High-pressure synthesis of the electron-excess compound CaSi6

The binary phase CaSi6 is prepared at a pressure of 10(1) GPa and a temperature of 1520(150) K. X-ray single-crystal structure refinements and powder diffraction data of quenched samples reveal that the compound crystallizes in the orthorhombic crystal system (space group Cmcm, a=4.4953(5) Å, b=10.078(1) Å, c=11.469(1) Å). At ambient pressure, exothermic decomposition into CaSi2 and Si at 737(5) K indicates that the compound is a metastable high-pressure phase. Physical property measurements reveal that the new hexasilicide is diamagnetic and a bad metallic conductor, with resistivity ρ≈900 μΩ cm at 300 K.