Thermodynamic properties of Al-Mn melts

The thermochemical properties of Al-Mn melts have been studied at 1835 ± 3 K by high-temperature calorimetry under isoperibolic conditions. The Δ_mix H and Δ_mix \(\overline H _i\), data obtained correlate well with earlier data obtained at a lower temperature of 1628 K. The enthalpies of formation of manganese aluminides determined by calorimetry agree only qualitatively with the Δ_mix H of Al-Mn melts. We have calculated the partial and integral entropies of mixing of Al-Mn melts. Analysis of the entire set of thermodynamic properties indicates that, in liquid Al-Mn alloys, the interaction between dissimilar atoms is significant even well above the liquidus temperature.     

Thermodynamic properties of liquid Ga-Si-Mn alloys

The partial enthalpies of mixing of the constituent components (Δ_mix \(\bar H_i \)) have been determined by high-temperature calorimetry and then used to evaluate the integral enthalpies of mixing (Δ_mix H) of Ga-Si-Mn alloys along three cuts at 1770 ± 5 K. The results demonstrate that, in the composition region studied, the formation of Ga-Si-Mn alloys is an exothermic process. Δ_mix H is calculated over the entire composition region by the Bonnier-Caboz method.     

Thermodynamic properties of Si-Y and Ge-Y melts

Using high-temperature isoperibol calorimetry, we have determined the partial enthalpy of mixing of yttrium in Si-Y and Ge-Y melts at 1770 (1780) ± 5 K in the composition ranges 0 < x _Y < 0.2 (0.4). The results have been used to evaluate the integral enthalpies of mixing for these melts. Their formation has been shown to be accompanied by significant heat release. The mixing enthalpies of the liquid alloys have been optimized using the present and earlier data. The activities of the components of Si-Y and Ge-Y melts have been evaluated from the liquidus coordinates in the corresponding phase diagrams and have been found to exhibit very large negative deviations from Raoult’s law.     

Thermodynamic properties of the Al-Eu-Sn melts

Mixing enthalpies of melts of the binary systems Al-Eu at 1300–1473 K (in the concentration ranges 0 < x _Eu < 0.2 and 0.57 < x _Eu < 1) and Eu-Sn at 1250–1300 K (0 < x _Sn < 0.2; 0.51 < x _Sn < 1) were studied for the first time by the isoperibolic calorimetry technique. It was determined that there are moderate (ΔH_min = ?23 kJ/mol at x _Eu = 0.39) and large (ΔH_min = ? 63 kJ/mol at x _Sn = 0.42) exothermic formation effects for these melts, correspondingly. Using the information obtained by us and taken from literature, thermodynamic properties of these melts were calculated in the wide temperature range by the model of ideal associated solutions (IAS). The mixing enthalpies of melts of the ternary Al-Eu-Sn system were modeled using the analogous data for the binary boundary systems.     

Thermodynamic properties of Ge-Ni melts

Using high-temperature isoperibol calorimetry, we have determined the partial enthalpy of mixing of nickel in Ge-Ni melts at 1800 ± 3 K in the composition range 0 < x _Ni < 0.7 (\(\Delta _{mix} \bar H^\infty \) (Ni) = ?76.0 ± 4.8 kJ/mol). The results have been used to evaluate the partial enthalpy of mixing of germanium and the integral enthalpy of mixing (Δ_mix H _min = ?37.9 ± 0.6 kJ/mol at x _Ni = 0.6). The thermochemical data and germanium activity in Ge-Ni melts have been analyzed in comparison with those reported earlier, and the most reliable thermodynamic functions of the Ge-Ni melts at 1870 K have been determined.     

Thermodynamic Properties of Si–Ge and Si–Sn Melts

The mixing enthalpies of Si–Ge and Si–Sn liquid alloys were measured in an isoperibolic calorimeter. The results demonstrate that the formation of Si–Ge melts is accompanied by a small heat release, while the formation of Si–Sn melts is an endothermic process. Calculations of the Si activity in Si–Sn melts by Schroeder's equation indicate large positive deviations from Raoult's law.     

Drop Calorimetric Measurements on Binary Bi–In System

Measurements of integral enthalpies of mixing of Bi–In system have been taken at 767, 813 and 855 K by a drop calorimeter over the entire composition range. Bismuth was used as the base metal, and indium was dropped by motorized dropping device. Calibration of the calorimeter was done by dropping four pieces of α-Al₂O₃ at the drop temperatures. The measured enthalpies of mixing are plotted against indium composition and found exothermic in nature for all the compositions. The minimum enthalpies were observed in the range of compositions x_In?~?0.40–0.50. A slight temperature dependency of enthalpy was observed for each composition. The experimental data were used to determine the binary interaction parameters using Redlich–Kister polynomial at 767, 813 and 855 K.     

Effect of Disorder on Electronic,Magnetic, and Optical Properties of Co2CrZ Heusler Alloys (Z = Al,Ga, Si,Ge)

This paper presents the effect of disorder on electronic, magnetic, and optical properties of Co₂CrZ (Z = Al, Si, Ga, Ge) Heusler alloy using density functional theory. Binary mixing is the most common form of atomic disorder in these compounds. We have considered three types of disorders: DO ₃, A2, and B2 disorder which corresponds to X-Y, X-Z, and Y-Z mixing, respectively. After structural optimization, we found that A2 disorder has high formation energy and is most unlikely to occur. The half-metallic nature of the alloy is destroyed in the presence of DO ₃ and A2 disorder. The destruction of half-metallicity is due to reconstruction of energy states. B2 disorder retains the half-metallic nature of the alloy but spin-polarization value is reduced slightly as compared to the ordered alloy. In addition, the optical properties such as dielectric function, refractive index, absorption spectra, optical conductivity, reflectivity, and energy loss function of these alloys have also been investigated.     

Thermodynamic Properties of Metal-Carbon Melts

The partial and total enthalpies of mixing of Si-C and Ni-C liquid alloys at 2000 K are determined by isoperibol calorimetry. The mixing enthalpies in these systems are found to be small and negative, in agreement with earlier results. The thermochemical properties of dilute Al-C solutions are studied at 1773 K for the first time. The mixing enthalpies of metal-carbon melts are estimated from the standard enthalpies of formation of metal carbides. The calculated mixing enthalpies of liquid metal-carbon alloys agree with experimental data.__________Translated from Neorganicheskie Materialy, Vol. 41, No. 6, 2005, pp. 682–686.Original Russian Text Copyright © 2005 by Kudin, Makara.     

First-Principle Investigation of Structural,Electronic and Magnetic Properties in Mn<Subscript>2</Subscript>RhZ (Z = Si,Ge, and Sn) Heusler Alloys

Mn ₂-based Heusler compounds exhibit different types of anti-site disorder. The electronic structure and magnetism of Heusler alloys Mn₂RhZ (Z = Si, Ge, and Sn) have been studied by first-principle calculations. Mn₂RhSi and Mn₂RhGe are ordinary half-metallic ferrimagnetic metals at equilibrium lattice constants, with a magnetic spin moments obeys to the Slater-Pauling rule and spin polarization of 100 % at the Fermi energy. The tetragonal phase transformation is studied for Mn₂RhSn. The total magnetic moment of Mn₂RhSn in the tetragonal structure is higher compared to the other materials, which results in a large ΔM between the saturation moments of tetragonal and a cubic. The tetragonal Mn₂RhSn predicted to a high spin polarization ratio of 93 %. These properties of these materials are particularly interesting due to their perpendicular magnetic anisotropy (PMA), which was realized in thin films opening the door for application in STT magnetic random access memories (STT-MRAMs)     

Carrier mobility in Si<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>Ge<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> crystals

We have studied the 300-K carrier mobility in Czochralski-grown single crystals of undoped and heavily boron doped Si_{1 ? x} Ge _x (0 < x < 0.02) alloys. Comparison of our experimental data with theoretical predictions indicates that the Ge atoms in dilute Si_{1 ? x} Ge _x alloys do not act as neutral scattering centers. The carrier mobility related to the scattering by Ge atoms is governed by disorder (alloy) scattering. The carrier mobility in the boron-doped Si_{1 ? x} Ge _x alloys is much lower than that in the undoped alloys, depends very little on Ge content, and is governed by ionized impurity scattering.     

The Effect of Sn Substitution of Pb on Microstructure and Superconducting Properties of Bi–Pb–Sr–Ca–Cu–O Superconductor

The effect of substitution of Pb by Sn in Bi_1.6Pb_0.4?x Sn _x Sr₂Ca₂Cu₃ O _δ samples at x = 0.0, 0.1, 0.2, and 0.3 on the critical transition temperature and structural properties was investigated in this work. All the samples were prepared by the solid-state reaction method. The prepared samples were characterized by X-ray diffraction (XRD), resistance–temperature curve (R–T), scanning electron microscopy (SEM) and energy-dispersive spectroscopy (EDS). The Sn ⁴⁺ substitution of Pb ²⁺ caused significant changes in the properties of the samples. The formation of the (Bi, Pb)-2212 phase was stabilized and the T _c (onset) was improved at the x = 0.2 level of Sn ⁴⁺ substitution. The SEM micrographs have shown that the structure of the sample with x = 0.2 became more dense. However, samples with x = 0.1 and 0.3 have not shown zero resistance by EDS analysis because of oxygen deficiency.     

Interaction of hydrogen with the intermetallic compound Nd<Subscript>2</Subscript>Fe<Subscript>17</Subscript> studied by calorimetry

Interaction of hydrogen with the intermetallic compound Nd₂Fe₁₇ has been studied for the first time by calorimetry using a differential heat conduction calorimeter coupled to a Sieverts apparatus. Hydrogen absorption and desorption reactions were run at 200°C, and two types of data were obtained: p–C–T and ΔH–C–T (where p is the equilibrium hydrogen pressure, C = H/Nd₂Fe₁₇, ΔH is the reaction enthalpy, and T is the measurement temperature). The p–C–T curves obtained for the hydrogen absorption and desorption processes have no plateau or two-phase region, in contrast to what is characteristic of the formation of a hydride phase. At the same time, the ΔH(C) curves have a few portions where the enthalpy of reaction between hydrogen and the intermetallic compound remains constant: 0 < C < 2.0, with ΔH _abs =–85.05 ± 0.65 kJ/mol H ₂; 2.0 < C < 2.7, with ΔH _abs =–80.64 ± 1.00 kJ/mol H₂; and 1.9 < C < 2.7, with ΔH _des = 76.48 ± 0.85 kJ/mol H₂. The data obtained in this study suggest that positions 9e and 18g in the intermetallic compound are occupied by hydrogen in a particular order.     

Thermodynamic properties of Ge-Mn melts

The enthalpies of mixing of Ge-Mn melts are determined in the range 1550–1840 by isoperibol calorimetry.The formation of these melts is shown to be accompanied by significant heat release: _mix H _max = -25.12 ± 1.4 kJ/mol at x _Mn = 0.7. Ge activity is evaluated from the position of the liquidus line. The Mn and Ge activities in this system exhibit negative deviations from Raoults law. The new and earlier data on the thermodynamic properties of Ge-Mn melts are analyzed.Translated from Neorganicheskie Materialy, Vol. 41, No. 2, 2005, pp. 240–245.Original Russian Text Copyright © 2005 by Kotova, Beloborodova, Zinevich, Dubina, Sudavtsova.     

Thermodynamic properties and homogeneity regions of Tl<Subscript>6</Subscript>SCl<Subscript>4</Subscript> and Tl<Subscript>5</Subscript>Se<Subscript>2</Subscript>Cl

In this activity system Tl-Tl₂X-X (X = S, Se)are studied using emf measurements of concentration chains relative thallic electrode. The solid phase diagrams of these systems are clarified, homogeneity areas of the compounds Tl₆SCl₄ and Tl₅Se₂Cl are determined. On the basis of emf measurement results, relative partial molar functions of thallium in alloys and standard integral thermodynamic functions (ΔG ⁰(298 K), ΔH ⁰ (298 K), ΔS ⁰ (298 K)) of the ternary compounds Tl₆SCl₄ and Tl₅Se₂ Cl and phases of variable composition based on the latter are calculated.     

Enthalpy of Mixing of Liquid Al—Cr and Cr—Ni Alloys

The partial and the integral enthalpies of mixing of liquid Al-Cr and Ni-Cr binary alloys have been determined by high temperature isoperibolic calorimetry at 1723±5 K and 1729±5 K, respectively. The results were analytically described by the thermodynamically adapted power series (TAPS). The enthalpies of mixing values for both binary liquid melts are small and negative and in good agreement with the available literature data. Minima of the mixing enthalpies of liquid Al-Cr and Ni-Cr alloys are -7.0 kJ·mol-1 at 46 at. pct Cr and -3.0 kJ·mol-1 at 37 at. pct Cr, respectively.     

Evaluation of charge displacement and the radii of Wigner-Seitz spheres for the components of A-Te (A = Ge,Sn, Pb) melts

Thermodynamic and structural data for A-Te (A = Ge, Sn, Pb) melts are used to evaluate the charge displacement (in Tamaki’s approach) and the radii of Wigner-Seitz spheres. The results indicate that the interaction between dissimilar components and the formation of the ATe compounds prevail in the melts. In the Ge-Te system, there is a tendency toward the formation of Ge_0.85Te_0.15 and Ge_0.33Te_0.66 associates, in which, respectively, covalent and ionic bonding prevails.     

Half-Metallic Ferromagnetism in New Half-Heusler Compounds: an Ab Initio Study of CrTiX (X = Si,Ge, Sn,Pb)

In this work, half-metallic (HM) properties of new Half-Heusler (HH) ferromagnetic compounds CrTiX (X = Si, Ge, Sn, Pb) are studied by means of first principle band structure calculation within the framework of density functional theory (DFT). From the spin-polarized calculations using full-potential linearized augmented plane-wave (FP-LAPW)method, we found that all of these compounds are stable in ferromagnetic MgAgAs-type crystal structure. The latticeparameters of CrTiX compounds increase with increasing atomic radius of X atom and ranges from 5.76 to 6.38 Å. The calculated electronic structure of these compounds in MgAgAs-type structure shows that they are HM materials with an integer magnetic moment of 4 μ _B. Densities of states, electronic band structure, and origin of ferromagnetism have been discussed, and robust HM nature of these compounds is analyzed which makes them fascinating compounds for spintronic devices.     

多元低熔点共晶合金Sn16Bi52Pb32和In21Sn12Bi49Pb18凝固组织和相组成研究

随着环境保护的需要,具有较低Pb含量或不含Pb元素的多元低熔点合金越来越受到工业界的重视和青睐,但是该类合金的组织结构形态、相组成和基本的物理化学数据比较缺乏,不利于其工业化应用。鉴于此,文章对两种具有较低Pb含量的Sn_(16)Bi_(52)Pb_(32)(质量分数)合金和In_(21)Sn_(12)Bi_(49)Pb_(18)(质量分数)合金进行了凝固组织、相组成以及物化性能方面的研究。扫描电镜(SEM)、差示扫描量热法(DSC)、X射线衍射(XRD)等分析测试结果表明:Sn_(16)-Bi_(52)Pb_(32)合金由Bi-(Pb)固溶体相、Sn-(Bi,Pb)固溶体相以及Pb_7Bi_3化合物相组成,具有准规则共晶凝固组织结构。而In21Sn12Bi49Pb18合金由InBi化合物相、PbBi化合物相以及Sn-(Bi,In)固溶体相组成,具有复杂规则的共晶组织形貌。     

Thermal Dissociation of RMnO<Subscript>3</Subscript> (R = Dy,Yb, Lu)

The phase equilibria involved in the thermal dissociation of RMnO₃ (R = Dy, Yb, Lu) were studied in the range 973–1173 K by a static method in a vacuum circulation unit and by x-ray diffraction analysis of quenched solid phases. The RMnO₃ manganites were shown to dissociate by the reaction RMnO₃ = 1/2R₂O₃ + MnO + 1/4O₂. The temperature dependences of the equilibrium oxygen pressure and Gibbs energy change in this reaction were determined for the three compounds. The experimental data were used to evaluate the standard thermodynamic functions of formation of RMnO₃ from R₂O₃ and Mn₂O₃: ΔH⁰(T) = ?88.93 kJ/mol, Δ S⁰(T) = 46.56 J/(mol K) for DyMnO₃; ΔH⁰(T) = ?130.95 kJ/mol, Δ S⁰(T) = 86.25 J/(mol K) for YbMnO₃; ΔH⁰(T) = ?142.94 kJ/mol, Δ S⁰(T) = 102.87 J/(mol K) for LuMnO₃.