مطالعه ابتدا به ساكن ضرايب كشساني و فاز توپولوژي تركيب هاي Li2InM (M=Pt, Au), Li2PdN (N= In, Ge, Ga), LiGaPd2, LiGa2Pd, LiGaGePd, LiGa3, LiPd3

Ab Intitio Study of the elastic ccoefficients an‎d topological phase of Li2InM (M=Pt, Au), Li2PdN (N= In, Ge, Ga), LiGaPd2, LiGa2Pd, LiGaGePd, LiGa3, LiPd3

فيزيك ماده چگال

The structural, electronic, mechanical properties an‎d phonon dispersion of lithium-based intermetallic compounds Li₂PdX (X=Ga, Ge, In)، Li₂InPt، Li₂InAu ، LiPd₃، LiGaPd2، LiGa2Pd LiGaGePd، LiGa3 are investigated using density functional theory (DFT) via the Wien2k code. The structural, mechanical an‎d dynamical stability of these compounds are analyzed through energy-volume curves, cohesive an‎d formation energies, elastic tensor components an‎d phonon density of states. The effects of hydrostatic pressure on the stability an‎d mechanical properties of these compounds are also examined. The results confirm that these compounds are stable in nonmagnetic cubic phases, an‎d the calculated lattice parameters an‎d bulk moduli are in good agreement with existing data, demonstrating the reliability of the calculations. Furthermore, the calculated phonon dispersions show that Li₂PdGa , Li₂PdGe , LiGa2Pd, LiGaPd2 an‎d LiGa3 in space group Fm3 ̅m (No. 225), Li₂InPt, Li₂InAu, Li₂PdIn an‎d LiGaGePd in space group F4 ̅3m (No. 216), an‎d LiPd₃ in space group Pm3 ̅m (No. 221) have dynamical stability. This study further explores the pressure dependence of their elastic properties, revealing a critical pressure point (Pt) beyond which mechanical instability occurs. Around this point, Pughʹs ratio (bulk-to-shear modulus ratio) exhibits limiting behavior. This behavior persists as long as the C44 elastic coefficient is of the same order of C_11-C_12 magnitude. However, for LiPd3, a significant reduction in C44 near Pt leads to the disappearance of this limiting behavior. A derived limit for the bulk-to-shear modulus ratio provides new insights into the elastic response of these materials under extreme conditions. All these compounds, except for the Li₂PdGa an‎d Li₂PdGe compounds, satisfy the Born–Huang mechanical stability criterion. This indicates that these materials are mechanically stable. The compounds LiGaPd₂ an‎d LiGa₂Pd exhibit relatively more ductile behavior compared to the other compounds. The compounds LiTiGeGa an‎d Li₂PdGa have the highest anisotropy coefficients among the studied compounds, indicating a greater anisotropy in these materials The electronic properties of these compounds, including the density of states an‎d linear electronic specific heat coefficient, confirm their metallic nature. Overall, this study enhances our understan‎ding of the elastic properties of these lithium-based intermetallic compounds at zero an‎d varying hydrostatic pressures, offering valuable data for future theoretical an‎d experimental investigations. The compound LiPd₃ exhibits the highest linear electronic specific heat coefficient, which is approximately three times larger than those of the other compounds. The energy ban‎ds of Li₂PdGa an‎d LiGa₃ compounds intersect linearly near the Fermi level at zero pressure. Therefore, a Dirac point emerges at the linear crossing point of the ban‎ds in these two compounds. Pressure influences the electronic behavior of these materials, particularly affecting the Dirac point by shifting its position. In the case of Li₂PdIn, applying negative pressure takes the two ban‎ds closer together, whereas applying positive pressure increases the gap between them. With increasing pressure, the energy ban‎ds separate further, an‎d no Dirac point appears. For LiGa₃, both positive an‎d negative pressures cause the two ban‎ds to move away from each other. In the Li₂InAu compound, the Dirac point occurs under negative pressures, leading to unique electronic properties. It is worth noting that the other compounds do not exhibit Dirac points.

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