First-principles studies of Ti n+1 SiN n (n = 1, 2, 3) MAX phase

Abstract

In this study, the structural, electronic, mechanical, lattice dynamical and thermodynamic characteristics of Tin+1SiNn (n=1, 2 and 3) MAX phase compounds were investigated using the first principle calculations. These ternary nitride compounds were found to be stable and synthesisable, and the results on the stability nature of them were also evaluated for the possible ? and phases. ß - ?-Ti4SiN3 was found to be the most stable one among these new class of layered MAX phases for which limited works are available in the literature. The band structures, that are essential for the electronic properties, were determined along with the partial density of states (PDOS) indicating the metallic behaviour of these compounds. The polycrystalline elastic moduli were calculated based on the single-crystal elastic constants and the mechanical stabilities were verified. Some basic physical parameters, such as bulk modulus, shear modulus, Young’s modulus, Poisson’s ratio, Debye temssssperature, and sound velocities, were also predicted. Furthermore, the anisotropic elastic properties were visualised in three dimensions (3D) for Young’s modulus, linear compressibility, shear modulus and Poisson’s ratio as well as with the calculation of the anisotropic factors.?-Ti4SiN3) phase showed the most isotropic characteristics with minimum deviations. These theoretical values were also used to identify the stiffness and ionic characteristics. The phonon dispersion curves and corresponding PDOS indicated that Tin+1SiNn compounds were dynamically stable. Moreover, thermodynamic properties obtained from phonon dispersion curves were investigated in detail. © 2020 Informa UK Limited, trading as Taylor & Francis Group.