Unravelling the stability, electronic and physical properties in bulk and (001)-surfacesof newlysynthesized Ti2ZnX (X=C, N)MAX phases

TL;DR

This study uses density functional theory to analyze the stability, electronic, and surface properties of newly synthesized Ti2ZnX (X=C, N) MAX phases, revealing their potential for functional applications.

Contribution

It provides a comprehensive comparison of the stability and properties of Ti2ZnX phases with conventional Ti2AlX, including surface and bulk characteristics.

Findings

Ti2ZnN is nearly isotropic elastically, Ti2ZnC is anisotropic.

Both phases exhibit metal-like electronic structures.

Zn-terminated surfaces are most stable and energetically favorable.

Abstract

MAX phase family has been extended by the addition of late transition metals at the A-site with the expectation of diverse functional properties, such as magnetism and catalysis. Here, we present our systematic density functional investigation on the phase stability and physical properties of newly synthesized Ti2ZnX (X = C, N) phasesin comparison with conventional Ti2AlX (X = C, N).Due to smaller size of N as compared to C, the unit cell dimensionis reduced when C atoms are replaced by N atoms atthe X-site. The thermodynamic, mechanical and dynamical stabilities are validatedby estimating the formation energies, elastic constants and phonon dispersions, respectively. The elastic properties of Ti2ZnN are nearly isotropic while those of Ti2ZnC are completely anisotropic. To understand the thin-film characteristicsin Ti2ZnX, the surface properties with (001)-terminated slabs are investigated. Both Ti2ZnX bulk and (001)-surfaces exhibit metal-like electronic structure. There is a strong covalent bonding between Ti-X and Ti-Zn atoms.Additional states are generated at the Fermi level (EF) due to the unusual d-pstates hybridization between Ti and Zn atoms.The anisotropy in chemical bonding is confirmed by the cleavage energy difference between Ti-X and Ti-Zn atoms. Here,Ti(X)-001 and Zn-001 terminations are stable surfaces, however, in terms of chemical potentials, Zn-001 termination is the most favorable.