Silicon Nitride Ceramics with Sodium Ion Conductive Grain Boundary Phase

Sodium ion-conductive silicon nitride ceramic with Na₂O–Al₂O₃–SiO₂ glass as the grain boundary phase was fabricated by adding Na₂CO₃, Al₂O₃, and SiO₂ as sintering additives. The electrical conductivity was two and four orders of magnitude higher than that of Si₃N₄ ceramic with Y₂O₃ and Al₂O₃ additives at 100 and 1000°C, respectively. This result clearly indicates that ionic conductivity can be provided to insulating structural ceramics by modification of the grain boundary phase without dispersion of conductive particles.