Multilayer ceramic capacitors (MLCCs) are attracting great interest recently, especially in energy-storage applications due to their high volumetric capacitance, high power density, and fast charge-discharge capability. However, the low dielectric breakdown strength of ferroelectric ceramics always leads to a low discharge energy density, which limits their applications in high-voltage energy-storage systems. In this work, a phase-field electromechanical breakdown model is introduced to give a fundamental understanding of the dielectric breakdown behavior of MLCCs and provide a resource-efficient design strategy for the structure of MLCCs to enhance their dielectric breakdown strength and discharge energy density. Three types of margin lengths of 100 μm, 200 μm, and 400 μm are designed and applied on the MLCCs consisting of ten dielectric layers with the single-layer thickness of 11 μm, to confirm and practice our phase-field breakdown model. A large discharge energy density of 7.8 J cm−3 can be achieved under the applied electric field of 790 kV/cm, together with a high efficiency of 88% in a 400 μm-margin-length MLCC.

In this study, SrZrO 3 doped K 0.5 Na 0.5 NbO 3 ceramics with Cu, Sn, and Mn as sintering aid are prepared to modulate the temperature stability by conventional solid-state sintering, and samples are denoted as KNNC-100xSZ, KNNS-100xSZ, and KNNM-100xSZ, respectively, where x is the doping amount. The average grain size of the KNNC-12.75SZ sample was ~150 nm. The dielectric constant of KNNC-13.00SZ was 2072 and its dielectric loss was 1.8% at room temperature, with a wide temperature stability range from −55°C to 220°C satisfying the X9R criteria. The discharge energy density of KNNC-12.75SZ reached 1.47 J/cm 3 at room temperature; therefore, the modified KNN is a promising candidate for X9R dielectrics with a fine grain structure and potential anti-reduction capability due to the absence of variable valence elements. The modified KNN can also be applied to energy storage capacitors subjected to high working temperatures.

We fabricated x(Bi0.5Na0.5)TiO3–(1−x)[BaTiO3–(Bi0.5Na0.5)TiO3–Nb] (BNT‐doped BTBNT‐Nb) dielectric materials with high permittivity and excellent high‐temperature energy storage properties. The initial powder of Nb‐modified BTBNT was first calcined and then modified with different stoichiometric ratios of (Bi0.5Na0.5)TiO3 (BNT). Variable‐temperature X‐ray diffraction (XRD) results showed that the ceramics with a small amount of BNT doping consisted of coexisting tetragonal and pseudocubic phases, which transformed into the pseudocubic phase as the test temperature increased. The results of transmission electron microscopy (TEM) showed that the ceramic grain was the core‐shell structure. The permittivity of the 5 mol% BNT‐doped BTBNT‐Nb ceramic reached up to 2343, meeting the X9R specification. The discharge energy densities of all samples were 1.70‐1.91 J/cm3 at room temperature. The discharge energy densities of all samples fluctuated by only ±5% over the wide temperature range from 25°C to 175°C and ±8% from 25°C to 200°C. The discharge energy density of the 50 mol% BNT‐doped BTBNT‐Nb ceramic was 2.01 J/cm3 at 210 kV/cm and 175°C. The maximum energy efficiencies of all ceramics were up to ~91% at high temperatures and were much better than those at room temperature. The stable dielectric properties within a wide temperature window and excellent high‐temperature energy storage properties of this BNT‐doped BTBNT‐Nb system make it promising to provide candidate materials for multilayer ceramic capacitor applications.

Low energy conversion efficiency from absorbed photon to catalytic species remains the major obstacle for real application of photocatalysis. In recent years, the introduction of built-in electric field is proved...

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