  Typical ferroelectrics possess a large spontaneous polarization Ps but
simultaneously a large remnant polarization Pr as well, resulting in an
inferior energy storage density.A mechanism that can reduce the Pr while
maintain the Ps is demanded to enhance the energy storage property of
ferroelectrics.In the present study, it is shown that after acceptor doping and
aging treatment, the domain switching in ferroelectrics becomes reversible,
giving rise to a pinched double hysteresis loop. The pinched loop with a large
Ps and a small Pr thus results in an enhanced energy storage density. The
physics behind is a defect induced internal field that provides a restoring
force for the domains to switch back.The idea is demonstrated through a
time-dependent Ginzburg-Landau simulation as well as experimental measurements
in BaTiO$_3$ based single crystal and ceramics. The mechanism is general and
can be applied to various ferroelectrics, especially the environment-friendly
ones.
