Lattice-based Monte Carlo simulations of the electrocaloric effect in ferroelectrics and relaxor ferroelectrics

Ma, Yang-Bin; Albe, Karsten; Xu, Bai‐Xiang

doi:10.1103/physrevb.91.184108

Cited by 27 publications

(21 citation statements)

References 51 publications

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“…In addition, deeper insights into the contributions of ferroelectric switching, 105,106 domain growth, 107,108 and domain wall [109][110][111][112] to the electrocaloric effect are highly desired in order to provide basic understandings. For instance, a recent study using non-adiabatic direct measurement on PZT-5 ceramics showed that DT displays a hysteresis behavior with E and the sign of electrocaloric effect reverses at the coercive field where polarization switching occurs.…”

Section: F Heat Capacity and Kineticsmentioning

confidence: 99%

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

Liu

Scott

Dkhil

2016

Applied Physics Reviews

243

150

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It has been ten years since the discovery of the giant electrocaloric effect in ferroelectric materials showed that it is possible to employ this effect for substantial cooling applications. This last decade has been marked by increasing research interest, especially in characterizing and measuring the electrocaloric effect using both the so-called indirect and direct approaches. In this context, a comprehensive summary and careful reexamination of these approaches are very timely and of great importance to justify the assumptions used in different measurement techniques. This review is therefore dedicated to cover recent important and rapid advances from both the indirect and direct measurements and provides critical insights relevant for quantifying the electrocaloric effect. It involves electrocaloric materials from normal ferroelectrics, antiferroelectrics, and relaxors, and it fundamentally focuses on how the electrocaloric entropy changes in response to electric field in these typical electrocalorics. The article addresses recent developments, especially during the past three years, such as technical selection of proper polarization-electric field loops, negative electrocaloric effect in antiferroelectrics and relaxors, the controversial debate on the indirect method in relaxors, the important role of field dependence of specific heat, kinetic factors, and so on. Moreover, this review also is concerned with extracting reliable data by direct measurements. Four typical techniques and devices used recently, such as thermocouples, differential scanning calorimeters, specifically designed calorimeters, and scanning thermal microscopy, are briefly reviewed, while infrared cameras are emphasized. We hope that our review will not only provide a useful background to understand fundamentally the electrocaloric effect and what one really measures but also may act as a practical guide to exploit and develop electrocalorics towards the design of suitable devices. Published by AIP Publishing. [http://dx

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Section: F Heat Capacity and Kineticsmentioning

confidence: 99%

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

Liu

Scott

Dkhil

2016

Applied Physics Reviews

243

150

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“…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.…”

Section: -3mentioning

confidence: 99%

Optimized electrocaloric effect by field reversal: Analytical model

Novak

Albe

et al. 2016

Applied Physics Letters

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Application of a negative field on a positively poled ferroelectric sample can enhance the electrocaloric cooling and appears as a promising method to optimize the electrocaloric cycle. Experimental measurements show that the maximal cooling does not appear at the zero-polarization point, but around the shoulder of the P-E loop. This phenomenon cannot be explained by the theory based on the constant total entropy assumption under adiabatic condition. In fact, adiabatic condition does not imply constant total entropy when irreversibility is involved. A direct entropy analysis approach based on work loss is proposed in this work, which takes the entropy contribution of the irreversible process into account. The optimal reversed field determined by this approach agrees with the experimental observations. This study signifies the importance of considering the irreversible process in the electrocaloric cycles.The electrocaloric (EC) effect shows great application potential in the technology of solid state refrigeration. 1-3Even though much effort has been made to explore material candidates with large EC effect and device concepts, there are few work concerning the optimization of electrocaloric cycle. In a conventional EC cycle of a solid refrigerant, the cooling effect is obtained simply by removing the previously applied electric field. Using direct heat flux calorimetry on poly(vinylidene fuoridetride-trifuoroethylene) films, Basso et al. 4 demonstrated that the electrocaloric cooling can be doubled if a negative electric field to a positively poled sample is applied. 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. 1). This phenomenon was also observed in Ref. 4. It is of scientific and engineering importance to deter- mine and understand this optimal reversed electric field. In the literature, as reviewed in Ref. 7, the EC cycle is considered to be reversible, with constant total entropy under the adiabatic condition. This assumption leads to the conclusion that the maximal cooling takes place at the zero polarization point, since at this point the dipolar entropy takes maximum (see Model I). This conclusion deviates obviously from the experimental observations. In fact, the total entropy S total should satisfy:where S dip and S vib are the dipolar and the vibrational entropy, respectively. In the case of applying a reversed electric field, the irreversible contribution becomes considerable. In other words, to correctly determine the optimal reversed electric field, the change of the total entropy induced by the work loss W loss due to the irreversible process s...

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“…We apply a lattice-based microcanonical Monte Carlo scheme to directly calculate the electrocaloric effect (ECE) [17]. This Hamiltonian consists of the potential energy and the thermal energy .…”

Section: Modelmentioning

confidence: 99%

“…We modified a widely accepted model [11]- [16] to evaluate the ECE in relaxor ferroelectrics in the previous work [17]. In that work, the random fields are introduced to reproduce the relaxor behavior, and are randomly distributed between 0 ∘ and 360 ∘ , and the magnitude is between 0 and an allowed maximum value | |.…”

Section: Introductionmentioning

confidence: 99%

Monte Carlo simulations of the electrocaloric effect in relaxor ferroelectrics

Albe

2015

2015 Joint IEEE International Symposium on the Applications of Ferroelectric (ISAF), International Symposium on Integrated Func

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By combination of the canonical and microcanonical Monte Carlo simulations a direct evaluation of the electrocaloric (ECE) effect is carried out in relaxor ferroelectrics. A Hamiltonian is introduced, which includes a thermal energy, a GinzburgLandau static ground state term, a dipole-dipole interaction energy, a domain wall energy that arising from the short-range interaction and an electrostatic energy contribution describing the coupling to external and random fields. By incorporating the frozen random dipoles random fields are induced to reproduce the relaxor behavior. The influence of the density of the frozen dipoles on the hysteresis and ECE is investigated. The hysteresis begins to resemble a relaxor-type with 20% density of the frozen dipoles. Upon increasing the density of the frozen random dipoles, the ECE peak position shifts to a lower temperature but the temperature variation is reduced. In relaxor ferroelectrics the ECE is maximum at the freezing temperature where the nonergodic-toergodic transition takes place. Our results, especially the evolving domain structures, imply that the entropy variation in an ECE cycle is reduced since the random frozen dipoles destabilize the polarization of their neighbor sites.

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Lattice-based Monte Carlo simulations of the electrocaloric effect in ferroelectrics and relaxor ferroelectrics

Cited by 27 publications

References 51 publications

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

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

Optimized electrocaloric effect by field reversal: Analytical model

Monte Carlo simulations of the electrocaloric effect in relaxor ferroelectrics

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