Although vapor compression cooling has been used for over 200 years, it is neither environmentally friendly nor efficient. In recent years, alternatives to such technologies have received increased attention. The most promising ones are based on caloric effects, which is the temperature change within a material due to an external stimulus. However, most reports focus on the electrocaloric (EC) or magnetocaloric (MC) effect independently. Recently, there has been increased interest in the multicaloric effect, where the application of both electric and magnetic fields can enhance the total caloric performance or broaden the operating temperature range of the cooling device. In addition to novel cooling technologies, flexible electronics are also highly desired due to their promising applications. In light of this, in this contribution we investigate, the feasibility of preparing multicaloric composite thick films by aerosol deposition (AD) on flexible substrates. Among the materials candidates, 0.9Pb(Mg_1/3Nb_2/3)O₃–0.1PbTiO₃ (PMN–10PT) is a suitable EC candidate, as it shows excellent bulk electrocaloric properties, such as, a large EC temperature change ΔT_EC ∼3.5 °C at 110 °C and a wide working temperature range of ∼100 °C. Furthermore, PMN–10PT powder exhibits a high AD rate. The magnetocaloric material, on the other hand, is a La–Fe–Si-based MC alloy which shows a temperature change of ΔT_MC∼2.5 °C at room temperature and a temperature range of ∼20 °C.
In this work, we prepared thick-film samples with different MC concentrations, spanning from 2 wt% to 15 wt%. The films were prepared using the AD method with N₂ as the carrier gas on a flexible gold-sputtered polymer substrate. In this way, we prepared films of thickness above 5 μm. To release the internal stresses from the AD, the films were annealed at 400 °C and their electrical were properties characterized. For example, the 10 wt% of MC composition showed a saturation polarization of 36 μC/cm² at 600 kV/cm, while PMN–10PT films, prepared via the same methods, show the same polarization at 900 kV/cm. This enhancement in polarization is a result of the Maxwell-Wagner effect, namely, metallic content within a dielectric matrix act as electric dipoles, therefore increasing the dielectric permittivity and polarization. However, due to the metallic nature of particles, the enhancement comes at the cost of more electrically conductive materials. In addition to electrical measurements, the cross-sectional structure of the films was characterized using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The SEM investigations showed dense thick films with great adhesion to the substrate with a homogeneous distribution of MC content throughout the matrix. On the other hand, the TEM revealed details about the grain size distribution, spanning from few nanometers to few hundreds of nanometers. The EC performance of 2 wt% and 5 wt% were investigated and they exhibited similar temperature change to PMN–10PT thick films, i.e., with the application of both electric and magnetic fields, the total caloric performance should be enhanced. During the presentation of this contribution, other compositions and the magnetic properties of the composites will be discussed