Crystal structure, phase stability, and magnetism in Ni3V

High-throughput computational discovery of ternary-layered MAX phases and prediction of their exfoliation for formation of 2D MXenes

The rush to synthesize novel two-dimensional (2D) materials has excited the research community studying ternary-layered carbide and nitride compounds, known as MAX phases, for the past two decades in the quest to develop new 2D material precursors. The objective of this study is to expand the family of MAX phases and to investigate their feasible exfoliation to generate 2D systems. To expand the family of MAX phases, we conduct systematic and fundamental research using elemental information and data from high-throughput density functional theory calculations performed on 1122 MAX candidates. Our results suggest that 466 MAX compounds can be synthesized, among which 136 MAX phases can be exfoliated to produce 26 MXenes. We investigate the transition metal or A elements that could be suitable for the formation of novel MAX phase carbides or nitrides and determine promising MAX phases that can be exfoliated to form 2D systems.

Role of W-site substitution on mechanical and electronic properties of cubic tungsten carbide

In order to understand the role of W-site substitution on properties of cubic tungsten carbide ([Formula: see text]-WC), we have investigated the structural, mechanical, and electronic properties of WXC₂ (X  =  Si, Sc, Ti, V, Cr, Ge, Y, Zr, Nb, Mo, Ru, Rh, Pd, Ag, Cd, Sn, Hf, Ta, Re, Os, Ir, Pt, Th, U) using first principles calculations based on density functional theory, within generalized gradient approximation. The structural optimization has carried out for all these compounds using force as well as stress minimization. The optimized structural parameters for experimentally known compounds are in good agreement with the available x-ray diffraction measurements and structural parameters for nineteen WXC₂ compounds are newly predicted. The W-site substitution of the above-listed elements into [Formula: see text]-WC reduces the symmetry of the primitive lattice to tetragonal structure. The heat of formation ([Formula: see text]) and the mechanical stability studies are carried out to investigate the stability of these systems. The single-crystal elastic constants c _ij , elastic moduli of the polycrystalline aggregates, anisotropy in elastic constants and related properties of the WXC₂ materials have calculated and discussed in detail. The hardness of the above materials is predicted using two different criteria, based on the softest elastic mode as well as the Pugh's modulus ratio. There is a correlation in the hardness predicted from these two approaches except in the case of [Formula: see text]-WC. The chemical bonding interaction between the constituents is analysed using the density of states, crystal orbital Hamiltonian population, and charge density for selected systems. All these compounds are predicted to be metal and our calculations suggest that W-site substitutions do not improve the hardness of [Formula: see text]-WC. However, from the heat of formation studies, we have identified five new stable compounds such as CrWC₂, NbWC₂, ScWC₂, YWC₂, and UWC₂ with reasonably good hardness and those need experimental verifications.

Trends in electronic structures and structural properties of MAX phases: a first-principles study on M(2)AlC (M = Sc, Ti, Cr, Zr, Nb, Mo, Hf, or Ta), M(2)AlN, and hypothetical M(2)AlB phases

MAX phases are a large family of layered ceramics with many potential structural applications. A set of first-principles calculations was performed for M(2)AlC and M(2)AlN (M = Sc, Ti, Cr, Zr, Nb, Mo, Hf, or Ta) MAX phases as well as for hypothetical M(2)AlB to investigate trends in their electronic structures, formation energies, and various mechanical properties. Analysis of the calculated data is used to extend the idea that the elastic properties of MAX phases can be controlled according to the valence electron concentration. The valence electron concentrationcan be tuned through the various combinations of transition metal and nonmetal elements.

First-principles calculation of structural, mechanical, magnetic and thermodynamic properties for γ-M23C6 (M = Fe, Cr) compounds

We report the results of our first-principles calculations of structural stability, mechanical, magnetic, and thermodynamic properties for γ-M(23)C(6) (M = Fe, Cr) compounds with each of the four metal Wyckoff sites being occupied in turn by Fe. The thermodynamic properties and the temperature dependence of the mechanical behavior of γ-M(23)C(6) compounds are investigated based on the quasi-harmonic Debye model. The results show that the thermodynamic properties of γ-M(23)C(6) (M = Fe, Cr) compounds are more dependent on the position of Fe atoms than the amount of Fe.