Chemical conversion of MoAlB into Mo2AlB2 single crystals: Structure and electronic properties

MAB phases are a class of layered ternary transition metal borides with large chemical and structural diversity. In this work, we used the Lewis acid etching method to topochemically convert MoAlB into Mo₂AlB₂ single crystals with a typical size of 0.5–1.5 mm. We comprehensively characterized the single crystals and confirmed the high quality and preferred orientation of the converted Mo₂AlB₂ crystals using X-ray diffraction, polarized Raman spectroscopy, and transmission electron microscopy. The converted Mo₂AlB₂ crystals are metallic and exhibit lower resistivity compared to the precursor phase, which is associated with the higher density of states at the Fermi energy of Mo₂AlB₂ as compared to MoAlB. We show that the chemical conversion is a pathway to produce M₂AlB₂ phases and this approach can be further extended to other members of M₂A₂B₂ phases for conversion.