Quasicrystal stability in complex aluminum alloys: Insights from first principles models on structural motifs in crystalline approximants

Al81Cu7Fe4Cr8 is an alloy that readily forms quasicrystalline phases but understanding the complex atomic arrangements in the structure of such quasicrystals is challenging. For the Al-Cu-Fe-Cr system, the structures of crystalline approximants have been identified. These exhibit atomic motifs similar to those for the quasicrystalline configurations. We employ here a comprehensive methodology to analyze statistically generated ground states of orthorhombic approximants using density functional theory to shed light on the role of elemental variations of such complex alloys. Our findings show that the stability of QC approximants has a strong dependence on the specific locations of Cu and Cr atoms. The geometry of the atomic motifs from structural optimization suggests that the icosahedral phase is more favorable than the decagonal phase. The formation energy difference between these is small which indicates that the two quasicrystalline phases may coexist.