Grain size engineered high-performance nanograined BaTiO3-based ceramics: Experimental and numerical prediction

The ultra-thin multilayer ceramic capacitors (MLCCs) with layer thickness less than 1 μm or even 0.5 μm are in urgent demand due to the rapid development of modern electronic industries. Notably, the dielectric and ferroelectric properties of nanograined BaTiO₃-based ceramics, which are widely used as dielectric materials in MLCCs, are highly related to grain size. In this work, nanograined BaTiO₃-based ceramics with various grain sizes (50-100 nm) were prepared via the chemical coating method. The grain size effect on the dielectric and energy storage properties were systematically investigated. TEM and EDS images demonstrate that the typical core-shell structure is obtained inside ceramic grains even if the grain size is reduced to 50 nm. The fine-grain ceramic displays a lower maximal polarization but a higher breakdown strength, which ascribes to its weaker ferroelectric contribution and higher grain boundary ratio, respectively. As a result, it is confirmed that there exists an optimal grain size around 70 nm where maximum discharge energy density is achieved under the synergy effect of breakdown strength and polarization, which is also verified by a finite element analysis based on a modified hyperbolic tangent model. All these features provide important guidance towards the design of ultra-thin layer MLCCs by optimizing the dielectric properties and energy storage performance while pursuing miniaturization.