Enhanced electrocaloric cooling in ferroelectric single crystals by electric field reversal

Abstract

An improved thermodynamic cycle is proposed, where the cooling effect of an electrocaloric refrigerant is enhanced by applying a reversed electric field. In contrast to conventional adiabatic heating or cooling by on-off cycles of the external electric field, applying a reversed field is significantly improving the cooling efficiency, since the variation in configurational entropy is increased. By comparing results from computer simulations using Monte-Carlo algorithms and experiments using direct electrocaloric measurements, we show that the electrocaloric cooling efficiency can be enhanced by more than 20% in standard ferroelectrics and also relaxor ferroelectrics, like Pb(Mg 1/3 /Nb 2/3 )0.71Ti0.29O3.

Optimized electrocaloric effect by field reversal: Analytical model

“…In other words, ignoring the irreversible contribution leads to the conclusion that the maximum EC cooling appears at P = 0. This deviates from the previous experimental 4,6 and numerical observation 6 .…”

“…In comparison with the model II, the work loss in the model III is corrected through consideration of the extra contribution. Hence, the maximum EC cooling point is further shifted away from the zero-polarization point, and reaches around the point D, showing good agreement with the experimental results 4,6 . The exact position is also defined as the point where dS total /dP catches up with dS dip /dP (see the gray dashed line).…”

“…The EC hysteresis of ferroelectric ceramics measured by Thacher et al 5 indicated also that a reversed electric field can increase the cooling effect of ferroelectric ceramics. In the authors' previous work, 6 experimental and numerical studies were carried in PMN-29PT and BaTiO 3 , which demonstrated that there exists an optimal reversed electric field, corresponding to a position around the shoulder of the dielectric hysteresis. At this point, the EC cooling effect reaches its maximum (also see Fig.…”

“…The adiabatic condition can be strictly fulfilled in MonteCarlo and Molecular Dynamics simulations by utilizing the direct method. 6,[10][11][12][13][14] In these methods, the information of the entropy change can be hardly extracted, which is, however, very important for the understanding of the maximal EC cooling point. In this study, we propose a direct method to analyze the entropy changes in an irreversible process, and apply it to reveal the optimal reversed electric field which maximizes the EC cooling.…”

Thermodynamic analysis of a cooling system using electrocaloric effect

“…24,33) On the bases of the above historical situation, basic concepts for a larger EC effect were proposed from the view point of analyzing heat efficiency [34][35][36][37] and the theoretical approaches have been carried out from the viewpoint of statistical mechanics. [38][39][40][41] The above previous studies focused on the temperature change of dielectric=ferroelectric materials. However, as clearly seen in the derivation of Eqs.…”