Unraveling Crystalline Structure of High-Pressure Phase of Silicon Carbonate

Abstract

Although CO 2 and SiO 2 both belong to group-IV oxides, they exhibit remarkably different bonding characteristics and phase behavior at ambient conditions. At room temperature, CO 2 is a gas, whereas SiO 2 is a covalent solid with rich polymorphs. A recent successful synthesis of the silicon-carbonate solid from the reaction between CO 2 and SiO 2 under high pressure [M. Santoro et al., Proc. Natl. Acad. Sci. U.S. A. 108, 7689 (2011)] has resolved a long-standing puzzle regarding whether a Si x C 1−x O 2 compound between CO 2 and SiO 2 exists in nature. Nevertheless, the detailed atomic structure of the Si x C 1−x O 2 crystal is still unknown. Here, we report an extensive search for the high-pressure crystalline structures of the Si x C 1−x O 2 compound with various stoichiometric ratios (SiO 2 ∶CO 2 ) using an evolutionary algorithm. Based on the low-enthalpy structures obtained for each given stoichiometric ratio, several generic structural features and bonding characteristics of Si and C in the high-pressure phases are identified. The computed formation enthalpies show that the SiC 2 O 6 compound with a multislab three-dimensional (3D) structure is energetically the most favorable at 20 GPa. Hence, a stable crystalline structure of the elusive Si x C 1−x O 2 compound under high pressure is predicted and awaiting future experimental confirmation. The SiC 2 O 6 crystal is an insulator with elastic constants comparable to typical hard solids, and it possesses nearly isotropic tensile strength as well as extremely low shear strength in the 2D plane, suggesting that the multislab 3D crystal is a promising solid lubricant. These valuable mechanical and electronic properties endow the SiC 2 O 6 crystal for potential applications in tribology and nanoelectronic devices, or as a stable solid-state form for CO 2 sequestration.

Computational Analysis of Stable Hard Structures in the Ti–B System

“…The PSO algorithm has been benchmark tested for many known systems with various chemical bonding, and is able to predict 4 the most stable and low-energy metastable 2D and 3D solid-state structures of various elements and compounds at different pressures [23][24][25][26][27][28] The structure relaxation and total-energy calculation are performed using the density functional theory within the generalized gradient approximation (GGA) 29 , as implemented in the VASP 5.3 package 30 . All-electron plane-wave basis set with the projector augmented wave (PAW) potentials are adopted with 2s 2 2p 1 and 3d 2 4s 2 treated as valence electron configuration for B and Ti, respectively.…”

Structural Evolution of CO2-Filled Pure Silica LTA Zeolite under High-Pressure High-Temperature Conditions

“…These results suggest the existence of novel CO2-SiO2 chemistry systematics with a wealth of uncharacterized compounds, and with potentially interesting chemical properties. Several theoretical total-energy studies have predicted novel silicon carbonate phases at HP-HT and their results need to be experimentally confirmed [8][9][10]. Note that the supposedly advantage of using zeolites to maximize surface chemical reactivity due to the large effective interaction area between the framework SiO2 and the confined-CO2 seems to be restricted to temperatures below 1300 K [3,4].…”

An Isolable Silicon Dicarbonate Complex from Carbon Dioxide Activation with a Silylone

“…However, pressure‐induced reaction (at 18–26 GPa) between CO 2 and a microporous SiO 2 was reported, giving a metastable silicon carbonate phase . The stable crystalline structure of the elusive silicon dicarbonate under high pressure was predicted by theory and is awaiting experimental confirmation . We envisioned that molecular SiO 2 generated in situ in the pocket of a bis(NHC) ligand may react with CO 2 to afford an isolable Si(CO 3 ) 2 complex.…”