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.     

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.     

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.     

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.     

Effect of vibration frequency and sample composition on acoustic properties of Y?Ba?Cu?O high-Tc superconductors

Temperature dependences of absorption and velocity of longitudinal ultrasound in high-T_c ceramics Y Ba Cu O with different Y and Ba content at frequencies 100 kHz and 7.5 MHz are studied in the temperature range 6 to 300 K. For 100 kHz three peaks at 60, 140, and 230 K are observed in the temperature dependences of decrement. Temperature dependences of sound velocity show a broad hysteresis for thermocycling. The temperature boundaries of hysteresis and peak locations are almost independent of sample composition. Sizes of hysteresis and peak heights are very different in samples of various composition. For 7.5 MHz, a peak was found at 210 K in the temperature dependences of ultrasound absorption increment. It is shown that the acoustic anomalies are due to a structural phase transition of martensitic type. Thermoactivation parameters of the main microscopic mechanism responsible for the phase transition are estimated.     

Oxygen potentials,stoichiometry, superconducting,and magnetic properties in the Y?Ba?Cu?O system

The relationship between stoichiometry in YBa₂Cu₃O_x and oxygen potential was investigated by barometry and compared with in-situ X-ray diffraction experiments between 300 and 1000 °C (6 < x < 7). The physical properties are influenced even by small deviations in x. Y₂BaCuO₅ was included in the investigations and found to be antiferromagnetic with T_N ≈ 30 K.     

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.     

Formation and Structure of Ti?Zn-Oxides

In powder mixtures of ZnO and TiO₂ the compounds Zn₂TiO₄, ZnTiO₃ and Zn₂Ti₃O₈ can be formed as a result of solid state reactions. The mechanism of the double oxide formation is essentially determined by the microstructure of the powder mixture. Furthermore, the kind of the double oxide depends on the TiO₂-modification. There exist structural similarities between Zn₂TiO₄ (spinel) and TiO₂ (anatase) on the one hand and ZnTiO₃ and TiO₂ (rutile) on the other hand. The compound Zn₂Ti₃O₈ is formed only on the basis of the Zn₂TiO₄-phase. The crystal structure of Zn₂Ti₃O₈ was derived as a defect spinel. The unoccupied sites of cations are not arranged statistically, but they are ordered in the structure. This order leads to the decrease of the space group symmetry from Fd-3 m to P4₃32.     

Combined surface analytical and electrochemical investigations of Ru?Ti?Sn mixed oxide electrocatalysts

Using a galvanostatic oxygen exposure, it can be shown by XPS and SEM that admixtures of Sn (2 at.%) to RTO anodes inhibit the corrosion of both the bulk ruthenium species and the titanium substrate interface. The inhibitor effect is strongly dependent on the Sn segregation to the surface region blocking the channels of oxygen diffusion in incoherent active layers for Cl₂ evolution.     

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).