Abstract
Research on low-dimensional materials has increased drastically in the last decade, with the discovery of two-dimensional transition metal carbides and nitrides (MXenes) produced by atom-selective chemical etching of laminated parent Mn+1AXn (MAX) phases. Here, we apply density functional theory and subsequent materials synthesis and analysis to explore the phase stability and Mo/Sc intermixing on the M site in the chemically ordered quaternary i-MAX phase (MoxSc1-x)2AlC. Transmission electron microscopy confirms the theoretical predictions of preferential in-plane ordering of Mo and Sc, with the highest crystal quality obtained for the ideal Mo:Sc ratio of 2:1 (predicted as the most stable), as well as a retained i-MAX structure even for an increased relative Sc content, with Sc partially occupying Mo sites. The results are supported by refined neutron diffraction data, which show space group C2/c (no. 15), and a C occupancy of 1. Subsequent chemical etching produces MXene for x=0.66, while for x=0.33 and 0.5 no MXene is observed. These results demonstrate that a precise control of the i-MAX composition is crucial for derivation of MXene, with a MXene quality optimized for a Mo:Sc ratio of 2:1 with minimal intermixing between Mo and Sc.
| Original language | English |
|---|---|
| Article number | 113607 |
| Journal | Physical Review Materials |
| Volume | 3 |
| Issue number | 11 |
| DOIs | |
| State | Published - Nov 27 2019 |
Funding
J.R. acknowledges support from the Swedish Foundation for Strategic Research (SSF) for project funding (EM16-0004) and from the Knut and Alice Wallenberg (KAW) Foundation for a fellowship grant and project funding (KAW 2015.0043). All authors also acknowledge support to the Linköping Electron Microscopy Laboratory (KAW) and from the Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linköping University (Faculty Grant No. SFO-Mat-LiU No. 2009 00971). The Swedish Research Council is also gratefully acknowledged through Project No. 642-2013-8020 and VR International Postdoc Grant No. 2015-00607. The calculations were carried out using supercomputer resources provided by the Swedish National Infrastructure for Computing (SNIC) at the National Supercomputer Centre (NSC), High Performance Computing Center North (HPC2N), and the PDC Center for High Performance Computing. The project used resources at the High Flux Isotope Reactor, a DOE Office of Science User Facility operated by the Oak Ridge National Laboratory.