Synthesis and high-temperature evolution of single-phase amorphous Si–Hf–N ceramics

Novel amorphous polymer-derived Si–Hf–N ceramics were prepared via ammonolysis of single-source precursors which were synthesized by the chemical reaction of a commercially available perhydropolysilazane (PHPS) with different amounts of tetrakis(dimethylamido) hafnium(IV) (TDMAH). The prepared Si–Hf–N materials were annealed in nitrogen atmosphere at different temperatures ranging from 1100 °C to 1800 °C and investigated with respect to their chemical composition, crystallization behavior and phase evolution. The single-source precursors converted upon heat treatment in ammonia environment at 1000 °C into amorphous single-phase ceramics and remained amorphous even after annealing at 1400 °C in nitrogen atmosphere. Electron microscopy investigation showed that the annealing of the highly homogeneous single-phase Si–Hf–N induces local enrichment (clustering) of Hf, leading to amorphous HfN/SiNx nanocomposites. Annealing in nitrogen at 1600 °C leads to the crystallization of HfN and Si3N4. The results of the present work emphasize a convenient preparative access to silicon–metal–nitride nanocomposites from suitable single-source precursors.