Prediction of T‐ and H‐Phase Two‐Dimensional Transition‐Metal Carbides/Nitrides and Their Semiconducting–Metallic Phase Transition

Abstract

The discovery of various two-dimensional (2D) nanomaterials with different phases is fundamentally and technologically intriguing, leading to diverse physical and chemical properties for expanded applications. Herein, we performed systematic first-principles calculations to explore a series of single-layer MXenes (M X: M=Sc, Ti, V, Cr, Mn, Zr, Nb, Mo, Hf, Ta; X=C, N). The new H-phase MXenes are firstly predicted, which are compared with the usually synthesized MXenes named as T-phase MXenes on their structure and electronic properties. Semiconducting-metallic transitions could be realized by T-/H- phase transition for Sc CO , Sc CO H , and Ti CO . Besides, the differences between MXenes and MoS on energy storage are discussed. Our work will provide valuable directions for the discovery of new MXene phases and give a systematic understanding of 2D MXenes.

Surface Modifications of Ti2CO2 for Obtaining High Hydrogen Evolution Reaction Activity and Conductivity: A Computational Approach

“…2×2×1 supercell of Ti 2 CO 2 is selected as a study model, denoted as Ti 8 C 4 O 8 , contains four upper O and four lower O atoms, as shown in Figure a. The terminal O group located in the hollow sites of Ti 8 C 4 on both sites has been reported as the most thermally stable structure ,. Δ G H has been found to be dependent upon hydrogen coverages in Ti 2 CO 2 , which presented Δ G H =0.12 eV at low hydrogen coverage (1/9 ML) and larger values with increasing hydrogen coverages .…”

“…where E totol , E vac and E bulk correspond to the total energies of the doping system, vacancy and P/S bulk, and n is the number of atoms in P/S bulk. [47] In addition, the dynamical stability of the catalysts is also explored by using temperature molecular dynamics (MD), [48] which are performed in the NVT ensemble for 5000 time-steps. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 within 50 K and the structures are remaining unchanged, as displayed in Figure S3.…”

A structure map for AB2 type 2D materials using high-throughput DFT calculations

“…In the following subsections, we discuss the obtained 1T/1H (TMDCs and TMDOs, metal dihalides, MXenes/BiXenes, and other 1T/1H), planar and distorted planar structures, memory structures, and other characteristic structures in detail. Experimental data reported by J. Zhou et al 48 and other groups 88,[90][91][92][93][94][95]111 are shown in Table 1 and shown in Fig. 7, T 0 indicates the one-dimensional distorted 1T phase in which pairs of metal atoms move closer to each other perpendicularly, and 1T 00 indicates the two-dimensional distorted 1T phase in which four nearby metal atoms move closer to each other.…”

First-principles study of magnetism in some novel MXene materials

“…This work focuses on the magnetism of pristine MXenes, whose geometric structures are similar to transition metal chalcogenides in two common phases (1H and 1T). 36,37 Theoretical exploration via rst-principles calculations was conducted on the stability, magnetism, and electronic properties of the 1H and 1T M 2 C MXenes with various transition metals (M ¼ Sc, Ti, Fe, Co, Ni, Cu, Zn). The corresponding parameters, including the lattice parameters, total energies, magnetic moments, and spin exchange coupling parameters, were calculated and compared, and the critical temperatures T c for particular magnetic MXenes were evaluated through Monte Carlo (MC) simulations.…”