Characterization of hexabarium 17-titanate and its effects on the dielectric properties of barium titanate ceramics

The formation of the Ba6Ti17O40 (B6T17) phase is inevitable in BaTiO3 ceramics with excess TiO2. And B6T17 phases in a dendritic morphology were frequently reported. In this study, the formation mechanism for B6T17 having a dendritic morphology, and the effect of this B6T17 phase on the dielectric properties of BaTiO3 ceramics have been investigated.; In non-doped BaTiO3, the B6T17 phase exhibited a needle-like morphology when sintered above the eutectic temperature. The needle-like B6T17 phase was more likely to occur on the as-sintered surface of the sample, as the eutectic melt was squeezed out during sintering and densification. The topotactic relationship between the BaTiO3 and B6T17 phases can be used to interpret the formation mechanism for the needle-like B6T17 morphology.; When BaTiO3 was doped with Nb5+ or other donor dopants (Ta5+, La3+) and sintered in an oxidizing atmosphere, the B6T17 phase exhibited a dendritic morphology. This dendntic morphology was not observed in Co2+ doped samples. The dendritic morphology may be due to the topotactic relationship between the BaTiO 3 and B6T17 phases and the formation of Ti2O9 groups for hexagonal stacking.; Based on experimental results, the B6T17 phase in a dendritic morphology in BaTiO3 ceramics occurs under the following conditions: (1) presence of excess TiO2; (2) sintering above the eutectic temperature to form a eutectic melt; (3) presence of a suitable donor doping level; (4) sintering in an oxidizing atmosphere; and (5) the presence of a fine grain size BaTiO3 matrix.; X-ray diffraction analysis was used to characterize the B6T17 phase. The needle-like B6T17 and the dendritic B6T17 have the same preferred (041) reflection showing that they may have the same mechanism for their formation. The content of B6T17 phase in the BaTiO3 ceramics was also estimated by theoretical calculation and by X-ray diffraction phase analysis using the Rietveld method.; B6T17 is a linear dielectric material, with a dielectric constant of 59. It has a high breakdown strength of 1387 kV/cm. Its coefficient of thermal expansion is 12.5 ppm/K. Field distribution modeling results showed that for a spherical B6T17 particle in the center of a BaTiO3 film, the field enhancement factor is 1.51, while for a B6T17 phase in needle-like morphology, a field enhancement factor of 4.20 was determined. (Abstract shortened by UMI.)...