Abstract text (incl. figure legends and references)

Through the pyrolysis of polymeric precursor infiltrated cellulose-based paper templates, ceramic composites with paper-like morphology can be successfully manufactured. Such polymer-derived ceramic papers (PDCPs) are pseudomorphic after their template, closely resembling the original paper structure, with randomly interwoven carbonized fibers encased by a polymer-derived ceramic layer.

For this study, several PDCPs were prepared with varying synthesis parameters by pyrolysis of cellulose paper templates dip-coated with two different polysilazane-based single-source precursors, each modified with one of three different transition metals (Fe, Ni, Pd).

The resulting ceramic papers were studied by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and energy-dispersive X-ray spectroscopy (EDS) analyses in combination with X-ray diffraction (XRD) as well as Raman and Fourier-transform infrared (FTIR) spectroscopy.

In order to reveal the in-situ generated microstructure, electron transparent thin-foils of the filigree and inherently brittle ceramic composites were prepared for TEM investigations. For this purpose, conventional polishing in combination with ion thinning as well as ultramicrotomy slice-cutting was comparatively employed to assess their suitability for these materials and to evaluate preparation artifacts introduced.

Overall, ultramicrotomy preparation led to a much better sample quality, allowing the core-shell structure of the composite ceramic fibers to be resolved in great detail (Figure 1). This points out that ultramicrotomy has high potential for TEM sample preparation of ceramic material systems, although it is seldomly used. Based on the results, the phase evolution and the role of the cellulose template during pyrolysis is discussed.

Figure 1: SEM BSE image (left) of a SiFeO(C,N)-based ceramic paper pyrolyzed in ammonia at 1000 °C and TEM BF image (middle) of an ultra-thin fiber cross-section prepared by ultramicrotomy preparation revealing the core-shell structure of the ceramic composite fibers. The electron diffraction patters (right) show that the ceramic layer is amorphous and contains numerous nanosized α-Fe particles, while the cellulose-derived fiber consists of semicrystalline turbostratic carbon.