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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

The Si-C bond causes an out-of-plane distortion of the carbon atoms.The magnitude of the binding energy varies with the concentration of the Si/C bonds, at first increasing linearly but then declining when the strain energy in the adjacent carbon atoms begins to overlap.
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f5: The Si-C bond causes an out-of-plane distortion of the carbon atoms.The magnitude of the binding energy varies with the concentration of the Si/C bonds, at first increasing linearly but then declining when the strain energy in the adjacent carbon atoms begins to overlap.

Mentions: The calculated change in with the concentration of Si bonds, , is shown in Fig. 5. Note that at first declines linearly with concentration, but only up to . Then it begins to rise, reaching nearly zero when there is one silicon for every two carbon atoms. As shown in the molecular diagram, the sp3 Si-C bond pulls the carbon atoms upwards from the graphene plane, thereby inducing strain in the neighboring carbon atoms. The strain extends to the first nearest carbon. Thus if two silicon bonds were to be brought closer than the spacing between two nearest neighbor carbon atoms then the strain fields will overlap, thereby placing a penalty on the binding energy of the Si molecule to the graphene layer. (Note that the elastic strain energy is proportional to the square of the strain. Therefore the sum of the square of two equal quantities of strain is only one half of the square of twice that quantity of strain.) In summary, the energy does indeed decline linearly up to the point that silicon atoms are spaced two carbon atoms apart, but then rises when the strain fields begin to overlap.


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

Yu L, Raj R - Sci Rep (2015)

The Si-C bond causes an out-of-plane distortion of the carbon atoms.The magnitude of the binding energy varies with the concentration of the Si/C bonds, at first increasing linearly but then declining when the strain energy in the adjacent carbon atoms begins to overlap.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

f5: The Si-C bond causes an out-of-plane distortion of the carbon atoms.The magnitude of the binding energy varies with the concentration of the Si/C bonds, at first increasing linearly but then declining when the strain energy in the adjacent carbon atoms begins to overlap.
Mentions: The calculated change in with the concentration of Si bonds, , is shown in Fig. 5. Note that at first declines linearly with concentration, but only up to . Then it begins to rise, reaching nearly zero when there is one silicon for every two carbon atoms. As shown in the molecular diagram, the sp3 Si-C bond pulls the carbon atoms upwards from the graphene plane, thereby inducing strain in the neighboring carbon atoms. The strain extends to the first nearest carbon. Thus if two silicon bonds were to be brought closer than the spacing between two nearest neighbor carbon atoms then the strain fields will overlap, thereby placing a penalty on the binding energy of the Si molecule to the graphene layer. (Note that the elastic strain energy is proportional to the square of the strain. Therefore the sum of the square of two equal quantities of strain is only one half of the square of twice that quantity of strain.) In summary, the energy does indeed decline linearly up to the point that silicon atoms are spaced two carbon atoms apart, but then rises when the strain fields begin to overlap.

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