Sintering of Semiconducting BaTiO₃ Doped with Si₃N₄

Abstract

BaTiO₃-ceramics was prepared by the addition of Si₃N₄ or SiO₂ to the starting material and the resistivity was measured. For lower Si contents, and lower sintering temperatures, the room temperature resistivity of the Si₃N₄-doped specimens was lower than that of SiO₂-doped specimens. Observations of surface microstructure for specimens quenched during heating process revealed that marked grain growth took place in specimens doped with 1wt% Si₃N₄ at the eutectic point. No remarkable structural changes were observed in the specimen doped with 1wt% SiO₂. For 3wt% SiO₂ addition only heterogeneous grain growth was observed at the eutectic temperature. When heated in N₂ atmosphere, however, the specimen doped with 1wt% SiO₂ showed marked grain growth, and surface morphology suggested the presence of a liquid phase. Thermal analysis made in the temperature range 25°-1400°C suggested the formation of a larger amount of liquid phase in specimens doped with Si₃N₄ than those doped with SiO₂. These results indicate that nitrogen from Si₃N₄ enhances the grain growth. Resistivity vs. Si content relations may be explained in terms of the liquid phase formed at the eutectic point.