First-principles prediction of phase transformation and mechanical properties of Mn₂AlB₂ under high pressure

We employ the particle swarm optimization (PSO) algorithm in combination with first-principles calculations to systematically investigate the phase stability and physical properties of Mn₂AlB₂ under pressures of up to 80 GPa. The results reveal a pressure-induced phase transition from orthorhombic oC10-Mn₂AlB₂ to tetragonal tP10-Mn₂AlB₂ at approximately 21.5 GPa, accompanied by a volume collapse of approximately 1.6%, confirming a first-order phase transition. Both phases are mechanically and dynamically stable, with the bulk and shear moduli increasing under compression. The B/G ratio and Poisson’s ratio indicate a pressure-driven brittle-to-ductile transition occurs at pressures above 50 GPa. The calculated Vickers hardness suggests that the two Mn₂AlB₂ phases are potential hard materials rather than superhard ones. Furthermore, the minimum thermal conductivity of both phases exceeds 1.25 W·m⁻¹·K⁻¹, and they are not suitable as thermal barrier coating materials. Electronic structure and bonding analyses reveal that pressure strengthens Mn–B and Al–B bonds and reduces magnetic moments, providing a microscopic explanation for the pressure-dependent mechanical behavior. Finally, a high-pressure and high-temperature phase diagram of Mn₂AlB₂ is constructed for the first time using the quasi-harmonic approximation (QHA) method. The results show that the transformation pressure from oC10-Mn₂AlB₂ to tP10-Mn₂AlB₂ decreases with increasing temperature. These findings deepen our understanding of the pressure-induced behavior of Mn₂AlB₂ and provide theoretical guidance for its mechanical optimization and high-pressure synthesis.