Superior Energy Storage Capability and Fluorescence Negative Thermal Expansion of NaNbO3‐Based Transparent Ceramics by Synergistic Optimization

Abstract Transparent dielectric ceramics are splendid candidates for transparent pulse capacitors (TPCs) due to splendid cycle stability and large power density. However, the performance and service life of TPCs at present are threatened by overheating damage caused by dielectric loss. Here, a cooperative optimization strategy of microstructure control and superparaelectric regional regulation is proposed to simultaneously achieve excellent energy storage performance and real‐time temperature monitoring function in NaNbO 3 ‐based ceramics. By introducing aliovalent ions and oxides with large bandgap energy, the size of polar nanoregions is continuously reduced. Due to the combined effect of increased relaxor behavior and fine grains, excellent comprehensive performances are obtained through doping appropriate amounts of Bi, Yb, Tm, and Zr, Ta, Hf in A‐ and B‐sites of the NaNbO 3 matrix, including recoverable energy storage density (5.39 J cm −3 ), extremely high energy storage efficiency (91.97%), ultra‐fast discharge time (29 ns), and superior optical transmittance (≈47.5% at 736 nm). Additionally, the phenomenon of abnormal fluorescent negative thermal expansion is realized due to activation mechanism of surface phonon at high temperatures that can promote the formation of [Yb···O]‐Tm 3+ pairs, showing great potential in real‐time temperature monitoring of TPCs. This research provides ideas for developing electronic devices with multiple functionalities.