First-order Raman scattering of rare-earth containing i -MAX single crystals ( Mo 2 / 3 RE 1 / 3 ) 2 AlC ( RE = Nd , Gd , Dy , Ho , Er )
Résumé
Herein, we report on the growth of single crystals of various (Mo2/3RE1/3)2AlC (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.