Two sets of (Mg,Y)-doped BaTiO 3 samples were prepared to investigate the effects of the core/shell volumetric ratio on the dielectric-temperature behavior of BaTiO 3 : one set with samples of the same grain size but different core sizes and the other with samples of the same core size but different shell thicknesses. The microstructural variation of the samples was characterized and their dielectric properties were measured. For both sets of samples, the temperature stability of the dielectric properties was generally improved with a reduction of the volumetric shell ratio regardless of the grain and core sizes. There existed, however, a limit of the reduction; for the studied range, shell thickness of one third of the core radius appeared to be an optimum thickness for the given amounts of dopants. It was concluded that the volumetric shell ratio should be optimized so as not to exceed a specific limit, for our case two thirds of the grain volume, to secure temperature stability of the dielectric properties of BaTiO 3 .
The dedensification of BaTiO 3 by residual BaCO 3 has been demonstrated. By changing compaction pressure or presintering time in H 2 , samples with different relative densities were prepared. During subsequent sintering at 13501C in air, abnormal grain growth, which was suggested to be a cause of dedensification, was completely suppressed. As the presintering time or compaction pressure increased, the relative density of the presintered samples also increased. During sintering in air, however, the relative density of the samples decreased and large pores and cracks formed in the presintered samples with high relative density. This tendency intensified with increasing relative density of the presintered samples. These results indicate that the decomposition of residual BaCO 3 caused the dedensification of BaTiO 3 . The dedensification effect of residual BaCO 3 also critically depended upon the time for pore closure during sintering.
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