Effects of Grain Growth on the Distribution of Nb in BaTiO ₃ Ceramics

Abstract

Measurements of Nb diffusion into large‐ and small‐grained BaTiO 3 disks show a high ratio of grain boundary to bulk diffusivity. Well defined X‐ray diffraction lines are found in Nb‐doped BaTiO 3 only when significant grain growth occurs during sintering. When grain growth of a 0.65 μm grain size powder is limited at ∼1 μm, excess line broadening results. This is attributed to the simultaneous presence of Nb‐free and Nb‐rich regions. Because of its low bulk diffusivity little Nb penetrates into the original BaTiO 3 grain cores, and a solid solution forms only in the regions of recrystallization. When grain growth is limited, the “sintering reaction” results in a non‐homogeneous system; when appreciable grain growth occurs, most of the original grain cores are eliminated and an essentially uniform system is obtained.