Lead‐free high permittivity quasi‐linear dielectrics for giant energy storage multilayer ceramic capacitors with broad temperature stability

Electrostatic energy storage capacitors are essential passive components for power electronics and prioritize dielectric ceramics over polymer counterparts due to their potential to operate more reliably at &gt; 100 ˚C. Most work has focused on non‐linear dielectrics compositions in which polarization (P)/electric displacement (D) and maximum field (E<jats:sub>max</jats:sub>) are optimized to give values of energy density, 6≤U≤21 J cm<jats:sup>−3</jats:sup>. In each case however, either saturation (dP/dE = 0, AFE) or “partial” saturation (dP/dE → 0, RFE) of P limits the value of U which can be achieved before breakdown. It is proposed that U can be further improved with respect to relaxors (RFEs) and anti‐ferroelectrics (AFEs) by designing high permittivity quasi‐linear dielectric (QLD) behaviour in which dP/dE remains constant up to ultrahigh E<jats:sub>max</jats:sub>. QLD multilayer capacitor prototypes with dielectric layers composed of 0.88NaNb<jats:sub>0.9</jats:sub>Ta<jats:sub>0.1</jats:sub>O<jats:sub>3</jats:sub>‐0.10SrTiO<jats:sub>3</jats:sub>‐0.02La(Mg<jats:sub>1/2</jats:sub>Ti<jats:sub>1/2</jats:sub>)O<jats:sub>3</jats:sub> deliver room temperature U ≈ 43.5 J cm<jats:sup>−3</jats:sup>, supporting an extremely‐large E<jats:sub>max</jats:sub> ≈ 280 MV m<jats:sup>−1</jats:sup>, both of which exceed current state‐of‐art by a factor of two for devices based on powder, tape‐cast technology. Importantly QLD capacitors exhibit scant variation in U (≈15 J cm<jats:sup>−3</jats:sup>) up to &gt; 200 ˚C and robust resistance to cyclic degradation, offering a promising new approach for the development of sustainable technology.