From molecular precursors to ultra-high temperature ceramics: A novel synthesis of hafnium carbonitride nanoceramics

Hafnium carbonitride (HfC_xN_1–x) ceramics have drawn considerable interest due to their exceptional mechanical and thermophysical properties. Herein, we report a novel single-source precursor with Hf–N bonds as the main chain and fabricate HfC_xN_1–x ceramics after pyrolysis of the precursor. The synthesis, ceramic conversion, and microstructural evolution of the single-source precursor as well as the derived HfC_xN_1–x ceramics treated under various atmospheres were investigated. The results indicate that in an argon atmosphere, the nitrogen content within HfC_xN_1–x decreases with rising temperature. While under a nitrogen atmosphere, the high concentration of N₂ facilitates the rapid conversion of HfO₂ to Hf₇O₈N₄, which subsequently promotes the transformation of the HfC_xN_1–x solid solution ceramics. During this process, there is also an inhibitory effect of N₂ on the tendency of HfN into HfC. Moreover, the desired chemical composition of HfC_xN_1–x can be regulated by adjusting the N₂ concentration in the heat treatment atmosphere. The present work proposes a novel strategy for the single-source precursor-derived carbonitride ceramics and provides a deep understanding of the preparation and property modulation of HfC_xN_1–x ceramics.