Formation Energy Of Alloys Research Articles

Structural descriptors evaluation for MoTa mechanical properties prediction with machine learning

Considering all possible crystal structures is essential in computer simulations of alloy properties, but using density functional theory (DFT) is computationally impractical. To address this, four structural descriptors were evaluated using machine learning (ML) models to predict formation energy, elasticity and hardness of MoTa alloys. A total of 612 configurations were generated by the Clusters Approach to Statistical Mechanics software and their corresponding material properties were calculated by DFT. As input features of ML models, the CORR and SOAP performed best (R 2 > 0.90, some up to 0.99), followed by Atomic-centred Symmetry Functions, while Coulomb matrix performed worst. Furthermore, SOAP shows excellent performance in extrapolation for larger supercell structures of the MoTa alloy system and transfer learning for the MoNb alloy system.

Endergonic Hydrogenation at Ambient Conditions Using an Electrochemical Membrane Reactor.

Here, we determine how the hydrogen loading (x) of an electrochemical palladium membrane reactor (ePMR) varies with electrochemical conditions (e.g., applied current density, electrolyte concentration). We detail how x influences the thermodynamic driving force of an ePMR. These studies are accomplished by measuring the fugacity (P) of hydrogen desorbing from the palladium-hydrogen membrane and subsequently relating P to pressure-composition isotherms to determine x. We find that x increases with both applied current density and electrolyte concentration, but plateaus at a loading of x ≅ 0.92 in 1.0 M H2SO4 at -200 mA·cm-2. The validity of the fugacity measurements is supported experimentally and computationally by: (a) electrochemical hydrogen permeation studies; and (b) a palladium-hydrogen porous flow finite element analysis (FEA) model. Both (a) and (b) agree with the fugacity measurements on the following x-dependent properties of the palladium-hydrogen system during electrolysis: (i) the onset for spontaneous hydrogen desorption; (ii) the point of steady-state hydrogen loading; and (iii) the function describing hydrogen desorption between (i) and (ii). We proceed to detail how x defines the free energy of palladium-hydrogen alloy formation (ΔG(x)PdH), which is a descriptor for the thermodynamic driving force of hydrogenation at the PdHx surface of an ePMR. A maximum value ΔGPdH of 11 kJ·mol-1 is observed, suggesting that an ePMR is capable of driving endergonic hydrogenation reactions. We empirically demonstrate this capability by reducing carbon dioxide to formate (ΔGCO2/HCO2H = 3.4 kJ·mol-1) at ambient conditions and neutral pH.

First-principles calculation of Fe-Mo-Cr alloys based on special quasi-random structure

Mo element has an important effect on ferritic stainless steel. It is of great significance to study the role of the Mo element in the composition design of stainless steel alloys. In this paper, the formation energy, magnetic moment, electronic structure, mechanical and high-temperature mechanical properties of Fe-Mo binary alloys and Fe-Mo-Cr ternary alloys were obtained by density functional theory of first principles. The results showed that the formation energy increases gradually with the increase of Mo content. The alloys have a stable system when the Mo concentration is less than 3.125%. The addition of Cr increases the formation energy, but when Mo content is 3.125%, the formation energy is lower than that of Fe-Mo binary alloys. Fe atoms are ferromagnetic state and Mo atoms are anti-ferromagnetic state, there is an opposite magnetic effect between them. With the increase of Mo concentration, Mo atoms change from anti-ferromagnetic to paramagnetic. Mo atoms become paramagnetic when Mo concentration reaches 100%. Mo element has little effect on the shear modulus of the alloys. The hardness and compressive strength decrease with increasing Mo concentration. The addition of Cr atom also reduces the hardness. Fe-Mo alloys have better thermal stability when Mo concentration is 12.5%. The Cr atom significantly changes the thermodynamic properties of the alloys. The volume thermal expansion coefficient of Fe-Mo-Cr ternary alloys decreases with the increase of Mo concentration, and the highest temperature appears near the Mo concentration of 12.5∼18.75%.

Investigation of structural, mechanical, dynamic stability and electronic properties of anti-perovskite nitrides ANLa3 (A = Al, Ga): a DFT and DFPT studies

Various properties of anti-perovskites ANLa3 (A = Al, Ga) are investigated using the density functional theory (DFT). The GaNLa3 properties are studied for the first time. The computed lattice parameter of AlNLa3 is found to be close to other theoretical and experimental results. The mechanical stability of the present compounds are confirmed by the elastic constants estimated through the calculations. Furthermore, bulk modulus, shear modulus and Young’s modulus are evaluated. In this report, the dynamic stability and formation energy of AlNLa3 and GaNLa3 alloys are also highlighted. The state density functional perturbation theory (DFPT) is used to reveal the phonon calculation showing that the studied compounds are dynamically stable. Indeed, with a negative formation energy, it has been predicted that the GaNLa3 compound can be synthesized experimentally. Moreover, the electronic properties are studied using the Perdew–Burke–Ernzerhof Generalized Gradient Approximation (GGA-PBE) as well as a more sophisticated exchange-correlation Yukawa Screened PBE0 (YS-PBE0) hybrid functional.It has been found that the computed energy band structures within both approaches, that the anti-perovskites AlNLa3 and GaNLa3 are metallic nature. The total density of states (TDOS) and partial density of states (PDOS) are also calculated to show in evidence the contribution of atoms orbitals in the formation of bands.

Predicting thermodynamic stability of magnesium alloys in machine learning

Density functional theory (DFT) have been widely used to screen thermodynamically stable material; however, its high computational cost limits its use. In this paper, we explore the use of DFT data from high-throughput calculations to create faster machine learning (ML) models that can be used to screen thermodynamically stable magnesium alloy materials. Our methods work by utilizing the kernel ridge regression (KRR) algorithm, as well as Deep Potential Molecular Dynamics (DeePMD) to train ML models for predicting the formation energy of magnesium alloys. The accuracy, stability, and generalization ability of the ML models created under both methods are evaluated in detail. Meanwhile, we have conducted in-depth comparative analysis of the two methods, which concluded that the accuracy of DeePMD model performs better and time efficiency of KRR model has more advantages. The results show that the best performing DeePMD model and KRR model achieve the RMSE of 0.43 meV/atom and 6.80 meV/atom, indicating that our methods provide a reliable idea for obtaining the formation energy of magnesium alloys.

Identifying Descriptors for Promoted Rhodium-Based Catalysts for Higher Alcohol Synthesis via Machine Learning.

Rhodium-based catalysts offer remarkable selectivities toward higher alcohols, specifically ethanol, via syngas conversion. However, the addition of metal promoters is required to increase reactivity, augmenting the complexity of the system. Herein, we present an interpretable machine learning (ML) approach to predict and rationalize the performance of Rh-Mn-P/SiO2 catalysts (P = 19 promoters) using the open-source dataset on Rh-catalyzed higher alcohol synthesis (HAS) from Pacific Northwest National Laboratory (PNNL). A random forest model trained on this dataset comprising 19 alkali, transition, post-transition metals, and metalloid promoters, using catalytic descriptors and reaction conditions, predicts the higher alcohols space-time yield (STYHA) with an accuracy of R 2 = 0.76. The promoter's cohesive energy and alloy formation energy with Rh are revealed as significant descriptors during posterior feature-importance analysis. Their interplay is captured as a dimensionless property, coined promoter affinity index (PAI), which exhibits volcano correlations for space-time yield. Based on this descriptor, we develop guidelines for the rational selection of promoters in designing improved Rh-Mn-P/SiO2 catalysts. This study highlights ML as a tool for computational screening and performance prediction of unseen catalysts and simultaneously draws insights into the property-performance relations of complex catalytic systems.

A machine learning approach to predict the structural and magnetic properties of Heusler alloy families

Random forest (RF) regression model is used to predict the lattice constant, magnetic moment and formation energies of full Heusler alloys, half Heusler alloys, inverse Heusler alloys and quaternary Heusler alloys based on existing as well as indigenously prepared databases. Prior analysis was carried out to check the distribution of the data points of the response variables and found that in most of the cases, the data is not normally distributed. The outcome of the RF model performance is sufficiently accurate to predict the response variables on the test data and also shows its robustness against overfitting, outliers, multicollinearity and distribution of data points. The parity plots between the machine learning predicted values against the computed values using density functional theory (DFT) shows linear behavior with adjusted R2 values majorly lying in the range of 0.80 to 0.94 for all the predicted properties for different types of Heusler alloys. Feature importance analysis shows that the valence electron numbers plays an important feature role in the prediction for most of the predicted outcomes. Case studies with one full Heusler alloy and one quaternary Heusler alloy were also mentioned comparing the machine learning predicted results with our earlier theoretical calculated values and experimentally measured results, suggesting high accuracy of the model predicted results.

Electronic properties and stability of M2O3 (M = Al, Ga, In) and alloy (MxGa1‐x)2O3 in α and β phases: A theoretical study

AbstractGa2O3 is clearly emerging as an important wide band‐gap semiconductor. Band‐gap engineering is now highly demanded for expanding its applications. Alloying with the same group of metal oxides is a straightforward and effective way. In this work, by using hybrid density functional theory calculations, the structural, electronic properties, and phase stability of group IIIA (Al, Ga, In) metal oxides and their ternary alloys (MxGa1‐x)2O3 (M = Al, In) in the corundum and monoclinic phases are systematically investigated. The lattice constants, elastic constants, modulus, formation energies, band‐gaps, band‐gap deformation potentials, band‐edge alignments, band‐gap bowing, and ternary alloy formation energies are obtained. The basic relations between the geometric structure and electronic properties are discussed. It is found that the cation ordered structure is the most stable alloy structure in the monoclinic phase, rather than the random alloy structure as is commonly thought. A phase stability diagram of the (MxGa1‐x)2O3 alloys is established, showing that the stable phase of the alloy changes from the monoclinic phase to the corundum phase when the incorporation of Al2O3 (In2O3) is greater than 69% (76%). These results can be used to understand the relative experimental data and shed some light on the synthesis and device design efforts of Ga2O3.

Thermodynamic insights into strong metal–support interaction of transition metal nanoparticles on titania: simple descriptors for complex chemistry

Usingab initiomodelling, we demonstrate that a simple parameter – alloy formation energy – is a good descriptor of an interaction strength between metal substrates and oxide monolayers, which allows constructing structure–material–environment maps.

Formation energy puzzle in intermetallic alloys: Random phase approximation fails to predict accurate formation energies

We performed density functional calculations to estimate the formation energies of intermetallic alloys. We used two semilocal approximations, the generalized gradient approximation (GGA) by Perdew-Burke-Ernzerhof (PBE) and the strongly constrained and appropriately normed (SCAN) meta-GGA. In addition, we utilized two nonlocal DFT functionals, the hybrid HSE06, and the state-of-the-art random phase approximation (RPA). The nonlocal functionals such as HSE06 and RPA yield accurate formation energies of binary alloys with completely-filled d-band metals, where semilocal functionals underperform. The accuracy at the nonlocal functionals is greatly reduced when a partially-filled d-band metal is present in an alloy, while PBE-GGA outperforms in these cases. We show that the accurate prediction of formation energies by any DFT method depends on its ability to predict the accurate electronic properties, e.g., valence d-band contribution to the density of states (DOS). The SCAN meta-GGA often corrects the PBE-DOS, however, it does not provide accurate formation energies compared to PBE. This is assumed to be due to the lack of proper error cancellation that should be expected due to the similar bulk nature of both alloys and their constituents, which may improve with the modification of meta-GGA ingredients. RPA yields too negative formation energies of alloys with partially-filled d-band metals. RPA results can be corrected by restoring the exchange-correlation kernel, thereby improving the short-range electron-electron correlation in metallic densities.

First-principles study of de-twinning in a FCC alloy

First-principles calculations were used to study the effects of several alloying elements X (i.e., Al, Sc, Zn, and Ce) on the de-twinning of Cu alloys. The results show that the nanotwin (Nt) formation energy of Cu-X alloy gradually decreases with the de-twinning, but Ce improve the Nt formation energy and segregation energy of Cu alloys in T4. Furthermore, charge transfer and redistribution were investigated to explore the physical mechanisms of twinning and de-twinning. When the alloying atom is introduced, a “local effect” is formed in its neighboring regions. The anisotropic distribution of the density charges around Ce improves its bonding strength with Cu atoms, while the Sc atom and Ce atom have a smaller electronegativity and a larger atomic radius, forming strong bonds and high mechanical energy.

Phase stability of TiPd1-xRux and Ti1-xPdRux shape memory alloys

TiPd alloys have been suggested for commercial applications due to their high strength and good corrosion resistance. An improvement upon its stability through alloying with Ru requires an understanding of its thermodynamics, which currently is not clear. A cluster expansion based Monte Carlo simulations have been used to investigate the phase stability of TiPd1-xRux and Ti1-xPdRux shape memory alloys. The cross-validation score (CVS) was used to verify the fitting accuracy and was found to be reasonable. The cluster expansion generated 27 new structures on B2 TiPd1-xRux (Pd site) and 17 new structure for B2 Ti1-xPdRux (Ti site). The ground state line predicted no stable structures relative to the predicted enthalpies of formation for TiPd1-xRux alloys. All formation energies of TiPd1-xRux alloys are positive, showing that there is a miscibility gap in the system and thermodynamic instability. The result showed that Ru prefers being substituted on the Ti-site than the Pd-site. Monte-Carlo simulations were employed to determine phase changes and high temperature properties of mixed TiPd1-xRux and Ti1-xPdRux alloys for the entire range of Ru concentrations (0 ≤ x ≤ 1). The phase diagram of TiPd1-xRux and Ti1-xPdRux systems were constructed. These findings can have important implications for future shape memory materials design in aerospace industries for actuators.

A first-principles study on the site occupancy behavior of transition metals in L12-Al3Li phase

The main strengthening mechanism in Al-Li alloys is generally achieved by the existence of a high volume fraction of the L12-Al3Li precipitation from Al matrix. In this work, we do density functional theory (DFT) total energy calculations on the site occupancy behaviour of transition metals in L12-Al3Li compound. The ground state properties of L12-Al3Li, fcc-Al, and bcc-Li are determined and compared to the available literature data. The formation energies of intrinsic point defects in L12-Al3Li phase as well as Al3LiX alloy formation energy are calculated and identified. We show that the Li antisite is preferential to from in the L12-Al3Li phase. Finally, the site occupancy behaviour of transition metals in L12-Al3Li as well as the solute atomic volume effect on the solute site preference and lattice expansion of the L12-Al3Li have been studied, the later results can be used for an indirect estimation of the site substitution behaviour of the alloying elements in L12-Al3Li phase.

First-principles study of bcc Fe-Cr-Si binary and ternary random alloys from special quasi-random structure

Using a combination of first-principles calculations with special quasi-random structure and quasi-harmonic approximation methods, we have calculated formation energy, magnetic moments, mechanical properties and thermodynamic properties of binary FeCr and ternary FeCrSi random alloys. The results agree well with available theoretical and experimental data. The body centered cubic structures and ferromagnetic phase are employed to calculate these properties in this work. The phase stability studies show that FeCr alloys are stable systems in Cr concentrations below 6% region. However, binary FeCr alloys are the systems with a miscibility gap for Cr concentrations above 6%. The ternary FeCrSi systems show much less formation energy than FeCr systems. For ternary FeCrSi alloys, Fe9Cr22Si1 shows maximum value of formation energy. Studies on magnetism have shown that Si is a kind of nonmagnetic material, it can be used to reduce magnetic moments of FeCr alloys. Doping a little Si into FeCr alloys can form more stable systems and improve bulk modulus, shear modulus and young's modulus in both low-Cr and rich-Cr concentration regions. Si element can generate effects on Debye temperature and volumetric thermal expansion coefficient of the alloy. But Si element can not generate obvious effects on constant volume heat capacity of FeCr alloys.

Structural, electronic and magnetic properties of Ni2XAl (X= V, Cr, Mn, Fe, and Co) Heusler alloys: An ab initio study

Nickel-based Ni2XAl (X ​= ​V, Cr, Mn, Fe, and Co) Heusler alloys for both L21 and L10 crystal structures are studied by using the density functional theory. The magnetization energy and formation energy of Ni2XAl Heusler alloys are calculated. We found that in the ideal L21 structure, ferromagnetic (FM) state is more stable than nonmagnetic (NM) and antiferromagnetic (AF) states, except Ni2VAl. The ground state for Ni2VAl is the nonmagnetic state. The so-called Bain paths method is applied to study the stability of Ni2XAl alloys under tetragonal distortion. We found that Ni2FeAl and Ni2CoAl are possible ferromagnetic shape materials (FSMs). We also found that Ni2CrAl and Ni2CoAl are energetically favorable in the antiferromagnetic state in the L10 structure. To study the stability between L21 and L10 crystal structure, we calculate the cohesive energy for comparison. We also calculate the elastic constants, bulk modulus, shear modulus, and universal elastic anisotropy to study the mechanical stability in L21 and L10 crystal structure. The spin polarization for the L21 structure is calculated whilst the largest spin polarization is smaller than 80%.

Magnetic properties of Fe16−x(Ta/W)xN2 ternary alloy: first principles and atomistic simulations

Using the first principles method, we explored the magnetic properties of Fe16−x(Ta/W)xN2 alloy. We calculated the alloy formation energy, dynamical and thermal stabilities and proved the possibility of materialization of Fe16−x(Ta/W)xN2 alloy. The Fe14Ta2N2 had a Curie temperature of 1020 K while it was 950 K in Fe14W2N2. We found greatly enhanced uniaxial anisotropy in ternary alloy systems. Particularly, the Fe14W2N2 alloy has a uniaxial anisotropy constant of 2.68 MJ m−3 which is almost a five times enhancement of the value of 0.57 MJ m−3 in the Fe16N2. The increase in the uniaxial anisotropy resulted in an enhancement of the coercive field (HC). The Fe14W2N2 had a coercive field of 27 kOe at 300 K and this is comparable to that of 25.6 kOe in Dy-doped Nd based magnet. Besides, the (BH)max of 54.5 MGOe in Fe14W2N2 alloy was even larger than the value of 40 MGOe in Dy-doped Nd-based magnet. Overall, we propose that the Fe16−x(Ta/W)xN2 can be a potential rare-earth-free permanent magnet.

Stabilization of Ca7Ge-type magnesium compounds by alloying of non-metal elements: A new family material for reversible hydrogen storage applications

A new family material of MgnTMX2 consisted by alloying non-metal element X into the Ca7Ge-type MgnTM (TM = V, Ti, or Nb; X = C, N, O, F, P, S, or Cl; n = 6 for TM = Nb and V or 7 for TM = Ti) to keep its structural stability during the de/hydrogenations was proposed. Formation energy of MgnTMX2 alloys was calculated using density functional theory to clarify the possibility of synthesizing these compounds. Calculations illustrated that compounds with X = F, O, and S satisfy both the thermal stability with negative formation energies and mechanical stability at zero pressure. The hydrogen absorption is proceed in a manner of stepwise, and finally all tetrahedron interstices were filled by 56 hydrogen atoms in the unit cell forming formula hydrides as MgnTMX2H14. It is obvious that the interstice composition plays an important role in hydrogen adsorption performance. The tetrahedral interstices composed by three Mg atoms and one transition metal own more strong ability to capture H atoms than those constituted by four Mg atoms in the initial hydrogenation process Results indicate that new family compound Mg6VO2 could be possibly ideal hydrogen storage materials in terms of dehydrogenation temperature (170–246 K) and hydrogen storage capacity (∼5.81 mass %).

Understanding Chemical Bonding in Alloys and the Representation in Atomistic Simulations

Alloys are widely used in catalysts and structural materials. The nature of chemical bonding and the origin of alloy formation energies, defect energies, and interfacial properties have not been well understood to date but are critical to material performance. In this contribution, we explain the polar nature of chemical bonding and an implementation in classical and reactive atomistic simulations to understand such properties more quantitatively. Electronegativity differences between metal atoms lead to polar bonding, and exothermic alloy formation energies are related to charge transfer between the different elements. These differences can be quantified by atomic charges using pairwise charge increments, determined by matching the computed alloy formation energy to experimentally measured alloy formation energies using pair potentials for the pure metals. The polar character of alloys is comparable to organic molecules and partially ionic minerals, for example, AlNi and AlNi3 alloys assume significant a...

МОДЕЛЮВАННЯ ТЕРМОХІМІЧНИХ ВЛАСТИВОСТЕЙ ТА СХИЛЬНОСТІ ДО АМОРФІЗАЦІЇ РОЗПЛАВІВ ПОТРІЙНОЇ СИСТЕМИ Mn–Al–Gd

In the present work, the enthalpies of mixing of liquid alloys of the ternary Mn-Al-Gd system have been calculated using the regular solution model by the Redlich-Kister-Muggianu formula. Also a comparison was made of calculated values of enthalpies of mixing in this system with the experimentally determined thermochemical properties of liquid alloys of the Mn-In-Gd ternary system obtained previously. In general, we estimate that the values of the enthalpies of mixing in the Mn-Al-Gd ternary system should be more exothermic than in the Mn–In-Gd one. This fact can be explained taking into consideration the main features of the component interaction in the boundary binary systems, namely, such important characteristics as electronegativity of the components, their electron work functions and a large difference in size of atoms. It can be concluded that it is the binary Mn–Al system that makes a significant contribution to the formation energy of ternary alloys. An imaginary line drawn through the points of maximum curvature of the isoenthalpic lines is considerably shifted towards the binary Mn–Al boundary, thus expanding significantly the region of rather exothermic enthalpies of mixing in the corresponding ternary system. For the two indicated ternary systems the size mismatch entropy has been calculated within the framework of hard spheres model and the Sσ/kB parameter has been determined. On the basis of the comprehensive analysis carried out, the criteria for the probability of occurrence of regions of easy amorphization in these ternary systems are proposed. The determination of the topology of the mixing enthalpy surface and the Sσ/kB parameter for the melts of studied ternary systems together with the data on binary and ternary compounds existing in these systems allowed to reasonably assume the concentration regions where the investigated ternary alloys have tendency for easy amorphization while rapid cooling of the melt. The simultaneous realization of the following three conditions was taken as a criterion for the possible existence of a region of easy amorphization: the absolute value of the enthalpies of mixing is at least 6 kJ/mol, the Sσ/kB parameter is not less than 0.3–0.4 and a certain distance from the concentration region corresponding to the exact composition of binary or ternary compounds.

Magnetic states of Ni2MnZ and Ni2CrZ (Z = Al, As, Bi, Ga, Ge, In, P, Pb, Sb, Si, Sn, Tl) Heusler alloys

In this work we study the magnetic states of ternary Ni2CrZ (Z = Al, As, Bi, Ga, Ge, In, P, Pb, Sb, Si, Sn, Tl) Heusler alloys in comparison with Ni2MnZ ones by ab initio methods. It is shown that the Ni-Mn based alloys are ferromagnetic. Contrary, the Ni-Cr based alloys with Z = Ga, In, Tl, Si, Ge, Sn, Pb are compensated aniferromagnets and with Z = Al, P, As, Sb, Bi are ferromagnets. The formation energy of alloys studied is calculated and stable compounds are predicted. The possible martensitic transitions in Ni-Mn and Ni-Cr based Heusler alloys are estimated. Within the Heisenberg model and Monte Carlo technique, the Curie temperatures are obtained. Theoretical results are compared with other theoretical end experimental results.