Fundamentals of Self-Diffusion in Amorphous Si-(B-)C-N

1. Introduction Using solid state thermolysis of pre-ceramic polymers, it is possible to produce amorphous Si-(B-)C-N ceramics which are a new form of a glassy-like state with an enormous stability range up to 1700 °C (see e. g. [1,2]). Si-(B-)C-N ceramics are promising candidates for the design of ultra-high temperature stable structure materials. The thermal stability and the crystallization depend sensitively on diffusion controlled atomic rearrangement processes [3], which necessitates the investigation of self-diffusion. The determination of the B, C, N, and Si self-diffusivities is carried out with ion implanted stable isotopes and Secondary Ion Mass Spectrometry (SIMS). Details on synthesis and on the experimental setup can be found in Refs. [4,5]. Two types of ceramics are investigated, Si 3 BC 4.3 N 2 (pre-annealed at 1720 °C) and Si 2.6 C 4.1 N 3.3 (pre-annealed at 1460 and 1350 °C).