Superparaelectric (Ba0.95,Sr0.05)(Zr0.2,Ti0.8)O₃ Ultracapacitors

Analogous to the superparamagnetic state, a superparaelectric state is both scientifically intriguing and technologically important. In this state, a ferroelectric material shows a high dielectric constant and a nonhysteretic response to an external electric field, ideal for high k and capacitive energy storage applications. Despite many explorative studies, only circumstantial evidences for its existence are reported. Here, the existence of a superparaelectric state is directly proven in engineered nanocrystalline perovskite films of (Ba 0.95 , Sr 0.05 )(Zr 0.2 ,Ti 0.8 )O 3 , which are grown on Si at a low temperature and consist of many well‐dispersed, nanometer‐size polar clusters. These nanoparticles are locally polar, and only lose their short‐range order after being heated up to ≈460 °C, above which they become paraelectrics. Furthermore, they collectively present a pseudo‐linear, frequency‐insensitive dielectric response, which is characterized by a close‐to‐zero remnant polarization and a large relative dielectric constant (≈65–70). Capacitors based on these superparaelectric films display high recyclable energy densities (≈100 J cm −3 ) and efficiencies (≈90%) at room temperature, as well as a reliable high field endurance and good frequency (up to ≈15 GHz) and temperature (up to ≈300 °C) stabilities in their dielectric properties.