High capacitance behavior in Sr0.6Ba0.4Nb2O6-based tungsten bronze ferroelectrics

Dielectric capacitors with superior energy storage performance are attracting growing attention due to ultrahigh power density and rapid charge/discharge speed. In this work, perovskite Sr0.6Ba0.4TiO3 (SBT) is introduced into tungsten bronze Sr0.6Ba0.4Nb2O6 (SBN), maintaining an identical Sr/Ba ratio, to enhance the energy storage performance of Bi/Na/Pb-free (1 − x)SBN-xSBT ferroelectrics. The sample with increasing x ≤ 0.3 forms a solid solution corresponding to the unfilled–filled tungsten bronze structure transition, accompanied by dramatically decreased grain anisotropy and average grain size. However, the perovskite second phase gradually appears, and the average grain size further decreases slightly when x > 0.3. Such phase and microstructure evolution induces monotonously enhanced relaxor degree γ and breakdown strength Eb around x = 0.4. As a result, this optimal composition shows high recoverable energy storage density Wrec = 9.5 J/cm3, energy storage efficiency η = 82.1%, both of which vary less than 7% within 20–150 °C. Encouragingly, excellent charge–discharge performances, t0.9 = 23 ns and WD = 6.2 J/cm3, are obtained. This work provides insights into developing high energy storage performance tungsten bronze oxide through phase and microstructure design.