Comparative study of phase structure, dielectric properties and electrocaloric effect in novel high-entropy ceramics

Unique structure and performance in prominent high-entropy ceramics (HECs) have attracted enormous attentions recently. In this work, we have successfully synthesized pure-phase (Bi1/6Na1/6Sr1/6Ba1/6Pb1/6Ca1/6)TiO3 (BNSBPC) and (Bi1/6La1/6Na1/6K1/6Sr1/6Ba1/6)TiO3 (BLNKSB) HECs by conventional solid-state method. Rietveld refinement results show that BNSBPC composition possesses tetragonal phase (P4mm) while the BLNKSB one exhibits cubic phase (Pm3¯\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\overline{3}$$\end{document}m). Dielectric characterization reveals distinct relaxation behaviors between BNSBPC and BLNKSB compositions. Relaxor-like nature in BNSBPC and Debye medium in BLNKSB one are verified by dielectric, ferroelectric and Raman spectra characterizations. Maximal electrocaloric effect (ECE, ΔTmax) reaches 0.63 K with relatively narrow temperature span (ΔTspan) of ~ 20 K at 60 kV cm−1 for BNSBPC ceramic, while the BLNKSB one possesses superior temperature stability (ΔTspan = 100 K) with ΔTmax = 0.14 K. Room-temperature ECE is also obtained by home-made adiabatic calorimeter, which indicates a positive ECE for both compositions. Finally, phase structure, dielectric properties and ECE in two high-entropy compositions are comparatively discussed to explore structure–ECE relationships in HECs. The superior thermal stability of ECE in BLNKSB samples provides a broad prospect for designing solid-state refrigeration.