Crystallization Heat Treatment Research Articles

Heat treatment of CdS large single crystals under controlled conditions

Heat treatment of CdS large single crystals under controlled conditions

Effects occurring during heat treatment of aluminium single crystals

Abstract The formation of pits and tops after a temperature change has been studied. It is found that the time which the specimen is kept at high temperature has a marked effect on the critical ΔT for pit formation, possibly because of changes taking place in the oxide layer. It is also found that it takes a certain time, after the final temperature is reached, until the first pits appear. The pits are also observed to disappear when the sample is kept at the final temperature.

Investigation of the Energy-Level Scheme ofGd+3in CaF2using Thermoluminescence

The energy-level scheme of ${\mathrm{Gd}}^{+3}$ in Ca${\mathrm{F}}_{2}$ is investigated using thermoluminescent techniques. A large number of emission lines is found in the thermoluminencence spectrum. This large number of lines is attributed to different site spectra. The effect on the emission spectra of heat treatment and different origins of crystals is shown. The differences in spectra between samples result from the variations in abundance of the various rare-earth ion sites. This abundance is primarily determined by growth conditions and impurity concentrations.

1186. Vacuum heat treatment of CdS single crystals: K W Boer and C A Kennedy, Phys Status Solidi, 19, 1967, 203–210

1186. Vacuum heat treatment of CdS single crystals: K W Boer and C A Kennedy, Phys Status Solidi, 19, 1967, 203–210

Effect of Heat Treatment on Electrical Conduction in DPPH Single Crystals Grown from Benzene Solution

The dependence of conduction on the concentration of Benzene contained in DPPH recrystallized from a benzene solution is reported. The concentration is varied by heat treatment of as-grown single crystals at about 63°C. The conductivity of a single crystal which contains one benzene molecule per DPPH molecule is 1.6×10 10 \(\varOmega\) -1 cm -1 . The conductivity decreases with decreasing concentration of benzene. The activation energy increases in such a way that the decrease in conductivity can be attributed to the increase in activation energy. This correlation between the activation energy and the conductivity is explained by the polarization effect of benzene by assuming that the activation energy can be expressed as E = I - A -2 P , where I , A , and P are the ionization energy, the electron affinity, and the polarization energy, respectively.

Effect of Impurities on the Optical Properties of Yttrium Iron Garnet

The optical absorption spectrum of single-crystal YIG is dominated at the short wavelengths by electronic transitions due to iron ions. For the long wavelengths, it is dominated by lattice vibrational transitions. Between about 1 μ and 6 μ there is a region of great transparency which can be modified in several ways. The valence of the iron ions can be altered by heat-treatment of crystals in oxidizing or reducing atmospheres, or by doping with divalent or tetravalent ions. The altered valence leads to increased optical absorption, as well as increased electrical conductivity. Foreign ions such as cobalt or the rare earths may have characteristic absorption lines in the region of transparency, and when yttrium is completely replaced by a rare earth, the short-wavelength edge absorption may be shifted appreciably due to lattice expansion or contraction. Another anomaly in the transparent region of YIG is found in hydrothermally-grown crystals, where OH-group stretching vibrations occur.

Heat Treatment of InSb Crystals with Different Dislocation Densities

Heat Treatment of InSb Crystals with Different Dislocation Densities

Vacuum Heat Treatment of CdS Single Crystals

AbstractChanges of the spectral distribution of photoconductance and conductance glow curves after heat treatment between 370 and 620°K and immediate quenching of undoped CdS single crystal platelets in ultrahigh vacuo are described. After annealing, the electrical properties after heat‐treatment quenching sequences are largely reproducible. The results are interpreted as the dissociation of larger defect associates containing Cd vacancies and consequent production of single Cd vacancies causing a trap level at Ec – Et ≈︁ 0.4 eV and vacancy pairs with trap levels at Ec – Et ≈︁ 0.95 eV. Dissociation and stress enhanced diffusion of vacancies in the neighborhood of associates becomes noticeable at treatment temperatures above 350°K.

Effect of Crystallization Conditions and Heat Treatment on Polyethylene: Lamellar Thickness, Melting Temperature, and Density

Lamellar thickness, melting temperature, and density were measured for bulk polyethylene crystallized by the application of a fixed pressure to molten polymer at different temperatures. Melting temperature varied from 135.2° to 139.2°C, and density varied from 0.9759 to 0.9842 g/cc. Small-angle x-ray diffraction yields two maxima which apparently are not first and second orders of diffraction. Electron micrographs of fracture surfaces exhibit lamellae, which support the suggestion that the lamellar thickness is the shorter of the two dimensions (469≤L1≤981 Å and 193≤L2≤440 Å) corresponding to the diffraction maxima. However, the functional relationship of both dimensions to melting temperature and density are in accord with existing or easily derived equations. Analysis of these data, together with the result obtained from paraffin data, yields an equilibrium melting temperature of 141.9±1.7°C. Dimensions of the unit cell did not vary with lamellar thickness. Single crystals of polyethylene were collected into mats and heated at a fixed temperature under various pressures. The observed effect of pressure was to limit the fold period attained during heat treatment. The data suggest that the refolding process follows a relationship which describes crystallization from the melt.

Growth and Heat Treatment of Zinc Sulfide Single Crystals

Zinc sulfide crystals grow readily from the vapor phase if small traces of certain impurities, such as zinc oxide and copper, are present. The decrease of ambient impurity concentration leads first to very thin, flexible, ribbon‐like crystals which are hexagonal, and finally to nucleation with little growth. The purity of crystals depends not only on the composition of the starting material but also on the purity of the combustion tube employed; contamination during growth leads to an impurity gradient in crystals and to impurity variations among crystals. Crystals usually exhibit disorder of the crystal structure, although pure cubic or hexagonal structure can be achieved by annealing or quenching. Heat treatment also changes the impurity content and attendant properties, such as physical color, luminescence behavior, electrical properties, and disorder of the crystal structure.

Mechanism of the Formation of Donor States in Heat-Treated Silicon

A mechanism for the donor formation during heat treatment of silicon crystals is presented which accounts quantitatively for the complex kinetic phenomena and which is consistent with the known extra-kinetic information concerning this system. Atomically dissolved oxygen introduced during the growth of the silicon crystal reacts, in the course of heat treatment, to form a sequence of kinetically linked aggregates till finally a polymeric silica (Si${\mathrm{O}}_{2}$) is formed. Only those aggregates which possess fewer than five bound oxygen atoms appear to act intensively as donors at room temperature, and in particular donor states produced around 450\ifmmode^\circ\else\textdegree\fi{}C appear to consist principally of a donor [Si${\mathrm{O}}_{4}$] complex. The kinetic equations are integrated using a general-purpose analog computer for a variety of initial concentrations of oxygen, temperature, etc., and the results compare favorably with existing experimental observations.

A "super-elastic" single crystal calibration bar

Elastic strains of up to 4% can be attained in a copper-aluminium-nickel alloy in the form of a single crystal suitably heat treated. The high elasticity is due to a reversible martensite transformation induced by stressing. The methods of production and heat treatment of large crystals are described together with details of mechanical properties. The alloy can be machined by conventional methods. Suggestions are made for the development of other super-elastic alloys.