Polar Vortices in Relaxor Ferroelectric Ceramics for High-Efficiency Capacitive Energy Storage.

Polar vortices are predominantly observed within the confined ferroelectric films and the ferroelectric/paraelectric superlattices. This raises the intriguing question of whether polar vortices can form within relaxor ferroelectric ceramics and subsequently contribute to their energy storage performances. Here, we incorporate 10 mol % CaSnO into the 0.7NaNbO-0.3SrBiTiO matrix, yielding a coexistence of phases: 48.8% orthorhombic 2/, 49.1% tetragonal 4, and 2.1% tetragonal 4/ SnO, which is confirmed by the combination of X-ray diffraction and transmission electron microscopy. The ceramic features a pronounced core-shell structure with the shell region rich in stripe nanoscale domains of the 2/ phase and the core region consisting of polar nanoregions deficient in the 2/ phase, forming polar vortices. Consequently, the ceramic achieves an impressive recoverable energy storage density of 6.83 J cm and an exceptional efficiency of 95.7% at a high breakdown strength of 750 kV cm, along with superior stability in frequency, temperature, and cycling. These results not only offer a viable approach for developing high-performance energy storage ceramics through the controlled formation of polar vortices but also offer the potential for direct electric-field control of polar vortices for high-speed data processing and storage.