Pressure-induced metallization of silane

doi:10.1073/pnas.0710473105

Pressure-induced metallization of silane

*Geophysical Laboratory, Carnegie Institution of Washington, Washington, DC 20015;
^†School of Physics, South China University of Technology, Guangzhou 510641, China; and
^‡Department of Chemistry, The University of Western Ontario, London, ON, Canada N6A 5B7

Contributed by Russell J. Hemley, November 6, 2007 (received for review September 29, 2007)

Abstract

There is a great interest in electronic transitions in hydrogen-rich materials under extreme conditions. It has been recently suggested that the group IVa hydrides such as methane (CH₄), silane (SiH₄), and germane (GeH₄) become metallic at far lower pressures than pure hydrogen at equivalent densities because the hydrogen is chemically compressed in group IVa hydride compounds. Here we report measurements of Raman and infrared spectra of silane under pressure. We find that SiH₄ undergoes three phase transitions before becoming opaque at 27–30 GPa. The vibrational spectra indicate the material transforms to a polymeric (framework) structure in this higher pressure range. Room-temperature infrared reflectivity data reveal that the material exhibits Drude-like metallic behavior above 60 GPa, indicating the onset of pressure-induced metallization.

Footnotes

^§To whom correspondence may be addressed. E-mail: h.mao{at}gl.ciw.edu or r.hemley{at}gl.ciw.edu
Author contributions: X.-J.C., V.V.S., H.-k.M., and R.J.H. designed research; X.-J.C., V.V.S., Y.S., A.F.G., M.A., Z.L., H.-k.M., and R.J.H. performed research; X.-J.C., V.V.S., and A.F.G. analyzed data; and X.-J.C., V.V.S., A.F.G., H.-k.M., and R.J.H. wrote the paper.
The authors declare no conflict of interest.
↵ ** The model parameters are: at 60.7 GPa, n _d = 2.38, ε_∞ = 8.0, γ₁ = 384 cm⁻¹, ω_p2 = 7.20 × 10⁴ cm⁻¹, ω₂ = 6.70 × 10³ cm⁻¹, and γ₂ = 9.20 × 10³ cm⁻¹; at 67.2 GPa, n _d = 2.38, ε_∞ = 8.0, γ₁ = 94.86 cm⁻¹, ω_p2=8.36 × 10⁴ cm⁻¹, ω₂ = 4.87 × 10³ cm⁻¹, and γ₂ = 9.19 × 10³ cm⁻¹.