Although ceramic dielectric materials have been extensively explored owing to their numerous advantages, there are still obstacles in the collaborative enhancement of recoverable energy density (W rec ) and efficiency (η). In this work, a combinatorial optimization strategy is proposed to optimize energy storage properties of (K, Na)NbO 3 -based ceramics, that is, drive a specific temperature region between the temperature of maximum dielectric constant and the Burns temperature to room temperature under the guidance of phase field simulation to induce the polar nanoregions, then further improve the breakdown strength by repeated rolling process. As a result, an ultrahigh W rec of 6.7 J cm −3 and a high η of 92% at 600 kV cm −1 are achieved simultaneously in the 0.85K 0.5 Na 0.5 NbO 3 -0.15Bi(Zn 2/3 Ta 1/3 )O 3 ceramic prepared by repeated rolling process, together with excellent temperature stability under 400 kV cm −1 over a temperature range of 25 to 150 °C, outperforming all reported (K, Na)NbO 3based energy storage ceramics. This approach should also be generalizable for designing high-performance dielectrics for electrical energy storage applications.

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In this work, we propose a family of single-node second-order boundary schemes for the lattice Boltzmann method with general collision terms. The construction of the schemes is quite universal and simple, it does not involve concrete lattice Boltzmann models and uses the half-way bounce-back rule as a central step. The constructed schemes are all second-order accurate if so is the bounce-back rule. In addition, the proposed schemes have good stability thanks to convex combinations. The accuracy and stability of several specific schemes are numerically validated for multiple-relaxation-time models in both 2D and 3D.

We propose using the Maxwell iteration to derive the hydrodynamic equations from the lattice Boltzmann equation (LBE) with an external forcing term. The proposed methodology differs from existing approaches in several aspects. First, it need not explicitly introduce multiple-timescales or the Knudsen number, both of which are required in the Chapman-Enskog analysis. Second, it need not use the Hilbert expansion of the hydrodynamic variables, which is necessary in the asymptotic analysis of the LBE. The proposed methodology assumes the acoustic scaling (or the convective scaling) δ(t)∼δ(x), thus δ(t) is the only expansion parameter in the analysis of the LBE system, and it leads to the Navier-Stokes equations in compressible form. The forcing density derived in this work can reproduce existing forcing schemes by adjusting appropriate parameters. The proposed methodology also analyzes the numerical accuracy of the LBE. In particular, it shows the Mach number Ma should scale as O(δ(t)(1/3)) to maintain the truncation errors due to Ma and δ(t) in balance when δ(t)→0, so that the LBE can converge to the expected hydrodynamic equations effectively and efficiently.

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