High-dielectric-constant nanograin BaTiO3-based ceramics for ultra-thin layer multilayer ceramic capacitors via grain grading engineering

Four BT-based ceramic samples were prepared using a grain grading approach. ​The bigger-grained (∼100 ​nm) and smaller-grained (∼70 ​nm) BaTiO3 (BT) powders were mixed. The smaller-grained BT powder controlled the average grain size and guaranteed the reliability, while the bigger-grained powder enhanced the dielectric constant. Various percentages of bigger-grained BT powder were introduced to balance the average grain size and the dielectric constant. As the proportion of bigger grains increased, the dielectric constant (εr) improved significantly. The room-temperature εr of 25% bigger-grain mixed BT (2623) was ∼50% higher than that of the sample with a similar average grain size without grain grading. The ceramic mixed with 15% bigger-grained BT showed comprehensive dielectric performance, which met the EIA X5R standard and provided a considerable εr of 1841 along with a low dielectric loss of 0.78%. Notably, the average grain size was 90 ​nm, which favors the applications in ultra-thin multilayer ceramic capacitors.