Electrocaloric properties of Ba0.8Sr0.2Ti1-xZrxO3 (0 <= x <= 0.1) system: The balance between the nature of the phase transition and phase coexistence

We investigate the electrocaloric effect of Ba0.8Sr0.2Ti1-xZrxO3 (0 <= x <= 0.1) system by comparing the electrocaloric temperature change (Delta T) of different compositions belonging to the different regions of the phase diagram. We show that as the amount of Zr increases, electrocaloric temperature change initially decreases as the phase transition gets diffuse then increases again as the composition of the samples are located closer to the critical point where different ferroelectric phases coexist. Since the critical point is reached at relatively low Zr substitution levels (i.e. around x = 0.07), the phase transition doesn't get too diffuse and thefore the compositions between x = 0 and x = 0.10 (which contains higher Zr than the critical point composition) have comparable Delta T values. Electrocaloric efficiency of these compositions (x = 0.03, 0.05 and 0.07) is around 0.20 K mm/kV at 20 kV/cm. We discuss the results in terms of the balance between the nature of the phase transition and proximity to the critical point, based on the phase diagram.