High Temperature-Stability of Novel Linear Relaxor Ferroelectric of (Sr1-1.5xBix)(Mg1/3Nb2/3)O3 for Dielectric and Energy Storage Performance

As an indispensable component in power equipment and electronic circuits, dielectric ceramic capacitors are rapidly advancing while facing more rigorous working conditions such as high temperature and high frequency. However, dielectric ceramics capable of achieving high breakdown strength ($E_{b}$) and low energy loss under harsh temperature conditions $\left({\gt}200{ }^{\circ} \mathrm{C}\right)$ are extremely rare in current research. In this work, we demonstrate a novel linear relaxor ferroelectrics, $\left(\mathrm{Sr}_{1-1.5 x} \mathrm{Bi}_{x}\right)\left(\mathbf{M g}_{1 / 3} \mathrm{Nb}_{2 / 3}\right) \mathrm{O}_{3}$, exhibiting exceptional performance in ultra-high $E_{\mathrm{b}}$, energy storage efficiency $(\eta)$, and thermal resistance. The $\left(\mathrm{Sr}_{1-1.5 x} \mathrm{Bi}_{x}\right)^{\mathbf{2 +}}$ ion combination, characterized as originating from weakly polar nanodomains, is selected as the A-site ion sequence in the $\mathbf{A B O}_{3}$-type $\left(\mathbf{S r}_{1-1.5} \mathrm{Bi}_{x}\right)\left(\mathbf{M g}_{1 / 3} \mathbf{N b}_{2 / 3}\right) \mathbf{O}_{3}$ ceramics to achieve the ferroelectric relaxation property, while simultaneously utilizing the $\left(\mathrm{Mg}_{1 / 3} \mathrm{Nb}_{2 / 3}\right)^{4+}$ with induced diffusion phase transition characteristics to occupy the B-site and further enhance ferroelectric relaxation. Ultimately, (Sr_ $\left.{ }_{1.5 x} \mathrm{Bi}_{x}\right)\left(\mathrm{Mg}_{1 / 3} \mathrm{Nb}_{2 / 3}\right) \mathrm{O}_{3}$ achieves an effective energy storage density of $3.29 \mathrm{~J} / \mathrm{cm}^{3}$ under an ultra-high $E_{\mathrm{b}}$ of $860 \mathrm{kV} / \mathrm{cm}$, along with the $\boldsymbol{\eta}$ of $\mathbf{9 2. 5 \%}$. Impressively, the dielectric constant of $\left(\mathrm{Sr}_{0.7} \mathrm{Bi}_{0.2}\right)\left(\mathrm{Mg}_{1 / 3} \mathrm{Nb}_{2 / 3}\right) \mathrm{O}_{3}$ ceramics varies by only $50 \pm 3 \%$ across a wide temperature range of $-150{ }^{\circ} \mathrm{C}$ to $450{ }^{\circ} \mathrm{C}$, with a record-breaking variation of 1% for $\left(\mathrm{Sr}_{0.85} \mathrm{Bi}_{0.10}\right)\left(\mathrm{Mg}_{1 / 3} \mathrm{Nb}_{2 / 3}\right) \mathrm{O}_{3}$ ceramics. Therefore, an outstanding $\eta$ of 90% was achieved in $\left(\mathbf{S r}_{0.7} \mathbf{B i}_{0.2}\right)\left(\mathbf{M g}_{1 / 3} \mathbf{N b}_{2 / 3}\right) \mathbf{O}_{3}$ ceramic under the condition of 500 $\mathrm{kV} / \mathrm{cm}$ and $200{ }^{\circ} \mathrm{C}$, which is remarkably rare at an equivalent level. This study provides a new guidance for design of high performance dielectric energy storage ceramics utilized over a wide temperature.