Spatially Resolved Imaging of Electrocaloric Effect and the Resultant Heat Flux in Multilayer Capacitors

Abstract

Multilayer capacitors (MLCs) are one of the most studied electrocaloric (EC) systems because they are regarded as the most promising configuration for developing electrocaloric prototype devices. Indeed, (1) they combine thin films prone to exhibit the socalled giant EC effect; (2) they are made of several hundred active layers; and (3) their internal interdigitated structure alternating highly thermally conductive electrodes with EC layers should dramatically increase their propensity to extract heat. Although the latter has been foreseen by modeling, it has never been observed experimentally. Here we use an infrared camera to observe for the first time the heat flux crossing standard EC MLCs during operation. Interestingly, we observed that heat flux perpendicular to the terminal−terminal direction accounts for only 20% of the total heat flux. This observation strongly suggests that all future electrocaloric cooling devices should rely on a design favoring heat exchange through the MLC terminals.

Direct and indirect measurements on electrocaloric effect: Recent developments and perspectives

“…132,133,138,[143][144][145][146][147][148][149] Typically, the camera consists of an arrangement of lenses with a digital detector semiconductor (i.e., InSb) having a broadband spectral sensitivity of several micrometers. Thermal images captured by the camera usually have an effective spatial resolution of several micrometers with a thermal sensitivity of about 25 mK.…”

“…For instance, higher frequencies (i.e., 100 Hz) can ensure the adiabatic conditions in most of the measurements on bulk materials. 132,133,138,[143][144][145][146][147][148][149] In this case, the camera is sensitive enough to capture thermal change in each pixel in near adiabatic conditions.…”

“…138 This can be overcome by measuring the intensity of the thermal radiation at two adjacent temperatures and interpolating linearly but at expense of the high accuracy temperature measurements. 138 This can be also achieved by manually adjusting the emissivity of different selected regions without compromising the resolution of camera, 149 which corresponds to setting the temperature of the sample to a specific measurement temperature.…”

“…132,133,138,[143][144][145][146][147][148][149] A non-contact IR camera is compact and fast compared with the other techniques, i.e., DSC, and its use is rather simple. More importantly, an IR camera can directly image spatial caloric response, which is the main advantage over other techniques such as DSC, thermocouple, and other specifically designed calorimeters.…”

Towards multicaloric effect with ferroelectrics

“…[6] Among the ferroic materials ferroelectrics can be good potential candidates for developing multicaloric effect, due to the fact that the phase transition in ferroelectrics can be triggered by electric field, uniaxial stress and hydrostatic pressure. [7] According to the literature, individual caloric effects such as electrocaloric, [8][9][10][11][12][13][14][15][16][17][18][19][20] elastocaloric [21][22][23][24][25][26][27][28] and barocaloric [28][29][30][31][32][33] scenarios have all been reported in ferroelectric materials. In this context only a few theoretical studies have been published to understand the multicaloric effect in ferroelectric bulk and thin films driven by simultaneous application of electric and mechanical fields.…”