Realization of diversity in physical properties of Zr₂Se(B_1-xSe_x) MAX phases through DFT approach

The discovery of a series of MAX phases, Zr2Se(B1-xSex), with Se at both A- and X-sites, drives a new chemical diversity to the MAX family. Here, we employed the density functional theory (DFT) approach to realize the diversity in physical properties of Zr2Se(B1-xSex). All compositions of Zr2Se(B1-xSex) are mechanically stable and the dynamical stability of the end member Zr2SeSe is confirmed. The elastic constant C-33 and bulk moduli B show a decrease almost monotonically with Se-content x while other constants and moduli change irregularly. All elastic constants and moduli except C-12 and C-13 are highest for the end member Zr2SeB. Additionally, the Vickers hardness, Debye temperature, minimum thermal conductivity, and lattice thermal conductivity are highest for Zr2SeB. The increase of Se-content x at X-site reduces most of the properties of Zr2Se(B1-xSex). The electronic band structures change drastically with increasing Se-content x. This diversity in electronic band structures is mainly the reason for the diversity in physical properties of Zr2Se(B1-xSex). All compositions of Zr2Se(B1-xSex) have the potential to be thermal barrier coating materials, and Zr2SeB has the potential to be etched into 2D MXene, Zr2B.