Micro‐/nanostructure evolution of C/SiFeO(N,C) polymer‐derived ceramic papers pyrolyzed in a reactive ammonia atmosphere

SiFeO(N,C)-based ceramic papers were prepared via a one-pot synthesis approach by dip-coating a cellulose-based paper template with a polymeric perhydropolysilazane precursor modified with iron(III)acetylacetonate. The preceramic composites were subsequently pyrolyzed in ammonia atmosphere at 500, 700, and 1000°C, respectively, and the characteristics of the three resulting ceramic papers were comparatively investigated.

Scanning electron microscopy revealed that in each sample, the morphology of the template is successfully transferred on the ceramic system, with the cellulose-derived fibers being converted to elemental carbon encased by a SiFeO(N,C) coating. Electron transparent cross-sectional samples for transmission electron microscopy (TEM) were prepared from the ceramic papers, employing a standard ultramicrotomy slice cutting procedure, allowing for a detailed characterization of their in situ generated micro-/nanostructure as well as occurring crystalline phases.

TEM imaging and diffraction revealed that depending on pyrolysis temperature a different microstructure with a distinct phase assemblage is generated in the polymer-derived ceramic papers. Crystallization from the polymer precursor starts with the precipitation of wüstite (Fe(1-x)O) nanoparticles at 700°C inside the ceramic coating and secondary ε-FexN at the fiber-coating interface. Upon pyrolysis at 1000°C however, the sample primarily accommodates metallic α-iron nanocrystals that impart ferromagnetic characteristics to the ceramic paper.

The results show that the template-assisted polymer-derived ceramic route is a feasible approach in the production of complex ceramic compounds with fibrous paper-like morphology. By adjusting the pyrolysis temperature, microstructure and phase composition of the ceramic paper can be conveniently tailored to the needs of its respective application.