  The large electrocaloric coupling in PbZrO3 allows using high-speed infrared
imaging to visualize antiferroelectric switching dynamics via the associated
temperature change. We find that in ceramic samples of homogeneous temperature
and thickness, switching is nucleation-limited and fast, with devices
responding in the milisecond range. By introducing gradients of thickness,
however, it is possible to change the dynamics from nucleation-limited to
propagation-limited, whereby a single phase boundary sweeps across the sample
like a cold front, at a speed of c.a. 20 cm/s. Additionally, introducing
thermostatic temperature differences between two sides of the sample enables
the simultaneous generation of a negative electrocaloric effect on one side and
a positive one on the other, yielding a Janus-like electrocaloric response.
