Dielectric capacitors with ultrahigh power densities are fundamental energy storage components in electrical and electronic systems. However, a long-standing challenge is improving their energy densities. We report dielectrics with ultrahigh energy densities designed with polymorphic nanodomains. Guided by phase-field simulations, we conceived and synthesized lead-free BiFeO3-BaTiO3-SrTiO3 solid-solution films to realize the coexistence of rhombohedral and tetragonal nanodomains embedded in a cubic matrix. We obtained minimized hysteresis while maintaining high polarization and achieved a high energy density of 112 joules per cubic centimeter with a high energy efficiency of ~80%. This approach should be generalizable for designing high-performance dielectrics and other functional materials that benefit from nanoscale domain structure manipulation.

Oxide-based ceramics could be promising thermoelectric materials because of their thermal and chemical stability at high temperature. However, their mediocre electrical conductivity or high thermal conductivity is still a challenge for the use in commercial devices. Here, we report significantly suppressed thermal conductivity in SrTiO3-based thermoelectric ceramics via high-entropy strategy for the first time, and optimized electrical conductivity by defect engineering. In high-entropy (Ca0.2Sr0.2Ba0.2Pb0.2La0.2)TiO3 bulks, the minimum thermal conductivity can be 1.17 W/(m·K) at 923 K, which should be ascribed to the large lattice distortion and the huge mass fluctuation effect. The power factor can reach about 295 μW/(m·K2) by inducing oxygen vacancies. Finally, the ZT value of 0.2 can be realized at 873 K in this bulk sample. This approach proposed a new concept of high entropy into thermoelectric oxides, which could be generalized for designing high-performance thermoelectric oxides with low thermal conductivity.

Layered oxyselenides have been widely investigated as promising thermoelectric materials due to their unique merits such as super‐lattice structural features and intrinsic complexity, which contributes to low thermal conductivity and easily controllable electrical properties. Newly developed Bi2LnO4Cu2Se2 (Ln stands for lanthanide) oxyselenides are found to be potential thermoelectric systems since they have excellent electrical conductivity over 103 S cm−1. In this work, unique energy and time‐saving method combined self‐propagating high‐temperature synthesis (SHS) with spark plasma sintering (SPS) is adopted to successfully prepare a highly pure Bi2LnO4Cu2Se2 instead of a traditional solid‐state reaction. To explore the most suitable lanthanide for Bi2LnO4Cu2Se2, thermoelectric performance in a wide temperature range (300 to 923 K) of Bi2LnO4Cu2Se2 (Ln = Nd, Sm, Eu, Gd, Tb, Dy, Ho, and Er) is deeply evaluated and studied. Ultimately, with a relatively high electrical conductivity, moderate Seebeck coefficient, and extremely low thermal conductivity, a maximum ZT value of ≈0.27 at 923K is achieved in Bi2DyO4Cu2Se2, which is 4 times larger than that of the ever‐reported Bi2YO4Cu2Se2 and proves a potential thermoelectric system for further investigation. This work may provide some enlightenment and broaden the horizon in finding new thermoelectric materials, especially for complex layered compounds.

Zinc oxide (ZnO) is a potential thermoelectric material with good chemical and thermal stability as well as an excellent Seebeck coefficient. However, the extremely low carrier concentration brings poor electrical transport properties. Although Gallium (Ga) doping could increase the carrier concentration of ZnO film, its thermoelectric performance is still limited due to the deteriorated Seebeck coefficient and enhanced thermal conductivity. Interface engineering is an effective strategy to decouple electron-phonon interaction for thermoelectric materials. Thus, in this work, GZO (Ga-doped ZnO)/NAZO (Ni, Al co-doped ZnO) multilayer films were designed to further improve the thermoelectric properties of GZO films. It was found that GZO/NAZO multilayer films possessed better electrical conductivity, which was attributed to the increased carrier concentration and Hall mobility. Meanwhile, benefiting from the energy filtering that occurred at GZO/NAZO interfaces, the density of states effective mass increased, resulting in comparable Seebeck coefficient values. Ultimately, an enhanced power factor value of 313 μW m−1 K−2 was achieved in the GZO/NAZO multilayer film, which is almost 46% larger than that of GZO film. This work provides a paradigm to optimize the thermoelectric performance of oxide films and other thermoelectric systems by multilayer structure design with coherent interfaces.

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