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 (Pm (3) over bar 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, Delta T-max) reaches 0.63 K with relatively narrow temperature span (Delta T-span) of similar to 20 K at 60 kV cm(-1) for BNSBPC ceramic, while the BLNKSB one possesses superior temperature stability (Delta T-span = 100 K) with Delta T-max = 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.