NMR studies of short and intermediate range ordering of amorphous Si–B–N–C–H pre-ceramic at the pyrolysis stage of 600 °C

Abstract

Inorganic random networks of a pre-ceramic stage of the amorphous ceramic SiBN₃C, derived from the single-source precursor Cl₃Si(NH)BCl₂ (TADB), have been synthesized with isotope-labeled materials. This allowed characterization at an atomic level of the development of the pre-ceramic polymer at a crucial pyrolysis stage of 600 °C by solid-state NMR. Using several techniques including ¹³C{¹⁵N}REDOR, ¹¹B{¹³C}REDOR, ¹¹B{¹⁵N}REDOR and ¹³C-2D-RFDR, the atomic network of the ¹³C, ¹⁵N enriched sample was investigated. These combined experiments have lead to the important result that carbon forms unsaturated bonds at this stage of the pyrolysis but remains bonded to nitrogen, maintaining a homogeneous distribution of the elements. Carbon atoms seem to be incorporated into the network by using nitrogen atoms as bridges, similar to boron and silicon. The coordinations of boron and silicon are quite similar to those in the final ceramic SiBN₃C after pyrolysis at 1400 °C.