Cooling through solid-state electrocaloric materials is an attractive replacement for vapor compression. Despite recent efforts, devices that are potentially commercially competitive have not been developed. We present an electrocaloric cooler with a maximum temperature span of 20.9 kelvin and a maximum cooling power of 2.1 watts under the moderate applied electric field of 10 volts per micrometer without any observed breakdown. Moreover, the maximum coefficient of performance, even taking into account energy expended on fluid pumping, reaches 54% of Carnot’s efficiency as long as energy is properly recovered. We believe that this demonstration shows electrocaloric cooling to be a very promising alternative to vapor compression cooling.

Coming up with sustainable sources of electricity is one of the grand challenges of this century. The research field of materials for energy harvesting stems from this motivation, including thermoelectrics¹, photovoltaics² and thermophotovoltaics³. Pyroelectric materials, converting temperature periodic variations in electricity, have been considered as sensors⁴ and energy harvesters^5–7, although we lack materials and devices able to harvest in the joule range. Here we develop a macroscopic thermal energy harvester made of 42 g of lead scandium tantalate in the form of multilayer capacitors that produces 11.2 J of electricity per thermodynamic cycle. Each pyroelectric module can generate up to 4.43 J cm⁻³ of electric energy density per cycle. We also show that two of these modules weighing 0.3 g are sufficient to sustainably supply an autonomous energy harvester embedding microcontrollers and temperature sensors. Finally, we show that for a 10 K temperature span these multilayer capacitors can reach 40% of Carnot efficiency. These performances stem from (1) a ferroelectric phase transition enabling large efficiency, (2) low leakage current preventing losses and (3) high breakdown voltage. These macroscopic, scalable and highly efficient pyroelectric energy harvesters enable the reconsideration of the production of electricity from heat.

Emerging haptic technology based on piezoelectric actuators enables to realize innovative tactile human–machine interface. The standard solution is based on stand-alone bulk ceramics glued directly on the haptic device. Thin-film actuators with metal–insulator–metal structure have been developed to directly integrate actuators on haptic plates. The thickness of thin films is limited to 2 μm, leading to large capacitance and, thus, too high-power consumption. To solve this issue, we developed haptic devices based on a 10 μm-thick PZT film deposited on a 0.65 mm-thick platinized silicon substrate. These thick films are made of a PZT composite slurry associated with sol-gel sol infiltration. They are dense and exhibit a permittivity of 1000 and dielectric loss lower than 0.05. Our fabricated haptic device containing three actuators connected in series exhibits an antisymmetric Lamb wave resonant mode at 62.0 kHz, in line with finite element modeling. At the limit of touch detection (1 μm out of plane deflection), the power consumption of the haptic device is 150 mW at 40 V. This represents a 15-fold consumption reduction with respect to the same haptic device made with 0.5 μm-thick PZT thin films.

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(Sc_0.5Ta_0.5)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.