Ultrawide Temperature Range with Stable Permittivity and Low Dielectric Loss in (1 − x)[0.90Na₀.₅ Bi₀.₅TiO₃‐0.10BiAlO₃]‐ xNaNbO₃ System

High‐temperature capacitors have become an important research topic recently as commercially available capacitors cannot fulfill the new requirements from industry. In this work, a new ceramic ternary system (1 − x)[0.90Na₀.₅Bi₀.₅TiO₃‐0.10BiAlO₃]‐ xNaNbO₃ is introduced, and the effects of NaNbO 3 concentration on macroscopic phase structure, locally disordered structure, dielectric properties, conduction properties, and energy storage properties are studied. At the optimum composition of x = 0.30, an ultrawide temperature range (−90 and 320 °C) covering both stable permittivity (Δε′/ε′ 25°C ≤ ± 15%) and low dielectric loss (tan δ ≤ 0.02) can be obtained. Additionally, this material has a high RC constant of 2.8 s and a high energy storage efficiency of 88% under the electric field of 60 kV cm⁻¹ at room temperature. Therefore, this work provides a very promising candidate for dielectrics used in multilayer ceramic capacitors (MLCC) in an ultrawide operating temperature range.