Phase evolution of SiOC‐based ceramic nanocomposites derived from a polymethylsiloxane modified by Hf‐ and Ti‐alkoxides

SiOC/HfO 2 ‐based ceramic nanocomposites with in situ formed HfO 2 nanoparticles were prepared via a single‐source precursor (SSP) approach starting from a polymethylsilsesquioxane (PMS) modified by Hf‐ and Ti‐alkoxides. By varying the alkyl‐group of the employed Hf‐alkoxides, SiOC/HfO 2 ‐based ceramic nanocomposites with different HfO 2 polymorphs formed via thermal decomposition of the SSP under the same heat‐treatment conditions. Using PMS chemically modified by Hf(O n Bu) 4 , tetragonal HfO 2 phase was formed after the synthesis at 1100°C in Ar, whereas both, tetragonal and monoclinic HfO 2 nanocrystals, were analyzed when replacing Hf(O n Bu) 4 by Hf(O i Pr) 4 . After oxidation of the synthesized nanocomposites in air at 1500°C, a facile formation of oxidation‐resistant HfSiO 4 (hafnon) phase occurred by the reaction of HfO 2 nanocrystals with silica present in the SiOC nanocomposite matrix derived from Hf(O i Pr) 4 ‐modified SSPs. Moreover the amount of hafnon is dramatically increased by the additional modification of the polysiloxane with Ti‐alkoxides. In contrast, ceramic nanocomposites derived from Hf(O n Bu) 4 ‐modified SSPs, almost no HfSiO 4 is detected after oxidation at 1500°C even though in the case of Ti‐alkoxide‐modified single‐source precursor.