematical models are deduced for the evaluation of the growth interface shift due to the solute redistribution during the normal Bridgman process and the ACRT-B process. Hg 0.78Cd 0.22Te and other II–VI quasi-binary alloys are taken as examples in the calculation. The results show that: (1) in the normal Bridgman process, the shift of the growth interface mainly takes place in the intial transient region. At the growth temperature gradient of 10 K/cm, displacement of the growth interface as large as about 80 mm occurs in this region. In the steady growth region, the interface position becomes fixed until the final transient region starts, then the interface moves downward again. Increasing the growth rate results in a sharper shift speed in the initial transient regions even though the total shift distance does not change. (2) In the ACRT-B process, the shift of the growth interface takes place continuously in the whole growth process and is independent of the growth rate.

A simplified approach to non-collinear magnetism in amorphoustransition metals

A theory of non-collinear magnetism in structurally disordered metals ispresented on the basis of the Gaussian model for the distribution ofthe interatomic distance and the saddle-point approximation to theintegral equation for the distribution of local magneticmoments. Simple self-consistent equations for the local moments,which significantly reduce the numerical calculations, are obtained.Magnetization and the spin-glass order parameters are calculated as afunction of the d-electron occupation number N and temperature.It is shown that the theory describes the transition from theferromagnetism to the non-collinear spin glass with decreasing N,which is expected experimentally.The calculated magnetic phase diagram isshown to be consistent with previous results based on the Monte Carlosampling method as well as the recentexperimental data on the quasi-binary amorphous Fe-Mn alloys.

HRTEM Observation of G.P. Zones and Metastable Phase in Al-Mg-Si Alloys

A high resolution transmission electron Microscopy (HRTEM) was performed by the microstructure analyses of a Al-1.6mass%Mg 2 Si alloy in order to elucidate the characteristic two-step aging behavior of Al-Mg-Si alloys. The optical conditions (accelerating voltage, defocus and crystallographic orientations ) for the HRTEM observation of fine precipitates were determined. In the alloy aged at 343-423 K for 60ks, the fine G.P.zones with mono layer or multi layer structures could be found. When the specimens containing such G.P.zones are finally aged at 473K up to their maximum hardness conditions, a number of random-type precipitates, which are assumed to contain high concentration vacancies, are homogeneously formed. These precipitates results in the increasing of hardness, exhibiting so-called positive effect of the two-step aging. On the contrary, the alloy aged at 293 K for 60 ks, the primary G.P. zones with the diameter of-1nm are formed with high number density. When this alloy is finally aged at 473 K up to a maximum hardness, parallelogram-type precipitates are preferentially formed. These parallelogram-type precipitate results in the decreasing of hardness, exhibiting negative effect of the two-step aging. Based on the microstructure analysis, it is concluded that both the primary and mono layer G.P.zones almost dissolve into the matrix at the beginning of 473 K aging, while multi layer G.P. zones continuously transform into random-type precipitate or act as effective nucleation sites for the random-type precipitates. There were no β and β phase at peak aged condition in this quasi-binary alloy.

Bulk growth of quasi-binary quaternary alloys

Crystal growth experiments were conducted by: (a) melting together two III–V compounds (InAs, GaSb) and (b) melting together one III–V compound (InSb or GaSb) and one II–VI compound (CdTe or HgTe). These melts contain four different atoms, but in comparison to the conventional quaternary alloys A x C 1− x B y D 1− y , have a constrain in the composition given by x= y, and therefore can be designated as “quasi-binary”. The composition of these melts is (AB) 1− x (CD) x . Bulk crystals were produced from these melts by directional solidification and Czochralski pulling. Our goal was to determine whether the grown crystals will remain “quasi-binary” or, due to segregation will turn conventional quaternary x≠ y. The grown crystals were free of cracks, which can be explained by low lattice mismatch. Using the electron probe micro-analysis (EPMA), it was determined that quasi-binary (InSb) 1− x (CdTe) x crystals were obtained. The other systems yielded conventional quaternary specimens with x≠ y.

Effects of alloying and pressure on magnetic properties of itinerant intermetallic compound UFe2

The ferromagnetic state of the itinerant compound UFe2 correlated with a peak in the density of states at the Fermi level is well known to be strongly suppressed by replacing Fe with other 3d elements. To separate the effect of change in filling of the band from that of its deformation under alloying, the magnetic susceptibility of both quasi-binary alloys U(Fe1−xMex)2 (Me=Mn, Co) with a varying number of valence electrons and isoelectronic quasi-ternary alloys U(Fe1−xTx)2, U(Fe0.9−xMn0.1Tx)2 and U(Fe0.9−xCo0.1Tx)2 (T=Mn0.5Co0.5) was studied in the temperature range 4.2 K⩽T⩽300 K. Both effects were found to play important roles in suppression of the ferromagnetic state in UFe2-based alloys. In addition, the magnetic susceptibility of U(Fe1−xMnx)2 and U(Fe1−xTx)2 alloys and UCo2 compound have been studied under pressure up to 4 kbar at T=78 and 293 K. The volume dependence of the exchange enhancement in spin paramagnetism of the UFe2 compound and its alloys has been derived from analysis of the pressure effects in the framework of the Stoner model.

Melt growth of quasi-binary (GaSb) 1− x(InAs) x crystals

A new class of III–V quasi-binary [A IIIB V] 1− x [C IIID V] x semiconductor alloys has been synthesized and bulk crystals grown from the melt for the first time. The present investigation is focused on (GaSb) 1− x (InAs) x (0< x<0.05) due to its importance for thermophotovoltaic applications. The structural properties of this melt-grown quasi-binary alloy are found to be significantly different from the conventional quaternary compound Ga 1− x In x As y Sb 1− y with composition x= y. Synthesis and growth procedures are discussed.

Pre-precipitate clusters and precipitation processes in Al–Mg–Si alloys

The solute clusters and the metastable precipitates in aged Al–Mg–Si alloys have been characterized by a three-dimensional atom probe (3DAP) and transmission electron microscopy (TEM). After long-term natural aging, Mg–Si co-clusters have been detected in addition to separate Si and Mg atom clusters. The particle density of β″ after 10 h artificial aging at 175°C varies depending on pre-aging conditions, i.e. pre-aging at 70°C increases the number density of the β″ precipitates, whereas natural aging reduces it. This suggests that the spherical GP zones formed at 70°C serve as nucleation sites for the β″ in the subsequent artificial aging, whereas co-clusters formed at room temperature do not. Atom probe analysis results have revealed that the Mg:Si ratios of the GP zones and the β″ precipitates in the alloy with excess amount of Si are 1:1, whereas those in the Al–Mg 2Si quasi-binary alloy are 2:1. Based on these results, the characteristic two-step age-hardening behavior in Al–Mg–Si alloys is discussed.

Strong band gap narrowing in quasi-binary (GaSb) 1− x(InAs) x crystals grown from melt

Large crystals of a quasi-binary semiconductor alloy (GaSb) 1− x (InAs) x with x =0.02–0.05 have been grown from melt for the first time. The family of quasi-binary crystals (GaSb) 1− x (InAs) x grown and reported here are different from the conventional Ga 1− x In x As y Sb 1− y quaternaries due to growth behavior and physical properties. Significant narrowing of the band gap was observed in these crystals compared to the conventional quaternary Ga 1− x In x As y Sb 1− y (with x= y). With an InAs content of about 2–5 at%, band gaps in the range of 0.6–0.65 eV have been demonstrated. The possible origins of the band gap narrowing (i.e., high bowing parameter) include chemical and structural alterations in the grown crystals, resulting from the association of Ga–Sb and In–As in the melt.

Transport properties of RuSi, RuGe, OsSi, and quasi-binary alloys of these compounds

RuSi, RuGe, OsSi and the solid solutions RuSi 0.5Ge 0.5 and Ru 0.5Os 0.5Si are investigated. All of them crystallize in the cubic B20 structure. The systems RuSi–RuGe and RuSi–OsSi form solid solutions which obey Vegard's law. RuSi, RuSi 0.5Ge 0.5, and RuGe are semiconductors with band gaps of 0.26, 0.20 and 0.15 eV, respectively. OsSi and Ru 0.5Os 0.5Si are degenerate semiconductors; their band gaps are larger than 0.26 eV. The thermal conductivity of the materials is dominated by the contributions of the lattice. The magnetic behavior is temperature independent and diamagnetic. RuSi and RuSi 0.5Ge 0.5 exhibit large Seebeck coefficients of almost 300 μV K −1, but their dimensionless thermoelectric figure of merit ZT does not exceed 0.03.