Prediction of pressure-induced phase transformations in Mg₃As₂

Abstract

Pressure is a fundamental tool that can induce structural and electronic transformations, which is helpful to search for exotic materials not accessible at ambient conditions. Here, we have performed an extensive structural study on cubic Mg 3 As 2 in a pressure range of 0-100 GPa by using a combination of structure predictions and first-principle calculations. Interestingly, two novel structures with space groups C2/m and P 1 were uncovered that become energetically most stable at pressures of 12 GPa and 30 GPa, respectively. Phonon dispersions demonstrate that the three phases are dynamically stable in their respective low-enthalpy pressure ranges. The electronic calculations show that Mg 3 As 2 keeps semiconductor properties at pressures up to 100 GPa. The interesting thing is that the direct semiconducting property of Mg 3 As 2 transforms into indirect semi-conducting when the pressure is above 12 GPa. The current results provide new insights for understanding the behavior of Mg 3 As 2 at high pressures.

High-Pressure Phases and Properties of the Mg3Sb2 Compound

“…At ambient conditions, the Ia 3̅ structure is the ground-state phase for the Mg 3 Sb 2 compound, which has a well-known configuration as shown in Figure a. The Mg–Sb bond length in this interesting configuration is about 2.87–3.94 Å and slightly larger than that of Mg 3 As 2 (about 2.62–2.73 Å) . This is mainly caused by the larger ionic core of Sb than that of the As atom.…”

“…The results reveal that all the phase transitions belong to the first-order nature, as the volume collapsed at the phase transition. This phenomenon also occurred in its sister systems, like Mg 3 P 2 and Mg 3 As 2 . , This can regard as a common character of the A 3 B 2 compounds under high pressure.…”

“…This phenomenon is consistent with the previous study and also occurred in the sister systems like Mg 3 P 2 . and Mg 3 As 2 . Interestingly, when the pressure increases to 5 GPa, we predict that a novel monoclinic phase with the Cm symmetry becomes stable.…”

“…et al studied the phase transformations and electronic properties of Mg 3 As 2 under high pressure and they found that two novel semiconductor phases are stable under high pressure. 19 As one member of the A 3 B 2 -type family, Mg 3 Sb 2 has attracted much focus on its structure configuration and electronic properties. The Mg 3 Sb 2 compound adopts Ia3̅ and P3̅ m1 symmetry at ambient conditions and high pressure, which are provided by early works.…”

“…In addition, we considered some metastable structures with similar energies and the other A 3 B 2 (e.g. Mg 3 N 2 , 10 Mg 3 P 2 , 11 and Mg 3 As 2 , 19 ) stable phases, which act as prototype structures for this system. From our calculation, we conclude that the ground state structure of Mg 3 Sb 2 adopts the Ia3̅ symmetry at ambient conditions.…”