Modeling the sol–gel synthesis route of amorphous Si3B3N7

Abstract

The amorphous high-performance ceramic a-Si₃B₃N₇ can only be synthesized via a sol–gel process. Using a separation of time scales approach, we model various aspects of the sol–gel process explicitly including the fact that the polymerization step occurs via the cross-linking of single-source precursor molecules. For chemically reasonable choices of process parameters, this approach yields satisfactory agreement with the structural data of the amorphous ceramic. In particular, the coexistence of medium range order observed in NMR experiments and the high degree of homogeneity on larger length scales appears to be due to merging many oligomers formed by the linkage of only a few monomers that contain a boron- or silicon-rich core, instead of due to the linking of a few large clusters.