Phase equilibria in the Ga–P system. Calculation of activities and vapour pressures using a simple asymmetrical solution model

KRUPKOWSKI'S expression of activity coefficients has been applied to the liquid binary mixed phase of Ga–P. An interaction parameter of α = 1909 – 4.107 T and an asymmetry coefficient of m = 1.448 were determined from liquidus data and an entropy of fusion of GaP of 16.8 e.u. per mole at 1743 K. The activity coefficient of phosphorus along the liquidus curve shows a minimum at x_P = 0.032. There is an excellent agreement between calculated and experimental activities and vapour pressures over the whole controllable range of concentrations of the liquid phase. A total phosphorus pressure of 30.8 atms was calculated for the melting point of GaP.     

The lattice constants of ternary and quaternary alloys in the PbTe–SnTe–MnTe system

The study of structural properties of quaternary Pb_1−x−ySn_xMn_yTe alloys revealed that they crystallise in a cubic structure of NaCl-type for a wide region of manganese content (up to y=0.16). It was found from X-ray measurements and microprobe analysis that Vegard's law is obeyed. The dependencies of the lattice constants on composition for Pb_1−x−ySn_xMn_y, Pb_1−yMn_yTe and Sn_1−yMn_yTe were used to extract the lattice parameter of NaCl-type MnTe phase by extrapolation. The experimental data were also used to obtain an improved estimate of the covalent octahedral radius for Mn.     

Growth of InAs1–ySby solid solutions for obtaining decreased lattice mismatch in the InAs-GaSb (AlxGa1–nSb) system

This paper presents the results of investigation of the technological conditions of LPE growth of InAs_1–ySb_y solid solutions on InAs substrates. It is shown that the chosen regions of composition of InAs_1–ySb_y solid solutions and experimentally determined technological conditions allow the obtaining of InAs_1–ySb_y solid solutions with lattice parameter values close to those of the Al_xGa_1–xSb (0 ≦ x ≦ 0.2) solid solutions.     

Studies on the lattice match and strain in the epitaxial growth of III – V alloys on inas and GaSb substrates

The compositional conditions to deposit the epitaxial films of III – V materials lattice matched to InAs and GaSb substrates have been investigated and the results are presented in the form of charts. The validity of our theoretical predictions has been tested by comparing with the available experimental results. Strain in the Ga_xIn_{1 − x}As_ySb_{1 − y} quaternary alloy has been visualised as three-dimensional perspective plots.     

Preparation of low-density xerogels from mixtures of TEOS with substituted alkoxysilanes. II. Viscosity study of the sol–gel transition

Mixtures of TEOS with substituted methoxysilanes generate low-density xerogels due to a nucleation mechanism involving the substituted alkoxysilane. The sol–gel transition of these mixtures was followed by rheological characterisation. The transition from sol to gel takes place in a few minutes at ambient temperature. For the series exhibiting nucleation by the additive, the gel time goes through a slight minimum when the ratio of additive/main reagent increases. The elastic modulus increases with increasing ratio of additive/main reagent as the particle size decreases because of the nucleation mechanism by the additive. Samples with smaller particles exhibit the highest modulus for equal silica concentrations.     

Influence of cationic substitution on lattice constants and optical characterization in solution grown mixed crystals of potassium‐ ammonium zinc chloride

Mixed crystals of potassium‐ammonium zinc chloride in different concentrations were grown from aqueous solution employing the techniques of slow cooling and controlled evaporation. Powder x‐ray diffraction studies were carried out on the grown crystals. The comparison between lattice parameters a, b and c are experimentally determined and calculated by Vegad's law. The concentration of K⁺ ions in the crystals was measured by the atomic absorption technique. The crystal morphology changed considerably by increasing K⁺ concentration. The optical absorption coefficient (α) indicated strong influence changing concentration. The optical energy gap was found to decrease with increasing K⁺ concentration. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Preparation of low-density xerogels from mixtures of TEOS with substituted alkoxysilanes. I. O NMR study of the hydrolysis–condensation process

Low-density xerogels were synthesised by incorporation of an additive to base catalysed tetraethylorthosilicate (TEOS) alcogels directly during the preparation of the sol. The nucleation mechanism by the additive was established by experiments during sol–gel transition. ¹⁷O NMR spectroscopy on TEOS–ethanol–water, 3-(2-aminoethylamino)propyltrimethoxysilane (EDAS)–ethanol–water and EDAS–TEOS–ethanol–water solutions shows that the hydrolysis–condensation of EDAS is much faster than that of TEOS. Consequently it can be assumed that EDAS forms nuclei, onto which TEOS condenses later to form the silica particles.     

Al–O–Al and Si–O–Si sites in framework aluminosilicate glasses with Si/Al=1: quantification of framework disorder

We present for the first time, direct and clear experimental evidence of Al–O–Al and Si–O–Si linkages in charge-balanced aluminosilicate glasses with Si/Al=1, such as NaAlSiO₄ (nepheline) and LiAlSiO₄ (β-eucryptite) compositions using ¹⁷O triple quantum MAS (3QMAS) NMR and quantify the extent of disorder in framework cations (Si/Al). The degree of Al avoidance in NaAlSiO₄ glass is 0.942 at 1050 K, and in LiAlSiO₄ glass is 0.928 at 930 K (0.902 at 1050 K), which demonstrates the effect of cation field strength on the extent of disorder. In addition, we find a remarkable similarity between the ordering state of the liquid and that of the first, disequilibrium phase to crystallize.     

In situ surface passivation of III–V semiconductors in MOVPE by amorphous As and P layers

A new process for chemical passivation of III–V semiconductor surfaces in metalorganic vapour phase epitaxy (MOVPE) is developed. A passivation layer is deposited directly after growth in the reactor. It consists of amorphous arsenic or a double-layer package of amorphous phosphorus and arsenic, which are grown by photo-decomposition of the group-V hydrides. These layers (caps) serve to protect the surfaces against contamination in air after removing the samples from the MOVPE growth reactor. Such passivation is applicable e.g. for a two-step epitaxy or for further surface characterizations.     

P–T–X phase equilibrium and vapor pressure scanning of non-stoichiometry in the Cd–Zn–Te system

Technical applications of artificial crystals strongly depend on tailoring the defect structure. In compound semiconductors, native defect concentration is closely related to non-stoichiometry. Vapor pressure scanning (VPS) is a direct high precision method of in situ investigation of the composition of non-stoichiometric crystals at high temperatures. It is based on experimental measurements of the vapor pressure, from which three-dimensional P–T–X (pressure–temperature–composition) range of existence of the crystalline phase is outlined. In this communication VPS data on non-stoichiometry in the Cd–Zn–Te system are presented. Geometrical analysis of the phase equilibrium is performed, and composition of the crystal, melt and vapor is determined in the technologically most important melting region. It will be shown how to apply experimental P–T–X phase equilibrium data for preparation of the material with pre-determined composition, either stoichiometric or with a certain deviation from stoichiometry. Different technologies are analyzed: vapor-phase growth, vertical, horizontal and high-pressure Bridgman. VPS has proved to be a powerful analytical tool. For CdZnTe the accuracy of the VPS determination of non-stoichiometry was shown to be as high as 10⁻⁴ at.% for temperatures up to the melting point.     

An apparent critical point in binary mixtures of m-nitrotoluene with n-alkanes; experimental and simulation study

We report a simulation study of the system m-nitrotoluene–n-decane, showing an apparent critical point, which lies in their metastable, experimentally inaccessible state, below their melting point, affecting physical and chemical properties of this systems in the stable liquid phase. The presence of the apparent critical point in this mixture has been experimentally observed by the non-linear dielectric effect (NDE) as an anomalous increase in the NDE values typical of critical concentrations. The phase diagrams of this mixture have evidenced that the system freezes in the homogenous phase and its melting point is higher than its critical temperature [M. Śliwińska-Bartkowiak, B. Szurkowski, T. Hilczer, Chem. Phys. Lett. 94 (1983) 609, M. Śliwińska-Bartkowiak, Ber. Bunsengess. Phys. Chem. 94 (1990) 64, M. Śliwińska-Bartkowiak, Phys. Lett. A 128 (1988) 84]. For such a system, we performed Monte Carlo simulations aimed at analyzing the kind of phase transition observed, and their conditions of their occurrence in a Lennard-Jones mixture. The enthalpy, configurational energy and radial distribution function have been estimated by the MC simulation method in the NPT system. Immiscibility conditions according to Hoheisel [M. Schoen, C. Hoheisel, Mol. Phys. 57 (1986) 65] approach have also been discussed.     

Synthesis and characterization of compounds LixMn1+xFe2–2xO4 with spinel structure in the quasiternary system “LiO0,5 – MnOx – FeOx“

The thermal decomposition of freeze‐dried Li‐Mn(II)‐Fe(III)‐formate precursors was investigated by means of DTA, TG and mass spectroscopy. By the thermal treatment of the prefired precursors between 400 and 1000°C, single phase solid solutions Li_xMn_1+xFe_2–2xO₄ (0 ≤ x ≤ 1) with cubic spinel structure were obtained. To get single phase spinels, special conditions concerning the temperature T and the oxygen partial pressure p(O₂) during the synthesis are required. Because of the high reactivity of the freeze‐dried precursors, in comparison with the conventional solid state reaction, the reaction temperature can be lowered by 200°C. The cation distribution and the properties of the Li‐Mn‐ferrites were studied by chemical analysis, X‐ray powder diffraction and magnetization measurements. It was found that for high substitution rates, almost all lithium occupies the tetrahedral coordinated A‐sites of the spinel lattice AB₂O₄, while at small x‐values, lithium ions are distributed over the tetrahedral and octahedral sites. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Phase equilibria and prospects of crystal growth in the system LiF–GdF3–LuF3

Scheelite type LiGdF₄, LiLuF₄, and mixtures of both end members were prepared by a hydrofluorination route from the rare earth oxides and commercial LiF. The samples were purified by melting in HF/Ar mixtures, and were investigated by differential scanning calorimetry (DSC), scanning electron microscopy (SEM), and energy dispersive X‐ray spectroscopy (EDX) techniques. Both end members show unlimited miscibility in the solid phase. Mixed crystals containing at least 65 mol‐% LiLuF₄ melt under direct formation of the liquid phase. The gap between solidus and liquidus is narrow. LiGdF₄ and mixed crystals with less then 65 mol‐% LiLuF₄ decompose peritectically under formation of (Gd,Lu)F₃. Crystal growth is expected to be possible either from Lu‐rich melts with the appropriate scheelite composition or from Gd‐rich melts containing an excess of LiF. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Solubility data of trisodium citrate hydrates in aqueous solution and crystal‐solution interfacial energy of the pentahydrate

In this paper, the solubility of trisodium citrate dihydrate and trisodium citrate pentahydrate in water was experimentally determined. From solubility data, it was found that the relationship between trisodium citrate dihydrate and trisodium citrate pentahydrate is enantiotropic with a transition temperature at 315.4±1.0 K. Different hydrates can be isolated safely by controlling the crystallization temperature. The induction periods of trisodium citrate pentahydrate in aqueous solution were measured at different temperatures. The crystal–solution interfacial energy was calculated by using classical nucleation (CL) theory, mononuclear (MN) and polynuclear (PL) mechanisms through the relationship between induction period and supersaturation. It was found that the interfacial energy values calculated by using the CL theory and the MN model are nearly the same while interfacial energy calculated by PN model are about 40% higher. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Influence of the temperature and the oxygen partial pressure on the phase formation in the system Cu – Fe – O

Copper iron oxides, Cu_1‐xFe_2+xO₄ (0 ≤ x ≤ 0.5), have been synthesized by thermal oxidation of copper ‐ iron mixtures. In this process, the phase formation and the phase stability were investigated as function of the temperature (800°C – 1200°C) and the oxygen partial pressure (1.013 x 10¹ – 1.013 x 10⁵ Pa). The phase formation starts with the reaction of the metallic components to simple oxides (Fe₃O₄, Fe₂O₃, CuO). From these simple oxides, the formation of complex oxides requires a minimum temperature of 800°C. The synthesis of single phase spinel compounds Cu²⁺_1‐2x Cu¹⁺_xFe_2+xO_4±δ is realized for 0.1 ≤ x ≤ 0.5, using specific temperature – p(O₂) – conditions for a given value of x. Remarkably, to achieve our goal, we found that the increase of x implies that of the reaction temperature and/or a decrease of the p(O₂) in the reaction gas stream. Besides, a single phase spinel CuFe₂O₄ does not exist in the temperature / p(O₂)‐field investigated. Using the results of XRD ‐ phase analysis, T ‐ p(O₂) – x – diagrams were constructed. These diagrams allow the prediction of phase compositions expected for different synthesis conditions. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Synthesis and characterization of phosphates in the pseudo‐ternary melted systems Cs2O‐P2O5‐MIIO (MII – alkaline earth)

The crystallization of alkali‐earth phosphates in the melts of Cs₂O‐P₂O₅‐M^IIO (M^II – Ca, Sr, Ba) pseudo‐ternary systems have been investigated at various Cs/P molar ratios and at fixed value of M^II/P equal to 0.15. Type of the phosphate which crystallizes in melts depends on the Cs/P initial ratio. Crystallization fields of CsM^IIP₃O₉, M^II₂P₂O₇ and Cs₂M^IIP₂O₇ were briefly investigated and characterized. The new diphosphate Cs₂CaP₂O₇ has been obtained and investigated by the single crystal and powder X‐ray diffraction and FTIR‐ spectroscopy. It crystallizes in C 2/m space group, with the following parameters of the monoclinic cell: a = 10.261(2), b = 5.9316(12), c = 7.2404(14) Å, β = 118.54(3)°. The architecture of [CaP₂O₇]^2‐ anionic sublattice, which is built up from [CaO₆] octahedra and [P₂O₇] bitetrahedra, interlinked via the common oxygen vertices, gives rise to formation of hexagonal tunnels along crystallographic direction b, where caesium atoms are located. One of the most remarkable features of the structure is specific positional disorder of the diphosphate group, which is connected with the existence of two equiprobable half‐occupied sites of the bridging oxygen. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Calculation of composition variation of In1−vGavAs ternary crystals for diffusion and electromigration limited growth from a temperature graded solution with source material

A theoretical model was proposed to calculate composition variation of III-V ternary crystals during growth. In this model, for the first time, phase equilibrium between crystal and growth solution is maintained together with constancy between the transported and incorporated mass or solute atoms at the crystal/solution interface at the same time. This model can be applied to the calculation of the diffusion and electromigration limited growth in a temperature-graded solution with source material such as the source-current-controlled (SCC) growth method. The composition variation of In_1−vGa_vAs crystals grown by diffusion and electromigration was calculated by this model. Incorporation of two kinds of solute elements, Ga and As, into crystals through the crystal/solution interface was considered on the basis of the laws of the phase equilibrium and the constancy of mass. In comparison of the experimental results with the calculated ones, it is found that in the In-Ga-As solution the diffusion coefficient of Ga, D_Ga, is about two times as large as that of As, D_As, and μ_Ga is larger than μ_As. The calculated results of the composition variation show that the composition uniformity in In_1−vGa_vAs crystals can be largely improved by controlling the growth parameters such as temperature gradient in the solution, solution length, existence of source material, and electric field.     

The structure and electrical resistance of thin scandium films (II). F.C.C.–lattice phase observed in films obtained in a vacuum of 10−8 Torr

Phase composition of the Sc-films up to 200 Å thick obtained in a vacuum of 3 · 10⁻⁸ Torr, condensation rate being ω ⋍ 1 to 6 Å/s and ω ⋍ 40 å/s up to 10⁻⁷ Torr, have been studied by an electron-diffraction examination. A phase with an f.c.c.-lattice and a lattice parameter a = 4.76 to 4.80 ± 0.01 Å 0.01 Å is observed in films d ≲ 60 Å thick, whilst with films having a thickness d ≳ 90 Å a h.c.p.-phase is characteristic for solid specimens. Two-phase composition is observed in an interjacent interval of thicknesses. An analysis performed permitted to conclude that the f.c.c.-phase observed is a ScH_x-hydride forming during the post-condensation delay time on a basis of a poly-morphic modification.     

Dissolution of Si in Al–Si Melts. Effect of Sb on the Crystallization Process and As-cast Structure of Al–Si Alloys

The effect of Sb on the dissolution of Si single crystals (face {111}) in Al–Si melts is studied. The dissolution isotherms at three temperatures and fixed undersaturation are obtained. The experimental data are treated according to the Bliznakov's ratio. Some conclusions are made with reference to the crystal growth process. A probable mechanism of the influence of Sb on the structure of Al–Si alloys is given.     

Improved approaches to the determination of residual stresses in micro regions with the KOSSEL and the XRT technique

A new application of the KOSSEL and the XRT (X‐ray Rotation‐Tilt) technique arises from local residual stress measurements in micro regions. Already in 1996/97, we started to conduct such investigations based on the KOSSEL method. Because of the high lateral resolution residual stresses of the third kind can be determined. Some further evaluation procedures are described. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)