Anwendung der Temperaturgradient-Lösungskristallisation zur Züchtung von Zn?Si?P-Phasen

After giving the principles of the temperature gradient method of growing crystals from solution the experimental methodology of recrystallisation of ZnSiP₂ to a regulus as well as the deposition of ZnSiP₂ on an Si substrate is explained. Based on phase analytical investigations by metallographic methods, measuring of microhardness, and investigations by electron beam microanalizer the various phases are discussed formed in dependence on growing conditions, paying attention to the concentration relations in the ranges of transition when deposition occurs on a substrate.     

Liquid Phase Epitaxy of SiC in the System Si?Tb?SiC by Temperature Gradient Zone Melting (I). Investigation of Solubilities in the System Si?Tb?SiC

In the paper which is divided into three parts the liquid phase epitaxy of SiC by temperature gradient zone melting with the solvent Si Tb is discussed. In the first part the solubility of SiC at different initial compositions of the Si Tb solvent is studied in the temperature range 2000–2500 K.     

Preparation of Al?Ga?P?As heterostructures

The present paper reports on the results of an investigation of crystallization of multilayer structures with a narrow-gap semiconductor surrounded by two wide-gap ones in the Al-Ga-P-As system on GaAs and GaP substrates. Influence of the lattice parameters' difference on the value of thermal stress in structures with a composition gradient was determined by the bend of structures separated from the substrate. It has been proved that with the P concentration in solid solutions being less than 1% heterojunctions with less tensions than in the Al–Ga–As system are available. A new method of obtaining Al_xGa_1–xP_yAs_1–y solid solutions with the concentration of P proportional to that of Al has been worked out on the basis of which multilayer heterolight-emitting structures have been prepared.     

Stabilization of the melt composition in Ga?Al?Sb?As

In this work we present a new effect of stabilization of the Ga Al Sb As melt composition when it is in contact with the GaAs substrate. It was found that the As content in the Ga Al Sb As melt did not depend on the initial Sb concentration when the liquid phase was formed by saturating the Ga Al Sb melt from the GaAs substrate. This effect is supposed to be due to the change in phase equilibria conditions caused by large lattice mismatch between the substrate and the solid in equilibrium with the liquid.     

Thermal Expansion and Superconductivity in Alkali Metal- and Silver-doped Bi?Sr?Ca?Cu?O System

Samples with the nominal composition Bi₂Sr₂CaCu₂O_y with na doped at the Ca site and K doped at the Sr site are prepared by solid state reaction method. From the X-ray diffraction data it is found that all the the samples have exhibited a single phase 2212. The D.C. electrical resistivity data show that for Na-doped samples the T_c (zero) varies from 80 K to 85 K and for K-doped samples it is from 79 K to 82 K. The loss of oxygen from these samples around 400°C was confirmed by high temperature dilatometry. The variation of the thermal expansion coefficient (“α”) with temperature for different alkali dopings are discussed. Also the samples with the nominal composition Bi₄Sr₃Ca₃Cu_4−xAg_xO_y (with x = 0, 0.1, 0.2, 0.3) were studied.     

A microstructural examination of Zn?Al?Cu alloys

A microstructural examination of a Zn-11 wt% Al-1 wt% Cu alloy in dependence on the applied heat treatment was carried out by means of scanning electron, transmission electron and optical microscopy as well as X-ray investigations.     

Isochronal Phase Transformation in Al?Zn?Cu Alloys

Two Al-Zn alloys with 40 wt% and 74wt% Zn, respectively, and copper additions between 0 and 10 wt% were investigated by means of X-ray diffraction methods, X-ray small angle scattering, resistivity, and dilatometric investigations during continuous cooling from 673 K applying a cooling rate of 2 K/min. It was found that copper additions lower the driving forces for the onset of the homogeneous nucleation after crossing the range of homogeneity, but accelerate the formation of the η-phase. The reasons for this facts are discussed.     

Liquid Phase Epitaxy of SiC in the System Tb?Si?SiC by Temperature Gradient Zone Melting (II). Liquid Phase Epitaxy of SiC from Tb?Si Solvent

The liquid phase epitaxy of SiC by the gradient temperature zone melting in the Si Tb solvent is studied. A new variant of this growth method is presented. The comparison of the new variant with the previous one shows that the new variant allows for epitaxial layers with significant better electrophysical properties. It is easier and can be carried out at lower temperature.     

Small angle neutron scattering in Al?Cu?Mg alloys

The structure changes proceeding in AlCu 2.1 at.% Mg(x) alloys with magnesium concentration form 0 to 1.2 at.% at room temperature and 100 °C are followed by small-angle neutron investigation. The results are fitted on different models. The most important result is that with increase of the Mg contents clearly a growth of the thickness opposite to the growth of the growth of the diameter to discern. The results give a good idea of the formation of GPZI(Mg) with the adequate portion of magnesium in the AlCuMg(x)-alloys and their transition to GPZII(Mg) respectively θ″ (Mg).     

Hydrogen in Cu?Ti and Ni?Ti Metallic Glasses

The hydrogen solubility and its effect on the crystallization of Cu Ti and Ni Ti glasses were studied by differential scanning calorimetry, thermogravimetry, and X-ray diffraction. Dependence of the crystallization products of the hydrogenated Ti-based alloys on the hydrogen content was found. Whereas in Cu-Ti alloys hydrogenation leads to drastic decreasing in the thermal stability due to phase separation in the amorphous state and to formation of microcrystalline structure during crystallization, in Ni Ti system hydrogen produces hydrides with Ni as well with Ti, which after heat treatment decompose, and finally the same crystalline phases as in unhydrogenated alloy are formed. The isothermal crystallization kinetics of the maximum hydrogenated Cu₅₀Ti₅₀ amorphous alloy was also investigated to obtain additional information about this transformation leading to nano-crystalline material.     

Resistance and Current Density Studies on Plasma Sprayed Coatings of Bi(Pb)?Ca?Sr?Cu?O Superconducting Materials

Plasma spraying is a potential technique for forming flexible tapes from brittle high T_c oxides. It is possible to obtain superconducting Bi(Pb) Ca Sr Cu O coating by suitable heat treatment schedule after spraying. In an effort to get maximum transport current densities (J_c) of the coating, the content of lead and sintering time have been optimised. A J_c value of 200 Amp/cm² is obtained in Bi_1.4Pb_0.6 · Ca₂Sr_1.9Cu₃O_y specimen coated on silver sprayed Fe[(Ag)/Fe] substrate. Remarkable improvement in J_c values up to 694 Amp/cm² is obtained in the same specimen coated on Ca₂Sr_1.9Cu₃O_y sprayed Fe[Ca₂Sr_1.9Cu₃O_y)/Fe] substrate. The observed decrease in J_c(B) curves with increase in magnetic field shows the presence of weak coupling between the grains.     

Liquid phase epitaxy of SiC in the system Tb?Si?SiC by temperature gradient zone melting (III). Epitaxial layer properties

In the present work the electrophysical and structural properties of the SiC epitaxial layers grown by the temperature gradient zone melting method in vacuum conditions is considered. Some correlations between the epitaxial layer properties and the process conditions are observed. It is shown that the performence of the growth process in vacuum leads to a significant improvement of the layer quality, if one observes some requirements – how to decrease significantly the number of the second phase inclusions and how to improve the structural perfection of the layers.     

Vapour Phase Epitaxy of GaxIn1−xAs in the Ga?In?HCl?AsH3?H2-System Using a Mixed Ga/In Source

The mixed crystal composition of Ga_xIn_1−xAs layers is analysed as a function of the composition of a mixed Ga/In source during VPE in the hydride system. Experimental results are compared with thermodynamic calculations. Both thermodynamics of the deposition reactions and thermodynamies of the souree reactions are considered in the calculations.