First-Principles Studies of Amorphous Silicon Oxycarbide: Correlating Structural Properties with 29Si-NMR Chemical Shifts John Paul Nimmo II and Peter Kroll  We investigate the correlation between structural properties and 29Si-NMR chemical shifts in silicon oxycarbide glasses and ceramics. Following our previous investigations of vitreous-SiO2 (Charpentier, Kroll, Mauri, J. Phys. Chem. C 2009, 113, 7917), we model disordered SiCO structures of various compositions using a combination of network modeling and ab-initio molecular dynamic simulations. Subsequently, we compute 29Si-NMR chemical shifts using the gauge-including projector augmented wave (GIPAW) method.Analyzing the data of more than 200 models each comprising about 100 atoms, we determine correlation functions for the relation between isotropic 29Si-NMR chemical shift and structural parameters of its environment. For {Si}O4 centers the only relevant parameters are the adjacent Si-O-Si angles. We find no significant difference between a simple linear relation and the more complex fit using trigonometric functions suggested previously. {Si}O3C centers are well described by the adjacent Si-O-Si angles via a linear relation, with only minor dependency on the Si-C bond length. The 29Si-NMR chemical shifts of {Si}O2C2 and {Si}OC3 centers depend on Si-O-Si angles, Si-C bond lengths and angles in increasing complexity.We use the computed angular correlation functions to analyze experimental 29Si-NMR data provided for a variety of SiCO ceramics. We show that via de-convolution of experimental spectra additional structural data emerges that pertains to phase segregation in SiCO ceramics as well as to local structure at phase boundaries.

First-principles studies of amorphous silicon oxycarbide: Correlating structural properties with <sup>29</sup>Si-NMR chemical shifts

247th National Meeting (2014)

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First-principles studies of amorphous silicon oxycarbide: Correlating structural properties with 29Si-NMR chemical shifts

First-principles studies of amorphous silicon oxycarbide: Correlating structural properties with ²⁹Si-NMR chemical shifts