Poly(vinylidene fluoride)-based dielectric materials are prospective candidates for high power density electric storage applications because of their ferroelectric nature, high dielectric breakdown strength and superior processability. However, obtaining a polar phase with relaxor-like behavior in poly(vinylidene fluoride), as required for high energy storage density, is a major challenge. To date, this has been achieved using complex and expensive synthesis of copolymers and terpolymers or via irradiation with high-energy electron-beam or γ-ray radiations. Herein, a facile process of pressing-and-folding is proposed to produce β-poly(vinylidene fluoride) (β-phase content: ~98%) with relaxor-like behavior observed in poly(vinylidene fluoride) with high molecular weight > 534 kg mol⁻¹, without the need of any hazardous gases, solvents, electrical or chemical treatments. An ultra-high energy density (35 J cm⁻³) with a high efficiency (74%) is achieved in a pressed-and-folded poly(vinylidene fluoride) (670-700 kg mol⁻¹), which is higher than that of other reported polymer-based dielectric capacitors to the best of our knowledge.

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.

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.

Ag(Nb_0.8Ta_0.2)O₃ is used here as a model system to shed light on the nature of the low temperature phase behavior of the unsubstituted parent compound AgNbO₃, which is an important material for high-power energy storage applications.