R.A. Ligero

A study of the crystallization kinetics of some Cu-As-Te glasses

The crystallization kinetics of two amorphous alloys in the Cu-As-Te system was studied by differential scanning calorimetry, using continuous heating methods, and applying a new analysis procedure in order to calculate the kinetic parameters which define the crystallization reactions, in the Johnson-Mehl-Avrami model. In this analysis, the crystallized fraction interval at which the characteristic function of said model is constant was taken into account. The values obtained for these parameters made it possible to discuss the glass-forming ability of the compounds under study, and the types of crystalline growths in the alloys.

On the crystallization kinetics of glassy alloys in the Cu-As-Se system

Abstract A study of the crystallization kinetics of amorphous alloys in the Cu-As-Se system was made using a method in which the crystallization rate is deduced bearing in mind the dependence of the reaction rate constant on time, through temperature. The method was applied to the experimental data obtained by differential scanning calorimetry, using continuous-heating techniques. The kinetic parameters determined have made it possible to discuss the glass-forming ability, as well as the different types of nucleation and crystal growth exhibited by the alloys studied.

Determination of kinetic parameters of crystallization and study of glass forming ability for alloys in the GeAsTe amorphous system

Abstract A mathematical method which makes it possible to calculate the kinetic parameters of crystallization, activation energy, E , reaction order, n , and frequency factor, K 0 , was developed. The procedure was applied to chalcogenide glasses Ge 0.05 As 0.20 Te 0.75 , Ge 0.10 As 0.20 Te 0.70 and Ge 0.14 As 0.43 Te 0.43 , confirming the validity of the method. A criterion is discussed for analyzing the glass forming ability (GFA) of these alloys, from the thermal events observed on heating the glasses, and evaluated in terms of the reaction rate constant of each alloy.

Atomic configurations generation by a random method for glassy alloy Ge0.l4As0.43Te0.43

Three different models of the amorphous alloy Ge0.14As0.43Te0.43, obtained by quenching the molten mixture of the elements, were built by computer simulation of an X-ray diffraction experiment, taking the tetra- and tricoordinated germanium hypotheses into account. The main structural parameters of these models were analysed and the results did not vary greatly from those given in the literature for similar alloys.

Crystallization kinetics in the As-Se-Te system

Abstract This work consists of a study on the crystallization reaction kinetics of six alloys in the As-Se-Te glassy system, chosen as representatitve of the easy DTA crystallization zone, within the concentration triangle of the system. The study was carried out by differential scanning calorimetry, using continuous heating methods, and the corresponding kinetic parameters were evaluated by an iterative method based on the Johnson-Mehl-Avrami theoretical model. Finally, the glass-forming ability (GFA) of the alloys and of the system are discussed by calculating the rate constant of the crystallization reactions.

A theoretical method for determining basic parameters for the short-range order of amorphous ternary alloys, using X-ray diffraction

Abstract A procedure was developed for determining theoretical expressions for the area under the first radial distribution function (RDF) peak and for the relative coordination numbers (nij) which depend on the coordination hypotheses and on the number of bonds between atoms of a single element or a pair. In this method, two important facts were taken into account. On one hand, the products of atomic factors are functions of s (the scattering vector module) and so cannot always be considered constant; they were therefore approximated by the polynomial functions which best fit the results obtained for the atomic factors given in the International Tables. On the other hand, we considered the influence of the structural hypotheses (coordinations, existence of certain types of bond) on the area and coordination numbers mentioned and obtained expressions for these parameters which enable us to postulate the most probable local order. In order to test the reliability of the method, it was applied to a set of alloys, quoted in the literature and the theoretical results agreed very satisfactorily with the experimental values.

A comparative study of different methods for calculating the set of kinetic parameters which describe the crystallization reaction of a glassy alloy

Abstract The crystallization reaction of an As-Se-Te alloy was taken as a reference for determining the kinetic parameters which describe the said reaction by differential scanning calorimetry and using non-isothermal techniques. Three sets of kinetic parameters were obtained, using three calculation methods within the theoretical Johnson-Mehl-Avrami model. Each of the results obtained is discussed regarding its agreement with previous experimental data.

Short-range order in some alloys of the Ge-As-Te semiconducting glassy system by X-ray diffraction

A study of short-range order in amorphous semiconducting alloys of the Ge-As-Te system has been carried out by X-ray diffraction. The different hypotheses on germanium coordination have been taken into account, following the different criteria cited in the literature for binary Ge-Te alloys. The result of this study shows the possibility of structural units based on tetra-or tricoordinated germanium atoms, which bonded together give way to short-range order in these alloys. !t has also been found that, for these alloys, germanium dicoordination is not compatible with the data obtained experimentally.

GeAsTe glassy system. Atomic distribution models

Abstract Atomic structure models were generated for the semiconducting glassy alloys Ge x As 0.20 Te 0.80− x ( x =0.05, 0.10), from shortrange order information given by the corresponding radial distribution functions, obtained from X-ray diffraction intensities. The Metropolis Monte Carlo random method was used in the building of the models, and the fact that Ge atoms can be four- and three-coordinated has been taken into account. The structural parameters obtained from the models agree with those given in the literature for similar alloys.

Crystallization kinetics study of Fe-B-Si metallic glasses in the theoretical frame of the JMA model

The crystallization kinetics of Fe-B-Si metallic glasses, characterized by the effective activation energy E and the Avrami exponent n was studied by non-isothermal DSC technique. The data show values both for E and n in good agreement with the theoretical JMA model for the first crystallization stage, but not for the second.