Effect of annealing time on the structure and conductivity of amorphous polycarbosilane-derived silicon carbide ceramics

The isothermal evolution of free carbon structure and conductivity of polycarbosilane-derived SiC(O) ceramics pyrolyzed at 1100 °C, 1200 °C, and 1300 °C for 3–55 h was systematically investigated using different characterization methods, which include X-ray photoelectron spectrophotometer (XPS), Raman spectroscopy, Electron Paramagnetic Resonance (EPR), and Transmission electron microscope (TEM). At 1100 °C, increasing annealing time led to structural rearrangement of free carbon, anti-growth behavior, higher degree of order, and increasing and then decreasing number of defects. At 1200 °C, a complex structural evolution of free carbon was observed, which followed the sp³-to-sp² transition and increased the ordering degree. At 1300 °C, increasing annealing time resulted in both lateral growth and increasing ordering of free carbon, which enhanced the carbon cluster size and decreased the number of defects. Enhanced sample conductivity with prolonged annealing time was observed and is discussed based on structural evolution of SiC(O) ceramics at different temperatures.