Giant electrocaloric effect in high-polar-entropy perovskite oxides.

Abstract

Materials with a high electrocaloric effect (ECE)^1,2 tend to favour a disordered yet easily tunable polar structure. Perovskite ferroelectrics³ stand out as ideal candidates owing to their high dielectric responses and reasonable thermal conductivity. The introduction of multielement atomic distortions induces a high-polar-entropy state⁴ that notably increases the ECE by effectively overcoming the constraints imposed by highly ordered, polar-correlated perovskite structures. Here we developed a lead-free relaxor ferroelectric with strong polar disorder through targeted multielement substitution at both the A and B sites of the perovskite, effectively distorting the lattice structure and inducing a variety of nanoscale polar configurations, polymorphic polar variants and non-polar regions. A combination of these multielement-induced features led to an increased density of interfaces, significantly enhancing the polar entropy. Remarkably, a high ECE for an entropy change of about 15 J kg^-1 K^-1 under a 10 MV m^-1 field is observed for the material across a broad temperature range exceeding 60 °C. The formation of ultrafine, dispersed, multiphase lattice configurations leads to high-polar-entropy ferroelectric oxides with a high ECE and a long lifetime of over 1 million cycles that are suitable for manufacturing multilayer ceramic capacitors for practical electrocaloric refrigeration applications.