Crystal structure of Si H4 at high pressure

Abstract

The crystal structure of a high-pressure phase of silane (Si H4), observed between 10 and 25 GPa, is solved using powder synchrotron x-ray diffraction and shown to be of the Sn Br4 type. The phase is an insulating molecular solid with a monoclinic unit cell containing four tetrahedrally bonded molecules, space group P 21 c. Ab initio calculations show the Sn Br4 -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. © 2007 The American Physical Society.