High-Pressure Synthesis and Superconductivity of the Laves Phase Compound Ca(Al,Si)2 Composed of Truncated Tetrahedral Cages Ca@(Al,Si)12

The Zintl compound CaAl2Si2 peritectically decomposes to a new ternary cubic Laves phase Ca­(Al,Si)2 and an Al–Si eutectic at temperatures above 750 °C under a pressure of 13 GPa. The ternary Laves phase compound can also be prepared as solid solutions Ca­(Al1–xSix)2 (0.35 ≤ x ≤ 0.75) directly from the ternary mixtures under high-pressure and high-temperature conditions. The cubic Laves phase structure can be regarded as a type of clathrate compound composed of face-sharing truncated tetrahedral cages with Ca atoms at the center, Ca@(Al,Si)12. The compound with a stoichiometric composition CaAlSi exhibits superconductivity with a transition temperature of 2.6 K. This is the first superconducting Laves phase compound composed solely of commonly found elements.