Barium titanate (BaTiO₃, BT) is one of the key dielectric materials for multilayer ceramic capacitor (MLCC) industry. To meet the development trend of miniaturization and high capacity of MLCC, the sintered ceramic with nanosized grain is required. Herein, we demonstrate a controllable preparation of finegrain BaTiO₃ ceramic by using sol-gel glass encapsulation strategy to suppress the growth of nanocrystal during sintering. It is found that the BaTiO₃ nanocrystal with average lateral particle size of 70 nm and 200 nm (BT70 and BT200) can be coated with Bi₂O₃-B₂O₃-SiO₂ (BBS) glass shell to form core-shell structures. The fine crystal of barium titanate ceramics can be achieved under different encapsulation quantities and sintering temperature. However, BT70, with a larger specific surface area, higher reactivity, and lower crystallinity, was more prone to hydrolyze in the sol-gel process, leading to the formation of a new phase after sintering, Ba₂TiSi₂O₈, which adversely affected both the sintering behavior and dielectric properties. On the other hand, BT200 exhibited lower possibility to hydrolyze in the sol-gel process, resulting in single-phase ceramics after sintering. When the BT200 coated with 5% (in mass) BBS was sintered at 1100 ℃, a dense BaTiO₃ ceramic were obtained, with dielectric constant of 1194.23 and loss of 0.0139 at room temperature and 1 kHz. Therefore, this work provides a robust strategy for suppressing the nanocrystal growth during sintering for MLCC applications.

The influence of Al/(Al+Si) molar ratio on the short-/mid-range structure and elastic modulus of alkali aluminosilicate glass was investigated via molecular dynamics simulation. The results show that the non-bridging oxygen in the glass network transforms to bridging oxygen and triple-bonded oxygen as the ratio of Al/(Al+Si) increases. When the ratio of Al/(Al+Si)>0.3, the non-bridging oxygen mainly changes to triple bond oxygen. The structural units transform to a high degree of polymerization, the connectivity of the glass network increases, and the elastic modulus of the glass increases as the ratio of Al/(Al+Si) increases. The elastic modulus of glass increases with the increase of Al/(Al+Si) molar ratio. The data calculated by the simulation are consistent with the experimental results, thus verifying a feasibility of using the molecular dynamics simulation to improve the glass composition.