Premonitory effects in Cu<sub>3</sub>Au near the order-disorder transformation

Bardhan, P.; Chen, Haydn; Cohen, J. B.

doi:10.1080/14786437708232985

Cited by 23 publications

(4 citation statements)

References 15 publications

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“…The overall agreement is satisfactory even close to or above T~, contrary to the conclusions drawn by previous work [1]. This apparent contradiction of the present work is due to the fact that in [1] the comparison between experiment and calculations, close to or above T~, relies on Debye-Waller factor measurements by Bardhan et al [26,27]. These have been criticized in recent work by Lander et al [25] because Bardhan et al have inappropriately used the intensity of the diffuse superlattice peaks to extract the effective thermal motion amplitudes of atoms.…”

Section: Mean Square Displacementscontrasting

confidence: 56%

Thermodynamical properties and defect energetics of an n-body potential adapted to Cu3Au

et al. 1994

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By using molecular statics, molecular dynamics, and Monte Carlo techniques we validate a previously developed empirical n-body potential adapted to Cu3Au. At T = 0 K, predicted cohesive energies, lattice parameters, and elastic constants in CuAu and CuAu3 as well as the formation energy of vacancies in Cu3Au are in good agreement with experimental data. A satisfactory behavior is also obtained at T ~ 0 K in Cu3Au, for atomic mean-square displacements and elastic moduli. However, this model underestimates the vacancy migration energy and the order-disorder critical temperature when the latter is evaluated by Monte Carlo including both exchanges between atoms of different species and atomic moves simulating vibrations.

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Section: Mean Square Displacementscontrasting

confidence: 56%

Thermodynamical properties and defect energetics of an n-body potential adapted to Cu3Au

et al. 1994

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“…While the concept seems possible, there is as yet no direct evidence for the existence of the instability temperature, although in an experiment due to Bardhan et al (1977) on Cu aAu there is a strong suggestion. The analogue of the Schwahn-Schmatz experiment ( § 4.3) would be desirable.…”

Section: Ordering Reactionsmentioning

confidence: 99%

Phase transformations—a physicist’s perception

Venkataraman

1984

Bull. Mater. Sci.

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Echoing a recent remark by Prof. Ramaseshan, a perspective review is made of the field of phase transformation, highlighting areas that might appeal to physicists. Prominent in this category are the study of ground state structures, the study of phase diagrams and the study of kinetic phenomena. Enumeration of ground state structures calls for inputs from group theory as well as reliable potentials, and physicists are therefore well equipped to make significant contributions. The theoretical analysis of phase diagrams (concerning which mueh experimental information already exists) raises challenging questions in equilibrium statistical mechanics. Since the problems map to Ising models of varying complexity and their generalizations, there are also very interesting connections to magnetism. Lately, computer simulation has added a new dimension, opening up fresh vistas both for theory and experiments. The study of kinetics belongs to the newly emerging area of non-equilibrium statistical mechanics. The focus being on temporal phenomena, physicists can play a key role, particularly through the application of various types of relaxation spectroscopy. On the theoretical side too there are challenging problems, especially on account of the dominance of nonlinearities. Indeed if one is bold enough, one could even speculate on possible universalities underlying the complex microstructures invariably seen in late-stage evolution. In short, though the subject of phase transformations has thus far been nursed predominantly by metallurgists, there is enough room for physicists to make an independent entry and to make distinctive contributions. Keywards. Phase transformations; phase diagrams; spinodal decomposition; ordering kinetics. * Strictly speaking, we should have enthalpy H(= E + p V) instead of E. However, most material processing is done around atmospheric pressure. From a practical point of view therefore H is well approximated by E.

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“…energies were determined. Furthermore, these temperatures are now known to be within the range above Tc where there are heterophase fluctuations [25], not classical fluctuations. Accordingly, the values were plotted as shown in figure 5 along with the data for Cu-18.5 at pct Au, with corrections for the known B2(001), f and AS: for each alloy.…”

mentioning

confidence: 99%

“…-The term T/1lri$ at k*, the position of a superlattice reflection that would occur below Tc, was found to be linear us. T (except near Tc for Cu3Au, where heterophase fluctuations appear [25]). Thus F(k*) (from Eq.…”

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confidence: 99%

A Comparison of Experiment and the Theory of Continuous Ordering

Chen

Cohen

1977

J. Phys. Colloques

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RksurnC. -La transform& de Fourier de 1'Energie Libre d'Helmholtz q k ) , pour des fluctuations de composition de vecteur d'onde k, a Cte obtenue dans le cas de plusieurs alliages ordonnes audessus de T, en effectuant des mesures absolues, a haute temperature, de I'intensitt due a l'ordre local le long des rangtes de I'espace reciproque. Les monocristaux etudies etaient les suivants : Cu,Au, Cu-23 atomes "/, Au, Cu-18,s atomes % Au, et CoPt,. Les rtsultats sont compares B la theorie des transformations continues et il apparait que I'approxirnation harmonique linkaire est insuffisante. En particulier I'Cnergie due au gradient depend fortement de k. Ceci apparait aussi a partir des mesures des temps de relaxation effectuees suivant differentes directions cristallographiques : ceux-ci varient moins que prevu avec la direction quand on neglige la variation de l'energie due au gradient. I1 est possible de mesurer l'knergie d'activation de I'interdiffusion en volume dans les alliages a basse temperature en effectuant des mesures de I'intensitt absolue due I'ordre local en fonction de la temperature et en mesurant ensuite les variations de cette intensite avec le temps lorsque la temperature varie. Les rksultats sont donnes pour les alliages dkja cites et pour l'alliage Fe-29,2 atomes % Al.Cette recherche a ete financee par la U.S. National Science Foundation grdce a un contrat no DMR 73-07549 A01 et par le Centre de Recherche des MatCriaw de la Northwestern University subventionne par la NationalScience Founda~ion sous contrat no DMR 7601 57.Abstract. -The Fourier transform of the Helmholtz Free Energy F(k), for composition Buctuations of wave vector k, has been obtained for several ordering alloys above T, by measuring the absolute X-ray diffuse scattering intensity due to local order, at high temperatures, along lines in reciprocal space. The single crystals examined were Cu,Au, Cu-23 at pct Au, Cu-18.5 at pct Au, and CoPt,. The values obtained are compared to the theory of continuous transformations and it is found that the linear theory is satisfactory but the nearest-neighbour approximation is inadequate. In particular, the gradient energy is a strong function of k. This is also indicated from measured relaxation times in different crystallographic directions ; these vary less with direction than predicted when the dependence of the gradient energy on k is ignored. It is possible to measure the activation energy for interdiffusion in bulk alloy crystals at low temperatures by measuring the absolute intensity due to local order us. temperature and then measuring changes in this intensity with time when the temperature is varied. Values are given for the above alloys and for Fe-29.2 at pct Al.

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Premonitory effects in Cu₃Au near the order-disorder transformation

Cited by 23 publications

References 15 publications

Thermodynamical properties and defect energetics of an n-body potential adapted to Cu3Au

Thermodynamical properties and defect energetics of an n-body potential adapted to Cu3Au

Phase transformations—a physicist’s perception

A Comparison of Experiment and the Theory of Continuous Ordering

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Premonitory effects in Cu3Au near the order-disorder transformation

Cited by 23 publications

References 15 publications

Thermodynamical properties and defect energetics of an n-body potential adapted to Cu3Au

Thermodynamical properties and defect energetics of an n-body potential adapted to Cu3Au

Phase transformations—a physicist’s perception

A Comparison of Experiment and the Theory of Continuous Ordering

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Product

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Premonitory effects in Cu₃Au near the order-disorder transformation