Crystalline aluminum silicides with electride state and superconductivity under high pressure

Abstract

Metal-containing silicides are of fundamental interests in the fields of physics, chemistry, and material science due to their exotic structures and unique properties, such as electride state or superconductivity. However, crystalline compounds of elemental Al and Si remain poorly understood despite their abundance on Earth as well as Earth's interior where the pressure is dominated. In this work, we carry out an exhaustive research on the pressure-stabilized compounds of the Al–Si system through an advanced structural searching approach assisted with first-principal computations. Unexpectedly, a plethora of hitherto unknown metallic aluminum-silicon crystal phases (i.e., Al5Si, Al3Si, Al2Si, Al3Si2, AlSi, Al2Si3, AlSi2, AlSi4, AlSi6, and AlSi8) were identified with fascinating silicon motifs containing from isolated atom, ladder-like arrangement, linear chain, to three-dimensional framework. Our simulations further reveal the electride behaviors in Al5Si, Al3Si, Al2Si, and Al3Si2, in which Al could donate its valence electron into interstitial regions. Remarkably, Al2Si3 is predicted to possess a high superconducting critical temperature of 16 K at a relatively low pressure of 5 GPa, which allows it to become the best metal-silicon binary superconductor under high pressures. The present results provide a comprehensive understanding of metal-bearing silicides and will stimulate the future investigation and verification of our newly predicted metal silicides.