Structural, mechanical, electronic, and thermodynamic properties of pure tungsten metal under different pressures: A first‐principles study

Mo 5 SiB 2 is an ideal candidate for high temperature material. Although the D8 l -Mo 5 SiB 2 has been published, the other phases and the related properties of Mo 5 SiB 2 are still unclear. Here, two possible Mo 5 SiB 2 phases (D8 m -Mo 5 SiB 2 and Cmcm-Mo 5 SiB 2 ) are predicted by using the first principles method. The structural stability, mechanical properties, melting point and electronic structure of Mo 5 SiB 2 are studied. The results show that the D8 m -Mo 5 SiB 2 and Cmcm-Mo 5 SiB 2 are thermodynamically and dynamically stables. The calculated bulk elastic modulus, shear modulus and Young's modulus of the Cmcm-Mo 5 SiB 2 are close to D8 l -Mo 5 SiB 2 . In addition, the predicted Cmcm-Mo 5 SiB 2 has high melting point (2518.5 C) compared to the D8 l -Mo 5 SiB 2 and D8 m -Mo 5 SiB 2 . In particular, the predicted D8 m -Mo 5 SiB 2 exhibits better plasticity than the D8 l -Mo 5 SiB 2 . The calculated density of states and Mulliken overlap population shows that the D8 m -Mo 5 SiB 2 and Cmcm-Mo 5 SiB 2 all exhibit metallic behavior. The metallic behavior mainly depends on the electronic interaction between Mo atom and B atom near Fermi level. Furthermore, the bond length of Mo-B bond in the D8 m -Mo 5 SiB 2 is longer than the other two structures, which may be the reason why the ductility of the former is better than the latter. K E Y W O R D S first-principles method, mechanical properties, melting point, Mo 5 SiB 2 , structural prediction 1 | INTRODUCTION The search for excellent high-temperature materials is also a big challenge for the development of modern industrial [1-8]. Mo 5 SiB 2 ternary silicide is regarded as an ideal candidate material for aero-engine turbine blades and industrial gas turbine hot-end components because of its high melting point, good mechanical properties and good oxidation resistance [9-15]. In 1957, Nowotny et al. have been studied the phase diagram of Mo-Si-B ternary silicide by using the phase diagram method. The Mo-Si-B ternary phase is discovered for the first time [16]. In 1958, Aronsson discovered by powder photography that this Mo-Si-B ternary phase has a body-centered tetragonal structure (D8 l ) similar to Cr 5 B 3 , and gave its lattice parameters a = b = 6.02 Å, c = 11.07 Å [17]. As we all know, the good oxidation resistance, excellent mechanical properties and good ductility are necessary conditions for high temperature materials [18][19][20][21][22][23][24]. In terms of mechanical properties, Mo 5 SiB 2 ternary silicide has high single crystal elastic constants at room temperature (RT): C 11 = 480 GPa, C 33 = 415 GPa, C 12 = 166 GPa, C 13 = 197GPa, C 44 = 174GPa and C 66 = 143 GPa [25]. Furthermore, the bulk elastic modulus, shear modulus and Young's modulus of Mo 5 SiB 2 are 271GPa, 152GPa and 385GPa, which indicate that Mo 5 SiB 2 is an extremely high temperature material [26]. In addition, it is found that there are numerous dislocations in the Mo 5 SiB 2 crystal, which will benefit its ductility [27,28]. In terms of oxidation resistance, Akinc et al. have been ...

Section: Model and Calculated Methodsmentioning

confidence: 99%

Prediction the structure, mechanical properties and melting point ofD8_m‐Mo₅SiB₂andCmcm‐Mo₅SiB₂

Pan

2021

“…During the structural optimization, all atomic positions, lattice parameters, and internal coordinates in a system were fully relaxed. [59][60][61][62]…”

Section: Theoretical Methodsmentioning

confidence: 99%

First‐principles investigation of structural, electronic, and optical properties of transition metal‐dopedC40 CrSi₂

Pan

2020

Although CrSi 2 silicide is an attractive advanced functional material, the improvement of electronic and optical properties is still a challenge for its applications. Here, we apply the first-principles calculations to investigate the influence of transition metals (TMs) on the electronic and optical properties of C40 CrSi 2 silicide. Five possible TMs, Ti, V, Pd, Ag, and Pt, are considered in detail. The calculated results show that the additive metals Ti, V, Pd, and Pt are thermodynamically stable in C40 CrSi 2 because the calculated impurity formation energy of TM-doped C40 CrSi 2 is lower than zero. In particular, the V dopant is more thermodynamically stable than that of the other TMs. The calculated electronic structure shows that the band gap of C40 CrSi 2 is 0.391 eV, which is in good agreement with the other results. In particular, the additive TMs improve the electronic properties of C40 CrSi 2 due to the role of the d-state of TMs. Naturally, the additive TMs result in band migration (Cr-3d state and Si-3p state) from the valence band to the conduction band. Interestingly, the additive TMs lead to a red shift for optical adsorption of C40 CrSi 2 silicide. K E Y W O R D S alloying, C40 CrSi 2 , electronic properties, first-principles calculations, optical properties 1 | INTRODUCTION Transition metal (TM) silicides are attractive advanced functional materials due to their excellent electronic properties, good thermoelectric properties, high temperature strength, excellent oxidation resistance, etc. [1-13] For example, the previous works have shown that tungsten silicides are regarded as fascinating renewed thermoelectric or energy materials. [14-17] Molybdenum (Mo) or niobium (Nb) silicides are attractive hightemperature structural materials due to their high melting point, greater hardness, good thermodynamic stability, etc. [18-24] Recently, chromium silicide (CrSi 2) has received great attention as thermoelectric and storage energy materials. [25-27] It is well known that the overall performances of TM silicides or compounds are markedly influenced by their structural feature. [28-32] Regarding thermoelectric materials, Zhang and Wang have found that the higher anisotropy of electrical conductivity results in the thermoelectric properties of the hexagonal CrSi 2 , [33] while the narrow band gap of C40 CrSi 2 is 0.3 to 0.35 eV. Oader and Venkat prepared a CrSi 2 thermoelectric thin film using the magnetron sputtering method. [34] Furthermore, Mikami and Kinemuchi studied the microstructure and thermoelectric performance of WSi 2 on CrSi 2 silicide. [35] They found that the additive WSi 2 reduces the grain size of CrSi 2 and improves the ZT value of CrSi 2-based material. Regarding promising storage energy material, Menda and Ozdemir studied the capacitance voltage temperature (C-V-T) and current voltage temperature (I-V-T) of p-CrSi 2 /Si using the physical vapor deposition (CAPVD) method, [36] while the measured building voltage was about 0.7 V. Bhamu and Ahuja theoretically studied the electronic st...

“…In order to study the mechanical properties of HECs (HfTaZrTi)C and (HfTaZrNb)C, three independent elastic constants, C 11 , C 12 and C 44 , in the cubic lattices are calculated using the energy‐strain method. After applying the strain, the total energy change (Δ E ) of the system can be expressed as [ 32 ] :

normalΔ E = \frac{V}{2} \sum_{i, j = 1}^{6} C_{ij} e_{i} e_{j}

, where V and C ij are the volume and elastic constants of HECs, respectively; e i and e j are the components of strain matrix. The details are described in Jiang et al [ 32 ] and Zhang et al [ 33 ] Once the elastic constants have been achieved, the polycrystalline bulk modulus B , Young's modulus E , and shear modulus G are calculated from elastic constants using the Voigt‐Reuss‐Hill (VRH) method.…”

Section: Theoretical Methodsmentioning

confidence: 99%

“…In order to study the mechanical properties of HECs (HfTaZrTi)C and (HfTaZrNb)C, three independent elastic constants, C 11 , C 12 and C 44 , in the cubic lattices are calculated using the energy-strain method. After applying the strain, the total energy change (ΔE) of the system can be expressed as [32] :…”

Section: Theoretical Methodsmentioning

confidence: 99%

“…C ij e i e j , where V and C ij are the volume and elastic constants of HECs, respectively; e i and e j are the components of strain matrix. The details are described in Jiang et al [32] and Zhang et al [33] Once the elastic constants have been achieved, the polycrystalline bulk modulus B, Young's modulus E, and shear modulus G are calculated from elastic constants using the Voigt-Reuss-Hill (VRH) method. [34,35] 3 | RESULTS AND DISCUSSION…”

Section: Theoretical Methodsmentioning

confidence: 99%

See 1 more Smart Citation

Mechanical behavior of high entropy carbide (HfTaZrTi)C and (HfTaZrNb)C under high pressure: Ab initio study

Jiang

Shao

Fan

et al. 2020

The evolution of structural, elastic, and electronic properties of high entropy carbide (HfTaZrTi)C and (HfTaZrNb)C under high pressure have been studied within the framework of density functional theory (DFT) in conjunction with special quasirandom structures. With increasing pressure, lattice constants of high entropy carbides (HfTaZrTi)C and (HfTaZrNb)C gradually decrease, so volumes shrink, and densities gradually increase. Under high pressure up to 200 GPa, elastic stiffness coefficients for both carbides are almost linearly hardened and meet the elastic stability criteria. With increasing pressure, elastic moduli and Debye temperature of both high entropy carbides (HfTaZrTi)C and (HfTaZrNb)C increase, while theoretical Vickers hardness decreases, although Vickers hardness of (HfTaZrNb)C is always higher than (HfTaZrTi)C in the whole pressure. The ductility of (HfTaZrTi)C and (HfTaZrNb)C is improved under pressure, and brittle‐ductile transition occurs at about 50 and 60 GPa, respectively. The electronic structure demonstrates that, with increasing pressure, covalent bonds between transition metal atoms and carbon atoms are strengthened, accompanying delocalization. This effect is responsible for high values of bulk modulus and shear modulus under pressure and enhanced ductility. The ionic bonds of both high entropy carbides weaken with increasing pressure, and (HfTaZrTi)C is affected more strongly by the pressure.