Crystal Structure of SiH4 under Pressure

The crystal structure of a high-pressure phase of silane (SiH4), observed between 10 and 25 GPa, is solved using powder synchrotron x-ray diffraction and shown to be of the SnBr4 type. The phase is an insulating molecular solid with a monoclinic unit cell containing four tetrahedrally bonded molecules, space group P21∕c. Ab initio calculations show the SnBr4-type structure to be favored in this pressure range relative to other recently proposed structures. The fit of the pressure dependence of volume to the Birch-Murnagham equation of state gives the following parameters at ambient pressure if K0′ is fixed to 4: V0=250(9) Å3 and K0=7.8(9) GPa for the experimental data, and V0=255(2) Å3 and K0=6.1(2) GPa for the data obtained from ab initio calculations.