Effect of carbothermal reduction on microstructure, oxygen concentration, and thermal conductivity of Si 3 N 4 ceramics

Abstract This study elucidates the role of carbothermal reduction in tailoring the microstructure, oxygen concentration, and thermal conductivity of Si₃N₄ ceramics synthesized via two‐step gas pressure sintering. Carbon incorporation promoted the evolution of elongated β‐Si₃N₄ grains and altered the nature of intergranular phases. Electron energy loss spectroscopy (EELS) revealed substantial lattice oxygen depletion in C‐doped specimens, alongside a pronounced diffusion gradient from grain interiors to boundaries in undoped samples—indicative of oxygen redistribution driven by concentration gradients. These modifications, combined with thinner grain boundary films and a reduced volume fraction of secondary phases, substantially boosted heat conduction. As a result, the thermal conductivity of the C‐doped ceramic reached 97 W·m⁻¹·K⁻¹, representing a 54% enhancement over its undoped counterpart. This work underscores the efficacy of carbothermal reduction as a microstructural and chemical engineering approach to advance the thermal performance of Si₃N₄ ceramics for next‐generation thermal management technologies.