The development of lead-free bulk ceramics with high recoverable energy density (W_rec) is of decisive importance for meeting the requirements of advanced pulsed power capacitors toward miniaturization and integration. However, the W_rec (<2 J cm⁻³) of lead-free bulk ceramics has long been limited by their low dielectric breakdown strength (DBS < 200 kV cm⁻¹) and small saturation polarization (P_s). In this work, a strategy (compositions control the grain size of lead-free ceramics to submicron scale to increase the DBS, and the hybridization between the Bi 6p and O 2p orbitals enhances the P_s) was proposed to improve the W_rec of lead-free ceramics. (K_0.5Na_0.5)NbO₃–Bi(Me_2/3Nb_1/3)O₃ solid solutions (where Me²⁺ = Mg and Zn) were designed for achieving large P_s, and high DBS and W_rec. As an example, (1 − x)(K_0.5Na_0.5)NbO₃–xBi(Mg_2/3Nb_1/3)O₃ (KNN–BMN) ceramics were prepared by using a conventional solid-state reaction process in this study. Large P_s (41 μC cm⁻²) and high DBS (300 kV cm⁻¹) were obtained for 0.90KNN–0.10BMN ceramics, leading to large W_rec (4.08 J cm⁻³). The significantly enhanced W_rec is more than 2–3 times larger than that of other lead-free bulk ceramics. The findings in this study not only provide a design methodology for developing lead-free bulk ceramics with large W_rec but also could bring about the development of a series of KNN-based ceramics with significantly enhanced W_rec and DBS in the future. More importantly, this work opens a new research and application field (dielectric energy storage) for (K_0.5Na_0.5)NbO₃-based ceramics.

Ceramic-based dielectric materials are regarded as the best candidates for advanced pulsed power capacitors because of their excellent mechanical and thermal properties. Nevertheless, lead-free bulk ceramics show relatively low recoverable energy storage density (W_rec < 2 J cm⁻³) owing to their low dielectric breakdown strength (DBS < 200 kV cm⁻¹). In order to significantly increase W_rec, we proposed a strategy (compositions drive the grain size to submicrometer) to improve the DBS of lead-free ceramics. In this work, (1 − x)(K_0.5Na_0.5)NbO₃–xSrTiO₃ (KNN–ST) ceramics were chosen as a representative to verify the validity of this strategy. The (1 − x)KNN–xST ceramics (x = 0.15 and 0.20) with submicrometer grains (about 0.3 μm) were prepared using pressureless solid state sintering. A large W_rec (4.03 J cm⁻³) and DBS (400 kV cm⁻¹ with a thickness of 0.2 mm) were achieved for 0.85KNN–0.15ST ceramics. The value of 4.03 J cm⁻³ is superior to all other W_rec in lead-free bulk ceramics and 2–3 times larger than that of other lead-free bulk ceramics. A large W_rec (3.67 J cm⁻³) and energy storage efficiency (72.1%) were simultaneously achieved for 0.80KNN–0.20ST ceramics. The results confirm that the (1 − x)KNN–xST ceramics (x = 0.15 and 0.20) are desirable materials for advanced pulsed power capacitors. The findings in this study could push the development of a series of KNN-based ceramics with enhanced DBS and W_rec in the future. On the other hand, this work could broaden the applications of KNN materials in a new field.

Solid-state dielectric energy storage is the most attractive and feasible way to store and release high power energy compared to chemical batteries and electrochemical super-capacitors. However, the low energy density (ca. 1 J cm⁻³) of commercial dielectric capacitors has limited their development. Dielectric materials showing field induced reversible phase transitions have great potential to break the energy storage density bottleneck. In this work, dense AgNbO₃ ceramic samples were prepared successfully using solid state methods. Ferroelectric measurements at different temperatures reveal evidence of two kinds of polar regions. One of these is stable up to 70 °C, while the other remains stable up to 170 °C. The associated transition temperatures are supported by second harmonic generation measurements on poled samples and are correlated with the occurrence of two sharp dielectric responses. The average unit cell volume is seen to increase with increasing DC field and has been interpreted in terms of increasing levels of structural disorder in the system. At a high electric field the structure becomes ferroelectric with high polarization. This field induced transition exhibits a recoverable energy density of 2.1 J cm⁻³, which represents one of the highest known values for lead-free bulk ceramics.

With the urgent demand for generalized deep models, many pre-trained big models are proposed, such as bidirectional encoder representations (BERT), vision transformer (ViT), generative pre-trained transformers (GPT), etc. Inspired by the success of these models in single domains (like computer vision and natural language processing), the multi-modal pre-trained big models have also drawn more and more attention in recent years. In this work, we give a comprehensive survey of these models and hope this paper could provide new insights and helps fresh researchers to track the most cutting-edge works. Specifically, we firstly introduce the background of multi-modal pre-training by reviewing the conventional deep learning, pre-training works in natural language process, computer vision, and speech. Then, we introduce the task definition, key challenges, and advantages of multi-modal pre-training models (MM-PTMs), and discuss the MM-PTMs with a focus on data, objectives, network architectures, and knowledge enhanced pre-training. After that, we introduce the downstream tasks used for the validation of large-scale MM-PTMs, including generative, classification, and regression tasks. We also give visualization and analysis of the model parameters and results on representative downstream tasks. Finally, we point out possible research directions for this topic that may benefit future works. In addition, we maintain a continuously updated paper list for large-scale pre-trained multi-modal big models: https://github.com/wangxiao5791509/MultiModal_BigModels_Survey.

Ceramics of composition Ag_1−3xBi_xNbO₃ (0.005 ≤ x ≤ 0.040) were prepared by solid state methods and their structure and electrical behavior were characterized with a view to their potential use as high power energy storage materials.