Calculated Enthalpies Of Formation Research Articles

Exploring the radiation stability and electronic properties of bcc Zr1−xNbx (0 ≤ x ≤ 1) alloy from first-principles

First-principles studies on the radiation stability of Zr and Zr-based alloys are very popular in nuclear material development research. The present work is performed by utilizing the density functional theory for investigating the radiation stability and electronic properties of Zr1-xNbx alloys (0 ≤ x ≤ 1). The simulation study is performed with a structural phase in which Zr and Nb remain distributed in solid solution ratio with bcc structure which resembles the phase as obtained at high temperature. The calculation of formation enthalpy for various structures exhibits that the solid solution is thermodynamically most stable with the 50% Nb concentration. The defect formation energy of the structures possessing defects via Zr or Nb vacancy in the structures is also found to be positive maximum, which suggests that the creation of defect is tougher in the Zr1-xNbx alloy for x = 0.5. Additionally, the observation of electronic properties in terms of electronic density of state reveals that introducing vacancy affected the electronic properties of the perfect structures. Notably, Zr0.5 Nb0.5 shows unique electronic behavior compared to other compositions of Zr-Nb alloy, making it the most stable composition in a harsh radiation environment.

First-principles investigation of the structural stability, elastic, and electronic properties of Mg-Al-X (X=Sn, Pb) ternary compounds

In this work, we employed the first-principles calculations to explore the structural stability, elastic modulus, and electronic behavior of the Mg-Al-X (X=Sn, Pb) ternary compounds. The calculated formation enthalpy indicates that the Mg16Al12Sn-C exhibits the best stability with a value of -0.057 eV/atom. Moreover, the Mg16Al12Pb-C possesses the highest modulus values with values of 58.37, 52.32, and 120.86 GPa for bulk, shear, and Young's modulus, respectively. The Mg16Al12Sn-C exhibits weak anisotropy of the lowest AU value of 0.04. Additionally, the Mg16Al12Pb-C possesses the largest melting temperature of 1142.85 K. The high modulus of the Mg16Al12Pb-C can be attributed to the contributions from the Al-Al and Mg-Al bonds. Moreover, the weighted average bond length results show that the Mg16Al12Pb-C (Mg16Al12Sn-C) in the Mg-Al-Pb (Mg-Al-Sn) system possesses the shortest bond length value of 3.067 Å (3.058 Å), resulting in a higher modulus.

Computational insights into the multifunctional properties of Li2AgBiX6 (X=Cl, Br, I) double perovskite materials

We investigate the potential of Li2AgBiX6 (X = Cl, Br, I) double perovskites for optoelectronic and transport applications using density functional theory. Structural stability is confirmed through lattice constant, tolerance factor, and formation enthalpy calculations. Using the HSE-06 functional, we determine indirect bandgaps of 1.78, 1.76, and 0.92 eV for Cl, Br, and I compositions, respectively. Maximum optical absorption occurs in the visible region, supporting their potential in optoelectronic devices. Spectroscopic limited maximum efficiency calculations reveal Li2AgBiI6 as the most efficient (29.3 %) due to higher absorbance. We evaluate thermoelectric properties using the Boltzmann semi-classical approach and assess mechanical stability through elastic constants. Thermodynamic properties, including Debye temperature and melting point, are calculated. Magnetic property calculations indicate zero magnetic moment. The comprehensive analysis of structural, electronic, optical, transport, elastic, thermodynamic, and magnetic properties provide valuable insights into these promising double perovskite materials for various applications.

Impact of boron substitution on the thermoelectric, mechanical stability, electronic and optical properties of InP alloys

Density Functional Theory (DFT) calculations, utilizing the full potential linearized augmented plane wave (FP-LAPW) method, were performed to investigate the effect of boron (B) substitution on the InP system through GGA and mBJ-GGA formalisms, aiming to improve its band gap energy. Lattice equilibrium optimization determined that the stable structure of the alloys at equilibrium energy shows a decrease in lattice constants with increasing boron concentration (x). The calculated formation enthalpies, which are negative, indicate that these systems are experimentally synthesizable. The elastic analysis confirms that the doped alloys are elastically stable and exhibit ductile properties. The optical parameter analysis reveals that the optical energy loss functions are minimal or zero in the infrared, visible, and ultraviolet ranges, suggesting their suitability for optical applications across these energy ranges. Specifically, the band gaps were found to range from 0.878 eV for x = 0.25–1.920 eV for x = 0.75 using the mBJ-GGA formalism. Furthermore, the role of B-doping in the InP system for thermoelectric technology was systematically investigated, revealing that our alloys possess good thermoelectric properties with a figure of merit (ZT) reaching up to 0.7 for x = 0.75. These results demonstrate that accurate tuning of the energy band gap through doping is an effective technique for discovering novel materials suitable for both thermoelectric and optoelectronic applications.

Predicting the formation enthalpy and phase stability of (Ti,Al,TM)N (TM = III-VIB group transition metals) by high-throughput ab initio calculations and machine learning

The development of transition-metal-alloyed (Ti,Al)N thin films has become a common strategy to achieve optimized mechanical and thermal properties. Selection of a suitable alloying element, however, should consider the effect on Al solubility, directly influencing phase stability during the deposition. Here we use high-throughput ab initio formation enthalpy calculations to assess stability of the cubic (c) vs. hexagonal wurtzite-type (w-) phase of TM-alloyed (Ti,Al,TM)N. This compositionally-limited ab initio dataset serves to fit several machine-learning (ML) models enabling phase stability predictions over the entire compositional range. Of all the models, the linear regression using Magpie feature descriptor pre-processed by a genetic algorithm has the highest accuracy. For Ta, Nb, Mo, and W addition below ∼10 at.%, our ML model predicts enhanced stability of c-(Ti,Al,TM)N due to increased solubility of Al. Other alloying elements, especially Sc and Y from IIIB group and Hf and Zr from IVB group, decrease the cubic metastable solubility limit. In agreement with available experimental data, all transition metals except for Cr and V increase the volume of c-(Ti,Al,TM)N and w-(Ti,Al,TM)N.

Theoretical exploration of novel compounds in Sr(B,C)x (x = 7,8) at high pressure

Boron-carbon-based compounds have attracted considerable attention due to their exceptional properties and increasing applications in industry. In this study, we conducted a systematic structural prediction of the SrBxC7-x and SrBxC8-x systems under ambient and high pressures up to 20 GPa using an unbiased global structure search. Through the calculations of formation enthalpy and phonon dispersion curves, we identified three new compounds, namely SrB5C2, SrB6C and SrB5C3, as thermodynamically and dynamically stable under ambient pressure and high pressures up to 20 GPa. Calculations of mechanical properties reveal that these three compounds have significant mechanical strength, with estimated theoretical Vickers hardness values ranging from 23.2 to 39.8 GPa. Electronic structure calculations suggest that both SrB5C2 and SrB5C3 are hole conductors, with the bands crossing the Fermi level, and SrB6C is a semiconductor with an indirect bandgap of 2.4 eV. The electron-phonon coupling calculations using the Migdal-Eliashberg theory indicate that SrB5C2 exhibits superconductivity at 10.5 K under ambient pressure, while SrB5C3 shows superconductivity at a much lower temperature of 0.4 K. This finding adds to our knowledge of boron-carbide materials and provides valuable insights for the development of similar materials with good mechanical properties.

Phase stability and physical behaviour of Fe3Pd, FePd and FePd3 binary intermetallic compounds

The FP-LAPW method is used to examine the physical properties of Fe–Pd binary intermetallic compounds. The calculated formation enthalpies indicate that FePd and FePd3 compounds are thermodynamically stable in L10 and L12 phases, respectively, and the ferromagnetic Fe3Pd can be formed in a tetragonal Z1 structure with a small negative formation enthalpy. The elastic coefficients and their related parameters show that all compounds are mechanically stable and ductile in nature. The FePd-L10 is the harder compound and Fe3Pd-Z1 exhibits the highest anisotropy. The band structure, the TDOS profile and the charge density distribution show that these compounds are ferromagnetic with a metallic character and covalent-metallic bonds. The PDOS shows that the Pd-4d and Fe-3d states are dominant, and the asymmetry of Fe-3d states is behind the system strong spin polarization. The calculated magnetic moments agree well with previous theoretical results. The thermodynamic parameters are determined using the quasi-harmonic Debye model.

First-Principles Study of Cu Addition on Mechanical Properties of Ni3Sn4-Based Intermetallic Compounds

Ni–Cu under-bump metallisation (UBM) can reduce stress and improve wetting ability in technology for electronic packaging technology advances with three-dimensional integrated circuit (3D IC) devices. The bond between the Sn-based solder and Ni–Cu UBM is affected by the formation of intermetallic compounds (IMCs), specifically Ni3Sn4 and (Ni,Cu)3Sn4. This paper investigates the mechanical properties of IMCs, which are critical in assessing the longevity of solder joints. First-principles calculations were carried out to investigate the phase stability, mechanical properties and electronic structures of Ni3Sn4, Ni2.5Cu0.5Sn4, Ni2.0Cu1.0Sn4, and Ni1.5Cu1.5Sn4 IMCs. The calculated formation enthalpies show that the doping of Cu atoms leads to a decrease in the stability of the phases and a reduction in the mechanical properties of the Ni3Sn4 crystal structure. As the concentration of Cu atoms in the Ni3Sn4 cells increases, the bulk modulus values of (Ni,Cu)3Sn4 formed with different compositions decrease from 107.78 GPa to 87.84 GPa, the shear modulus decreases from 56.64 GPa to 45.08 GPa, and the elastic modulus decreases from 144.59 GPa to 115.48 GPa, indicating that the doping of Cu atoms into the Ni3Sn4 cells may adversely affect their mechanical properties and increase the possibility of microcracking at the interface during actual service. The anisotropy of (Ni,Cu)3Sn4 is more significant than that of Ni3Sn4, with Ni2.0Cu1.0Sn4 showing the highest anisotropy. After evaluating the electronic structures, the metallic properties of Ni3Sn4 and the Ni2.5Cu0.5Sn4, Ni2.0Cu1.0Sn4, and Ni1.5Cu1.5Sn4 phases are revealed by electronic structure analysis. The total density of states (TDOS) for (Ni,Cu)3Sn4 structures is mainly influenced by Ni-d and Cu-d states. The addition of Cu atoms can increase the brittleness of Ni3Sn4. In addition, the region where d and p hybridisation occurs gradually increases with increasing Cu content. The electronic properties suggest that the binding energy between Ni and Sn atoms weakens with the addition of Cu atoms, resulting in a decrease in the elastic modulus. This research can serve as a valuable reference and theoretical guide for future applications of these materials.

An accurate prediction of electronic structure, mechanical stability and optical response of BaCuF3 fluoroperovskite for solar cell application

This study utilizes the first-principles modelling approach based on the density functional theory (DFT) framework to investigate the structural, mechanical, and optoelectronic properties of the BaCuF3 fluoroperovskite. Initially, the three distinct cubic structures of BaCuF3 were simulated based on the positioning of F atoms. This investigation aimed to determine the most stable configuration for BaCuF3. The structural stability of all compounds has been evaluated through the formation enthalpy calculations. In addition, the mechanical stability is assessed by the investigation of elastic stiffness constants. The mechanical stability of the α-BaCuF3 and β-BaCuF3 compounds has been observed. However, the γ-BaCuF3 compound is deemed unstable due to its failure to meet the Born-stability criterion (C44 < 0). The ductility of α-BaCuF3 and the brittleness of β-BaCuF3 have been determined by exploring Pugh's and passion ratios and the Cauchy pressure. The electronic characteristics have been evaluated by examining electronic band structure, density of states and partial density of states. The compounds α-BaCuF3 and β-BaCuF3 have been seen to have indirect and direct band gaps of 0.14 eV (M–Γ) and 1.22 eV (Γ–Γ), respectively. Several optical parameters have been calculated and compared. The materials that have been chosen exhibit significant optical conductivity and absorption coefficients when exposed to high-energy photons while also demonstrating transparency at lower incident photon energy ranges. Our investigations into the optical properties have determined that α-BaCuF3 and β-BaCuF3 exhibit favourable characteristics for solar cell implementation, high-frequency UV, and optoelectronic devices.

Crystal–melt interfaces in Mg2SiO4 at high pressure: structural and energetics insights from first-principles simulations

The interplay between crystal–melt and grain boundary interfaces in partially melted polycrystalline aggregates controls many physical properties of mantle rocks. To understand this process at the fundamental level requires improved knowledge about the interfacial structures and energetics. Here, we report the results of first-principles molecular dynamics simulations of two grain boundaries of (0l1)/[100] type for tilt angles of 30.4° and 49.6° and the corresponding solid–liquid interfaces in Mg2SiO4 forsterite at the conditions of the upper mantle. Our analysis of the simulated position time series shows that structural distortions at the solid–liquid interfacial region are stronger than intergranular interfacial distortions. The calculated formation enthalpy of the solid–solid interfaces increases nearly linearly from 1.0 to 1.4 J/m2 for the 30.4° tilt and from 0.8 to 1.0 J/m2 for the 49.6° tilt with pressure from 0 to 16 GPa at 1500 K, being consistent with the experimental data. The solid–liquid interfacial enthalpy takes comparable values in the range 0.9 to 1.5 J/m2 over similar pressure interval. The dihedral angle of the forsterite–melt system estimated using these interfacial enthalpies takes values in the range of 67° to 146°, showing a decreasing trend with pressure. The predicted dihedral angle is found to be generally larger than the measured data for silicate systems, probably caused by compositional differences between the simulation and the measurements.

Metastable aluminum boride: density functional theory study of prerequisites of formation

AbstractAluminum borides have significant practical interest as energetic additives to fuels, explosives and propellants due to their favorable thermodynamic and kinetic characteristics. Density functional theory calculations with periodic boundary conditions have been performed to evaluate the enthalpy of formation of two aluminum borides: the well‐known aluminum diboride AlB2 and the metastable Al1.28B phase, which precedes the formation of AlB2 during heat treatment of mechanically activated composite aluminum‐boron powders, as well as aluminum ion‐implanted with boron. The calculated formation enthalpy of AlB2 is −3.6 kcal/mol, which agrees well with estimates from literature. The enthalpy of formation of Al1.28B, calculated for the first time, is 4.8 ± 0.4 kcal/mol. To understand the prerequisites for the formation of Al1.28B observed in experiments, the enthalpy of formation of supersaturated solid solutions of B in Al has been evaluated. The reasons for the preferential formation of the metastable Al1.28B phase over the thermodynamically stable AlB2 phase are discussed.

Predicting the effects of doping and pressure on the structural, mechanical and electronic properties of B12P2*

Based on the first-principles calculations, the effects of doping and pressure on the B12P2 have been investigated and discussed systematically. The calculated formation enthalpy and phonon dispersion curves show that the pure and N-doped B12P2 are structurally stable. Mechanical properties demonstrated that the Vickers hardness of B12P2 was successfully improved (from 38.1 GPa to 43.4 GPa) by partially replacing P with N, which due to the short bond length between B and N atoms and can also be well understood by the band structure around the Fermi level. In addition, the calculated B/G and Poisson's ratio ν reveal that the pure and N-doped B12P2 are intrinsically brittleness and strongly prone to ductility under pressure, especially the pure B12P2 undergoes a brittle-to-ductile transition when the pressure is above 93.5 GPa, which is beneficial to the application of mechanical materials under extreme conditions. In addition, the visual elastic anisotropy also shows an enhanced trend under pressure. Finally, the electronic structure calculations indicate that the N-doped B12P2 becomes a wide-band-gap semiconductor under pressure, which is an attractive candidate for high voltage/high power devices.

Pressure induced structural, hardness, elastic and thermodynamic properties of three MoC

Insight into the high pressure behavior is very important for the engineering applications of high temperature ceramics. However, the mechanical and thermodynamic properties of MoC carbide under high pressure are unknown. Here, we apply the first-principles approach to study the influence of high pressure on the structural stability, elastic modulus, hardness, elastic anisotropy and Debye temperature of three MoC carbides. The cubic and hexagonal phases under high pressure are selected. The results show that the calculated formation enthalpy under high pressure follows the sequence of hexagonal (P-6 m2) < hexagonal (P63/mmc) < cubic. Importantly, it is found that the hexagonal (P-6 m2) MoC has better thermodynamic stability in comparison to the cubic and the hexagonal (P63/mmc) MoC. Although the elastic modulus of three MoC increases with increasing pressure, the hardness of three MoC decreases with increasing pressure. In particular, the elastic modulus and hardness of the hexagonal (P-6 m2) MoC are higher than the cubic MoC. In addition, the high pressure results in brittle-to-ductile transition of the hexagonal (P-6 m2) MoC. Naturally, the high elastic modulus and hardness of the hexagonal (P-6 m2) MoC are determined by the network MoC bonds. Finally, the calculated Debye temperature of the hexagonal (P-6 m2) MoC is higher than the cubic MoC under high pressure.

Synergistic effects of alloy elements on the structural stability, mechanical properties and electronic structure of Ni3Sn4: Using first principles

Ni3Sn4 and Ni3Sn4-based ternary phases play an important role in the interfacial connection in solder joints. In this study, we provide a detailed investigation of the structural stability, mechanical properties and electronic structures of Ni3-xMxSn4 (M = Co, Pd, Pt and Cu，x = 0–1.5) and Ni3Sn4-xNx (NIn, Ge, Pb and Sb，x = 0–1.5) using first-principles methods. The calculated formation enthalpies reveal that the alloy elements (Pd, Pt, Ge and Sb) can improve the structural stability of Ni3Sn4, but Co, Cu, In and Pb do the opposite. The elastic constants (Cij) of Ni3-xMxSn4 and Ni3Sn4-xNx structures are typically lower than those of Ni3Sn4. Cu and Sb elements are detrimental to the ductility of Ni3Sn4, and the elements of Ge and Pb can improve the ductility of Ni3Sn4. The rest of elements (In, Co, Pd and Pt) have less influence on the ductility and brittleness of Ni3Sn4. Electronic structure analysis shows that the trend of the Fermi Level values (Ef) are consistent with the formation enthalpies (Hf) of Ni3-xMxSn4 and Ni3Sn4-xNx. The orbitals hybridization between Ni-d, M-d, Sn-p and N-p have a significant effect on Ni3Sn4. Finally, the bulk modulus (B), shear modulus (G), Young's modulus (E), Poisson's ratio (ν), and differential charge density are calculated completely.

Electronic, elastic and thermal properties of hexagonal TM5Si3N investigated by first-principles calculations

During the current study, structural, electrical, elastic, and thermal properties of TM5Si3N (TM = V, Nb, and Ta) Nowotny phase were researched using first-principles calculations. The calculated formation enthalpies and phonon dispersion spectrums of these TM5Si3N Nowotny phases indicate that they are dynamically and thermodynamically stable. Because of the strong hybridization between TM-d state and Si-p and N-p states, TM5Si3N can form TM-Si and TM-N bonds. The obtained elastic anisotropy indexes, two-dimensional (2D) planar projection, and three-dimensional (3D) surface constructions demonstrate that the elastic modulus of TM5Si3N is anisotropic, and the order of elastic anisotropy is Ta5Si3N > Nb5Si3N > V5Si3N. In addition, the minimum thermal conductivity of TM5Si3N was calculated using the Clarke's and Cahill's models, which was found to be anisotropic and in the following order of Ta5Si3N > Nb5Si3N > V5Si3N.

Substitution behavior of Cu doped into Fe3Si and its effect on the electronic structure and mechanical properties based on first-principles calculation

The substitution behavior of Cu doped into Fe3Si and its effect on the electronic structure and mechanical properties of Fe3Si were investigated using first principles plane-wave pseudopotential method based on density functional theory. Alloys with dopant Cu taking position of atoms Fe(I), Fe (II), and Si were labeled as Fe11CuSi4(I), Fe11CuSi4(II), and Fe12Si3Cu, respectively. The calculated formation enthalpy and cohesive energy of the three compounds and Fe3Si alloy were all negative, indicating their thermodynamic stability. However, the atomic fraction of dopant Cu substituting on Si atom was approximately zero, implying that the formation of Fe12Si3Cu is challenging. According to the analysis results of differential charge density and Bader charge, the covalent bond was weakened after Cu doping, while the ionic bond strength was in the order of Fe11CuSi4(I) > Fe3Si > Fe11CuSi4(II) > Fe12Si3Cu, which also indicated that the Fe12Si3Cu is less stable than the other three compounds. These results suggested that the dopant Cu atom preferred to substitute Fe atom, particularly Fe(I), but hardly substitute the Si atom. In order to gain a better understanding of the effect of Cu doping on the mechanical properties of Fe3Si compound, the antiphase boundary energy (ABPE) and elastic constants of Fe3Si, Fe11CuSi4(I), and Fe11CuSi4(II) were further calculated. The value of APBE was decreased, whereas the plasticity of Fe3Si compound is increased with the substitution of Fe atoms by the Cu dopant. The enhanced plasticity of Fe3Si alloy by Cu doping results from the dominant influence of the reduced APBE and weakened covalent bonds over the effect of reduction in ionic bonding.

Natural band alignment of MgO1−xSx alloys

We have calculated formation enthalpies, bandgaps, and natural band alignment for MgO1−xSx alloys by first-principles calculation based on density functional theory. The calculated formation enthalpies show that the MgO1−xSx alloys exhibit a large miscibility gap, and a metastable region was found to occur when the S content was below 18% or over 87%. The effect of S incorporation for bandgaps of MgO1−xSx alloys shows a large bowing parameter (b ≃ 13 eV) induced. The dependence of the band lineup of MgO1−xSx alloys on the S content by using two different methods and the change in the energy position of the valence band maximum (VBM) were larger than those of the conduction band minimum. Based on the calculated VBM positions, we predicted that MgO1−xSx with S content of 10%–18% can be surface charge transfer doped by high electron affinity materials. This work provides an example to design for p-type oxysulfide materials.

Effects of alloying elements on the super-lattice intrinsic stacking fault energy and ideal shear strength of Ni3Al crystals

The effects of alloying elements (Re,W,Ti,Ta,andMo) on the super-lattice intrinsic stacking fault energy and ideal shear strength (σmax) of Ni3Al crystals at 0 K was studied through first-principles calculation. The calculated formation enthalpy of point defects reveals that single solute atoms (i.e., Re,W,Ti,Ta,andMo) tend to occupy the Al site, while solute–solute complex defects (i.e., Re-Re, Re-W, Re-Mo, Re-Ta, Re-Ti, W-Mo, W-Ta, W-Ti, Mo-Ta, Mo-Ti, and Ta-Ti) tend to occupy the Al-Al site. The addition of single solute atom can increase the unstable stacking fault energy and ideal shear strength (σmax) of perfect Ni3Al crystals. Therefore, the doping of a single solute atom is beneficial for the creep strengthening of Ni3Al crystals. Compared with the doping of W,Ti,Ta,andMo, the doping of Re can more effectively impede the nucleation and movement of dislocations of Ni3Al crystals. Through the careful comparison of the creep properties of Ni3Al crystals with solute–solute complex defects, a conclusion can be drawn that the doping of alloy elements W and Re exhibit similar strengthening effects on the creep properties of Ni3Al crystals. W can be preliminarily predicted to replace part of Re in Ni3Al crystals without affecting creep properties. In addition, comprehensive evaluation reveals that the weak interaction between solute–solute complex defects should improve the strengths of Ni3Al crystals to a certain extent.

First-Principles Study of Structural Stability and Mechanical Properties of Ta–W–Hf Alloys

In order to obtain the effect of W and Hf elements on the mechanical properties of Ta–W–Hf alloys, the structural, mechanical, and electronic properties of Ta–xW–6.25Hf (x = 6.25, 12.50, 18.75, 25.00, 31.25, 50.00) alloys were studied using first-principles calculation based on density functional theory, and the supercell method. The calculated formation enthalpy and elastic constants clarify that Ta–W–Hf alloys have structural and dynamical stability. The formation enthalpy and the cohesive energy decrease with the increase in W content, and the cohesive energy increases when Hf element is added to Ta–W alloy. In addition, bulk modulus (B), shear modulus (G), and Young’s modulus (E) for each of the Ta–xW alloys increase gradually with the increase in W concentration. The B, G, and E of Ta–xW–6.25Hf alloys is lower than that of Ta–xW alloy under the same W content conditions, suggesting that Hf alloying with higher Ta–W concentration becomes softer than the Ta–W alloy. Based on the mechanical characteristic, the B/G and Poisson’s ratio of Ta–W–Hf alloys are higher than those of Ta–W alloys with W content over 25%, the ductility of Ta–W–Hf alloys improves with the addition of Hf, and Hf can reduce the anisotropy of Ta–W–Hf alloys. Furthermore, the electronic density of states shows that alloying W and Hf improves the metallicity of Ta. The results in this work provide the underlying insights needed to guide the design of Ta–W–Hf alloys with excellent mechanical properties.

Trends in mechanical, anisotropic, electronic, and thermal properties of MAX phases: a DFT study on M2SX phases

Based on the density functional theory, the structural, mechanical and thermal properties of 27 S-based M2SX (M=Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W; X = B, C, N) phases have been investigated systematically. The calculated formation enthalpies (ΔH) reveal that W2SC and W2SN are thermodynamically unstable phases due to the positive ΔH, and the V2SN, Nb2SN, and Mo2SC are mechanically unstable phases with C12 > C11. The calculated phonon spectrum indicates that 16 phases are dynamically stable phases except M2SN (M=V, Nb, Ta), M2SX (M=Cr, W; X = B, C, N), Mo2SC, and Mo2SN phases. Among the 16 stable phases, the Ti2SB, V2SB, Ta2SB and Ta2SC are predicted in this work, for the other 12 stable phases, the physical properties have been reported more or less. From the calculated results, V2SC, Nb2SC, and Ta2SC are resistant to compression and thermal shock, and which exhibit potential application in thermal barrier coatings. All the stable phases are more compressible along the a-axis, which means that c-axis is stiffer owing to strong atomic bond. Electronic structures indicate the stable phases are all metallic, and the Mo2SB and Ta2SC can be applied in thermoelectric material with very low lattice thermal conductivity. All the present results could motivate exploration and research on novel S-based MAX phases in the future.