Ab-initio predictions of phase stability, electronic structure, and optical properties of (0001)-MAX surfaces in M2AC (M = Cr, Zr, Hf; A = Al, Ga)

• Published in: The Journal of physics and chemistry of solids 2021-08, Vol.160
• Main Authors: Qureshi, Muhammad Waqas, Ma, Xinxin, Zhang, Xinghong, Tang, Guangze, Paudel, Ramesh, Paudyal, Durga
• Format: Article
• Language: English
• Subjects: DFT study; electronic structure; MATERIALS SCIENCE; MAX phases; optical properties; surface energy; thin-film
• ISSN: 0022-3697; 1879-2553

In this work, we report MAX phases' surface properties, which are essential for thin-film technology due to their excellent resistance to high-temperature oxidation, corrosion, and wear. The surface stability, electronic, and optical properties of 0001-surfaces in M2AC (M = Zr, Hf, Cr; A = Al, Ga) are investigated and compared with their bulk counterparts. The interplay between chemical bonding and charge distribution is discussed from electronic structure, including the Fermi surfaces. Four possible (0001)-terminated surfaces are considered by breaking M - C and M-A bonds in which cleavage energy of M - C is higher than M-A. The Cr–Al bond in Cr2AlC is stronger than other M-A bonds. The charge density of valance A-p electrons redistributes in the surface area, distinct from that of the bulk. The A- and M(C)-terminated (0001)-surfaces are the most stable and energetically favorable terminations due to lower surface energies. The optical properties of the most stable (0001)-surfaces were also investigated to understand the dielectric and photoconductive behavior in the (0001)-terminated surfaces of M2AC.