Aqueous-phase synthesis of hafnium carbonitride precursors via bidentate ligand coordination

The rapid advancement of hypersonic aerospace technologies greatly demands the development of ultra-high temperature ceramics. Among them, hafnium-based ceramics such as hafnium carbide (HfC) and hafnium carbonitride (HfC_xN_1-x) are promising candidates due to their high melting points, hardness, and excellent ablation resistance. However, the design and control of polymer-derived precursors for hafnium carbonitride has not been fully researched. Here, we report an aqueous-phase synthesis of HfC_xN_1-x precursor using ethylenediamine (EDA) in combination with cellulose. EDA, a bidentate ligand, coordinates with Hf as well as cellulose, thus forming polymeric networks and facilitating the generation of an amorphous carbon shell during heat treatment. Notably, induced Hf-N bonds promotes the intermediate formation of Hf₂ON₂ and HfN phases hence lowering the energy barrier for HfC_xN_1-x phase evolution. Finally, HfC_xN_1-x nanoparticles heat-treated at 1400 °C were sintered at 2100 °C, confirming the sintering feasibility of the aqueous-phase prepared precursors.