Dielectric capacitors have the highest charge/discharge speed among all electrical energy devices, but lag behind in energy density. Here we report dielectric ultracapacitors based on ferroelectric films of Ba(Zr_0.2,Ti_0.8)O₃which display high-energy densities (up to 166 J cm^–3) and efficiencies (up to 96%). Different from a typical ferroelectric whose electric polarization is easily saturated, these Ba(Zr_0.2,Ti_0.8)O₃films display a much delayed saturation of the electric polarization, which increases continuously from nearly zero at remnant in a multipolar state, to a large value under the maximum electric field, leading to drastically improved recyclable energy densities. This is achieved by the creation of an adaptive nano-domain structure in these perovskite films via phase engineering and strain tuning. The lead-free Ba(Zr_0.2,Ti_0.8)O₃films also show excellent dielectric and energy storage performance over a broad frequency and temperature range. These findings may enable broader applications of dielectric capacitors in energy storage, conditioning, and conversion.

We report the structural and longitudinal piezoelectric responses $\left(d_{33}\right)$ of epitaxial $\mathrm{Pb}\left({\mathrm{Zr}}_{0.52}{\mathrm{Ti}}_{0.48}\right){\mathrm{O}}_3$ (PZT) films on (001) $\mathrm{Sr}\mathrm{Ti}{\mathrm{O}}_3$ and Si substrates in the thickness range of $40\mathrm{nm}–4\mu \mathrm{m}$ . With increasing film thickness the tetragonality of PZT was reduced. The increase in $d_{33}$ value with increasing film thicknesses was attributed to the reduction of substrate constraints and softening of PZT due to reduced tetragonality. The $d_{33}$ values of PZT films on Si substrates $(\sim 330\mathrm{pm}∕\mathrm{V})$ are higher than those on $\mathrm{Sr}\mathrm{Ti}{\mathrm{O}}_3$ substrates $(\sim 200\mathrm{pm}∕\mathrm{V})$ . The epitaxial PZT films on silicon will lead to the fabrication of high performance piezoelectric microelectromechanical devices.

In this letter we report on the effect of thickness scaling in model $\mathrm{Pb}{\mathrm{Zr}}_{0.2}{\mathrm{Ti}}_{0.8}{\mathrm{O}}_3\left(\mathrm{PZT}\right)∕\mathrm{Sr}\mathrm{Ru}{\mathrm{O}}_3$ heterostructures. Although theoretical models for thickness scaling have been widely reported, direct quantitative experimental data for ultrathin perovskite $(<10\mathrm{nm})$ films in the presence of real electrodes have still not been reported. In this letter we show a systematic quantitative experimental study of the thickness dependence of switched polarization in (001) epitaxial PZT films, $4\text{to}80\mathrm{nm}$ thick. A preliminary model based on a modified Landau Ginzburg approach suggests that the nature of the electrostatics at the ferroelectric–electrode interface plays a significant role in the scaling of ferroelectric thin films.