III-Nitride Polymorphs: XN (X=Al, Ga, In) in the Pnma Phase

Investigation of half metallic properties of Tl2Mo(Cl/Br)6 double perovskites for spintronic devices

The manipulation of electronic device characteristics through electron spin represents a burgeoning frontier in technological advancement. Investigation of magnetic and transport attributes of the Tl2Mo(Cl/Br)6 double perovskite was performed using Wien2k and BoltzTraP code. When the energy states between ferromagnetic and antiferromagnetic conditions are compared, it is evident that the ferromagnetic state exhibits lower energy levels. Overcoming stability challenges within the ferromagnetic state is achieved through the manipulation of negative ΔHf within the cubic state. The analysis of the half metallicity character involves an analysis of band structure (BS) and DOS, elucidating its mechanism through PDOS using double exchange model p-d hybridization. The verification of 100% spin polarization is confirmed through factors such as spin polarization and the integer value of the total magnetic moment. Furthermore, the thermoelectric response, as indicated by the ratios of thermal-electrical conductivity and ZT, underscores the promising applications of these compounds in thermoelectric device applications.

Physical properties of Si2Ge and SiGe2 in hexagonal symmetry: First-principles calculations

We predict two novel group 14 element alloys Si2Ge and SiGe2 in P6222 phase in this work through first-principles calculations. The structures, stability, elastic anisotropy, electronic and thermodynamic properties of these two proposed alloys are investigated systematically. The proposed P6222-Si2Ge and P6222-SiGe2 have a hexagonal symmetry structure, and the phonon dispersion spectra and elastic constants indicate that these two alloys are dynamically and mechanically stable at ambient pressure. The elastic anisotropy properties of P6222-Si2Ge and P6222-SiGe2 are examined elaborately by illustrating the surface constructions of Young’s modulus, the contour surfaces of shear modulus, and the directional dependence of Poisson’s ratio; the differences with their corresponding group 14 element allotropes P6222-Si3 and P6222-Ge3 are also discussed and compared. Moreover, the Debye temperature and sound velocities are analyzed to study the thermodynamic properties of the proposed P6222-Si2Ge and P6222-SiGe2.

Novel III-V Nitride Polymorphs in the P42/mnm and Pbca Phases

In this work, the elastic anisotropy, mechanical stability, and electronic properties for P4₂/mnm XN (XN = BN, AlN, GaN, and InN) and Pbca XN are researched based on density functional theory. Here, the XN in the P4₂/mnm and Pbca phases have a mechanic stability and dynamic stability. Compared with the Pnma phase and Pm-3n phase, the P4₂/mnm and Pbca phases have greater values of bulk modulus and shear modulus. The ratio of the bulk modulus (B), shear modulus (G), and Poisson’s ratio (v) of XN in the P4₂/mnm and Pbca phases are smaller than those for Pnma XN and Pm-3n XN, and larger than those for c-XN, indicating that Pnma XN and Pm-3n XN are more ductile than P4₂/mnm XN and Pbca XN, and that c-XN is more brittle than P4₂/mnm XN and Pbca XN. In addition, in the Pbca phases, XN can be considered a semiconductor material, while in the P4₂/mnm phase, GaN and InN have direct band-gap, and BN and AlN are indirect wide band gap materials. The novel III-V nitride polymorphs in the P4₂/mnm and Pbca phases may have great potential for application in visible light detectors, ultraviolet detectors, infrared detectors, and light-emitting diodes.

First-Principles Study on III-Nitride Polymorphs: AlN/GaN/InN in the Pmn21 Phase

The structural, mechanical, and electronic properties, as well as stability, elastic anisotropy and effective mass of AlN/GaN/InN in the Pmn2₁ phase were determined using density functional theory (DFT). The phonon dispersion spectra and elastic constants certify the dynamic and mechanical stability at ambient pressure, and the relative enthalpies were lower than those of most proposed III-nitride polymorphs. The mechanical properties reveal that Pmn2₁-AlN and Pmn2₁-GaN possess a high Vickers hardness of 16.3 GPa and 12.8 GPa. Pmn2₁-AlN, Pmn2₁-GaN and Pmn2₁-InN are all direct semiconductor materials within the HSE06 hybrid functional, and their calculated energy band gaps are 5.17 eV, 2.77 eV and 0.47 eV, respectively. The calculated direct energy band gaps and mechanical properties of AlN/GaN/InN in the Pmn2₁ phase reveal that these three polymorphs may possess great potential for industrial applications in the future.

Six novel carbon and silicon allotropes with their potential application in photovoltaic field

By stacking up five novel cagelike structures, three novel three-dimensional (3D)sp3bonding networks, namedhP24,hP30 andhP36, were predicted in this work for the first time. These three newly discovered structures have trigonal unit cell with the space groups ofP-3m1,P-3m1 andP3m1, respectively. Using first-principle calculations, the physical properties, including structural, mechanical, electronic and optical properties of C and Si inhP24,hP30 andhP36 phases were systematically studied. All these newly discovered carbon and silicon allotropes were proven to be thermodynamically and mechanically stable. The wide indirect bandgap value in range of 3.89-4.03 eV suggests that C inhP24,hP30 andhP36 phases have the potential to be applied in high frequency and high power electronic devices. The direct bandgap value in range of 0.60-1.16 eV, the smaller electron and hole effective mass than diamond-Si, and the significantly better photon absorption characteristics than diamond-Si suggest thathP24-Si,hP30-Si andhP36-Si are likely to have better performance in photovoltaic applications than diamond-Si.hP24-Si also has the potential to be applied in infrared detectors.

Optical, Electronic Properties and Anisotropy in Mechanical Properties of "X" Type Carbon Allotropes

Based on first-principle calculations, the mechanical anisotropy and the electronic and optical properties of seven kinds of carbon materials are investigated in this work. These seven materials have similar structures: they all have X-type structures, with carbon atoms or carbon clusters at the center and stacking towards the space. A calculation of anisotropy shows that the order of elastic anisotropy in terms of the shear modulus, Young's modulus and Poisson's ratio of these seven carbon materials with similar structure is diamond < supercubane < T carbon < Y carbon < TY carbon < cubane-diyne < cubane-yne. As these seven carbon materials exhibit cubic symmetry, Young's modulus has the same anisotropy in some major planes, so the order of elastic anisotropy in the Young's modulus of these seven main planes is (111) plane < (001) plane = (010) plane = (100) plane < (011) plane = (110) plane = (101) plane. It is also due to the fact that their crystal structure has cubic symmetry that the elastic anisotropy in the shear modulus and the Poisson's ratio of these seven carbon materials on the seven major planes are the same. Among the three propagation directions of [100], [110], and [111], the [110] propagation direction's anisotropic ratio of the sound velocity of TY carbon is the largest, while the anisotropic ratio of the sound velocity of cubane-diyne on the [100] propagation direction is the smallest. In addition, not surprisingly, the diamond has the largest Debye temperature, while the TY carbon has the smallest Debye temperature. Finally, TY carbon, T carbon and cubane-diyne are also potential semiconductor materials for photoelectric applications owing to their higher or similar absorption coefficients to GaAs in the visible region.

Physical Properties of XN (X = B, Al, Ga, In) in the Pm-3n phase: First-Principles Calculations

Three direct semiconductor materials and one indirect semiconductor material, Pm-3n XN (X = B, Al, Ga, In), are investigated in our work, employing density functional theory (DFT), where the structural properties, stability, elastic properties, elastic anisotropy properties and electronic properties are included. The shear modulus G and bulk modulus B of Pm-3n BN are 290 GPa and 244 GPa, respectively, which are slightly less than the values of B and G for c-BN and Pnma BN, while they are larger than those of C64 in the I41/amd phase. The shear modulus of Pm-3n BN is the greatest, and the shear modulus of C64 in the I41/amd phase is the smallest. The Debye temperatures of BN, AlN, GaN and InN are 1571, 793, 515 and 242 K, respectively, using the elastic modulus formula. AlN has the largest anisotropy in the Young's modulus, shear modulus, and Poisson's ratio; BN has the smallest elastic anisotropy in G; and InN has the smallest elastic anisotropy in the Poisson's ratio. Pm-3n BN, AlN, GaN and InN have the smallest elastic anisotropy along the (111) direction, and the elastic anisotropy of the E in the (100) (010) (001) planes and in the (011) (101) (110) planes is the same. The shear modulus and Poisson's ratio of BN, AlN, GaN and InN in the Pm-3n phase in the (001), (010), (100), (111), (101), (110), and (011) planes are the same. In addition, AlN, GaN and InN all have direct band-gaps and can be used as a semiconductor within the HSE06 hybrid functional.

First-Principles Study on Structural, Mechanical, Anisotropic, Electronic and Thermal Properties of III-Phosphides: XP (X = Al, Ga, or In) in the P6422 Phase

The structural, mechanical, electronic, and thermal properties, as well as the stability and elastic anisotropy, of XP (X = Al, Ga, or In) in the P6₄22 phase were studied via density functional theory (DFT) in this work. P6₄22-XP (X = Al, Ga, or In) are dynamically and thermodynamically stable via phonon spectra and enthalpy. At 0 GPa, P6₄22-XP (X = Al, Ga, or In) are more rigid than F4¯3m-XP (X = Al, Ga, or In), of which P6₄22-XP (X = Al or Ga) are brittle and P6₄22-InP is ductile. In the same plane (except for (001)-plane), P6₄22-AlP and P6₄22-InP exhibit the smallest and the largest anisotropy, respectively, and P6₄22-XP (X = Al, Ga, or In) is isotropic in the (001)-plane. In addition, Al, Ga, In, and P bonds bring different electrical properties: P6₄22-InP exhibits a direct band gap (0.42 eV) with potential application for an infrared detector, whereas P6₄22-XP (X = Al or Ga) exhibit indirect band gap (1.55 eV and 0.86 eV). At high temperature (approaching the melting point), the theoretical minimum thermal conductivities of P6₄22-XP (X = Al, Ga, or In) are AlP (1.338 W∙m⁻¹∙K⁻¹) > GaP (1.058 W∙m⁻¹∙K⁻¹) > InP (0.669 W∙m⁻¹∙K⁻¹), and are larger than those of F4¯3m-XP (X = Al, Ga, or In). Thus, P6₄22-XP (X = Al, Ga, or In) have high potential application at high temperature.

Physical properties of Si-Ge alloys in C2/m phase: a comprehensive investigation

A new phase of C2/m Ge₁₆ is first proposed in this paper. The structures and mechanical, anisotropic, electronic, transport and optical properties of Si-Ge alloys in the C2/m phase are studied using first principles calculations. All Ge₁₆ and Si_16-x Ge _x alloys in the C2/m phase are proven to have mechanical and dynamic stability. By analyzing the three-dimensional (3D) perspective of the effective mass and Young's modulus, obvious anisotropies of transport and mechanical properties are found. Higher-resolution full band structures are obtained to determine the positions of the valence band maximum (VBM) and conduction band minimum (CBM). All materials have a higher photoelectron absorption than that of diamond Si. A high electronic mobility (16 527 cm² V^-1 s^-1) and hole mobility (3033 cm² V^-1 s^-1) are found in C2/m Si₈Ge₈ and Si₄Ge₁₂, respectively. Based on the large mobility and photoelectron absorption, the Si-Ge alloys in the C2/m phase are promising materials for electronics and optoelectronics applications.