Synthesis and temperature-dependent evolution of the phase composition in palladium-containing silicon oxycarbide ceramics

Palladium-containing silicon oxycarbide (SiPdOC) ceramics were synthesized using polymethylsilsesquioxane modified with palladium acetate as a single-source precursor. Thus, pyrolysis in argon at 1100 °C led to nanocomposites consisting of Pd2Si nanocrystallites dispersed in an amorphous SiOC matrix. Exposure of SiPdOC to higher temperatures resulted in the precipitation of PdSi in addition to Pd2Si. The temperature-dependent evolution of the phase composition and microstructure in SiPdOC were analyzed using XRD and TEM respectively and rationalized by a ThermoCalc-based thermodynamic assessment showing the feasibility of the possible reactions. The formation of PdSi was perceived because of the shift in the Pd-Si atomic composition towards the higher Si side, caused by the diffusion of Si present in the matrix into the Pd-Si melt, formed upon the heat-treatment above the melting point (1390 °C) of Pd2Si. Further, Raman spectroscopic investigation indicated that Pd catalytically enhanced the graphitization of the free carbon in SiPdOC ceramics.