Mediating the Confliction of Energy Storage Performance and Transparency in KNN-Based Ceramics via Synergistic Optimization Strategy

Transparent ferroelectrics with superior electrical properties have garnered significant attention as promising multifunctional material. Nevertheless, the high symmetry of the crystal structure required for high transmittance is not conducive to ferroelectric polarization, which makes it difficult for energy storage and transparent properties to coexist in ferroelectric ceramics. In this work, the optical transparency and energy storage performances were collaboratively enhanced in the (1-<i>x</i>)(K_0.5Na_0.5)_0.985La_0.015NbO₆-<i>x</i>SrZrO₃ (KNLN-<i>x</i>SZ) ceramics by modulating the phase structure, domain structure, and grain size. Thanks to the establishment of rhombohedral (<i>R</i>) and tetragonal (<i>T</i>) phase boundaries in the KNLN-<i>x</i>SZ ceramics, the dielectric constants can be stabilized in the range of -90 to 270 °C in compliance with the X9R criteria. The disruption of ferroelectric long-range ordering leads to the generation of nanodomains, enhancing the activity of nanodomains while improving relaxor behavior and promoting the growth of elongated <i>P</i>-<i>E</i> loops. Besides, the reduction in grain size not only is beneficial for improving the optical transparency but also enhances the breakdown field (<i>E</i>_b), which further improves the energy storage performance. Accordingly, the remarkable transparency (<i>T</i>% up to ∼55% in the near-infrared range) and satisfactory energy storage density and efficiency (<i>W</i>_rec = 4.06 J/cm³ and η = 75%) are simultaneously achieved in the KNLN-0.15SrZrO₃ ceramic. This research alleviates the contradiction between the optical transparency and energy storage performances of KNN-based ferroelectrics through a synergistic optimization strategy and establishes a robust foundation for the modulation of KNN-based multifunctional ceramics.