Influence of Si element and pressure on the thermodynamic, mechanical, and electronic properties of Mg17Al12 by first-principles calculations

In this work, the influence of Si element and pressure (0-60 GPa) on the structural properties, modulus, mechanical properties, thermodynamic properties, and brittle-ductile behavior of Mg17Al12 is investigated by first-principles calculations. The present calculated results show that all phases are thermodynamically stable in the whole pressure range according to the negative formation enthalpy. In addition, the moduli of Mg17Al12 are significantly improved at low pressure, and the doped Mg16Al12Si and doped Mg17Al11Si phases are improved faster at high pressure, showing Si atom may have a greater impact on doped phases at high pressure compared with other phases. According to the values of Pugh's ratio, doped Mg16Al12Si, doped Mg17Al11Si, and Mg17Al11Si undergo brittle-to-ductile transition. Moreover, a wider pseudogap of these phases is generated after pressurization according to the partial density of state, which enhances the interaction of Mg, Al, and Si atoms, thus the pressure improves the mechanical properties. Furthermore, the calculated mean bond population and mean bond length show that the Al-Al bond is the main reason for the variation in the mechanical properties of these phases.