Hydrothermal preparation of highly tetragonal BaTiO ₃ nanopowders for ultra-thin multilayer ceramic capacitors

BaTiO 3 nanopowders with high tetragonality ([Formula: see text] are essential for fabricating ultra-thin multilayer ceramic capacitors (MLCCs). The hydrothermal method commonly employed in the industry presents challenges in synthesizing BaTiO 3 nanopowders, primarily due to the occurrence of inner defects during the reaction process. In this work, BaTiO 3 nanopowder with an average particle size of 165[Formula: see text]nm, tetragonality ([Formula: see text] of 1.0089 and little crystal defects were prepared under the reaction condition of 240 ∘ C for 72[Formula: see text]h, mineralizer of 3[Formula: see text] [Formula: see text] and Ba/Ti stoichiometric ratio of 2. The formation mechanism of BaTiO 3 was explored by detecting the reaction process and conducting kinetic analysis, and the influence of hydrothermal reaction conditions on the tetragonality ([Formula: see text] values of BaTiO 3 was analyzed. A one-step hydrothermal reaction kinetics analysis reveals that dissolution-precipitation mechanism dominates the generation and growth of BaTiO 3 nuclei. Especially, the optimized two-step sintering had succeeded in preparing ultra-fine BaTiO 3 ceramics with a relative density of 94% and the maximum dielectric constant of 2476. In addition, BaTiO 3 -based ultra-thin MLCCs with X7R ([Formula: see text]–[Formula: see text]C, [Formula: see text]) and excellent reliability have been successfully manufactured. This work provides a comprehensive picture illustrating the significant role of reaction parameters in one-step hydrothermal method for BaTiO 3 nanopowders with higher tetragonality, and points out an avenue to obtain low thermal conductivity in BaTiO 3 -based ultra-thin MLCCs dielectric materials.