Chemical bonding, electron-phonon coupling, and structural transformations in high-pressure phases of Si.
J Phys Chem B
; 110(8): 3721-6, 2006 Mar 02.
Article
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| MEDLINE
| ID: mdl-16494429
ABSTRACT
The nature of chemical bonding of the stable phases of Si at high pressure was analyzed. The effect of pressure is to promote sp electrons into the d orbitals, thus increasing the metallic character and reducing the dimensionality of covalent bonding. Localized covalent bonds, however, persist up to approximately 40 GPa (Si-VI, Cmca) and help to stabilize directional framework structures. At high pressures, Si becomes a metal, and the usual dense packed structures prevail. The existence of conducting and localized electrons gives rise to a combination of "steep and flat bands" near the Fermi level in Si-V. This peculiar electron topology in conjunction with low-frequency vibrations contributes to the relatively high superconducting temperature in Si-V and VI.