Pressure-induced phase transformation and mechanical stability of HfAl2

Utilizing the particle swarm optimization algorithm in conjunction with first-principles calculations, we systematically investigated the structural evolution and mechanical properties of HfAl2 up to 300 GPa at 0 K. Our findings indicate that HfAl2 adopts the MgZn2-type structure (hP12-HfAl2) with space group P63/mmc under zero pressure, and a phase transition to oC12-HfAl2 occurs at approximately 260 GPa. This transition, characterized by a volume collapse, is identified as a first-order phase transition. Phonon dispersion curves provide supporting evidence for the structural stability of these two phases. Simultaneously, we conducted a comprehensive assessment of the elastic constants and modulus of these two phases under both zero and high pressure. The research findings substantially will enhance our understanding of the structural evolution in HfAl2 under high pressure.