Microstructural Investigation of Ba(Ti_((1-x))Mn_x)O_3 Ceramics with 6H-and 12R-Polytypes

摘要

Ba(Ti_(1-x)Mn_x)O_3 ceramics were synthesized by a traditional solid-state reaction. The Ba(Ti_(1-x)Mn_x)O_3 samples with x = 0.15, 0.3, 0.4, and 0.5 of MnO, Mn_2O_3, and Mn_3O_4 were sintered at 1450℃ for 2 h, then cooled to room temperature to obtain hexagonal barium titanate. The microstructures and dielectric properties of the Ba(Ti_(1-x)Mn_x)O_3 samples were analyzed by dielectric property measurement, X-ray diffractometry, scanning electron microscopy, and transmission electron microscopy (TEM). The results showed that the lattice parameters decrease as the x value increases from 0.15 to 0.5, and a secondary phase, which is similar to BaFeO_3 structure (JCPDS 74-0646), was detected at x = 0.5. With an increasing x, the grains developed a plate-like morphology. For samples with MnO additive, the secondary phase, which is similar to Ba_2TiO_4 structure (JCPDS 38-1481), was detected on the grain boundaries due to the excess of divalent Ba ions. For samples with Mn_2O_3 and Mn_3O_4 additives, the liquid phase and nanocrys-talline Mn_2O_3 grains were detected due to the excess of Ti and Mn atoms. For dielectric properties, the quality factor (Q × f) reaches the maximum value (18344 GHz) at x = 0.3 for the addition of Mn_3O_4. The TEM analysis was focused on the Ba(Ti_(0.5)Mn_(0.5))O-3 specimens in order to identify the relationship between the 6H- and 12R-structures, and their formation mechanism.