First-order Raman scattering of rare-earth containingi-MAX single crystals(Mo2/3RE1/3)

Abstract

Herein, we report on the growth of single crystals of various (Mo 2/3 RE 1/3 ) 2 AlC (RE = Nd, Gd, Dy, Ho, Er) i-MAX phases and their Raman characterization. Using first principles, the wave numbers of the various phonon modes and their relative atomic displacements are calculated and compared to experimental results. Twelve high-intensity Raman peaks are identified as the fingerprint of this new family of rare-earth containing i-MAX phases, thus being a useful tool to investigate their corresponding composition and structural properties. Indeed, while a redshift is observed in the low-wave-number range due to an increase of the rare-earth atomic mass when moving from left to right on the lanthanide row, a blueshift is observed for most of the high-wave-number modes due to a strengthening of the bonds. A complete classification of bond stiffnesses is achieved based on the direct dependence of a phonon mode wave number with respect to the bond stiffness. Finally, STEM images are used to confirm the crystal structure.

Achieving Macroscopic V4C3Tx MXene by Selectively Etching Al from V4AlC3 Single Crystals

“…The V 4 AlC 3 polycrystalline powders, Al powders, and Co powders were mixed in a 1:18:6 molar ratio with a total mass 1 g and pressed into a pellet. As reported in ref , the addition of Co powders can suppress the formation of VAl 3 . The pellet was placed in an alumina crucible, and the crucible then placed in the vertical tubular furnace.…”

“…In fact, the deviations between the experimental and calculated wavenumber are also existed in other MAXphase single crystals. 52,54 For comparison, the calculated and experimental Raman-active modes for Ti 4 AlN 3 , V 4 AlC 3 , and α-Ta 4 AlC 3 are listed in Table 2. 50,51 The Raman spectrum of V 4 AlC 3 is similar to those of isostructural Ti 4 AlN 3 and α-Ta 4 AlC 3 and more like that of Ti 4 AlN 3 because of the small difference in atom mass between Ti and V atoms.…”

“…To date, more than 70 kinds of MAX phases have been reported, but few MAX-phase single crystals have been obtained, such as Ti 2 GaC, Ti 2 SnC and its solid solutions, (Mo 2/3 RE 1/3 ) 2 AlC (RE = Nd, Gd, DY, Ho, or Er), Cr 2 GaC, Cr 2 AlC, V 2 AlC, , Ta 3 AlC 2 , Ti 3 SiC 2 , Ti 4 GaC 3 , V 4 AlC 3– x , and Ta 4 AlC 3 . Among these single crystals, Cr 2 AlC single crystals have been subjected to a hydrofluoric acid (HF) treatment to obtain the corresponding MXenes.…”

Theoretical Prediction and Synthesis of a Family of Atomic Laminate Metal Borides with In-Plane Chemical Ordering

“…In 2017, metal alloying of a MAX phase revealed the first chemically ordered i -MAX phase, (Mo 2/3 Sc 1/3 ) 2 AlC . Since then, 32 different i -MAX phases have been realized experimentally. − ,,− Out of these, four have so far been converted to 2D MXenes, ,,,− displaying properties that are highly promising for energy storage and catalysis. Most importantly, the 3D i -MAX phase alloys can be converted to 2D using the concept of “targeted etching”, realizing either chemical ordering or vacancy ordering depending on the etching protocol …”

Hetero‐MXenes: Theory, Synthesis, and Emerging Applications

“…[ 233,237,244 ] It should be noted that a new class of layered solid i ‐MAX phases (Mo 2/3 RE 1/3 ) 2 AlC, where RE elements are Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm, and where Lu has been discovered and characterized. [ 245,246 ] The magnetic properties reveal long‐range order ranging from 3.8 up to 28 K for all phases except Sm and Tm and some of them were labeled to be frustrated magnetic systems due to competing intra‐ and in‐plane magnetic interactions highly sensitive to applied temperature and magnetic field. Later, a similar family contained Ga interlayered atoms (Mo 2/3 RE 1/3 ) 2 GaC has been reported.…”