关键词: crystal structure prediction, high pressure, mechanical properties, phase transition

Abstract: We employ the particle swarm optimization (PSO) algorithm in combination with first-principles calculations to systematically investigate the phase stability and physical properties of Mn$_{2}$AlB$_{2}$ under pressures of up to 80 GPa. The results reveal a pressure-induced phase transition from orthorhombic oC10-Mn$_{2}$AlB$_{2}$ to tetragonal tP10-Mn$_{2}$AlB$_{2}$ 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 Mn$_{2}$AlB$_{2}$ phases are potential hard materials rather than superhard ones. Furthermore, the minimum thermal conductivity of both phases exceeds 1.25 W$\cdot$m$^{-1}\cdot$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 Mn$_{2}$AlB$_{2}$ is constructed for the first time using the quasi-harmonic approximation (QHA) method. The results show that the transformation pressure from oC10-Mn$_{2}$AlB$_{2}$ to tP10-Mn$_{2}$AlB$_{2}$ decreases with increasing temperature. These findings deepen our understanding of the pressure-induced behavior of Mn$_{2}$AlB$_{2}$ and provide theoretical guidance for its mechanical optimization and high-pressure synthesis.

Key words: crystal structure prediction, high pressure, mechanical properties, phase transition