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On the thermodynamically stable amorphous phase of polymer-derived silicon oxycarbide.

Yu L, Raj R - Sci Rep (2015)

Bottom Line: In this article we employ first-principles calculations to estimate how the interfacial energy of the graphene networks is favorably influenced by having mixed bonds attached to them.We analyze the ways in which this reduction in interfacial energy can stabilize the amorphous phase.In addition we discover a two-dimensional lattice structure, with the composition Si2C4O3 that is constructed from a single layer of graphene congruent with silicon and oxygen bonds on either side.

View Article: PubMed Central - PubMed

Affiliation: University of Colorado at Boulder Boulder, Colorado 80309, USA.

ABSTRACT
A model for the thermodynamic stability of amorphous silicon oxycarbide (SiCO) is presented. It builds upon the reasonably accepted model of SiCO which is conceived as a nanodomain network of graphene. The domains are expected to be filled with SiO2 molecules, while the interface with graphene is visualized to contain mixed bonds described as Si bonded to C as well as to O atoms. Normally these SiCO compositions would be expected to crystallize. Instead, calorimetric measurements have shown that the amorphous phase is thermodynamically stable. In this article we employ first-principles calculations to estimate how the interfacial energy of the graphene networks is favorably influenced by having mixed bonds attached to them. We analyze the ways in which this reduction in interfacial energy can stabilize the amorphous phase. The approach highlights how density functional theory computations can be combined with the classical analysis of phase transformations to explain the behavior of a complex material. In addition we discover a two-dimensional lattice structure, with the composition Si2C4O3 that is constructed from a single layer of graphene congruent with silicon and oxygen bonds on either side.

No MeSH data available.


Related in: MedlinePlus

A 2-D crystal of monolayers of silicon on graphene with a binding energy of −1.2 eV per silicon atom.The stoichiometry of this structure is 2:4:3::Si:C:O.
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f4: A 2-D crystal of monolayers of silicon on graphene with a binding energy of −1.2 eV per silicon atom.The stoichiometry of this structure is 2:4:3::Si:C:O.

Mentions: When exploring the various geometries for attaching Si-O molecules to graphene surfaces, the periodic structure, shown in Fig. 4, was discovered. The average composition of this 2-D structure is Si2C4O3, that is there are two carbon atoms and 1.5 oxygen atoms for every silicon atom. The mixed bond molecules, per silicon atom, have the composition SiC1/4O3/2, with the silicon being coordinated to one carbon and three oxygen atoms. Thus one half of all carbon atoms change their electronic structure from sp2 to sp3 in order to form a bond with silicon. The binding energy per Si bond is calculated to be −1.2 eV. Therefore the quantity for this structure, according to the definition in the previous section, is equal to −0.6 eV since the concentration of mixed bonds . Substituting this value into Eq. (9) gives a value of  J m–2. This would be the work required per unit area to separate the Si-O bonds from the graphene (the separated state is the zero energy state). This magnitude of this interfacial energy is very high (for example the energy of grain boundaries in ceramics, which is also the work of fracture for separating the boundary, are typically about 1 J m–2). The implication is the the 2-D structure shown in Fig. 4 is energetically highly favored.


On the thermodynamically stable amorphous phase of polymer-derived silicon oxycarbide.

Yu L, Raj R - Sci Rep (2015)

A 2-D crystal of monolayers of silicon on graphene with a binding energy of −1.2 eV per silicon atom.The stoichiometry of this structure is 2:4:3::Si:C:O.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4588588&req=5

f4: A 2-D crystal of monolayers of silicon on graphene with a binding energy of −1.2 eV per silicon atom.The stoichiometry of this structure is 2:4:3::Si:C:O.
Mentions: When exploring the various geometries for attaching Si-O molecules to graphene surfaces, the periodic structure, shown in Fig. 4, was discovered. The average composition of this 2-D structure is Si2C4O3, that is there are two carbon atoms and 1.5 oxygen atoms for every silicon atom. The mixed bond molecules, per silicon atom, have the composition SiC1/4O3/2, with the silicon being coordinated to one carbon and three oxygen atoms. Thus one half of all carbon atoms change their electronic structure from sp2 to sp3 in order to form a bond with silicon. The binding energy per Si bond is calculated to be −1.2 eV. Therefore the quantity for this structure, according to the definition in the previous section, is equal to −0.6 eV since the concentration of mixed bonds . Substituting this value into Eq. (9) gives a value of  J m–2. This would be the work required per unit area to separate the Si-O bonds from the graphene (the separated state is the zero energy state). This magnitude of this interfacial energy is very high (for example the energy of grain boundaries in ceramics, which is also the work of fracture for separating the boundary, are typically about 1 J m–2). The implication is the the 2-D structure shown in Fig. 4 is energetically highly favored.

Bottom Line: In this article we employ first-principles calculations to estimate how the interfacial energy of the graphene networks is favorably influenced by having mixed bonds attached to them.We analyze the ways in which this reduction in interfacial energy can stabilize the amorphous phase.In addition we discover a two-dimensional lattice structure, with the composition Si2C4O3 that is constructed from a single layer of graphene congruent with silicon and oxygen bonds on either side.

View Article: PubMed Central - PubMed

Affiliation: University of Colorado at Boulder Boulder, Colorado 80309, USA.

ABSTRACT
A model for the thermodynamic stability of amorphous silicon oxycarbide (SiCO) is presented. It builds upon the reasonably accepted model of SiCO which is conceived as a nanodomain network of graphene. The domains are expected to be filled with SiO2 molecules, while the interface with graphene is visualized to contain mixed bonds described as Si bonded to C as well as to O atoms. Normally these SiCO compositions would be expected to crystallize. Instead, calorimetric measurements have shown that the amorphous phase is thermodynamically stable. In this article we employ first-principles calculations to estimate how the interfacial energy of the graphene networks is favorably influenced by having mixed bonds attached to them. We analyze the ways in which this reduction in interfacial energy can stabilize the amorphous phase. The approach highlights how density functional theory computations can be combined with the classical analysis of phase transformations to explain the behavior of a complex material. In addition we discover a two-dimensional lattice structure, with the composition Si2C4O3 that is constructed from a single layer of graphene congruent with silicon and oxygen bonds on either side.

No MeSH data available.


Related in: MedlinePlus