Title: Large electrocaloric effect in Pb(Sc0.25In0.25Nb0.25Ta0.25)O3 medium-entropy ceramics

Abstract

Next generation EC cooling devices using electrocaloric effect of ferroelectric materials have been attracting more and more attentions. It is very desirable for a bulk ferroelectric ceramic to have a large electrocaloric (EC) effect at a very low electric field. However, limited to the low dielectric breakdown strength and the low pyroelectric effect, there is almost no breakthrough in a long period of time for the EC effect of bulk ceramics since the EC effect was found in 1930s. Although the large electrocaloric temperature change (T) could be obtained in some ferroelectric ceramic thin films, their EC strengths (T/E) are too small and unappreciable compared with bulk ceramics. Therefore, it is urgent to design and make ferroelectric bulk ceramics that a large EC effect at a relatively lower electric field can be obtained. In this work, two medium entropy-like, Pb(Sc0.25In0.25Nb0.25Ta0.25)O3 (PSINT) ceramics were successfully synthesized by one-step or two-step spark plasma sintering (SPS) processing technology. When the configurational entropy of B-site ions is enhanced, the dipolar entropy could also be increased simultaneously. Therefore, it is reasonable to believe that a large EC effect can be achieved in medium-entropy and high-entropy ferroelectric ceramics, especially when the ceramics is relaxor ferroelectrics because a lot of polar nano regions (PNRs) existed in the ceramics. For the two-step-SPS processed sample, a high EC strength (△T/△E ~ 0.021 K·cm/kV) and a large EC effect (△T ~ 0.85 K) with around room temperature are obtained at a very low electric field (~ 40 kV/cm). Moreover, the working temperature range is also very broad (~ 120 K), which is attributed to the high-degree relaxation of the dielectric peak.