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With the rapid growth of energy storage capacitors in advanced power systems, the pursuit of lightweight devices is gradually gaining importance despite the urgent need for device miniaturization. To reduce the mass of dielectric energy storage materials, certain light metal elements, such as potassium (K) and sodium (Na), offer promising prospects for achieving low material density. However, the intrinsic formation of point defects, including alkali metal vacancies and oxygen vacancies (Schottky defects), is inevitable during high-temperature sintering because of the volatilization of alkali metal oxides. These defects can lead to high conductivity under high electric fields, thereby deteriorating energy storage performance (ESP). In this work, we focus on a potassium-rich composition, K2La0.75Gd0.25Nb5O15, which is characterized by a tetragonal tungsten bronze (TTB) structure, to investigate the impact of volatile point defects. Different types of defects were designed by changing the K2O content, and energy storage properties were investigated. Based on leakage current measurements, impedance spectra, and DFT calculation results, it could be concluded that K–O defects with a shallow energy level cause conduction loss, thereby influencing polarization and ESP. Consequently, a high recoverable energy storage density (Wrec) of 5.02 J cm−3 and an energy efficiency of 85.6% were simultaneously achieved for the composition with the lowest defect content. This work reveals a mechanism in which volatile defects dominate conduction behavior and relevant ESP, stresses the significance of suppressing alkaline Schottky defects, and provides a feasible solution to developing lightweight dielectric energy storage materials. [ABSTRACT FROM AUTHOR]

Subjected to mechanical stimuli, a piezo-induced built-in electric field is favorable for promoting the catalytic performance of piezo-photocatalysts via effectively separating the excitons. However, the exact correlation between the electronic structure and catalytic properties of piezo-photocatalysts is still ambiguous. Conjugated microporous polymers (CMPs) with delocalized π-conjugation bonds are a unique class of photocatalytic materials, which exhibit intramolecular transport channels for electron transfer and could be further enhanced by a built-in electric field during photocatalysis. Herein, novel piezo-photocatalytic electrospun hybrid fiber films were prepared, which endow piezoelectric poly(vinylidene fluoride-co-trifluoroethylene) (PVDF–TrFE) with the high photocatalytic activity of a pyridine-based CMP (PCMP). The compatibility of these two components was enhanced via silane modification of the PCMP (m-PCMP). Hybrids of m-PCMP 50 wt%/PVDF–TrFE showed an excellent photo-degradation efficiency (97%) towards rhodamine B (RhB) with a high pseudo-first-order kinetic constant (k) of 0.0289 min−1 which is comparable to that of the neat m-PCMP (0.0304 min−1) and nearly 15 times higher compared to that of pure PVDF–TrFE (0.0019 min−1). The excellent catalytic performance was attributed to the synergetic effect, where the addition of the m-PCMP enhanced the piezo-response of PVDF–TrFE, and the piezo-potential of PVDF–TrFE regulated the energy band of m-PCMP, favoring the redox reactions to generate reactive oxygen species (ROS) for degrading RhB. The present study proposes a new paradigm for highly active piezo-photocatalysts in terms of tuning the electronic structure and interpreting the structure-to-property correlation. [ABSTRACT FROM AUTHOR]