Atmospherically hydrothermal assisted solid-state reaction synthesis of ultrafine BaTiO3 powder with high tetragonality

Ultrafine ceramic powders with high tetragonality are the fundamental for the multi-layer ceramic capacitors (MLCCs). In this study, an efficient method of atmospherically hydrothermal assisted solid-state synthesis for ultrafine BaTiO₃ particles is presented. The BaTiO₃ nanopowders with homogeneous distribution, a mean particle size ~ 260 nm and high tetragonality of 1.0095 were obtained by at the optimal parameters of hydrothermal time of 6 h, Ba(OH)₂·8H₂O/BaCO₃ = 0.25/0.75 and calcination temperature of 1000 ^oC. XRD and HRTEM analyses revealed a “core-shell” structure of TiO₂@BaTiO₃ formed in the first-step hydrothermal process, which reduces the diffusion distance between BaCO₃ and TiO₂, resulting in a lower calcination temperature at the second-step solid-state reaction. Compared with pure hydrothermal and solid-state reaction processes, the atmospherically hydrothermal assisted solid-state synthesis in this study shows larger ability for improving the particle size distribution and the tetragonality, reducing defects of BaTiO₃ particles. In particular, the grain size, sintering density, and dielectric constant at the Curie temperature of BaTiO₃ ceramics are 1.93 μm, 98%, and 7066, respectively. In the solid-state reaction stage, the lattice diffusion distance from BaO to TiO₂ tends to decrease due to the formation of BaTiO₃ shells, thus, high tetragonal and relatively small particle size of BaTiO₃ powder was synthesized. This work presents a method for preparing ultrafine BaTiO₃ powders with large tetragonality for MLCCs.