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Point defect formation in M2AlC (M?=?Zr,Cr) MAX phases and their tendency to disorder and amorphize.

ABSTRACT: First principles calculations are performed on Zr2AlC and Cr2AlC MAX phases to compare their ability to accommodate point defects under irradiation. Interatomic bonding is stronger in Cr2AlC than Zr2AlC but contrary to expectation Zr2AlC exhibits higher vacancy and antisite pair formation energies. However, interstitials and Frenkel defects are generally more difficult to form in Cr2AlC. The results are attributed to the mixed covalent/ionic/metallic nature of the bonding. Detailed comparison of all the energies suggests that the preferred defects in Zr2AlC and Cr2AlC are the VAl+Ali Frenkel and CrAl+AlCr antisite respectively. Thus the potential response of the two phases to irradiation is different and taking account of other competing defects it is suggested that Zr2AlC is less susceptible to amorphization.

SUBMITTER: Shah SH

PROVIDER: S-EPMC5574895 | biostudies-literature | 2017 Aug

REPOSITORIES: biostudies-literature

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Point defect formation in M2AlC (M = Zr,Cr) MAX phases and their tendency to disorder and amorphize.

Shah S H SH Bristowe P D PD

Scientific reports 20170829 1

First principles calculations are performed on Zr2AlC and Cr2AlC MAX phases to compare their ability to accommodate point defects under irradiation. Interatomic bonding is stronger in Cr2AlC than Zr2AlC but contrary to expectation Zr2AlC exhibits higher vacancy and antisite pair formation energies. However, interstitials and Frenkel defects are generally more difficult to form in Cr2AlC. The results are attributed to the mixed cov ...[more]

PMID: 28852165

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Project description:A DFT study of the synthesized MAX phase Zr2SeC has been carried out for the first time to explore its physical properties for possible applications in many sectors. The studied properties are compared with prior known MAX phase Zr2SC. The structural parameters (lattice constants, volume, and atomic positions) are observed to be consistent with earlier results. The band structure and density of states (DOS) are used to explore the metallic conductivity, anisotropic electrical conductivity, and the dominant role of Zr-d states to the electrical conductivity at the Fermi level. Analysis of the peaks in the DOS and charge density mapping (CDM) of Zr2SeC and Zr2SC revealed the possible variation of the mechanical properties and hardness among them. The mechanical stability has been checked using elastic constants. The values of the elastic constants, elastic moduli and hardness parameters of Zr2SeC are found to be lowered than those of Zr2SC. The anisotropic behavior of the mechanical properties has been studied and analyzed. Technologically important thermodynamic properties such as the thermal expansion coefficient (TEC), Debye temperature (Θ D), entropy (S), heat capacity at constant volume (C v), Grüneisen parameter (γ) along with volume (V) and Gibbs free energy (G) are investigated as a function of both temperature (from 0 to 1600 K) and pressure (from 0 to 50 GPa). Besides, the Θ D, minimum thermal conductivity (K min), melting point (T m), and γ have also been calculated at room temperature and found to be lowered for Zr2SeC compared to Zr2SC owing to their close relationship with the mechanical parameters. The value of the Θ D, K min, T m, and TEC suggest Zr2SeC as a thermal barrier coating material. The optical properties such as dielectric constant (real and imaginary part), refractive index, extinction coefficient, absorption coefficient, photoconductivity, reflectivity, and loss function of Zr2SeC are computed and analyzed to reveal its possible applications.

Dataset Information

Point defect formation in M2AlC (M?=?Zr,Cr) MAX phases and their tendency to disorder and amorphize.

Publications

Point defect formation in M<sub>2</sub>AlC (M = Zr,Cr) MAX phases and their tendency to disorder and amorphize.

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