Direct Visualization of Anti‐Ferroelectric Switching Dynamics via Electrocaloric Imaging

Abstract

or even the standard gas cooling cycle (50%). [1] First theorized in 1878 by William Thomson, [2] the high-temperature changes (ΔT = 12 K) calculated for ferroelectric (FE) thin films [3] and the discovery of an anomalous electrocaloric effect in anti-ferroelectrics (AFE) [3] have renewed its interest, with an eye put on its potential application as a solid-state cooling solution in integrated circuits.FE materials display what is regarded as the "conventional" electrocaloric effect (or positive electrocaloric effect), whereby the material increases temperature (ΔT > 0) when a voltage step is applied and decreases temperature (ΔT < 0) when it is removed. In contrast, AFE display the opposite response; they decrease temperature (ΔT < 0) when an electric field E is applied, and increase (ΔT > 0) when it is removed. The ability of anti-ferroelectrics to cool down despite electrostatic energy being pumped into them is intriguing, and different underlying mechanisms have been proposed for the negative electrocaloric effect. [4,5] Recent experimental evidence indicates that, in the archetypal anti-ferroelectric PbZrO 3 (PZO), the so-called giant negative electrocaloric effect is due to the latent heat absorbed during the adiabatic-field-induced AFE-FE transition, which is endothermic. [6] In PbZrO 3 , the direct link between the anomalous electrocaloric effect and the first-order anti-ferroelectric-ferroelectric switching implies that the field-induced nucleation and motion of the AFE-FE phase boundary will dictate the dynamics of the large negative ECE and, ultimately, the dynamics of electrocaloric devices based on first-order transitions. In ferroelectrics, the study of domain wall dynamics [7][8][9][10][11][12][13][14][15][16] has been examined in detail on account of their relevance for ferroelectric memories. In contrast, there are far fewer works regarding the dynamics of the ferroelectric-paraelectric phase boundaries in FE [17,18] or the anti-ferroelectric-ferroelectric ones in anti-ferroelectrics. [19][20][21][22][23] Yet, a priori, one cannot assume that the dynamics of domain walls will be the same as the dynamics of phase boundaries, while the former separate different domains within the same ferroelectric phase, the latter separate different phases-in antiferroelectrics, an antipolar phase from a field-induced polar one. Domain switching dynamics is defined by a nucleationpropagation process. On the one hand, nucleation refers to the appearance of "hotspots," where nanoscopic nuclei of switched domains appear and rapidly expand forward across the thickness The large electrocaloric coupling in PbZrO 3 allows using high-speed infrared imaging for visualizing anti-ferroelectric switching dynamics via the associated temperature change. It is found that in ceramic samples of homogeneous temperature and thickness, switching is fast due to the generation of multiple nucleation sites, with devices responding in the millisecond range. By introducing gradients of thickness, however, it is possible to change the dyn...

High resolution spatial mapping of the electrocaloric effect in a multilayer ceramic capacitor using scanning thermal microscopy

“…Experimentally, the IR thermal imaging camera has been an indispensable tool for exploring the spatial distribution of caloric heating and cooling. The IR camera provides an excellent non-contact thermal imaging platform that combines high spatial resolution, large field of view and high frame rate capture and has been leveraged for imaging EC temperature distributions in multi-layer ceramic capacitors (MLCCs) [6,7], polymer ferroelectrics [8,9] and antiferroelectric ceramics [10]. In the case of MLCCs, the dynamics of heat exchange with the surrounding inactive material and environment have been visualised, with complementary finite element modelling [11,12] providing a means for optimising the thermal design of the EC elements for heat extraction.…”

“…In the case of MLCCs, the dynamics of heat exchange with the surrounding inactive material and environment have been visualised, with complementary finite element modelling [11,12] providing a means for optimising the thermal design of the EC elements for heat extraction. In antiferroelectric PbZrO 3 ceramics, use of a wedged sample geometry allowed visualisation of a temperature front propagating through the sample spatially coincident with the phase transition front [10]. Because of its versatility, the IR camera has also been applied to monitor temperature changes in the related families of magnetocaloric [13,14] and elastocaloric materials [15][16][17].…”

Electrocaloric Coolers: A Review

“…An example is the antiferroelectric–FE phase transition, where recent works have shown inverse EC effects in the sense that the application of an electric field produces a negative temperature change instead of a positive one. [ 24–26 ]…”

“…An example is the antiferroelectric-FE phase transition, where recent works have shown inverse EC effects in the sense that the application of an electric field produces a negative temperature change instead of a positive one. [24][25][26] Differently from MC and eC prototypes though, EC demonstrators have struggled to maintain temperature spans (temperature difference between hot and cold side of the cooling device) larger than 10 K and have barely reported cooling power values. One of the reasons for these low and incipient performances is the relatively low EC effect of most common materials to date (<5 K).…”

Thermal management of chips by a device prototype using synergistic effects of 3-D heat-conductive network and electrocaloric refrigeration

“…When an electric field is applied to the composite, it induces a disorder-to-order orientational change of the electric dipoles in the polymer. Interaction of the oriented dipoles leads to nanoscale regions and release the heat to surround area 21 . These “hot spots” are randomly distributed in the thermal-insulated polymer.…”