Microstructures of core-shell or duplex-structured BaTiO3 materials were examined in detail by transmission electron microscopy (TEM) to correlate the microstructures of these materials with their dielectric properties. In core-shell structured materials, the grains, which contain a paraelectric shell surrounding the ferroelectric core, are frequently observed. The thickness of the shell decreased as the grains grew larger, whenever the samples were over-fired or were incorporated with SiO2 sintering aids. The variation of the core-shell microstructure of the samples with the thermal history of the materials clearly explains the extreme sensitivity of the dielectric constant-temperature (K-T) properties for these materials to processing parameters. In contrast, for duplex-structured materials, the heavily doped constituents of the samples remained as fine grains with paraelectric phase, whereas the lightly doped constituents of the materials grew, resulting in a core-shell microstructure via the incorporation of the MgO species. The K-T behavior of the duplex-structured materials is less process dependent than that of the core-shell structured ones.
Japanese journal of applied physics 43 pt.1(1), pp.226-231