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.

Biography

Qi Zhang has been an Ikerbasque research professor in BCMaterials since 2020. Before that, he worked in Cranfield University, UK as a research fellow in 1996, a senior research fellow in 1998, a senior lecturer in 2007. He was a full professor in Wuhan University of Technology, China since 2012. He is a fellow and charted scientist of Institute of Materials, Minerals & Mining. He is acting as a chief scientist in three international companies. His research work is focused on the areas of functional materials for energy storage and electrocaloric cooling, as well as on lithium batteries and on coatings for surface engineering. He has published more than 220 peer reviewed papers and 5 chapters in books, with a total citation of > 7500 and H-factor of 40. Some of his publications appeared in journals with high impact factors, such as, Science, Energy & Environ. Sci., Mater. Sci. and Eng. R: Report, Adv. Funct. Mater., Nano Energy and Nano Lett., among others. In addition, he co-edited the book entitled Electrocaloric Cooling (EC). He received Brian Mercer Feasibility Award, 2009, The Royal Society, UK.