Abstract
Polymer-derived silicon oxycarbide (SiCO) presents excellent performance for high temperature and lithium-ion battery applications. Current experiments have provided some information on nano-structure of SiCO, while it is very challenging for experiments to take further insight into the molecular structure and its relationship with properties of materials. In this work, molecular dynamics (MD) based on empirical potential and first principle calculation were combined to investigate amorphous SiCxO6/5 ceramics. The amorphous structures of SiCO containing silicon-centered mix bond tetrahedrons and free carbon were successfully reproduced. The calculated radial distribution, angular distribution and Young’s modulus were validated by current experimental data, and more details on molecular structure were discussed. The change in the slope of Young’s modulus is related to the glass transition temperature of the material. The proposed modeling approach can be used to predict the properties of SiCO with different compositions.
Highlights
Melt-quench simulations based on classical molecular dynamics were used to generate the initial structures of silicon oxycarbide (SiCO)
The first principles calculations according to the density functional theory (DFT) ultra-soft pseudo-potential method were performed by CASTEP code[24,25] in Material Studio 5.5
The first peaks of Si–C and C-C are slightly shift to lower values as carbon content increases, it relates to the formation of free carbon and structural change near the domains interfaces, as the enlargement of free carbon phase changes the Si-C and C-C correlations at its edge
Summary
SiCO from random distributed atoms, the temperature of system was adjusted by velocity scaling and canonical ensemble (NVT) using a Nosé–Hoover_thermostat. The systems were annealed at 1500 K by 5 ps of NVT simulations, and were quenched at a rate of 0.2 K/fs to 300 K with NPT ensemble It is followed by a 5 ps of NPT simulation and a 5 ps of NVT simulation at 300 K for equilibration. For the case with the lowest C content, i.e. the stoichiometric glass, there is no carbon network presented. They are carbon rich phase that like network expands to all the directions and the silica rich phase fill in the spaces of network which results in a ‘nano-domain’ like structure
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