First-principles thermodynamics from phonon and Debye model: Application to Ni and Ni3Al

We have performed accurate ab initio total energy calculations using the full-potential linearized augmented plane-wave (FP-LAPW) method with the generalized gradient approximation (GGA) for the exchange–correlation potential to systematically investigate elastic properties of 18 stable, metastable and hypothetical hexagonal (AlB2-like) metal diborides MB2, where M = Na, Be, Mg, Ca, Al, Sc, Y, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Ag and Au. For monocrystalline MB2, the optimized lattice parameters, independent elastic constants (Cij), bulk moduli (B) and shear moduli (G) are obtained and analyzed in comparison with the available theoretical and experimental data. For the first time, numerical estimates of a set of elastic parameters of the polycrystalline MB2 ceramics (in the framework of the Voigt–Reuss–Hill approximation), namely bulk and shear moduli, compressibility (β), Young's modulus (Y), Poisson's ratio (ν) and Lame coefficients (μ, λ), are performed.

http://iopscience.iop.org/article/10.1088/0953-8984/20/41/415218/pdf

Elastic properties of mono- and polycrystalline hexagonal AlB2-like diborides of s, p and d metals from first-principles calculations

Structural, magnetic, electronic and mechanical properties of full-Heusler alloys Co 2 YAl (Y = Fe, Ti): First principles calculations with different exchange-correlation potentials

Mechanical and electronic properties of diborides of transition 3d–5d metals from first principles: Toward search of novel ultra-incompressible and superhard materials

Traditional strengthening ways, such as strain, precipitation, and solid-solution, come into effect by pinning the motion of dislocation Here, through first-principles calculations we report on an extra-electron induced covalent strengthening mechanism, which alters chemical bonding upon the introduction of extra-valence electrons in the matrix of parent materials It is responsible for the brittle and high-strength properties of Al12W-type compounds featured by the typical fivefold icosahedral cages, which are common for quasicrystals and bulk metallic glasses (BMGs) In combination with this mechanism, we generalize ductile-to-brittle criterion in a universal hyperbolic form by integrating the classical Pettifor's Cauchy pressure with Pugh's modulus ratio for a wide variety of materials with cubic lattices This study provides compelling evidence to correlate Pugh's modulus ratio with hardness of materials and may have implication for understanding the intrinsic brittleness of quasicrystals and BMGs

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Extra-electron induced covalent strengthening and generalization of intrinsic ductile-to-brittle criterion

Ab initio calculations of elastic constants and thermodynamic properties of NiAl under high pressures

The transition phase of PtN from zincblende (ZB) structure to rocksalt (RS) structure is investigated by ab initio plane-wave pseudopotential density functional theory method, and the thermodynamic properties of the ZB and RS structures under high pressure and temperature are obtained through the quasi-harmonic Debye model. The transition phase from the ZB structure to the RS structure occurs at the pressure of 18.2 GPa, which agrees well with other calculated values. Moreover, the dependences of the relative volume V / V 0 on the pressure P , the Debye temperature Θ and heat capacity C V on the pressure P , together with the heat capacity C V on the temperature T are also successfully obtained.

Ab initio study of phase transition and thermodynamic properties of PtN

Transition phase and thermodynamic properties of PtC from first-principles calculations

The equations of state (EOS) and other thermodynamic properties of TiB 2 are investigated using ab initio plane-wave pseudopotential density functional theory method. The obtained results are in good agreement with the experimental measured data and other theoretical calculated ones. Through the quasi-harmonic Debye model, in which the phononic effects are considered, the dependences of relative volume V / V 0 on pressure P , cell volume V on temperature T , and Debye temperature Θ and specific heat C V on pressure P are successfully obtained.

First-principles calculations of thermodynamic properties of TiB2 at high pressure

First-principles calculations of the crystal structures (wurtzite (WZ) and rocksalt (RS)) and phase transition of AlN have been carried out with the plane-wave pseudopotential density functional theory (DFT) method. The calculated values (for crystal structures) are in agreement with available experimental value and other calculated data. Through the quasi-harmonic Debye model combined with the first-principles theory, the thermodynamic properties of different phases under high temperature and high pressure are investigated. The phase transition from WZ structure to RS structure occurs at the pressure of 15.0 GPa, which agrees well with experimental value. The evaluated equilibrium volume using this model agrees with the values obtained from ab intio and from experiment. The temperature and pressure dependence of quantities such as the equation of state (EOS), the isothermal bulk modulus, the heat capacity, and the thermal expansion are successfully obtained.

Hongzhi Fu

Papers

Ab initio calculations of elastic constants and thermodynamic properties of NiAl under high pressures

Ab initio study of phase transition and thermodynamic properties of PtN

Transition phase and thermodynamic properties of PtC from first-principles calculations

First-principles calculations of thermodynamic properties of TiB2 at high pressure

The phase transition and the elastic and thermodynamic properties of AlN: First principles