Aerosol Deposition of Thick Films for Caloric Applications

Most current activities in cooling research deal with one of the caloric effects - electrocaloric (EC), magnetocaloric (MC), or mechanocaloric. Among the caloric effects, the electrocaloric (EC) effect is triggered by voltage, which is readily available. Currently, one of the most studied inorganic EC materials is (1-x)Pb(Mg_1/3Nb_2/3)O₃–xPbTiO₃ (PMN–100xPT), which in bulk ceramic form exhibits an EC temperature change of 3.45 °C at an electric field of 160 kVcm^-1 [1,2].

To miniaturize functional devices, electroceramic components must be reduced in size. Due to the low thermal mass of the EC thin films (thickness < 1µm), the EC-induced heat immediately disappears into the substrate, which acts as a large heat sink/source. Therefore, the caloric film should not be too thin, so film thicknesses in the range of micrometres are desired. Furthermore, the films should be prepared on low-thermal conductivity substrates. The aerosol deposition (AD) process offers a cost-effective way to deposit dense, micrometre-thick films at room temperature, enabling the integration of ceramic components on various substrates, including low-thermal conductive polymers.

In this context, we investigated the feasibility of preparing PMN–PT thick films on thermally insulating polymer substrates using the aerosol deposition technique. The measured cooling effect in PMN–10PT films on polymer substrates annealed at 400 °C is ~1.6 °C at 400 kVcm^-1 and 100 °C (correction factor 3) [3]. The films also show promising polarization (~40 µCcm^-2) and energy storage performance (energy density of 10 Jcm⁻³ and efficiency 73%) at 1 MVcm^-1 and can withstand 100,000 mechanical bending cycles up to the radius of 3 mm without degradation of their functional properties [4]. PMN–35PT thick films are also piezoelectric [5]. In addition, PMN–10PT/La-Fe-Si alloy thick-film composites on polymer substrates show electrocaloric and magnetocaloric performance. Lead-free thick films based on BaTiO₃ will also be discussed.

[1] M. Vrabelj, H. Ursic, Z. Kutnjak, B. Rozic, S. Drnovsek, A. Bencan, V. Bobnar, L. Fulanovic, B. Malic, J. Eur. Ceram. Soc., vol. 36, pp. 75, 2016.
[2] H. Ursic, M. Vrabelj, M. Otonicar, L. Fulanovic, B. Rozic, Z. Kutnjak, V. Bobnar, B. Malic, Crystals, vol. 11, pp. 372, 2021.
[3] U. Prah, M. Sadl, A. Torello, P. Lheritier, V. Kovacova, H. Ursic, E. Defay, Small Methods, vol. 7, pp. 2300212, 2023.
[4] M. Sadl, A. Lebar, J. Valentincic, H. Ursic, ACS Appl. Energy Mater., vol. 5, pp. 6896−6902, 2022.
[5] M. Sadl, U. Prah, V. Kovacova, E. Defay, T. Rojac, A. Lebar, J. Valentinčič, H. Ursic, J. Mat. Chem. C, vol. 11, pp. 10058−10068, 2023.