Evolution of the composition, microstructure and electromagnetic properties of HfOC ceramics with pyrolysis temperature

The evolution of phase composition, microstructure, and dielectric characteristics of HfOC ceramics pyrolyzed at various temperatures was studied in this work. When the pyrolysis temperature increased from 900 to 1500 °C, the composition of HfOC ceramics varies from HfO₂ and amorphous carbon (C_amp) at 900 °C to coexistence of HfO₂, C_amp, and HfC at 1100–1300 °C, and HfC and C_amp at 1500 °C. With the continuous consummation of C_amp, its distribution is transformed from a slice-like structure accumulating around the particles to a shell-like structure wrapping around the particles. The atomic ratios of as-obtained HfOC ceramics are HfO_2.0C_2.8, HfO_1.9C_2.7, HfO_1.0C_1.8, and HfO_0.1C_1.1, respectively, after being pyrolyzed at 900, 1100, 1300, and 1500 °C. As the pyrolysis temperature increases, the average value of the real part increases from 13.5 to 16.5, and the imaginary part rises from 12 to 14. The microwave absorption properties of HfOC ceramics need to be enhanced further in the future work.