Influence of Different A Elements on Bonding and Elastic Properties of Zr₂AC (A = Al, Si, P, S): A Theoretical Investigation

Abstract

Extended Hückel tight-binding band structure calculations are used to address the chemical bonding and elastic properties of Zr 2 AC (A=Al, Si, P, and S). Elastic properties are interpreted by analyzing the density of states and the crystal orbital overlap population for the respective phases. Our results show that the bulk modulus of these ternary compounds is determined by the strength of Zr-A bonds.

Synthesis and DFT investigation of new bismuth-containing MAX phases

“…It is then possible we do not obtain either Zr 2 AlC or Zr 2 BiC because T d T f or because T d ≈ T f but for the tested temperatures k d k f . Whatever the reason for the experimental absence of Zr 2 AlC and Zr 2 BiC although nothing from DFT works directly suggests a non-stability34353637, the quaternary Zr 2 (Al 0.42 Bi 0.58 )C somehow produces an enhanced structural stability, which results in rendering the formation of the MAX phase more energetically favorable than competing phases and/or in favorably changing the T and k above-defined values, so that formation takes over decomposition. As it can be simply seen with a periodic table and the list of so far synthesized MAX phases, expectations about Zr 2 AlC stability (at least compared to ZrC + Zr y Al z ) have to be low since none of the Al neighbors (Si, Ga and Ge) forms a Zr 2 AC MAX phase42728293031.…”

Attempts to synthesise quaternary MAX phases (Zr,M)2AlC and Zr2(Al,A)C as a way to approach Zr2AlC

“…That does not indicate per se that the Al content in the formed MAX phases is low as S substitution by Al in the structure could potentially be achieved without notable unit cell parameter changes. This is, however, unlikely considering that DFT calculations [14,[31][32][33][34][35] and existing lattice parameters values for other Zr 2 AC and M 2 AlC MAX phases allow to predict that a hypothetical Zr 2 AlC compound should fall in the following ranges: 3.1 < a < 3.4 and 13.6 < c < 14.7 Å. Therefore, even considering the lowest projected value for Zr 2 AlC (13.6 Å) the c lattice parameter (12.1 Å for Zr 2 SC [1,28,36]) is expected to strongly increase even for limited S by Al substitution.…”