Order-disorder or phase-separation transition: Analysis of the Au-Pd system by the effective site energy model

Berthier, F.; Creuze, Jérôme; Gabard, Tony; Legrand, Bernard; Marinica, Mihai-Cosmin; Mottet, C.

doi:10.1103/physrevb.99.014108

Cited by 11 publications

(24 citation statements)

References 41 publications

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“…Our calculations (Table I) 300 K. Taken together, the data for a Pd-Au alloy are not fully consistent [24]. In the situation we are interested in (at f 0.2 and T 300 K), the experiments and theory, however, either support or at least do not contradict the assumption that the atoms in this alloy are distributed at random.…”

Section: Structure Of the Pd-au Alloymentioning

confidence: 57%

“…12 in [21]). The corresponding critical temperatures are low as well at all the compositions [24]. In particular, the ordered L1 2 state is predicted near f = 0.25 at T 170 K and the biphase domain for f < 0.25 at T 250 K ( Fig.…”

Section: Structure Of the Pd-au Alloymentioning

confidence: 85%

“…(ii) For pure Au, DFT is in favor of H absorption on the T sites, whereas the H location in the O sites is predicted to be unstable [13,19]. (iii) For a Pd-Au alloy, the theory was used to scrutinize the arrangement of atoms [20][21][22][23][24]. In addition, DFT indicates that hydrogen absorption becomes less favorable with increasing Au content [25,26].…”

Section: Introductionmentioning

confidence: 99%

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Suppression of hysteresis in absorption of hydrogen by a Pd-Au alloy

Mamatkulov

Zhdanov

2020

Phys. Rev. E

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Hydrogen absorption by Pd exhibits hysteresis loops (provided the temperature is not too high) and represents one of the classical examples of first-order phase transitions in metals. Experiments indicate that addition of even a small amount of Au is able to suppress hysteresis. From this perspective, we analyze the energetics of hydrogen in a Pd-Au alloy by using extensive density-functional-theory (DFT) calculations. The dependence of the hydrogen binding energy on the number (n) of Au atoms forming an adsorption site is found to be appreciably nonlinear. With the DFT input for statistical calculations, we reproduce special features of the hydrogen absorption isotherms and explain the rapid decrease of the corresponding critical temperature with increasing Au fraction. The key factor here is that the phase transition is related primarily to absorption in sites formed only by Pd. With increasing Au amount, the fraction of such sites rapidly decreases, the distance between H atoms located there becomes on average larger, the interaction between them becomes weaker, and accordingly the driving force for the phase transition decreases. It is of interest that all these effects can be illustrated by taking only the configurations with n 2 into account. This means that in the context under consideration the fine details of the dependence of the hydrogen binding energy on n are in fact not too important.

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Section: Structure Of the Pd-au Alloymentioning

confidence: 57%

Section: Structure Of the Pd-au Alloymentioning

confidence: 85%

Section: Introductionmentioning

confidence: 99%

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Suppression of hysteresis in absorption of hydrogen by a Pd-Au alloy

Mamatkulov

Zhdanov

2020

Phys. Rev. E

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“…For each configuration, we perform an energy relaxation by using LAMMPS [73]. Then, the phonon spectrum and vibrational entropy are computed using PHONDY package [74][75][76][77].…”

Section: System (N )mentioning

confidence: 99%

Machine learning surrogate models for prediction of point defect vibrational entropy

Lapointe

Swinburne

Thiry

et al. 2020

Phys. Rev. Materials

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The temperature variation of the defect densities in a crystal depends on vibrational entropy. This contribution to the system thermodynamics remains computationally challenging as it requires a diagonalisation of the system's Hessian which scales as O(N 3) for a crystal made of N atoms. Here, to circumvent such an heavy computational task and make it feasible even for systems containing millions of atoms the harmonic vibrational entropy of point defects is estimated directly from the relaxed atomic positions through a linear-in-descriptor machine learning approach of order O(N). With a size-independent descriptor dimension and fixed model parameters, an excellent predictive power is demonstrated on a wide range of defect configurations, supercell sizes and external deformations well outside of the training database. In particular, formation entropies in a range of 250 kB are predicted with less than 1.6 kB error from a training database whose formation entropies span only 25 kB (train error less than 1.0 kB). This exceptional transferability is found to hold even when the training is limited to a low energy superbasin in the phase space while the tests are performed for a different liquid-like superbasin at higher energies.

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“…We propose a detailed CE analysis using the effective site energies (ESEs) description [46][47][48]. Let us recall the principles of this approach.…”

Section: Introductionmentioning

confidence: 99%

Effective site energy and cluster expansion approaches for the study of phase diagrams

2021

Self Cite

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We apply the cluster expansion (CE) method to determine the effective cluster interactions (ECIs) from a simple energetic model that depends on both local and global composition. This model is defined by the site energies of random solid solutions of a one-dimensional alloy Co-Pt. We explore how these local and global dependencies are reflected on the cluster interactions. The energies of the structures are not well reproduced with concentration-independent interactions. Moreover, the interactions have a larger range than the energetic model which is limited to the nearest neighbors. By fitting the ECIs on the site energies, we suggest a mean-field-type weighting of the excess variables present in clusters of large size. We show that the site energy formalism controls the size of the clusters required for CE convergence and their concentration dependence. Finally, we take advantage of the site energy formalism to describe the elastic and chemical effects that control the thermodynamics of the alloy as a function of the ECIs.

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Order-disorder or phase-separation transition: Analysis of the Au-Pd system by the effective site energy model

Cited by 11 publications

References 41 publications

Suppression of hysteresis in absorption of hydrogen by a Pd-Au alloy

Suppression of hysteresis in absorption of hydrogen by a Pd-Au alloy

Machine learning surrogate models for prediction of point defect vibrational entropy

Effective site energy and cluster expansion approaches for the study of phase diagrams

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