This study is focused on the sensitivity of the final ceramic microstructure to the molecular structure of the precursor. Bulk ceramics with different polymers were synthesized and annealed at different temperatures. Subsequent examinations were carried out with Transmission Electron Microscopy (TEM), including High Resolution Transmission Electron Microscopy (HRTEM) and the calculation of the Pair Distribution Function (PDF) from electron diffraction patterns of the predominantly amorphous matrix. Afterwards the experimental PDF are compared to calculated PDFs obtained from structure models determined via classical Molecular Dynamics simulation.
The Pair Distribution Function is a powerful technique to investigate the short range order in disordered materials like the amorphous Polymer-Derived Ceramics up to ~1400°C. The PDF is already well established for example in X-ray or neutron diffraction but the advantage of the PDF from electron diffraction is that a very small sample volume can be analyzed in conjunction with the corresponding image information (HRTEM). Therefore, this technique is used for a better understanding of the crystallization behavior of these ceramics. By now, it is known that the onset of crystallization in boron-containing ceramics is shifted towards higher temperatures; however, the resulting crystal-size differs significantly and the amorphous matrix shows distinctly different features. The relationship between the molecular architecture and chemistry on the amorphous nature of the pre-ceramic and, in addition, its influence on the resulting crystallization behavior will be discussed.