Prediction of pressure-induced phase transformations in MgAs.

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 MgAs 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 2/ and 1̄ 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 MgAs keeps semiconductor properties at pressures up to 100 GPa. The interesting thing is that the direct semi-conducting property of MgAs transforms into indirect semi-conducting when the pressure is above 12 GPa. The current results provide new insights for understanding the behavior of MgAs at high pressures.