A mechanically robust, high electrically and low thermally conducting silicon oxycarbide ceramic composite by spark plasma sintering†

Silicon oxycarbide (SiOC) ceramics derived from pyrolysis of polymer precursors are important for their aerospace, automotive and electronics applications. Here, we investigate the structural and functional properties of a Si–O–C composite obtained via a high-temperature spark plasma sintering process of SiOC powders, derived from the pyrolysis of a polysiloxane polymer. Structural characterization reveals the presence of turbostratic carbon, SiO₂, and SiC domains in the Si–O–C matrix composite. Mechanically, it shows a hardness of ∼5.5 GPa and a Young's modulus of ∼40 GPa. The composite shows semiconducting behavior at room temperature with electrical conductivities of ∼95 S cm⁻¹ (in-plane) and ∼215 S cm⁻¹ (out-of-plane), p-type charges with a carrier density of ∼10²¹ cm⁻³ and a mobility of ∼0.25 cm² V⁻¹ s⁻¹, which remains almost temperature independent. The temperature coefficient of resistivity is found to be a very low value of −0.0012 °C⁻¹. We also measured a cross-plane thermal conductivity of ∼1.14 W m⁻¹ K⁻¹ at 300 K which exhibits temperature-independent behavior. Our observations are valuable for designing oxycarbide ceramic-based energy efficient devices for advanced applications.