Electrocaloric effect (ECE) is promising in realizing solid-state cooling as an alternative to the conventional refrigeration with environmentally harmful coolant and low efficiency. High ECE in lead-free ferroelectric ceramics is highly desirable for the EC cooling. In this work, different from the researches that tune the ECE by conventional compositional design or external stress engineering, we fabricated the (1-x)BaTiO₃-xNaNbO₃ (BTO-xNN) lead-free ceramics with a core-shell grain structure arising from the inhomogeneous stoichiometry of element distribution, leading to the internal compressing stress in the grains. It is interesting that the phase transition behavior, including the phase transition temperature and the diffusion property, is regulated by the core-shell grain structure induced internal stress, which can be capitalized on for the favorable ECE. Cooperated with 0.02 NN, a high ECE, e.g. adiabatic temperature change (ΔT) of 3.6 K and isothermal entropy change (ΔS) of 4.5 J kg⁻¹ K⁻¹, is attained in the BTO ceramic. As the internal stress further increases with more NN, the BTO-0.06NN exhibits an extremely stable ECE with a variety rate below ±4% in a wide temperature range from 300 K to 360 K. This work provides a novel approach to explore pronounced ECE in lead-free ferroelectrics for eco-friendly refrigeration.

电热效应（ECE）有望实现固态冷却，以替代对环境有害的冷却剂和低效率的传统制冷。对于EC冷却，非常需要无铅铁电陶瓷中的高ECE。在这项工作中，与通过常规成分设计或外部应力工程对ECE进行调节的研究不同，我们制造了（1-x）BaTiO ₃ -xNaNbO ₃（BTO-xNN）无铅陶瓷，其具有核壳结构，这是由于元素分布的化学计量不均匀而导致的，导致晶粒内部的压缩应力。有趣的是，相变行为，包括相变温度和扩散特性，是由核-壳晶粒结构引起的内应力调节的，可以利用它来获得良好的ECE。与0.02 NN配合使用时，ECE较高，例如绝热温度变化（ΔT）为3.6 K，等温熵变化（ΔS）为4.5 J kg ^-1  K ^-1在BTO陶瓷中达到。随着内应力随着NN的增加而进一步增加，BTO-0.06NN在300 K至360 K的宽温度范围内表现出极其稳定的ECE，变化率低于±4％。这项工作为探索显着的ECE提供了一种新颖的方法。用于环保制冷的无铅铁电材料。