Free energy regulation and domain engineering of BaTiO3-NaNbO3 ceramics for superior dielectric energy storage performance

Ferroelectrics with high electric polarization are preferred materials for dielectric energy storage capacitors, as they outperform their linear counterparts in energy density determining the miniaturization and lightweight progress of the electric power systems. However, it is very challenging to balance the performance between the energy density and other indispensable features including energy efficiency, temperature and frequency stabil-ities, and cycling fatigue resistance in ferroelectrics, all of which play a decisive role in practical applications. In this work, to suppress the dielectric loss for ideal energy efficiency while maintaining the high energy density, we proposed a domain engineering that smashed the domains of the materials into polar nano regions. Meanwhile, as guided by thermodynamics, we make the potential well of the free energy independent of temperature for the exceptionally high stability of the energy storage performance. Our concept was demonstrated in the typical BaTiO3-NaNbO3 (BN) lead-free solid-solution system. With the incorporation of Bi(Zn0.5Zr0.5)O3 (BZZ), the BN-BZZ shows an extremely slim hysteresis loop and yields a stunning energy density energy efficiency of 91.4% without compromise of energy storage density (10.2 J cm- 3), the highest value in lead-free ferroelectric ceramics with efficiency exceeding 90%. Furthermore, the high energy density and efficiency at 500 kV cm-1 vary only +/- 5% and +/- 3%, respectively, in the wide temperature and frequency ranges (-55 degrees C to 250 degrees C, 1 Hz-1000 Hz, far exceeding the requirement of X9R standard), and minute decay was observed with a long-term fatigue measurement. Our strategy would be available for designing ferroelectrics with various material systems for high energy storage properties.