High-pressure Synthesis of Strontium Hexasilicide

Abstract

The binary phase SrSi6 was prepared at a pressure of 10(1) GPa and a temperature of 1520(150) K. Single crystal refinements and powder diffraction data reveal that the compound crystallizes in the orthorhombic crystal system (Cmcm, a=4.4692(4), b=10.256(1), c=11.698(1)Å ) and is isopointal to EuGa2Ge4 and EuSi6. Exothermic decomposition of the compound into SrSi2 and Si at 797 K and ambient pressure indicates that the compound is a metastable high-pressure phase. Analysis of the chemical bonding using the electron localization function and calculated charge densities reveals covalent bonding within the polyanion of four-bonded silicon atoms. Strontium cations are enclosed in the 3D net resulting in an electron balance Sr2+[Si0]2− 6 . In the electronic density of states the excess electrons of the framework are assigned to a filling of antibonding bands. SrSi6 is a metallic conductor with an electrical resistivity of ρ ≈ 250 μΩ·cm at 300 K. Magnetization measurements indicate diamagnetic behaviour (χ0 = −50 · 10−6 emu·mol−1).