Abstract
The nanolaminated MAB phases have attracted great research interests due to their unusual combination of metal-like and ceramic-like properties, which is similar to MAX phases. Recently, ordered quaternary MAX phases have been discovered, which enriches the family of MAX phases, and opens a new window to tailor the properties of MAX phases and to develop new MXenes. In the present work, we explored possible ordered quaternary MAB phases with Cr3AlB4 structure (space group: Pmmm) by first-principles calculations. The predictions show that M2M'AlB4 phases with M = Mn, Fe, Co and M' = Cr, Mo, W exhibit strong tendency of ordering, where M locates at 2t site (0.5, 0.5, z2t) and M' locates at 1g site (0, 0.5, 0.5). The main driving force of ordering may be the differences in bonding strengths between Al and M elements. Analyses on chemical bonds reveal that bonding strengths increase following the order: Al-Mn < Al-Fe < Al-Co, which is consistent with the prediction that ordering tendency increases when M changes from Mn to Co, as derived from enthalpy differences. The ordered M2M'AlB4 phases with M = Mn or Fe are predicted ferromagnetic and ordered M2M'AlB4 phases display lower shear resistance and possibly better ductility in comparison to Cr3AlB4.
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