Metastable phases, phase transformation and properties of AlAs based on first-principle study
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Utilizing CALYPSO, three new metastable phases for AlAs are proposed: (1) a P6422 symmetric structure (hP6-AlAs), (2) a C222 symmetric structure (oC12-AlAs), and (3) a I3d symmetric structure (cI24-AlAs). With controlling unloading pressure rate, oC12-, hP6-, and cI24-AlAs may be acquired by quenching NiAs- or cmcm-AlAs. oC12-, and hP6-AlAs possess similar hardness, which is higher than that of cI24-AlAs. Meanwhile, oC12-, and hP6-AlAs hold similar shear anisotropic factors, which are smaller than that of cI24-AlAs. Electronic band structure calculation reveals that at zero pressure, oC12-AlAs and hP6-AlAs possess indirect band gaps of 0.468 eV and 1.356 eV, respectively. cI24-AlAs is a direct semiconductor with a gap value 1.761 eV.