Enhanced thermo-mechanical properties of 212 MAX phase borides Zr2AB2 (A = In, Tl): an ab-initio understanding

Abstract

The discovery of MAX phase borides has added a new dimension for research in the materials science community. In this paper, a first-principles study of the newly known MAX phase borides Zr2AB2 (A = In, Tl) has been carried out. The estimated lattice constants and volumes of the unit cell are found to be consistent with previous study. The dynamical and mechanical stability of the titled compounds have been checked. Fundamental insights into the stiffness constants, elastic moduli, hardness parameters, brittleness and anisotropy indices are presented. The Variation of these mechanical properties was explained based on the Mulliken population analysis and charge density mapping (CDM). The electronic properties have been dealt with by considering electronic band structure and density of states (DOS) which confirmed the metallic nature of Zr2AB2 (A = In, Tl). The lowly dispersive energy bands along the c-direction confirmed anisotropy in conductivity. The analysis of DOS revealed the dominant contribution from Zr-d orbitals to the conductivity with a small contribution from the In/Tl-p states contributing at the Fermi level. The Debye temperature (Theta-D), minimum thermal conductivity (Kmin), Gruneisen parameter and melting temperature (Tm) have been calculated. The higher values of Theta-D and Tm, and lower value of Kmin for Zr2AB2 (A = In, Tl) compared to those of Zr2AC (A = In, Tl). Besides, the specific heat capacities, thermal expansion coefficient, and different thermodynamic potential functions have been calculated. The optical constants have been studied to reveal their possible relevance for application purposes. The reflectivity spectra revealed the applicability of Zr2AB2 (A = In, Tl) as cover materials to diminish the solar heating. The studied physical properties of Zr2AB2 (A = In, Tl) are compared with those of other relevant 212 and 211 MAX phase nanolaminates.