Ultrahigh Temperature Lead-Free Film Capacitors via Strain and Dielectric Constant Double Gradient Design

With the development of miniaturization, lightweight and integration of electronic devices, the demand for high-temperature dielectric capacitors is becoming urgent. Nevertheless, the breakdown strength and polarization are deteriorated at high temperatures due to the thermal energy assisting the electron transport and impeding the dipole alignment. Here, a structure of capacitor with double gradients of dielectric constant gradient and strain gradient is designed to achieve high breakdown strength, high working temperature, and high energy storage density simultaneously. It is found that the designed structure of BaHf_0.17 Ti_0.83 O₃ /1mol% SiO₂ doped BaZr_0.35 Ti_0.65 O₃ /0.85BaTiO₃ -0.15Bi(Mg_0.5 Zr_0.5 )O₃ exhibits excellent energy storage performance. The energy storage density of 127.3 J cm^-3 with an energy storage efficiency of 79.6% is realized in the up-sequence multilayer with period N = 2 at room temperature. Moreover, when the working temperature varies from -100 to 200 °C, the energy storage density of the N = 4 capacitor keeps stably at 84.62 J cm^-3 with an energy storage efficiency 78.42% at 6.86 MV cm^-1 . All these properties promise great potential applications of the designed multilayer capacitors with the double gradients in harsh environments, and the design principle can be applicable to other systems to boost working temperature.