Large electrocaloric temperature change in lead-free (Bi_0.47Na_0.47Ba_0.06)TiO₃-based ceramics via regulating non-ergodic - ergodic transition

Ferroelectric materials exhibiting the electrocaloric effect (ECE) have emerged as promising candidates for next-generation solid-state refrigeration technologies. However, the relatively low adiabatic temperature change (ΔT) and narrow operational temperature range hinder their widespread application in practical refrigeration systems. In this study, lead-free Bi_0.47Na_0.47Ba_0.06Ti_1-xHf_xO₃ polycrystalline ceramics were synthesized via the solid-state reaction method, and the ECE was systematically investigated in relation to relaxor behavior evolution under varying hafnium concentrations. Hf⁴⁺ incorporation enhances relaxor characteristics and reduces the non-ergodic to ergodic transition temperature (T_d) from 110 °C toward a lower temperature. Direct measurements revealed a maximum ΔT of 0.67 K at 60 °C under an applied field of 60 kV/cm for x = 0.02. Additionally, phase structure, dielectric properties and electrocaloric performance were comprehensively characterized to elucidate the role of non-ergodic to ergodic transition in achieving enhanced ECE. These findings provide valuable guidelines for the design of high performance electrocaloric materials.