Effect of misfit strain on the electrocaloric effect of polydomain epitaxial ferroelectric thin films

The effect of misfit strain on the electrocaloric effect in polydomain epitaxial BaTi03 thin films at room temper- ature is investigated using the Ginzburg^Landau Devonshire thermodynamic theory. Numerical calculations indicate that the misfit strain has a large impact on the ferroelectric polarization states and the electrocaloric effect. Most importantly, the electrocaloric effect in the polydomain ca1/ca2/ca1/ea2 phase is much larger than that in the mon- odomain c phase and the other polydomain phases. Consequently, a large electrocaloric effect can be obtained by carefully controlling the misfit strain, which may provide potential applications in refrigeration devices.

Composition and misfit strain dependence of electrocaloric effect of Pb_(1-x) Sr_xTiO_3 thin films

A Landau-Devonshire thermodynamic theory is employed to investigate the effects of composition and misfit strain on the room-temperature electrocaloric effect of epitaxial Pbl-xSrxTiO3 thin films. The ＂temperature-misfit strain＂ phase diagrams with the Sr composition x of 0.1, 0.3, and 0.5 are constructed. The introduction of Sr composition reduces the Curie temperature greatly, and enhances the electrocaloric effect. Moreover, the electrocaloric effect largely depends on the misfit strain. Therefore, the Sr composition and the misfit strain can be controlled to obtain the giant room-temperature electrocaloric effect.

Effect of an electric field on the electrocaloric response of ferroelectrics

The electrocaloric effect of the model ferroelectric BaTiO3was investigated using phenomenological theory. The results indicate that the applied electric field strength is a key factor for the induced electrocaloric response and there are two distinguishing electrocaloric responses. When a moderate electric field is applied, the electrocaloric temperature variation is small but the electrocaloric strength is high. In contrast, the electrocaloric temperature variation is large but electrocaloric strength is low when a very high electric field is applied. These results are consistent with the experimental observations on BaTiO3based bulk and thin film ferroelectric materials.

Efficient Cooling System Using Electrocaloric Effect

The electrocaloric effect in thin films of an electrocaloric material has the potential to be used for efficient cooling systems for high power electronic devices. We numerically calculated the effect of parameters in electrocaloric refrigeration with a thermal switch of fluid motion on the thermal performance. The system of changing air and water flow with the pulse generation of cold energy increased the heat transfer efficiency to 67% at a frequency of 5 Hz. The optimum time delay of water flow to increase the heat transfer efficiency was zero at low frequency and became half of the time period to change heat for a high frequency of 100 Hz. When the heat transfer efficiency was high, the final temperature change in water flow was not the maximum temperature change.

Electrocaloric effect in ferroelectric materials:From phase field to first-principles based effective Hamiltonian modeling

Electrocaloric effect(ECE)of ferroelectrics has attracted considerable interest due to its potential application in environmentally friendly solid-state refrigeration.The discovery of giant ECE in ferroelectric thin films has greatly renewed the research activities and significantly stimulated experimental and theoretical investigations.In this review,the recent progress on the theoretical modeling of ECE in ferroelectric and antiferroelectric materials are introduced,which mainly focuses on the phase field modeling and first-principles based effective Hamiltonian method.We firstly provide the theoretical foundation and technique details for each method.Then a comprehensive review on the progress in the application of two methods and the strategies to tune the ECE are presented.Finally,we outline the practical procedure on the development of multi-scale computational method without experiemtal parameters for the screening of optimized electrocaloric materials.

Electrocaloric effect and pyroelectric properties of organic–inorganic hybrid （C2H5NH3）2CuCl4

The organic–inorganic hybrid(C2H5NH3)2 CuCl4(EA2CuCl4) single crystals are prepared by the solvothermal condition method. The x-ray diffraction, scanning electron microscopy, dielectric permittivity, pyroelectric current, and heat capacity are used to systematically investigate the electrocaloric performances of EA2CuCl4. The pyroelectric currents are measured under various voltages, and the electrocaloric effect(ECE) is calculated. Its ECE exhibits an isothermal entropy change of 0.0028 J/kg·K under an electric field of 30 kV/cm associated with a relatively broad temperature span. Further, the maximum pyroelectric coefficient(p) is 4× 10^-3 C/m^2·K and the coefficient β for generating ECE from electric displacement D is 1.068× 10^8 J·cm·K^-1·C^-2 at 240 K. Our results indicate that the ECE behavior of organic–inorganic hybrid EA2CuCl4 is in accordance with Jona and Shirane’s opinion in which the ECE should occur both below and above the Curie temperature Tc.

Electrocaloric effect enhanced thermal conduction of a multilayer ceramic structure

The electrocaloric effect of ferroelectric ceramics has been studied extensively for solid-state caloric cooling.Generally,most ferroelectric ceramics are poor thermal conductors.In this work,the possibility of enhancing the thermal conduction of ferroelectric ceramics through the electrocaloric effect is studied.A multilayer ceramic structure is proposed and the proper sequential electric field is applied to each ceramic layer.The result shows that the thermal conduction of the multilayer structure is significantly enhanced because of the electrocaloric effect of the ferroelectric ceramics.As a result,the work finds an alternatively way of applying the electrocaloric effect,prompting thermal conduction.

On the parameters for electrocaloric effect predicted by indirect method

The influences of specific heat capacity CP, temperature step ？T, electric field step ？E, and initial electric field E1 on predicted electrocaloric（EC） temperature ？T of monodomain Ba TiO3 are examined by combining the Maxwell equation and phenomenological theory. Since the procedure is similar to indirect measurement of the EC effect, the results can serve as a reference for experiments. The results suggest that（i） it is reasonable to use zero-field CP,（ii） optimized ？T should be 2 K,（iii） it is better to keep △E 〈 EC, and（iv） E1〈 EC. Here, EC is the coercive field of material.

Compact Thermal Management Device Using Electrocaloric Effect

The electrocaloric effect (ECE) is defined as the fact that the temperature of dielectric material changes, when an electric field is applied to or removed from the material [1]. It might be a possible solution for the increasing energy consumption for thermal management because of its high effectiveness. Previous research on the ECE has investigated several possible methods to build a model based on ECE and feasibilities to increase the efficiency of the model. But there has been no study on all the factors that may affect the performance of the device. Thus, in this paper, we designed a cooling device based on ECE and simulated it by using the control variates method showing that a high efficiency can be reached through stated model.

polydomain 的 electrocaloric 效果上的不合身的衣服紧张的效果取向附生的铁电体薄电影

The effect of misfit strain on the electrocaloric effect in polydomain epitaxial BaTiO 3 thin films at room temperature is investigated using the Ginzburg–Landau–Devonshire thermodynamic theory. Numerical calculations indicate that the misfit strain has a large impact on the ferroelectric polarization states and the electrocaloric effect. Most importantly, the electrocaloric effect in the polydomain ca 1 /ca 2 /ca 1 /ca 2 phase is much larger than that in the monodomain c phase and the other polydomain phases. Consequently, a large electrocaloric effect can be obtained by carefully controlling the misfit strain, which may provide potential applications in refrigeration devices.

Composition-tailor induced electrocaloric effect near room temperature in(Pb,Ba)HfO_(3)films

More and more researchers start to pay attention to the electrocaloric temperature change(DT)in polar materials,which is caused by an applied electric field.In this paper,Ba-doped PbHfO_(3)(PBH)films were prepared by sol-gel method.Their components,microstructures,dielectric polarization and electro-caloric effects(ECEs)were investigated.With the addition of Ba^(2+),PBH films went from antiferroelectric(AFE)to ferroelectric(FE).At the same time,their dielectric peaks shifted toward lower temperature.The maximum DT obtained in Pb_(0.8)Ba_(0.2)HfO_(3)FE film is 41.1 K,which is an order of magnitude larger than PbHfO_(3)film(△T<4 K at 50℃)and Pb_(0.9)Ba_(0.1)HfO_(3)film(△T<4 K at 120℃).In order to explain this phenomenon,the Landau-Devonshire theory was adopted.Our analysis shows that the rapid variation of energy barrier height near the phase transition temperature is beneficial to obtain large polarization change and high△T,which is needed in solid-state cooling devices.

Polymeric nanocomposites for electrocaloric refrigeration

Electrocaloric refrigeration represents an alternative solid-state cooling technology that has the potential to reach the ultimate goal of achieving zero-global-warming potential,highly efficient refrigeration,and heat pumps.To date,both polymeric and inorganic oxides have demonstrated giant electrocaloric effect as well as respective cooling devices.Although both polymeric and inorganic oxides have been identified as promising cooling methods that are distinguishable from the traditional ones,they still pose many challenges to more practical applications.From an electrocaloric material point of view,electrocaloric nanocomposites may provide a solution to combine the beneficial effects of both organic and inorganic electrocaloric materials.This article reviews the recent advancements in polymer-based electrocaloric composites and the state-of-the-art cooling devices operating these nanocomposites.From a device point of view,it discusses the existing challenges and potential opportunities of electrocaloric nanocomposites.

Direct measurement of electrocaloric effect in P(VDF-TrFE-CFE)film using infrared imaging

Poly(vinylidene fluoride-trifluoroethylene-chlorofluoroethylene)P(VDF-TrFE-CFE)is a relaxor ferroelectric polymer,which exhibits a temperature-independent electrocaloric effect at room temperature.In this work,the electrocaloric effect in P(VDF-TrFE-CFE)film was directly analysed using infrared imaging.P(VDF-TrFE-CFE)64.8%/27.4%/7.8%(in mole)film of(15±1)mm thickness was deposited on polyethylene naphthalate substrate.Direct ECE of P(VDF-TrFE-CFE)film was measured from 15 to 35
C at different electric fields.A maximum adiabatic temperature change(DTad)of 3.58 K was measured during the cooling cycle at a field of 100 V/mm at 30
C.Finite element analysis of temperature dissipation through the sample estimated that the actual temperature change within P(VDF-TrFE-CFE)film was 4.3 K.Despite the thermal mass of the substrate,a substantial ECE was observed in P(VDF-TrFE-CFE)films.This electrocaloric terpolymer composition could be of interest for electrocaloric cooling applications.

Correlation between multi-factor phase diagrams and complex electrocaloric behaviors in PNZST antiferroelectric ceramic system

Ferroelectric(FE)phase transition with a large polarization change benefits to generate large electrocaloric(EC)effect for solid-sate and zero-carbon cooling application.However,most EC studies only focus on the single-physical factor associated phase transition.Herein,we initiated a comprehensive discussion on phase transition in Pb_(0.99)Nb_(0.02)[(Zr_(0.6)Sn_(0.4))1−xTix]_(0.98)O_(3)(PNZST100x)antiferroelectric(AFE)ceramic system under the joint action of multi-physical factors,including composition,temperature,and electric field.Due to low energy barrier and enhanced zero-field entropy,the multi-phase coexistence point(x=0.12)in the composition–temperature phase diagram yields a large positive EC peak of maximum temperature change(ΔT_(max))=2.44 K(at 40 kV/cm).Moreover,the electric field–temperature phase diagrams for four representative ceramics provide a more explicit guidance for EC evolution behavior.Besides the positive EC peaks near various phase transition temperatures,giant positive EC effects are also brought out by the electric field-induced phase transition from tetragonal AFE(AFET)to low-temperature rhombohedral FE(FER),which is reflected by a positive-slope boundary in the electric field–temperature phase diagram,while significant negative EC responses are generated by the phase transition from AFET to high-temperature multi-cell cubic paraelectric(PEMCC)with a negative-slope phase boundary.This work emphasizes the importance of phase diagram covering multi-physical factors for high-performance EC material design.

A review on different theoretical models of electrocaloric effect for refrigeration

The performance parameters for characterizing the electrocaloric effect are isothermal entropy change and the adiabatic temperature change,respectively.This paper reviews the electrocaloric effect of ferroelectric materials based on different theoretical models.First,it provides four different calculation scales(the first-principle-based effective Hamiltonian,the Landau-Devonshire thermodynamic theory,phase-field simulation,and finite element analysis)to explain the basic theory of calculating the electrocaloric effect.Then,it comprehensively reviews the recent progress of these methods in regulating the electrocaloric effect and the generation mechanism of the electrocaloric effect.Finally,it summarizes and anticipates the exploration of more novel electrocaloric materials based on the framework constructed by the different computational methods.

Multi-element B-site substituted perovskite ferroelectrics exhibit enhanced electrocaloric effect

Electrocaloric(EC)refrigeration holds the promise to achieve next-generation refrigeration technology that can be efficiently powered by electricity.BaTiO_(3)(BT)-based ferroelectric materials are attractive owing to their environmentally benign compositions,large polarization,and existing manufacturing method for multilayer ceramic capacitors(MLCC),which have stimulated intensive research efforts on these materials.Here,we report an enhanced electrocaloric effect(ECE)and the refrigeration capacity of multi-element B-site substituted BT-based ceramics.The compositions of the proposed Ba(Hf_(x)Sn_(x)Zr_(y))-Ti_(1-2x-y)O_(3)(BHSZT)ceramics were selected by fine-tuning each substituent against Titanium ions Ti^(4+),aiming to their respective morphotropic phase boundary(MPB).The BHSZT exhibited an ECE that is greater than that of the single-element substituted BaTiO_(3) ceramics by at least 50%,reaching an adiabatic temperature change of above 1.7 K under 40 kV/cm.Meanwhile,the operating temperature window of the BHSZT ceramics is observed to cover the room temperature,which is a critical feature that allows the device implementation in our daily life.The multi-element substitution improved the overall ECE performances,providing a high degree of freedom for polar reorientation and hence the large polar entropy that could be utilized by the external electric field.

Peculiarities of the electrocaloric effect in relaxors

A comprehensive study and detailed analysis of pyroelectric and electrocaloric effects in relaxor ferroelectrics based on lead magnesium niobate as a promising object for such investigations have been carried out.It was found that even at the maximum values of pyroelectric coefficients the electrocaloric response inextricably linked with the pyroelectric effect does not exceed 1°C in the temperature range from 10 to 60°C under DC electric field up to 60 kV/cm.These conditions are the most demanded for the operation of electrocaloric cooling devices.Vision for the future as to increasing the efficiency of the main elements for such devices is discussed.

Large electrocaloric effect over a wide temperature span in lead-free bismuth sodium titanate-based relaxor ferroelectrics

For efficient solid-state refrigeration technologies based on electrocaloric effect(ECE),it is a great challenge of simultaneously obtaining a large adiabatic temperature change(DT)within a wide temperature span(Tspan)in lead-free ferroelectric ceramics.Here,we studied the electrocaloric effect(ECE)in(1-x)(Na_(0.5)Bi_(0.5))TiO_(3)-xCaTiO_(3)((1-x)NBT-xCT)and explored the combining effect of morphotropic phase boundary(MPB)and relaxor feature.The addition of CT not only constructs a MPB region with the coexistence of rhombohedral and orthorhombic phases,but also enhances the relaxor feature.The ECE peak appears around the freezing temperature(Tf),and shifts toward to lower temperature with the increasing CT amount.The directly measured ECE result shows that the ceramic of x=0.10,which is in the MPB region,has an optimal ECE property of DTmax=1.28 K@60℃under 60 kV/cm with a wide Tspan of 65C.The enhanced ECE originates from the electric-field-induced transition between more types of polar nanoregions and long-range ferroelectric macrodomains.For the composition with more relaxor feature in the MPB region,such as x?0.12,the ECE is relatively weak under low electric fields but it exhibits a sharp increment under a sufficiently high electric field.This work provides a guideline to develop the solidestate cooling devices for electronic components.

Enhanced electrocaloric effect at room temperature in Mn^(2+) doped lead-free(BaSr)TiO_(3) ceramics via a direct measurement

(Ba_(1-x)Sr_(x))(MnyTi1-y)O_(3)(BSMT)ceramics with x=35,40 mol%and y=0,0.1,0.2,0.3,0.4,0.5 mol%were prepared using a conventional solid-state reaction approach.The dielectric and ferroelectric properties were characterized using impedance analysis and polarization-electric field(P-E)hysteresis loop measurements,respectively.The adiabatic temperature drop was directly measured using a thermocouple when the applied electric field was removed.The results indicate that high permittivity and low dielectric losses were obtained by doping 0.1-0.4 mol%of manganese ions in(BaSr)TiO_(3)(BST)specimens.A maximum electrocaloric effect(ECE)of 2.75 K in temperature change with electrocaloric strength of 0.55 K·(MV/m)^(-1)was directly obtained at~21℃and 50 kV/cm in Ba_(0.6)Sr_(0.4)Mn_(0.001)Ti_(0.999)O_(3) sample,offering a promising ECE material for practical refrigeration devices working at room temperature.

Electrocaloric devices part Ⅱ:All-solid heat pump without moving parts

Various designs have been introduced to build heat pumps using the electrocaloric effect (ECE). Each of all the curent designs usesat least one moving part, which significantly reduces the reliability of the pump and adds complexities. In this work, a new all-soliddesign is introduced, in which two layers of an electrocaloric material (ECM) are permanently sandwiched in the source and sink,which would significantly increase the device's reliability since nothing moves and all are permanently bound together. Moreimportantly, the electric fields applied on two ECM layers are independently controlled. A special sequence for the electric fields on .two ECM layers is introduced. Numerical calculation was used to simlulate the device's performance by using the newly introducedanalytical solutions for the heat conduction in the system. It is concluded that a continuous heat transformation from the source tosink at the same temperature can be achieved when the contacting cofficient, K_(ε)=√(k^(c)p^(c)c^(c)_(p))/(k^(o)p^(o)c^(o)_(p)), is very small, where k,ρ, and Cp are thermal conductivity, density, and heat capacity, respectively, while the superscript c and 0 represent the ECM andsource/sink, respectively.