Thermoelectric Behaviour of Some Phases in the In?Se System

The differential e.m.f. of In₆Se₇ single crystals as a function of temperature have been measured. The electron to hole mobility ratio is determined to be μ_n/μ_p = 3.62. The effective masses of electrons and holes are 4.21 × 10⁻³³ kg and 9.01 × 10⁻²⁹ kg, respectively. The diffusion coefficient for holes and electrons as well as the diffusion length of free charge carriers have been determined.     

Mass transfer during growth of Ga?In?P?As solid solution in the equilibrium cooling growth technique

Kinetical analysis of crystallization of Ga In P As solid solutions grown by equilibrium cooling growth technique was performed. Theoretical data were compared with experimental data on LPE of the material. The dependencies of layer thickness, lattice mismatch variation between the substrate and layer and energy gap in the layers lattice matched to InP were calculated for different growth temperatures.     

Thermal analysis of the microsegregation phenomenon in some alloys from the Sb?Sn system

Thermal analysis in experimental verification to theoretical prediction of the maximum microsegregation phenomenon in the peritectic alloys solidification has been applied. Satisfactory agreement has been obtained between some results of theoretical calculations and experimental ones. Usibility of the DTA-5 apparatus (original construction of the Baykov Institute of Metallurgy) to detect quite small amounts of low-solidifying non-equilibrium phases has been proved.     

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.     

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.     

Crystallographic relations in the Fe?Zn system

The crystallographic relations between the various Fe Zn compounds have been investigated by means of single-crystal X-ray diffraction techniques. These techniques were applied to primary single crystals of each compound upon which after cooling a single crystalline layer of the neighbouring compound richer in zinc was grown. In this way it has been possible to determine relationships in the sequence α – Γ – Γ₁ – δ: No crystallographic relationship could be established for δ–ζ because it proved impossible to grow a single crystalline layer of ζ on δ. The apparently bad compatibility of the two lattices was reflected in the nucleation problems which were always encountered during efforts to grow ζ on δ. The influence of the relationships on the actually observed textures in the δ and ζ layers of hot dip galvanized specimens is discussed.     

Study of the reversible martensitic transformation in Cu?Zn?Al alloy by positron annihilation

The positron lifetime measurement to investigate phase transformations: martensitic phase (MP) ⇔︁ parent phase (PP) in Cu Zn Al alloy has been used. We have observed the generation of new defects by MP → PP transformation; these defects are liquidated by martensitic transformation. This effect is only observed in case of high concentration vacancies in alloy. In order to explain the nature of these defects we take into consideration the supervacancies idea.     

Investigations of phase relations in the system CaO?Na2O?K2O?P2O5

The lattice constants of the compound Ca₂NaK(PO₄)₂ have been studied at room temperature using an X-ray powder diffractometer and also in the temperature range from 20 up to 1000 °C by Guinier-Lenné-technology. A hexagonal lattice with the parameters a₀ = 5.4367 Å and c₀ = 7.3125 Å and a cell volume of 187.18 ų has been determined for the high temperature phase, existing from 670 °C upward. At temperatures below 670 °C a superlattice structure is formed by tripling the axis a, a ′, and c so that it results in a hexagonal superlattice structure cell with the lattice constants of a₀ = 16.311 Å and c₀ = 21.939 Å and a cell volume of 5054 ų.     

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.     

Structural aspects of thermal instability of polytypes in the Co?C system

The stability of the irregular long-period structures being formed in Co C alloys during β → α transformation has been studied according to the carbon content. In the concentration range 0.2 to 1.2 at.% C the type of the short-range order concerning the atomic layer stacking sequence remains unaffected on subsequent cooling of the alloy, whereas the α-phase crystalline structure of the alloys with the carbon content of 1.3 to 2.17% C suffers polytype transformation. The transition from one polytype structure to another is found to be due to the decrease in length of the cubic-type stacking sequences.     

Peculiarities in the X-ray Spectral Microanalysis of the Sn?Te?I System

This is an examination of the methodological specificities of the roentgenospectral microanalysis of the Sn Te I system, involving the application of a graphoanalytical method used in the analysis of ternary systems according to data calculated for the binary ones. The calculations were made on an ES 1060 computer in FORTRAN-4. The calculations are for different selection angles of the microanalyzer, and for a broad interval of values of the accelerating voltage. In this manner the method offered is applicable to any type of microanalyzer, and not only to the Cameca MS-46 used by us.     

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.     

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.     

Growth kinetics,morphology, and electrical properties of nGaAs?nGaN heterojunctions

nGaAs nGaN heterojunctions were fabricated by one-stage conversion of monocrystalline GaAs under varying conditions. Surface and cross section study, performed by means of optical and electron microscopy, indicates that the growth kinetics is essentially controlled by transfer of ammonia molecules across the already grown nitride layer; the diffusion coefficient value at 700°C being 3.1 × 10⁻¹⁰ cm² sec⁻¹. Current-voltage behaviour, describable by relations of the type I = I₀(T) exp (αV), appears to be dominated by tunneling processes.