First-principles investigation of the Al–Si–Sr ternary system: Ground state determination and mechanical properties

Abstract

Twelve different ternary phases of the Al–Si–Sr system were characterized using first-principles calculations based on Density Functional Theory. Two different exchange correlation functionals were considered to extract its influence on the global results. In addition to the four phases (AlSiSr, Al 2Si 2Sr, Al 2Si 2Sr 3 and Al 16Si 30Sr 8) reported for this system, we explored eight other ternary phases (Al 2Si 3Sr 3, Al 2Si 4Sr 3, Al 2Si 7Sr 5, Al 3Si 7Sr 10, Al 6Si 3Sr 20, Al 6Si 9Sr 10, Al 8Si 3Sr 14 and AlSi 6Sr 4) that has been reported in chemically analogous systems. The mechanical stability of the phases was determined through the analysis of the elastic constants, and the energetic stability was established using the calculated formation enthalpy. The thermodynamic and vibrational properties of the AlSiSr, Al 2Si 2Sr 3 and Al 2Si 4Sr 3 phases were studied considering the harmonic, quasi-harmonic as well as simple anharmonic corrections. All phases were found to be stable, except for the AlSi 6Sr 4 and Al 6Si 9Sr 10. An isothermal section of the phase diagram was calculated at 0 K with the Thermocalc software, where it was found that the Al 2Si 4Sr 3 and Al 6Si 3Sr 20 phases can belong to the ternary ground state. The surface energy sections show that the other phases are metastable with a ΔG 0 K ≈ 2 kJ/mol−atom, all stables and metastable phases show a metallic behavior and high compressibility.