Ab initio prediction of new 3D-like phases ThCuSiAs, ThCuGeAs and their structural, mechanical, and electronic properties

Abstract

New 1111-like quaternary tetragonal Th-based phases: silicide arsenide ThCuSiAs and germanide arsenide ThCuGeAs are proposed in this article. The stabilities of these materials are verified, and the value of their structural, elastic (elastic constants, bulk, shear, and Young's moduli, compressibility, Pugh's indicator, Poisson's ratio, indexes of elastic anisotropy), electronic (densities of electronic states, electronic heat capacity, molar Pauli paramagnetic susceptibility, and the so-called metallicity indexes), and some other properties (Vickers hardness and melting temperatures) are predicted from the first principles calculations. The proposed phases are the first Thbased oxygen-free 1111-like materials, and their syntheses seem very attractive to expand the rather rare group of nonconventional quasi-three-dimensional 1111-like materials.

25th Anniversary Article: MXenes: A New Family of Two‐Dimensional Materials

“…Removal of the A layers results in a redistribution of the Ti 3d states, or "dangling bonds", from the missing Ti-Al bonds into delocalized Ti-Ti metallic-like bonding states that appear around E f in Ti 2 C (Figure 8 b). Thus, in MXenes, N ( E f ) is 2.5-4.5 times higher than in the corresponding MAX phases for Ti n + 1 C n and Ti n + 1 N n according to Shein et al [ 30 ] ; or 1.9-3.2 times higher for Ti n + 1 C n and 2.8-4.8 times higher for Ti n + 1 N n according to Xie et al [ 39 ] , where the range of studied n was broader.…”

“…Note that the calculated cohesive energies of Ti n + 1 N n are less than those of Ti n + 1 C n , whereas the formation energies of Ti n + 1 N n from Ti n + 1 AlN n are higher than those of Ti n + 1 C n from Ti n + 1 AlC n . [ 30 ] The lower cohesion energy implies lower stability of the structure, whereas the higher formation energy of the MXenes from their corresponding Al containing MAX phases implies that the Al atoms are bonded more strongly in Ti n + 1 AlN n compared to Ti n + 1 AlC n and thus require more energy for their extraction. These two factors may explain why nitride MXenes have to date not been produced.…”

“…Bare MXene mono layers are predicted to be metallic, with a high electron density near the Fermi level. [ 5,30,[37][38][39] Interestingly, the electron DOS near the Fermi level ( N ( E f )) for bare individual MXene layers is higher than in their parent MAX phases. To understand these changes one needs to examine the partial electron density of states ( Figure 8 ).…”

“…To understand these changes one needs to examine the partial electron density of states ( Figure 8 ). [ 30,39,40,46 ] In the MAX phases, N (E f ) is dominated by M 3d orbitals. Referring to Ti 2 AlC (Figure 8 a), it is clear that the valence states below E f group into two sub-bands: sub-band A, which is near E f and is made up of hybridized Ti 3d-Al 3p orbitals; and sub-band B, which is between -10 and -3 eV below E f and is due to hybridized Ti 3d-C 2p and Ti 3d-Al 3s orbitals.…”

“…[ 30,[37][38][39]48 ] Magnetic MXenes can be both ferromagnetic (such as Cr 2 C, Cr 2 N, [ 38 ] or Ta 3 C 2 ) [ 48 ] or antiferromagnetic (such as Ti 3 C 2 or Ti 3 N 2 ). [ 30 ] The acquired total magnetic moments per unit cell are in the range 2-3 μ B for Ti n + 1 C n or fl uctuate around 1.2 μ B for Ti n + 1 N n as n increases from 1 to 9. [ 39 ] Although magnetism is an important property, for the most part it is only predicted for MXene with bare surfaces.…”