Tailoring Zr-doped tungsten bronze (Sr,Ba,Gd)Nb2O6 relaxor ferroelectric with high electrical insulation interface for dielectric capacitor

Abstract

Tetragonal tungsten bronze structure (TTB) compounds have attracted tremendous interest for their applications in energy storage, especially as dielectric capacitor mediums. However, constrained by the inverse correlation of polarization and electric breakdown field in relaxor ferroelectrics, there is still a major challenge in improving energy density. To addresse this challenge, a viable strategy of constructing relaxor behavior with robust electrical insulation in TTB-type Sr0.485Ba0.47Gd0.03Nb2-xZrxO6 (SBN-Gd-Zrx) by introducing ZrO2 during the preparation process was proposed. By introducing Zr4+ in the B-site, we have revealed how Zr4+ affects the dielectric and ferroelectric characteristics to explore the intrinsic relaxation. Based on the analysis of Rietveld refinement against synchrotron X-ray powder diffraction and Raman results, the substitution of Gd3+ and Zr4+ for Sr2+ and Nb5+ in Sr0.53Ba0.47Nb2O6 caused a decline in tetragonality and a shrinkage of the unit cell due to the lattice defect of [GdSr]• and [ZrNb]', which mutually compensates effectively alleviate the distortion of BO6 and then favors the balance of polarization and dielectric constant. The accrual of additional ZrO2 at grain boundaries significantly enhances electrical insulation characteristics, as validated by complex impedance spectroscopy. At near room temperature, all Zr-doped SBN-Gd compounds of the series exhibit heightened relaxation and undergo a phase transition from ferroelectric to paraelectric. As a result, in tandem with the synchronous augmentation in breakdown electric field (EB) and saturation polarization (Pm), optimal energy storage characteristic is realized in the SBN-Gd-Zr0.2 sample. It attains a remarkable Wrec of 2.67 J/cm3 and an efficiency ƞ of 91.21 %, showcasing excellent suitability in terms of different frequencies and temperatures, which far exceeds that of Gd-modified SBN ceramics and pure SBN ceramics. These results exemplify an efficacious strategy for designing novel TTB dielectrics by coupling relaxor modulation with electrical insulation, and position them competitively for implementation in dielectric storage capacitors utilized in pulsed power devices.