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.     

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.     

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.     

The influence of small deviations from stoichiometry on the properties of Y?Ba?Cu?O superconductor ceramics

According to a central composite design samples with deviations from stoichiometry YBa₂Cu₃O_7−x of ±2.5 wt% in the ingredients were prepared. The influence of these deviations on phase content, superconducting properties and microstructure of the ceramics was studied.     

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.     

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.     

Synthesis of AgI?AgCl?CuI solid solutions for ice nucleation studies

Lattice parameter calculation and the nucleation temperature of AgI AgCl CuI system are reported in this study. By vacuum fusion three samples of different molar compositions were prepared. The formation of the cubic solid solution of the above system was confirmed by X-ray analysis. It is found that the 50:25:25 mole% composition of AgI AgCl CuI has the highest nucleation temperature of −1.0 °C, which is far greater than −2.53 °C, −4.02 °C and −2.26 °C for pure AgI, AgCl, and CuI, respectively.