MnO2 as an effective sintering aid for difficult-to-sinter LiTaO3-based ceramics: Densification and dielectric properties

Abstract

Dense polycrystalline LiTaO3 (LTO) ceramics have rarely been reported due to their poor sinterability, although LTO single crystals are among the well-known piezoelectric and ferroelectric. In this study, LiTaO3-based ceramics with 3 wt% and 5 wt% MnO2 (referred to 3MLT and 5MLT, respectively) are prepared by pressure-less sintering at different temperatures of 1200 °C, 1250 °C, 1300 °C and 1350 °C, respectively, and the effects of sintering temperature on the sinterability, microstructure development and dielectric properties are investigated. The sintered density of the LiTaO3-based ceramics increases significantly at first with increasing of sintering temperature, and then decreases afterwards. Sintered densities of ∼92.6% and 93.1% were achieved for 3MLT and 5MLT sintered at 1250 °C, respectively, and both compositions show a rather homogeneous and well-developed grained microstructure. A moderate amount of MnO2 was entered into the LiTaO3 lattice to form a solid solution, however, Mn3O4 was formed at the grain boundaries and junctions when excess amount of MnO2 added, where the solid solubility is dependent on the sintering temperature. The dielectric properties of both 3MLT and 5MLT ceramics, studied as a function of frequency, show a strong dependence on sintering temperature, where the dielectric constant increases first and then decreases with the increasing of sintering temperature. The dielectric loss first decreases and then increases with the increasing of sintering temperature. Both 3MLT and 5MLT demonstrate a maximum in dielectric constant when sintered at 1250 °C and 1350 °C, respectively. The lowest dielectric loss could be obtained at 1250 °C, which was selected as the optimum sintering temperature for both compositions.