Hydrogen segregation and its roles in structural stability and metallization: silane under pressure

Area of Science:

• Materials Science
• Condensed Matter Physics
• Computational Chemistry

Background:

• Silane (SiH4) is a simple hydride with a rich phase diagram under pressure.
• Previous studies predicted various structures for SiH4 at high pressures.

Purpose of the Study:

• To investigate the structural stability and electronic properties of silane (SiH4) under extreme pressure using first-principles calculations.
• To identify new stable phases of SiH4 and understand their bonding characteristics.

Main Methods:

• First-principles density functional theory (DFT) calculations.
• Structure searching and phase stability analysis based on enthalpy.
• Electronic structure calculations to determine metallic and superconducting properties.

Main Results:

• A novel P-3 structure for SiH4 was identified as the most stable phase above 241 GPa.
• This P-3 structure features segregated H2 units intercalated within a polymeric Si-H framework.
• The stability is attributed to electron-deficient multicenter Si-H-Si bonds, leading to delocalized electrons and a potential metallic/superconducting state.
• The P-3 structure is thermodynamically stable against decomposition into binary Si-H compounds or elemental Si and H2.
• The calculated enthalpy suggests SiH4 (P-3) + Si (fcc) is more stable than Si2H6 under high pressure, questioning disilane's stability.

Conclusions:

• Silane (SiH4) exhibits a unique P-3 structure at high pressures, characterized by segregated H2 molecules and a polymeric Si-H network.
• This phase is predicted to be metallic and potentially superconducting due to multicenter bonding.
• The findings challenge the high-pressure stability of disilane (Si2H6) and highlight the complex chemistry of silicon hydrides under extreme conditions.