New series of MAX phases with MA‐triangular‐prism bilayers: synthesis, structure, and elastic properties

We report a new type of MAX phase, Nb3As2C, designated as 321 phase. It differs from all the known Mn+1AXn phases in that it consists of an alternate stacking of one MX layer and two MA layers in its unit cell, while only one MA layer is allowed in usual MAX phases. The new 321 phase exhibits a bulk modulus of Nb3As2C up to 225(3) GPa as determined by high pressure synchrotron X‐ray diffraction, one of the highest values among the known MAX phases. Isostructural 321 phases V3As2C, Nb3P2C and Ta3P2C are also found to exist. First‐principles calculations reveal the outstanding elastic stiffness in 321 phases. Among all 321 phases, Nb3P2C is predicted to possess the highest elastic properties. These 321 phases, represented by a chemical formula Mn+1AnX, were added as new members to the MAX family and their other properties deserve future investigations.

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