Manipulating Zr/Ti ratio based on phase diagram for large electrocaloric effects with multiple target operation temperatures in PLZT ceramics

Ferroelectric phase transition has been identified as a promising avenue for designing high-performanceelectrocaloric materials for zero-emission and solid-state refrigeration. However, extensive research has been limited todeveloping ferroelectric materials with large electrocaloric effects near room temperature, preventing them from meetingdiverse refrigeration requirements. In this study, by leveraging the room-temperature phase diagram of the (PbLa)(ZrTi)O_(3)solution, we prepared a series of Pb_(0.775)La_(0.15)Zr_(x)Ti_(1−x)O_(3) bulk ceramics spanning the ferroelectric and relaxor ferroelectricphase regions. This enabled the attainment of various phase transition features and temperatures. Finally, largeelectrocaloric effects, coupled with adjustable operation temperatures ranging from 150 to −45℃, are successfullyachieved through manipulation of the Zr/Ti ratio. This comprehensive range of operation temperatures effectively addressesdiverse refrigeration application requirements, ranging from industrial equipment to freezer cabinets. This work not onlyunderscores the expansion of the electrocaloric refrigeration application domain but also proposes a material designstrategy tailored to meet these evolving demands.

Polymer nanocomposite dielectrics with high electrocaloric effect for flexible solid-state cooling devices

Nanocomposite dielectrics show great promising application in developing next generation wearable all-solidstate cooling devices owing to the possessed advantages of high cooling efficiency, light-weight and small volume without the induced greenhouse effect or serious harm to ozone layer in the exploited refrigerants. However, low electrocaloric strength in nanocomposite dielectric is severely restricting its wide-spread application because of high applied operating voltage to improve electrocaloric effect. After addressing the chosen optimized ferroelectric ceramic and ferroelectric polymer matrix in conjunction with the analysis of crucial parameters, recent progress of electrocaloric effect(ECE) in polymer nanocomposites has been considerably reviewed. Subsequently, prior to proposing the conceptual design and devices/systems in electrocaloric nanocomposites, the existing developed devices/systems are reviewed. Finally, conclusions and prospects are conducted, including the aspects of materials chosen, structural design and key issues to be considered in improving electrocaloric effect of polymer nanocomposite dielectrics for flexible solidstate cooling devices.

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.

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.

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.

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 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.

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 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.

Giant negative electrocaloric effect measured by indirect method in X-ray irradiated P(VDF-TrFE)films

Flexible solid-state cooling devices with high efficiency are attracted to ferroelectric polymers with excellent negative electrocaloric(EC)effects.It is challenging to obtain a large negative EC effect in ferroelectric polymers due to the lack of tunable techniques.A giant negative EC response was obtained in the poly(vinylidene fluoride-trifluoroethylene)copolymers(P(VDF-TrFE),70/30,in mole ratio)irra-diated with high-energy X-ray.The irradiated P(VDF-TrFE)films showed an adiabatic temperature change of-13.5 K at 40 MV/m under a dose of 5 Mrad(1 Mrad=10^(4) J/kg)obtained by the indirect method.This significant negative EC effect is attributed to the enhancement of crystalline due to the entry of polymer molecules into the amorphous to crystalline structure and the reduction of heat ca-pacity due to the increase of crosslinking.In addition,X-ray irradiation improves the dielectric coefficient from 15 to 22.This research indicates that irradiation can modify the negative EC properties of ferro-electric polymers for solid-state cooling.

Unveiling a giant electrocaloric effect at low electric fields through continuous phase transition design

The reported electrocaloric(EC)effect in ferroelectrics is poised for application in the next generation of solidstate refrigeration technology,exhibiting substantial developmental potential.This study introduces a novel and efficient EC effect strategy in(1-x)Pb(Lu_(1/2)Nb_(1/2))O_(3)-xPbTiO_(3)(PLN-xPT)ceramics for low electric-fielddriven devices.Phase-field simulations provide fundamental insights into thermally induced continuous phase transitions,guiding subsequent experimental investigations.A comprehensive composition/temperature-driven phase evolution diagram is constructed,elucidating the sequential transformation from ferroelectric(FE)to antiferroelectric(AFE)and finally to paraelectric(PE)phases for x=0.10-0.18 components.Direct measurements of EC performance highlight x=0.16 as an outstanding performer,exhibiting remarkable properties,including an adiabatic temperature change(ΔT)of 3.03 K,EC strength(ΔT/ΔE)of 0.08 K cm kV-1,and a temperature span(Tspan)of 31℃.The superior EC effect performance is attributed to the temperature-induced FE to AFE transition at low electric fields and diffusion phase transition behavior contributing to the wide Tspan.This work provides valuable insights into developing high-performance EC effect across broad temperature ranges through the strategic design of continuous phase transitions,offering a simplified and economical approach for advancing ecofriendly and efficient solid-state cooling technologies.

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.

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.

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.

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.

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.

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.

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.

Field-driven merging of polarizations and enhanced electrocaloric effect in BaTiO_(3)-based lead-free ceramics

Solid-state cooling technology based on electrocaloric effect(ECE)has been advanced as an alternative to replace the vapour-compression approach to overcome the releasing of the global warming gases.However,the development in high ECE materials is still a challenge.In this work,polarization merging strategy was proposed to achieve a large ECE in xBa(Sn_(0.07)Ti_(0.93))O_(3)–(1−x)Ba(Hf_(0.1)Ti_(0.9))O_(3) ferroelectric ceramics,where x=0,0.2,0.4,0.6,0.8,and 1.Ba(Sn_(0.07)Ti_(0.93))O_(3) with an orthorhombic phase and Ba(Hf_(0.1)Ti_(0.9))O_(3) with a rhombohedral phase at room temperature were prepared beforehand as precursors,and phase-coexisted xBSnT–(1−x)BHfT ceramics were formed via a solid-state reaction approach.Phase coexisting structures were confirmed using the X-ray diffraction.The merged polarization was confirmed by the dielectric and ferroelectric properties.Optimal ECEs were obtained for 0.2BSnT–0.8BHfT ceramics,i.e.,adiabatic temperature change DT=2.16±0.08 K at 80℃and 5 MV/m,and DT=3.35±0.09 K at 80℃and 7 MV/m.

Toward artificial intelligent self-cooling electronic skins:Large electrocaloric effect in all-inorganic flexible thin films at room temperature

Intelligent robots have assisted mankind in achieving and operating thousands of functions,especially with the arrival of the artificial intelligent.However,heat dissipation and thermal management in the intelligent robots remain big challenges,which limit their miniaturization and performance.Electrocaloric(EC)materials,which exhibit temperature change in response to the application or withdrawal of an electric field,open a new strategy for cooling technology and have gained a flurry of research interest in recent years.Toward artificial intelligent self-cooling electronic skins,large-scale flexible materials with high EC effect near room temperature are in demand.Here,we report a large room temperature EC effect in flexible Pb_(0.82)Ba_(0.08)La_(0.1)Zr0.9Ti_(0.1)O_(3)(PBLZT)inorganic thin films via a transfer-free cost-effective sol-gel process,assisted by unique two-dimensional mica substrates.The maximum adiabatic temperature change and isothermal entropy change of the flexible PBLZT thin films reach to 22.5 K and 25.9 J K^(-1) kg^(-1) at room temperature.In particular,the flexible PBLZT thin films exhibit a stable EC effect both under bending state and after bending for 20000 times.Our flexible EC materials offer an alternative strategy to the development of cooling technologies for both artificial intelligent robots and personal wearable cooling devices.