Enhanced electrocaloric effect in the Sm and Hf co-doped BaTiO₃ ceramics

In this work, the electrocaloric (EC) effect was studied in the (100-x)BaHf_0.2Ti_0.8O₃-xBa_0.94Sm_0.04TiO₃ (BHT-xBST) ceramics fabricated by the conventional solid-reaction method. By tuning composition to their diffuse phase transition (DPT), invariant critical point (ICP) and first-order phase transition (FPT), the large electrocaloric response with a temperature change of ΔT = 0.46 °C (at 64 °C) under 30 kV/cm and an electrocaloric strength of ΔT/ΔE = 0.18 K mm/kV under 12 kV/cm were achieved in BHT-70BST. In addition, BHT-50BST shows a broad EC working temperature window from 28 °C to 68 °C because of its diffusion behavior near the ferroelectric-to-paraelectric phase transition and multiphase coexistence. The maximum ΔT of BHT-50BST is larger than that of BHT-40BST with only diffusion character but no multiphase coexistence. This work may provide a design strategy to enhance EC performance with a broad working temperature region in lead-free rare-earth doped BaTiO₃-based ceramics by combining the diffusion behavior, multiphase coexistence and heterovalent substitution.