Synergistic Defect Chemistry and Strain Engineering via Coating Layer Design for Enhanced Electrical Property of Nano-BaTiO3 Sintered in Reducing Atmosphere.

The semiconducting phenomenon of BaTiO3 induced by sintering in reducing atmospheres is the key bottleneck restricting its application in high-performance base metal electrode multilayer ceramic capacitors (BME-MLCCs). In this work, a surface modification strategy was innovatively developed via defect regulation to improve the reduction resistance of ceramic powders. A Ba-rich component (Ba/Ti = 1.02) was coated onto 100 nm BaTiO3 powders using the sol-gel method, denoted as BT@x(1.02) (x = 0-1.0). As x increases, the concentration of oxygen vacancies in ceramics sintered in a reducing atmosphere is significantly reduced, accompanied by a substantial increase in resistivity. Complex impedance spectroscopy analysis indicates that an increase in the coating amount significantly enhances the conductivity activation energies of both grains and grain boundaries. High strain was observed near the grain boundaries of BT@1.0 (1.02) ceramics. Electron energy loss spectroscopy (EELS) analysis indicated that this strain originated from the non-uniform distribution of the Ba/Ti ratio. From the grain boundary to the interior of the grain, the Ba/Ti ratio gradually decreases, and the polarization intensity increases accordingly. Furthermore, EELS results reveal oxygen enrichment at 200 nm from the grain boundary. Based on first-principles calculations, it is inferred that such oxygen originates from the grain interior, and the defect layer prevents oxygen from diffusing out of the grains, thereby enhancing the reduction resistance of the ceramic. This study provides a strategy for the development of high-performance reduction-resistance BaTiO3 ceramics.