Electrocaloric effect in BaTiO3 multilayer capacitors with first-order phase transitions

Abstract

Electrocaloric (EC) materials, presenting large adiabatic temperature change or isothermal entropy change under the application (or removal) of electric fields, offer an efficient alternative to caloric heat pumps for replacing hazardous gases used in traditional vapor-compression systems. Recently, a large EC temperature change of 5.5 K have been reported in Pb(Sc0.5Ta0.5)O3 multilayer ceramic capacitors (Nair et al 2019 Nature 575 468) thanks to its strong first-order phase transition and a temperature span of 13 K has been reported in a prototype based on these capacitors (Torelló et al 2020 Science 370 125). However, the toxicity of lead forces researchers to find eco-friendly materials exhibiting competitive EC performances. Here, we study the EC effect in lead-free BaTiO3 multilayer capacitors using an infrared camera. Unlike commercial BaTiO3 capacitors, we prepared our samples without sacrifying the first-order phase transition in BaTiO3 while a low amount of 0.2 mol% Mn was added as an acceptor dopant to improve electrical resistivity. Their EC adiabatic temperature variations show two peaks versus temperature, which match BaTiO3 two first-order phase transitions, as observed by differential scanning calorimetry. We measured a temperature drop of ∼0.9 K over a temperature range of 70 K under 170 kV cm−1, starting at 30 °C near the tetragonal-to-orthorhombic phase transition. Under the same electric field, a maximum temperature change of 2.4 K was recorded at 126 °C, at BaTiO3’s Curie temperature. Our findings suggest that further optimized BaTiO3 capacitors could offer a path for designing lead-free caloric cooling prototypes.