Hydrogen segregation and its roles in structural stability and metallization: silane under pressure.
We present results from first-principles calculations on silane (SiH4) under pressure. We find that a three dimensional P-3 structure becomes the most stable phase above 241 GPa. A prominent structural feature, which separates the P-3 structure from previously observed/predicted SiH4 structures, is that a fraction of hydrogen leaves the Si-H bonding environment and forms segregated H2 units. The H2 units are sparsely populated in the system and intercalated with a polymeric Si-H framework. Calculations of enthalpy of formation suggest that the P-3 structure is against the decomposition into Si-H binaries and/or the elemental crystals. Structural stability of the P-3 structure is attributed to the electron-deficient multicenter Si-H-Si interactions when neighboring silicon atoms are linked together through a common hydrogen atom. Within the multicenter bonds, electrons are delocalized and this leads to a metallic state, possibly also a superconducting state, for SiH4. An interesting outcome of the present study is that the enthalpy sum of SiH4 (P-3 structure) and Si (fcc structure) appears to be lower than the enthalpy of disilane (Si2H6) between 200 and 300 GPa (for all previously predicted crystalline forms of Si2H6), which calls for a revisit of the stability of Si2H6 under high pressure.
State Key Laboratory of Superhard Materials, Jilin University, Changchun 130012, China.
Wenwen
W
Cui
State Key Laboratory of Superhard Materials, Jilin University, Changchun 130012, China.
Jingming
J
Shi
Department of Physics and Engineering Physics, University of Saskatchewan, Saskatoon, Saskatchewan, S7N 5E2, Canada.
Hanyu
H
Liu
1] Department of Physics and Engineering Physics, University of Saskatchewan, Saskatoon, Saskatchewan, S7N 5E2, Canada [2] Canadian Light Source, Saskatoon, Saskatchewan, S7N 0×4, Canada.
Yansun
Y
Yao
State Key Laboratory of Superhard Materials, Jilin University, Changchun 130012, China.
Hui
H
Wang
Computational Astrophysics Laboratory, RIKEN, 2-1 Hirosawa, Wako, Saitama 351-0198, Japan.
Toshiaki
T
Iitaka
1] State Key Laboratory of Superhard Materials, Jilin University, Changchun 130012, China [2] Beijing Computational Science Research Center, Beijing 10084, China.
Yanming
Y
Ma