Influence of the critical point on the electrocaloric response of relaxor ferroelectrics

TLDR

The electrocaloric effect converts electric energy into heat and is promising for environmentally friendly cooling and heating devices. The study aims to investigate how the electrocaloric response depends on electric‑field magnitude near the critical point in bulk relaxor ferroelectric ceramics. Direct ΔT measurements were performed with a high‑resolution calorimeter while varying the electric‑field step to probe the ECE around the critical point. Large temperature changes of 2–3 K were achieved at modest fields of 90 kV/cm, with peak responsivity near the critical point and good agreement with spherical random‑bond random‑field model predictions.

Abstract

The electrocaloric effect (ECE), i.e., the conversion of electric energy into heat, is of great importance for application in new generation cooling or heating devices that would be friendlier to the environment. Here, utilizing direct measurements of the ECE change of the temperature ΔT via a high resolution calorimeter, we study the ECE as a function of the magnitude of the electric-field step E in the vicinity of the critical point in several bulk relaxor ferroelectric ceramic systems. Relatively large ΔT of ∼2 to 3 K were obtained at modest fields of 90 kV/cm, even in the case of ceramic materials. The effective responsivity ΔT/E as a function of the electric field shows a characteristic peak near the critical point, which demonstrates the importance of proximity to the critical point for the enhancement of the electrocaloric effect. Experimental results are in good agreement with the theoretical calculations based on the spherical random-bond random-field model.