Enhanced thermal conductivity in Si 3 N 4 ceramic with the addition of Y 2 Si 4 N 6 C

Si 3 N 4 ceramic was densified at 1900°C for 12 hours under 1 MPa nitrogen pressure, using MgO and self‐synthesized Y 2 Si 4 N 6 C as sintering aids. The microstructures and thermal conductivity of as‐sintered bulk were systematically investigated, in comparison to the counterpart doped with Y 2 O 3 ‐MgO additives. Y 2 Si 4 N 6 C addition induced a higher nitrogen/oxygen atomic ratio in the secondary phase by introducing nitrogen and promoting the elimination of SiO 2 , resulting in enlarged grains, reduced lattice oxygen content, increased Si 3 N 4 ‐Si 3 N 4 contiguity and more crystallized intergranular phase in the densified Si 3 N 4 specimen. Consequently, the substitution of Y 2 O 3 by Y 2 Si 4 N 6 C led to a great increase in ~30.4% in thermal conductivity from 92 to 120 W m −1  K −1 for Si 3 N 4 ceramic.