Sintering Characteristics in the BaTiO3–Nb2O5–Co3O4 Ternary System: II, Stability of So‐called “Core–Shell” Structure

Publisher Website
Google Scholar
Abstract
The sintering characteristics and the reaction of additives with BaTiO3 (BT) were examined for two materials having Nb‐rich composition (Comp.N) and Co‐rich composition (Comp.C) to elucidate the relation between the stability of the core–shell microstructure and the Nb/Co ratio in the BT–Nb2O5–Co3O4 system. TEM observation revealed that the concentration gradient of Nb and Co existed in the shell region although Nb and Co macroscopically distributed homogeneously. X‐ray diffraction analysis showed that the shell formation preceded the densification and completed at about 1280°C for both Comp.N and Comp.C as determined from differential scanning calorimetry. A diffusion couple experiment disclosed that Co had a larger diffusivity than Nb and that the diffusion of Co was suppressed when the sample was codoped with a sufficient amount of Nb. On the basis of these experimental results, new mechanisms of the formation and collapse of core–shell structure in the BT–Nb2O5–Co3O4 system were proposed.