Improved thermal conductivity of β‐Si3N4 ceramics by lowering SiO2/Y2O3 ratio using YH2 as sintering additive

A two‐step sintering process was conducted to produce β‐Si3N4 ceramics with high thermal conductivity. During the first step, native SiO2 was eliminated, and Y2O3 was in situ generated by a metal hydride reduction process, resulting in a high Y2O3/SiO2 ratio. The substitution YH2 for Y2O3 endow Si3N4 ceramics with an increase of 29% in thermal conductivity from 95.3 to 123 W m−1 K−1 after sintered at 1900°C for 12 hours despite an inferior sinterability. This was primarily attributed to the purified enlarged grains, devitrified grain boundary phase, and reduced lattice oxygen content in the YH2‐MgO‐doped material. During the first sintering step, native SiO2 was eliminated, and Y2O3 was in situ generated by a metal hydride reduction process. During the second sintering step, the phase transformation and grain growth occurred via the dissolution‐reprecipitation mechanism in an oxygen‐lacked liquid phase. Dense β‐Si3N4 ceramics with purified enlarged grains, devitrified grain‐boundary phase, and reduced lattice oxygen content was obtained.