Dielectric capacitors with high energy density and low energy loss are of great importance in high power electric and electronic systems. Traditional BaTiO 3 (BT) or its solid solutions have been widely explored as high energy density materials owing to their notably high dielectric constants. However, these materials often suffer from significant drawbacks of strong dielectric nonlinearity, low breakdown strength and high hysteresis loss, limiting the energy storage density and energy utilization efficiency. In this study, by using core-satellite structured nanocubic SrTiO 3 (ST) decorated BT assemblies, a composite capacitor with enhanced breakdown strength and weaker dielectric nonlinearity was successfully fabricated in contrast with the pure ferroelectric BT ceramic, resulting in elevated energy storage density and high energy efficiency as extracted from the polarization-electric field loops. The mechanism behind the improved electric and dielectric performances was discovered to be the remarkable suppression of grain size owing to the existence of the ST nanocubes and also the ferroelectric relaxor behaviors arising from the local compositionally graded structure due to the controlled sintering and modulated diffusion of Sr. This work provided a new approach for fabrication of dielectric materials with promising high energy density and low loss.
GN/BT nanocomposites were fabricated via colloidal processing methods, and ceramics were sintered through two-step sintering methods. The microstructure and morphology were characterized by X-ray diffraction, high-resolution transmission electron microscopy, and field emission scanning electron microscopy. XRD analysis shows that all samples are perovskite phases, and the lattice parameters a and c almost decrease linearly with the increase of graphene nanosheets. The dielectric properties were tested by using precision impedance. The maximum dielectric constant at the Curie temperature for the nanocomposites with graphene addition of 3 wt % is about 16,000, almost 2 times more than that of pure BaTiO3 ceramics. The relaxation, band structure, density of states, and charge density distribution of GN/BT superlattices were calculated using first-principles calculations for the first time, and results showed the strong hybrid interactions between C 2p states and O 2p and Ti 3d orbitals.
Two‐step sintering (TSS) in a reducing atmosphere has been employed to obtain fine‐grain BaTiO3 ceramics with a core‐shell microstructure, a more uniform grain‐size distribution, and superior reliability for multilayer ceramic capacitor applications. Compared to ceramics of the same composition conventionally sintered for about the same time, TSS ceramics feature a thinner shell thickness thus a stronger dopant localization, which leads to a lower VnormalO∙∙ concentration, higher internal resistance and more dopant‐VnormalO∙∙ association. Improved reliability is manifest in a 50% higher breakdown strength at ambient temperature and a 400% longer endurance time to withstand DC stress at 185°C, in addition to a less field‐and‐temperature‐dependent capacitance. A scaling analysis of the VnormalO∙∙ redistribution and endurance dynamics identifies VnormalO∙∙ transmission across the shell‐grain‐boundary region as the critical element beneficially impacted by core‐shell structure and two‐step sintering.
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