Origin of large negative electrocaloric effect in antiferroelectric $\mathrm{PbZr}{\mathrm{O}}_3$

We have studied the electrocaloric response of the archetypal antiferroelectric $\mathrm{PbZr}{\mathrm{O}}_3$ as a function of voltage and temperature in the vicinity of its antiferroelectric-paraelectric phase transition. Large electrocaloric effects of opposite signs, ranging from an electrocooling of −3.5 K to an electroheating of $+5.5\mathrm{K}$, were directly measured with an infrared camera. We show by calorimetric and electromechanical measurements that the large negative electrocaloric effect comes from an endothermic antiferroelectric-ferroelectric switching, in contrast to dipole destabilization of the antiparallel lattice, previously proposed as an explanation for the negative electrocaloric effect of antiferroelectrics.

Figure 1

(a) Capacitance and losses of $\mathrm{PbZr}{\mathrm{O}}_3$ ceramics and (b) electrocaloric temperature change vs temperature of $\mathrm{PbZr}{\mathrm{O}}_3$, characterized with an IR camera. Insets represent the polarization versus electric field hysteresis loops.

Figure 2

(a) Storage modulus of a PZO ceramic vs temperature obtained with DMA. The discontinuities represent switching between different phases of PZO. (b) DSC measurements of a $\mathrm{PbZr}{\mathrm{O}}_3$ ceramic at different electric fields for heating and cooling

Figure 3

Critical temperature of the AFE-FE phase transition as a function of field, measured by DMA (black) and DSC (blue), and onset temperature of giant negative electrocaloric effect measured by the infrared camera. The three independent measurements coincide.

Figure 4

(a) Tentative phase diagram for $\mathrm{PbZr}{\mathrm{O}}_3$ as a function of electric field. AFE-FE and FE-PE transitions are plotted with electromechanical results (DMA) while the ferroelectric/field-induced ferroelectric transition is plotted with electrocaloric data (IR camera). (b) Schematic T-S diagram of $\mathrm{PbZr}{\mathrm{O}}_3$ showing all phase transitions for $E=0$ and $E=21\mathrm{kV}/\mathrm{cm}$. The arrows represent the adiabatic $\left(\mathrm{\Delta }S=0\right)$ electrocaloric $\mathrm{\Delta }T$ when an electric field $E$ is applied or removed. All the different electrocaloric scenarios are labeled as in Fig. 1. The inset in (b) represents the connection between the phase transitions in $\mathrm{PbZr}{\mathrm{O}}_3$ and its positive and negative electrocaloric responses.