Capacitors are attractive in large-scale energy-storage applications, such as electric vehicles or grid storage, because of their ability to rapidly charge and discharge, but their energy densities have been too small to allow their use in such applications. Researchers at Lawrence Berkeley National Laboratory (Berkeley, Calif.; www.lbl.gov) have developed a technique to boost the energy density of a “relaxor ferroelectric,” a ceramic material commonly used as a capacitor in applications like ultrasonics, pressure sensors and voltage generators.
When a relaxor ferroelectric material is subjected to an electric field, a charge builds up, but the material will fail in the presence of strong electric fields. When discharging, the amount of energy available for use depends on the degree of electron polarization (orientation) in the ceramic. So the Berkeley team needed to find a way to render the material capable of withstanding high voltages while still retaining the electron polarization.
To do this, they bombarded a thin film of the relaxor ferroelectric material (specifically, niobite lead titanate) with high-energy helium ions, which introduced isolated point defects into the atomic structure of the film. The material with the targeted defects had more than twice the energy storage density than previously reported values, the researchers found.
Studies on the material revealed that the induced defects reduced the charge leakage, but also shifted the material’s polarization-electric-field relationship, which means that it takes a higher voltage to reach the maximum electron polarization. The results suggest that ion bombardment can help to overcome the trade-off between being a highly polarizable material and being easily breakable, the researchers say.