Giant electrocaloric effect in BaTiO3–Bi(Mg1/2Ti1/2)O3 lead-free ferroelectric ceramics

Highlights: • The electrocaloric effect was first investigated in the BT-BMT ceramics. • The negative electrocaloric effect was first reported in the BT-BMT ceramics. • The negative electrocaloric effect was related to the field induced phase transition. • The giant electrocaloric value of 1.21 K was observed in 0.98BT–0.02BMT ceramic. The microstructure, dielectric property and electrocaloric effect were investigated in the lead-free (1-x)BaTiO₃–x (BiMg_1/2Ti_1/2)O₃ ((1-x) BT–x BMT, x = 0.0–0.05) ferroelectric ceramics. Under the low electric field (E ≤ 20 kV cm⁻¹), the coexistence of a positive and negative electrocaloric effect was obtained in (1-x)BT–x BMT (x ≤ 0.04) ceramics system using the Maxwell relation. Negative electrocaloric behavior disappears and the positive electrocaloric effect was only observed at high electric field (E ≥ 25 kV cm⁻¹). Firstly, the values of both negative electrocaloric effect under low electric field of E ≤ 20 kV cm⁻¹ (NECE) and positive electrocaloric effect in the high electric field of E ≥ 25 kV cm⁻¹ (PECE) increase, then decrease with increasing BMT content in the ceramics. The 0.98BT-0.02BMT ceramic shows the excellent PECE and NECE capabilities. The corresponding giant electrocaloric effect values of −0.37 K (42 °C) at 20 kV cm⁻¹ and 1.21 K (143 °C) at 55 kV cm⁻¹ were observed. These results show great potential in achieving large cooling power as refrigerants.