The crystal structure of a high-pressure phase of silane (SiH4), observed between 10 and 25GPa, 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 K′0 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.

This work was supported by NSF (DMR, DOE Grant No. DEFG02-02ER4595, and DOE - CDAC). The x-ray measurements were performed at HPCAT Sector 16, Advanced Photon Source APS, Argonne National Laboratory. The HPCAT facility is supported by DOE-BES, DOENNSA - CDAC, NSF, DOD-TACOM, and the W.M. Keck Foundation. The use of the APS was supported by DOE-BES under Contract No. W-31-109-ENG-38. M.M.C. would like to thank the Spanish Ministry of Education and Science for providing a grant. M.M.C. and A.B. acknowledge partial support from the EC sixth Framework Network of Excellence NANOQUANTA NMP4-CT-2004-500198.

Peer reviewed