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 (Bi_1/6Na_1/6Sr_1/6Ba_1/6Pb_1/6Ca_1/6)TiO₃ (BNSBPC) and (Bi_1/6La_1/6Na_1/6K_1/6Sr_1/6Ba_1/6)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 ¯ 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, ΔT_max) reaches 0.63 K with relatively narrow temperature span (ΔT_span) of ~ 20 K at 60 kV cm⁻¹ for BNSBPC ceramic, while the BLNKSB one possesses superior temperature stability (ΔT_span = 100 K) with ΔT_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. [ABSTRACT FROM AUTHOR]