Fabrication of BaTiO3 nanopowders with high tetragonality via two-step assisted rotary furnace calcination for MLCC applications

Ultrafine ceramic powders with high tetragonality are essential for next-generation multi-layer ceramic capacitors (MLCC). The solid-state reaction synthesis commonly used in industry is challenging to prepare ultra-fine BaTiO3 powders due to issues of the coarse crystallization at high temperature calcinations. In this study, a two-step calcination combining with the rotary furnace was innovatively used to synthesize ultra-fine BaTiO3 powders with uniform particle and high tetragonality. Through the reaction kinetics study, it was found that the rotary furnace increases the point contact area of Ba2+ and Ti4+ by improving the heat transfer efficiency of the solid-phase reaction and decreases the diffusion rate of both, so that the diffusion-nucleation-growth rate is greater than the decomposition rate of BaCO3 to improve the tetragonality of BaTiO3 powders. The optimal process parameters were determined and the reaction mechanism was studied. Particularly, the optimized two-step assisted rotary furnace calcination had succeeded in preparing finer powders with an average particle size of 250 nm and tetragonality (c/a) of 1.0096. The BaTiO3 ultrafine powders sintered at 1200 °C has a ceramic density of 96%, dielectric constant of 9173 at the Curie temperature point (131 °C) and a grain activation energy of 0.821 eV, representing excellent dielectric properties and reliability.