29Si and 13C Solid-State NMR Spectroscopic Study of Nanometer-Scale Structure and Mass Fractal Characteristics of Amorphous Polymer Derived Silicon Oxycarbide Ceramics

Polymer derived silicon oxycarbide ceramics (SiOC-PDCs) with widely different carbon contents have been synthesized, and their structures have been studied at different length scales using high-resolution C-13 and Si-29 magic-angle-spinning (MAS) NMR spectroscopic techniques. The data suggest that the structure of these PDCs consists of a continuous mass fractal backbone of corner-shared SiCxO4-x tetrahedral units with voids occupied by sp(2)-hybridized graphitic carbon. The oxygen-rich SiCxO4-x units are located at the interior of this backbone with a mass fractal dimension of similar to 2.5 while the carbon-rich units display a slightly lower dimensionality and occupy the interface between the backbone and the free carbon nanodomains.