Preparation of GaAs₁-ₓPₓ compounds from the melt under controlled vapour pressures

Crystalline solid solutions between GaAs and GaP compounds were prepared from the melt under controlled vapour pressures. The experimental results were found to agree with the theoretical formulae derived in order to calculate the pseudo-equilibrium in a heterogeneous system consisting of two parts with different temperatures. It was assumed that all condensed phases would be regular or sub-regular and that the gas phase is ideal. In addition some of the thermodynamic properties of the Ga-As-P ternary system were dicussed. It was confirmed that one can apply the concept of the pseudo-equilibrium to preparation of crystalline solid solutions of III-V compounds containing two volatile components

Reversion and Reaging in an Al-2at%Zn-2at%Mg Alloy

Kinetics of reversion and reaging of an Al-2at%Zn-2at%Mg alloy have been studied by resistivity measurements and tensile tests. Perfect reversion occurred only when aged at 20°C. The formation of the transition phase was found to occur in parallel with the dissolution of zones when the specimen aged at 70°C was reverted at 200°C. An incubation period accompanied with initial fast and slow reactions was observed in reaging. When the aging prior to reversion was ceased before the end of fast reaction, the incubation period was not observed, similarly in the case of Al-Cu alloy. It will be clear that the nucleation is necessary for zone formation in Al-Zn-Mg alloys. The initial fast and slow reactions will be explained in terms of the amount of vacancies compared with the number of solute atoms after reversion

Infrared Absorption in Gallium Arsenide-Gallium Phosphide Alloys

The infrared absorption has been quantitatively investigated with respect to the shape, the temperature dependence and the carrier concentration dependence of the additional absorption band in the region from 1000 to 4000 cm⁻¹. The experimental method for the determination of the threshold energy was discussed. The present experimental results have given a reasonably clear indication of the difference between the additional absorptions in n-GaAs-rich alloys and ones in n-GaP-rich alloys. Especially, the additional bands in n-GaAs-rich alloys were concluded to occur by a transition of conduction electron from the lowest band minimum to the upper subsidiary one. The dependence of the threshold energy on composition x was found to be expressed as Eₜ＝0.29-0.67x (eV). The empirical cross over point occurred at 43 mol% GaP. On the other hand, in n-GaP and GaP-rich alloys, the additional band showed a relatively sharp peak and all the absorption shapes were similar to the previous analysis. The threshold energy was found to depend to a small extent on the composition. The dependence could be illustrated in terms of the composition dependence of the ionization energy

Electron-Microscopic Investigation on Precipitation Phenomena in Aluminium-Zinc Alloys

The precipitation process, its relation with lattice defects and the effect of cold working on precipitation and grain boundary reaction in the aluminium alloys containing ll.2, 17.4, 28.3 and 40.8% zinc respectively were investigated by means of X-ray diffraction, hardness measurements and transmission electron microscopy. It was found that face-centered cubic transition precipitates were formed in granular shape in ll.2% or 17.4% zinc alloys and were plate-like in 28.3% zinc alloys. The plate-like transition precipitates were formed on {110} matrix planes, perhaps preferentially on the prismatic dislocation loops. The results are shown to be consistent with the hypothesis that in the quenched alloys precipitation occurs on prismatic dislocation loops that result from the condensation of quenched-in vacancies. In Al-28.3 and 40.8% Zn alloys, the grain boundary reaction is predominant at lower aging temperatures

Aging Characteristics and Effects of Plastic Deformation on Precipitation in Al-4% Cu and Al-20% Ag Alloys with or without Trace Elements

The experiments have been carried out to examine the effects of plastic deformation and addition of small amounts of third elements on the aging process in Al-4%Cu and Al-20%Ag alloys by the X-ray Laue method, micro-hardness measurements, transmission electron microscopic studies and resistivity measurements. In binary Al-4% Cu alloys, the plastic deformation immediately after quenching retards the growth of G.P. (1) and G.P. (2), and accelerates the nucleation of the θ′ phase. In Al-20% Ag alloys, similar results are obtained. In undeformed ternary Al-Cu alloy, the retarding effects of third elements on aging become stronger in the order Be<Ti<Zr. In Al-Cu-Zr alloys, the plastic deformation much accelerates the growth of G.P. (1). The role of excess vacancies on aging and the interaction between dislocation and precipitates are discussed

Electrical and Optical Properties of Te doped GaSb

To examine the property of impurity states in n- and p-type GaSb, the crystals were prepared by doping it with Te. The Hall and resistivity measurements were made and, simultaneously, the free carrier absorption was measured. The undoped crystals were always p-type. The perfect compensation was found to occur at the 0.003 at% amount of Te added to the melt. In the p-type GaSb, it was found that the acceptor level, which results from vacancies in Sb sub-lattice site, is located at 0.021 eV. In the n-type GaSb, the donor concentration changed from 0.5 to 10 x10¹⁸cm⁻³ by increasing the Te amount. It was suggested that the acceptor introduced into the n-type crystal corresponds to the deeper acceptor level, which was observed in the highly compensated p-type sample. The concentration of its acceptor was found to be fairly larger than that of the native acceptor

On the Two-Stage Aging of Al-Mg-Si Alloys

The two-stage aging effect in three Al-Mg-Si alloys containing 0.5, 1.0 and 1.5% Mg₂Si respectively is investigated by electrical resistivity measurements, tensile tests and electron microscopy. The critical temperature for homogeneous nucleation of precipitates exists between 160 and 200°C for an 1.0% Mg₂Si alloy, and for an 1.5% Mg₂Si alloy between 200 and 260°C. The Temperatures are also correspoding to the highest temperatures for the resistivity increase respectively. The slight decrease in resistivity perhaps due to redissolution of clusters is observed for 0.5% Mg₂Si alloy in the initial stage of isothermal aging at a low temperature. The activation energy Eₛ for migration of solute atoms in the fast reaction is estimated as 0.77 eV for all three alloys in good agreement with the values reported for a 1.4% Mg2Si alloy. The deleterious effect of two-stage aging is observed in only limited cases, though it appearts unfortunately often in practice. The whole effect of two-stage aging appears to be explained only by the stability of clusters or zones formed during preaging. The conservation in zone number is not observed. The nucleation or stabilization of clusters which takes place during heating to aging temperature must be considered not only for quenching effect but also for two-stage aging effect

On the Precipitation in Aluminium-Zinc-Magnesium Alloys

The precipitation characteristics in Al-5wt% Zn-2wt% Mg alloys with or without a trace addition of Ag, Cu or Cr have been studied as the function of solution temperature and time, quenching temperature and medium, and pre-aging between quenching and artificial aging mainly by electrical resistivity measurement and tensile test. Imperfections such as sub-boundaries still remained after incomplete solution treatment, though it is particularly the case when added Cr, influence remarkably the following precipitation. Vacancy-solute clusters, which could be formed during or immediately after quenching, can act as precipitation nuclei of η' intermediate phase and, therefore, influence considerably the age-hardening at higher temperatures. Pre-aging and small additions of Ag have also many favorable effects on higher temperature aging

Transmission Electron Microscopic Investigation on Recrystallization and Precipitation of Magnesium and Magnesium Alloys

Experiments have been carried out to examine aging characteristics, recrystallization phenomena and effects of plastic deformation after water-quenching on the precipitation of Mg-Th alloys in the composition range from 1.7 to 4.0 w/t% thorium as compared with pure magnesium, Mg-Zn and Mg-Al alloys mainly with electron microscopic observations in thin foils. In Mg-4.0% Th alloys, G. P. zones were confirmed to exist before the appearance of the transition phase Mg2Th in accordance with the result of measurements of electrical resistance. The presence of thorium in a magnesium alloy greatly retarded such processes as recovery and recrystallization. This slowing up process seems to be reflected in the slow precipitation rate of Mg-Th compounds. The effects of cold working on precipitation in these alloys are not simple but complex

On Precipitation Phenomena in Magnesium-Zinc Alloys

The ageing characteristics of magnesium-zinc alloys in the composition range from 3.2 to 19.0 wt.% zinc were studied at temperatures from 70° to 200°C mainly with X-ray diffraction methods and electron-microscopic observations with thin foils. The G.P. zones were confirmed to exist on the {1011} matrix planes. The transition phase on the {1010} matrix planes is MgZn´ indistinguishable from the hexagonal Laves phase MgZn₂. The effects of plastic deformation were examined with direct observations by thin foils. The formation of G.P. zones on the {1011} matrix plane was hindered by cold working after water quenching, while the rates of precipitation of the transition phase β´ and equilibrium phase β were accelerated