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Lead-free [(Bi 0.5 Na 0.5) 0.94 Ba 0.06 ] 0.975 Sr 0.025 TiO 3 (BNBTS25), with morphotropic phase boundary, has attracted considerable attention due to its depolarization temperature, T d (Ferroelectric (FE)- Antiferroelectric (AFE) transition), which is in close proximity to room temperature (322K). Therefore, the research on electrocaloric and energy storage was limited to temperatures ranging from 223K to 363K. BNBTS25 presents firstly an intensive interests as promising candidate for environmental-friendly energy storage products. This material provides a good recoverable energy density up to W rec = 577 mJ/cm3 with an energy-storage efficiency of η = 68% in the vicinity of T d. The origin of enhanced energy storage performance is discussed from a scientific point of view. Secondly, BNBTS25 exhibits a high electrocaloric effect (ECE), including an adiabatic temperature change of Δ T = 1.24 K and an electrocaloric responsivity of ξ = 0.301K.mm/kV was observed under an electric field of E = 40 kV/cm at a temperature near 290K. This high ECE performance exceeds that of several reported lead-free ceramics and even performs better than some lead based ceramics. The obtained results suggest that BNBTS25 ceramic is a promising candidate for both electrocaloric and energy storage applications in operating temperature such as cooling in microelectronic devices. • The electrocaloric properties were analysed for BNBTS25 ceramic. • Existence of morphotropic phase transition (MPB) in BNBTS25 at room temperature. • BNBTS25 demonstrates a high recoverable energy density with an energy storage efficiency of η = 68% at RT. • A good coefficient electrocaloric effect was calculated near the room temperature. [ABSTRACT FROM AUTHOR]

The Ba 1- x La x Ti 0.9 Sn 0.1 O 3 ceramics (x = 0, 0.006, 0.007, 0.008) were prepared by the traditional solid-state reaction method. The influence of La3+ on the phase, dielectric properties, ferroelectric properties, and electrocaloric effect (ECE) was analyzed in detail. The results of refinement show that all ceramics are multiphase coexistence at room temperature, including the cubic phase, the tetragonal phase, and the orthogonal phase. With the increase of La3+, the polar phases decrease but the non-polar phase increases, which is the main reason for the decline in adiabatic temperature change (ΔT). The analysis of dielectric properties and ferroelectric properties demonstrate that the diffuse phase transition is strengthened by introducing La3+. It also means that polar nanoregions (PNRs) might be formed. Therefore, the temperature stability of the Ba 1- x La x Ti 0.9 Sn 0.1 O 3 ceramics in a wide temperature range near room temperature is improved. Simultaneously, the PNRs provide additional entropy to improve ECE. A higher ΔT = 0.88 K is obtained under 60 kV/cm for x = 0.007, which also possesses excellent temperature stability in the temperature range of 298 K–378 K. The doping of La3+ also improves the electric field threshold of the electrocaloric strength (ΔT max /ΔE) and stabilizes the ΔT max /ΔE under a higher electric field, which is conducive to improving ECE under a higher electric field and providing another possible solution for promoting the practical application of ECE. [ABSTRACT FROM AUTHOR]

Ferroelectric ceramic with a large electrocaloric (EC) effect at a very low electric field is very attractive in the next solid state refrigeration technology. In this work, two Pb(Sc 0.25 In 0.25 Nb 0.25 Ta 0.25)O 3 (PSINT) medium-entropy ceramics were successfully synthesized by a spark plasma sintering (SPS) technology, including one-step-SPS processed and two-step-SPS processed samples. A large EC effect (△ T ∼ 0.85 K) with a high EC strength (△ T /△ E ∼ 0.021 K cm/kV) around room temperature are obtained at a very low electric field (∼40 kV/cm) in the two-step-SPS processed sample. Moreover, the working temperature range is very broad (∼120 K), which can be responsible for the high relaxation degree of the dielectric peak. It can be believed that the PSINT medium-entropy ceramics can be promising candidates for application in the next-generation EC cooling devices. [ABSTRACT FROM AUTHOR]

This work harmonizes the experimental and theoretical study of electrocaloric effect (ECE) in (Pb 0. 8 Bi 0. 2) (Zr 0. 5 2 Ti 0. 4 8) O3 solid solution by optimizing sintering temperature. Bi 3 + -doped PbZr 0. 5 2 Ti 0. 4 8 O3 solid solutions were synthesized by the conventional solid-state reaction method. Different samples were prepared by varying the sintering temperature. X-ray diffraction study confirms the crystalline nature of all the samples. An immense value of polarization has been acquired in the optimized sample. The maximum adiabatic temperature change of order 2.53 K with electrocaloric strength of 1.26 K mm kV − 1 has been achieved experimentally. Whereas a comparatively close value of ECE has been acquired from the theoretical calculations using a phenomenological approach. Furthermore, a large value (218 mJ cm − 3) of thermal energy conversion has been obtained using the Olsen cycle. [ABSTRACT FROM AUTHOR]

The 1980s saw the development of ferroelectric chiral smectic C (SmC*) liquid crystals (FLCs) with a clear focus on their application in fast electro-optic devices. However, as the only known fluid ferroelectric materials, they also have potential in other applications, one of which is in heat-exchange devices based on the electrocaloric effect. In particular, ferroelectric liquid crystals can be both the electrocaloric material and the heat exchanging fluid in an electrocaloric device, significantly simplifying some of the design constraints associated with solid dielectrics. In this paper, we consider the electrocaloric potential of three SmC* ferroelectric liquid crystal systems, two of which are pure materials that exhibit ferroelectric, antiferroelectric, and intermediate phases and one that was developed as a room-temperature SmC* material for electro-optic applications. We report the field-induced temperature changes of these selected materials, measured indirectly using the Maxwell method. The maximum induced temperature change determined, 0.37 K, is currently record-breaking for an FLC and is sufficiently large to make these materials interesting candidates for the development for electrocaloric applications. Using the electrocaloric temperature change normalised as a function of electric field strength, as a function of merit, the performances of FLCs are compared with ferroelectric ceramics and polymers. [ABSTRACT FROM AUTHOR]

Innovative cooling technologies are recognized by many industries as a crucial part of their system design. A large electrocaloric effect (ECE) and extended working temperature are the key issues hindering the realization of electrocaloric refrigeration technology. In this work, large ECE (ΔT = 0.8–0.9°C @ 4 kV/mm) with an ultrawide temperature span from 30 to 120°C is noted for lead‐free (Na1/2Bi1/2)0.80Sr0.20(Zn1/3Nb2/3)xTi1‐xO3 ceramics. The excellent ECE performance can be ascribed to the evolution of polar nanoregions. Our work suggests that this material is promising for applications in solid‐state refrigeration systems with a broad range of operating temperatures. [ABSTRACT FROM AUTHOR]

In this study, NaNbO 3 (NN) was introduced into Ba(Zr 0.15 Ti 0.85)O 3 (BZT) to form a solid solution with relaxor ferroelectric characteristics. The dielectric breakdown strength (BDS) of the specimen with 6 mol.% NN reached 680 kV/cm, the corresponding recoverable energy storage density (W rec) was 5.15 J/cm3, and the energy storage efficiency (η) was 77%. The dissolution of Na + ions at the A position and Nb5+ ions at the B position of the perovskite structure reduced the concentration of oxygen vacancies in the lattice and compensated for defects. The doped ceramics exhibited lower dielectric loss and better thermal stability: the W rec value was 2 ± 1% J/cm3 at 30–120 °C. In particular, in the 0.02NN ceramics, a ΔT of 1.81 K was achieved at 130 kV/cm, and the operating temperature zone expanded with the increase in doping concentration. The introduction of NN resulted in BZT ceramics that possess excellent energy storage performance and electrocaloric effect properties. [ABSTRACT FROM AUTHOR]

The electrocaloric heat production in BaTiO 3 -based multilayer ceramic capacitors with Y5V specification was measured in a direct way by means of an adiabatic calorimeter setup. Applying an electric field of 30 MV m - 1 is found to result in a heat release of 0.94 J g - 1 and an electrocaloric temperature change of 0.46 K, in good agreement with direct results in previous studies. [ABSTRACT FROM AUTHOR]

This work harmonizes the experimental and theoretical study of electrocaloric effect (ECE) in (Pb[Formula: see text]Bi[Formula: see text](Zr[Formula: see text]Ti[Formula: see text]O3 solid solution by optimizing sintering temperature. Bi[Formula: see text]-doped PbZr[Formula: see text]Ti[Formula: see text]O3 solid solutions were synthesized by the conventional solid-state reaction method. Different samples were prepared by varying the sintering temperature. X-ray diffraction study confirms the crystalline nature of all the samples. An immense value of polarization has been acquired in the optimized sample. The maximum adiabatic temperature change of order 2.53 K with electrocaloric strength of 1.26 K mm kV[Formula: see text] has been achieved experimentally. Whereas a comparatively close value of ECE has been acquired from the theoretical calculations using a phenomenological approach. Furthermore, a large value (218 mJ cm[Formula: see text] of thermal energy conversion has been obtained using the Olsen cycle.

A new experimental approach to the complex study of electrocaloric, pyroelectric, and thermal effects associated with the bulk and local electrical conductivity of ferroelectrics and related materials is proposed. The key to this approach is the analysis of the dynamics of the sample temperature response to an arbitrary external action, including long-term electrical impacts. The metrological justification of the experimental technique is based on direct non-contact high-speed monitoring of the sample temperature using an IR photodiode sensor designed by Ioffe Institute. Its efficiency is confirmed by numerous experimental data on electrocaloric properties of ferroelectrics, relaxors, and relaxors-based multilayer structures. [ABSTRACT FROM AUTHOR]

The present work deals with the calculation of electrocaloric (EC) coefficients of BaTi1-xSnxO3 (x = 0.15, 0.20, 0.30) polycrystalline ceramics. Dielectric and polarization studies are carried out in a temperature range of 100 − 300 K to calculate the EC coefficients employing the indirect method based on Maxwell's equations. It is demonstrated that the EC effect is enhanced near the dielectric maxima for all the samples, including that of samples which exhibit relaxor behavior (x = 0.30). Furthermore, the maximum change in temperature, the temperature at which the maximum EC coefficient is achieved and the working range for EC effect are shown to be tunable with electric field and Sn substitution. [ABSTRACT FROM AUTHOR]

An outstanding challenge for high‐efficient and zero‐emissions ferroelectric refrigeration is to maintain a large adiabatic temperature change (ΔT) over a wide temperature span (Tspan) resulting from the electrocaloric effect (ECE). A multilayer ferroelectric structure with interlayer synergistic phase transitions as a means to address this problem is proposed. BaTi0.89Sn0.11O3, BaTi0.85Zr0.15O3, and BaTi0.89Hf0.11O3 were selected as the components of each layer, the compositions of which are fixed at the tricritical point (TP) in each system and where the transition temperatures increase sequentially. Ferroelectrics near TP have a high sensitivity to external fields and the good co‐firing adhesion leads to strong electrical and stress interface coupling between adjacent layers. The electric‐field‐induced phase transition in one layer then synergistically induces a phase transition in the near interface part of the adjacent layer, which is close to but is not at the transition point yet. As a result, the enhanced ECE performance, including both a large ΔTmax = 0.63 K and a wide Tspan = 57 °C (ΔT ≥ 80% ΔTmax), exceeds that associated with the sum of the individual components. An efficient composite materials design strategy to develop high‐performance electrocaloric materials with excellent ECE properties for practical refrigeration applications is thus proposed. [ABSTRACT FROM AUTHOR]

This paper presents compositional modifications on lead-free material system based on barium titanate to optimize its electrocaloric (EC) properties. By addition of strontium and tin we prepared solid solutions of Ba 1-x Sr x Sn y Ti 1-y O 3 (BSSnT-100∙x-100∙y) which allow for shifting of maximum EC effect to room temperature as well as broadening the temperature range of high EC temperature changes Δ T E C. Bulk ceramic samples of BSSnT were prepared by solid-state reaction route and the influence of Sn:Sr ratio on dielectric and ferroelectric properties was investigated. The EC temperature change was measured directly using resistance welded thermocouple wires. Most promising results could be achieved for BSSnT-18−6.5, which showed a maximum Δ T E C of 0.49 K around 30 °C with Δ T E C > 0.3 K in the temperature range from 10 °C to 50 °C under a comparatively low electric field change of 2 V μm−1. [ABSTRACT FROM AUTHOR]

Electrocaloric effect (ECE) is promising in realizing solid-state cooling as an alternative to the conventional refrigeration with environmentally harmful coolant and low efficiency. High ECE in lead-free ferroelectric ceramics is highly desirable for the EC cooling. In this work, different from the researches that tune the ECE by conventional compositional design or external stress engineering, we fabricated the (1-x)BaTiO3-xNaNbO3 (BTO-xNN) lead-free ceramics with a core-shell grain structure arising from the inhomogeneous stoichiometry of element distribution, leading to the internal compressing stress in the grains. It is interesting that the phase transition behavior, including the phase transition temperature and the diffusion property, is regulated by the core-shell grain structure induced internal stress, which can be capitalized on for the favorable ECE. Cooperated with 0.02 NN, a high ECE, e.g. adiabatic temperature change (ΔT) of 3.6 K and isothermal entropy change (ΔS) of 4.5 J kg−1 K−1, is attained in the BTO ceramic. As the internal stress further increases with more NN, the BTO-0.06NN exhibits an extremely stable ECE with a variety rate below ±4% in a wide temperature range from 300 K to 360 K. This work provides a novel approach to explore pronounced ECE in lead-free ferroelectrics for eco-friendly refrigeration.

Abstract Ba0.85Ca0.15Zr0.10Ti0.90O3 (BCZT) lead-free ceramics demonstrated excellent dielectric, ferroelectric, and piezoelectric properties at the morphotropic phase boundary (MPB). So far, to study the effect of morphological changes on dielectric and ferroelectric properties in lead-free BCZT ceramics, researchers have mostly focused on the influence of spherical grain shape change. In this study, BCZT ceramics with rod-like grains and aspect ratio of about 10 were synthesized by surfactant-assisted solvothermal route. X-ray diffraction (XRD) and selected area electron diffraction (SAED) performed at room temperature confirm the crystallization of pure perovskite with tetragonal symmetry. Scanning electron microscopy (SEM) image showed that BCZT ceramics have kept the 1D rod-like grains with an average aspect ratio of about 4. Rod-like BCZT ceramics exhibit enhanced dielectric ferroelectric (ɛr = 11,906, tanδ = 0.014, P r = 6.01 μgC/cm2, and E c = 2.46 kV/cm), and electrocaloric properties (ΔT = 0.492 K and gZ = 0.289 (K·mm)/kV at 17 kV/cm) with respect to spherical BCZT ceramics. Therefore, rod-like BCZT lead-free ceramics have good potential to be used in solid-state refrigeration technology.

The lead-free ferroelectric 0.4Ba _0.85 Ca _0.15 Zr _0.10 Ti _0.90 O _3 –0.6BaTi _0.89 Sn _0.11 O _3 (0.4BCZT–0.6BTSn) ceramics were successfully prepared by the sol–gel process. Raman spectroscopy was used to examine the structural properties of the 0.4BCZT-0.6BTSn sample. The findings indicate that the sample was well crystallized into a single perovskite structure. The phase transitions of the studied sample have been investigated using the DSC technique. The electrocaloric effect (ECE) properties were indirectly determined using the Maxwell approach. Under a relatively low applied electric field of 30 kV cm ^−1 , the results show enhanced electrocaloric temperature change and entropy change of ΔT = 1.32 K and ΔS = 1.41 J/kg.K, respectively. Besides, the electrocaloric responsivity ( ξ _max = 0.45 K·mm/kV) obtained is among the highest reported values in pb-free ferroelectrics near room temperature. These findings demonstrate that the lead-free 0.4BCZT–0.6BTSn ceramic is a promising candidate for solid-state cooling applications.

Electrocaloric (EC) materials, presenting large adiabatic temperature change or isothermal entropy change under the application (or removal) of electric fields, offer an efficient alternative to caloric heat pumps for replacing hazardous gases used in traditional vapor-compression systems. Recently, a large EC temperature change of 5.5 K have been reported in Pb(Sc _0.5 Ta _0.5 )O _3 multilayer ceramic capacitors (Nair et al 2019 Nature 575 468) thanks to its strong first-order phase transition and a temperature span of 13 K has been reported in a prototype based on these capacitors (Torelló et al 2020 Science 370 125). However, the toxicity of lead forces researchers to find eco-friendly materials exhibiting competitive EC performances. Here, we study the EC effect in lead-free BaTiO _3 multilayer capacitors using an infrared camera. Unlike commercial BaTiO _3 capacitors, we prepared our samples without sacrifying the first-order phase transition in BaTiO _3 while a low amount of 0.2 mol% Mn was added as an acceptor dopant to improve electrical resistivity. Their EC adiabatic temperature variations show two peaks versus temperature, which match BaTiO _3 two first-order phase transitions, as observed by differential scanning calorimetry. We measured a temperature drop of ∼0.9 K over a temperature range of 70 K under 170 kV cm ^−1 , starting at 30 °C near the tetragonal-to-orthorhombic phase transition. Under the same electric field, a maximum temperature change of 2.4 K was recorded at 126 °C, at BaTiO _3 ’s Curie temperature. Our findings suggest that further optimized BaTiO _3 capacitors could offer a path for designing lead-free caloric cooling prototypes.

We prepared a dense AgNbO3 ceramic using a conventional solid-state reaction method. The phase structure, electrical properties and electrocaloric effect (ECE) were systematically investigated. Large negative and positive ECEs (−4.38 °C at 65 °C and 2.3 °C at 210 °C) under an external electric field of 180 kV·cm−1 were obtained in the eco-friendly AgNbO3 antiferroelectric (AFE) ceramic due to affluent phase transition and a high electric field. The large positive and negative ECEs originated from the phase transition between ferrielectric (FIE) phases (the orthorhombic space group (Pmc21) and AFE phases (Pbcm) tuned by an applied external field. Additionally, a probable mechanistic model was proposed to illustrate the generation of positive and negative ECEs. This study may provide guidelines for the design of high-efficiency solid-state cooling devices.

In conventional knowledge, ferroelectric solid solutions were formed between members belonging to the same crystal structure family. Since both tungsten bronze and perovskite structures are constructed by connecting the corner-sharing oxygen octahedra, it offers a possibility for formatting an unusual solid solution between these two families. Herein, (1 - x )Sr 0.6 Ba 0.4 Nb 2 O 6 - x BaTiO 3 , (1 - x )SBN- x BT, solid solutions were synthesized and the solution mechanism was resolved from a structure viewpoint. With increasing BT content, the solid solution persists of tetragonal tungsten bronze structure, but the lattice parameter a (= b ) decreases whereas c increases, resulting in the significant reduction of grains anisotropy. The ferroelectric-relaxor phase transition temperature shows a monotonic increase as x increases. However, the ferroelectricity evolution is not monotonous as a function of BT content because of the competitive effects of Ba and Ti on the property. As a result, the x = 0.10 ceramic shows the strongest ferroelectricity and a remarkable electrocaloric effect of 1.4 K near room temperature. This work challenges the traditional view of solid solution formation and provides an alternative way to modulate the structure and properties of ferroelectrics.

High-performance electrocaloric materials are essential for the development of solid-state cooling technologies; however, the contradiction of the electrocaloric effect (ECE) and temperature span in ferroelectrics frustrates practical applications. In this work, through modulating oxygen octahedra distortion and short-range polar nanodomains with moderate coupling strength, an EC value of Δ T ∼ 0.30 K with an ultrawide temperature span of 85 K is obtained in the x = 0.04 composition [(0.88 - x )NaNbO 3 -0.12BaTiO 3 - x LiSbO 3 ( x = 0-0.06)]. The LiSbO 3 dopant induces a P4bm -to- R3cH phase transition and intensifies the oxygen octahedra distortion degree, accompanied by the ferroelectric domain smashing into polar nanodomains. Also, LiSbO 3 addition enhances the relaxation degree with a downshift of T fd (ferroelectric-to-diffuse phase transition temperature) and T J (temperature of the maximal current density value), and T fd is shifted to near room temperature with an absence of T J in x = 0.04. Local energy barriers induced by oxygen octahedra distortion inhibit the phase transition in conjunction with activation of short-range polar order switching under thermal stimuli, which is the underlying mechanism for an excellent EC performance for x = 0.04. This work not only clarifies that ferroelectrics with oxygen octahedra distortion and short-range polar order are expected to achieve remarkable EC performances but also provides a design strategy to seek emergent EC behaviors in complex oxygen-octahedra-distortion materials.

Among pyroelectric materials, Bi 0.5 Na 0.5 TiO 3 (BNT)-based relaxors are particularly noteworthy due to their significant polarization fluctuation near the depolarization temperature (T d ), resulting in a large pyroelectric response. What has been overlooked is the dynamic behavior of inherent polar structures, particularly the temperature-dependent evolution of polar nanoregions (PNRs), which significantly impacts the pyroelectric behavior. Herein, based on the large pyroelectric response origination (the ferroelectric-relaxor phase transition), the mixed nonergodic and ergodic relaxor (NR+ER) critical state is constructed, which is believed to trigger the easily fluctuating polarization state with excellent pyroelectric response. Composition engineering (with Li + , Sr 2+ , and Ta 5+ ) strategically controls the relaxor process and modulates the dynamic behavior of inherent polar structures by the random field effect. The pyroelectric coefficient of more than 1441 µCm -2 K -1 at room temperature (RT), more than 9221 µCm -2 K -1 (RT), and ≈107911 µCm -2 K -1 (T d ) are achieved in the Li + -doped sample, the Sr 2+ -doped sample, and the (Li + +Ta 5+ ) co-doped sample, respectively. This work earns the highest RT pyroelectric coefficient in BNT-based relaxors, which is suitable for pyroelectric applications. Furthermore, it provides a strategy for modulating the pyroelectric performance of BNT-based relaxors., (© 2024 Wiley‐VCH GmbH.)

Considering that the electric refrigeration temperature range of 0.94BNT-0.06BT ceramic materials is 100 ∼ 140 °C, the electric refrigeration performance of the 0.94BNT-0.06BT ceramic material system was modified by LiNbO3 doping to reduce the cooling temperature. As a result, the refrigeration temperature range of the 0.94BNT-0.06BT ceramic material system was lowered to 25 ∼ 80 °C, achieving its cooling effect near room temperature, and in this temperature range, the adiabatic temperature changes ΔT > 0.6K. [ABSTRACT FROM AUTHOR]

Undoped and Dy3+ doped 0.975 K 1/2 Na 1/2 NbO 3 -0.025Na 1/2 Bi 1/2 TiO 3 (0.975KNN-0.025NBT) ceramics were synthesized using the solid-state synthesis method. X-ray diffraction analysis revealed pure perovskite structure without any secondary phases. The dielectric investigations of both ceramics revealed low dielectric losses in the dysprosium doped ceramic, particularly for temperatures higher than 100 °C. The dielectric loss anomaly around room temperature corroborates the polymorphic phase boundary (PPB) between orthorhombic and tetragonal phases detected by XRD investigations. The electrocaloric effect (ECE) was investigated using the indirect method based on the Maxwell equation and thermal P–E hysteresis loops. The maximum ECE value was found equal to 0.63 K at 83 °C for KNNBT0.025. However, in Dy doped KNNBT0.025 ceramics, both direct and inverse ECE responses were found with values of 1.01 K at 118 °C and −1.79 K at 80 °C, respectively. Besides, yellow light emission was detected under an excitation wavelength of 350 nm. The simultaneous existence of high ECEs, good dielectric performance, and photoluminescence properties makes KNNBT-Dy a promising candidate for solid-state refrigeration and optoelectronic devices. [ABSTRACT FROM AUTHOR]

Dual‐peak electrocaloric effect (ECE) exists over a broad range significantly below Curie temperature in co‐mixed SrBi1.98La0.02Nb2–xTaxO9 (SBLNT) compositions exhibiting diffused phase transition. The indirect measurement method is used to study the influence of defect‐modified potential barrier distributions on the ECE of lead‐free SBLNT ceramics. Variation in isothermal entropy change and adiabatic temperature change with varying tantalum (Ta) content signify effects of morphology and impact of altered potential barriers in the parent lattice without involving structural phase transition. A unique appearance of twin‐peak positive–negative ECE in equally doped SrBi1.98La0.02Nb‐TaO9 matrix is attributed to doping‐induced formation of polar nanoregions and distinct dipole switching mechanisms controlled by evenly distributed Nb–Ta potential barriers in SBLNT lattice. Higher doping concentration reduces porosity and promotes electric polarization, thereby the relative cooling power gradually increases with increasing Ta at Nb sites. [ABSTRACT FROM AUTHOR]

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.

Lead-free relaxor ferroelectric Na 0·5 (Bi 1-x Nd x) 0.5 TiO 3 (xNdNBT, x = 0–30%) ceramics were synthesized using the conventional solid-state method. Detailed Rietveld refinement revealed transitions from rhombohedral (x = 0, 5%), to a coexistence of R 3 c and Pnma symmetries (x = 10, 15%), followed by a tetragonal P 4/ mmm phase for the high Nd-concentrations (x = 25, 30%). High-temperature dielectric stability was found over a large temperature range (for instance ±15% from -90 °C to 405 °C for x = 30%) with very low dielectric losses, especially at high temperatures. The substitution of Bi3+ by Nd3+ results in a perturbation of the ferroelectric order and favors short-range polar regions in the system. From the ferroelectric measurements, we demonstrated the stabilization of a coexistence of non-ergodic and ergodic relaxor state or ergodic relaxor state at specific doping concentrations. Besides, high-energy storage properties were obtained at high temperatures, with W rec > 1.15 J/cm3 in the temperature range 140 °C–200 °C for the 5NdNBT and a moderate W rec between 0.5 and 0.77 J/cm3 in a large temperature range from 25 °C to 200 °C and with high efficiency >70% for 10NdNBT composition. In addition, a high electrocaloric response (ΔT = 1.8 K at 95 kV/cm) was found using the indirect method for the 5NdNBT composition, with great temperature stability below 20% over a broad temperature range (80–140 °C) and with a high ΔT/ΔE > 0.19 K m/V. The obtained electrocaloric response was related to the thermal evolution of the polar regions in mixed ergodic and non-ergodic relaxor states under an applied electric field. [ABSTRACT FROM AUTHOR]

Achieving a colossal room‐temperature electrocaloric effect is essential for practical solid‐state refrigeration applications with low‐cost and high‐efficiency. Here, through the design of applying external stimuli (hydrostatic pressure and misfit strain), giant room‐temperature electrocaloric effects in the bulk and thin film of metal‐free organic perovskite [MDABCO](NH4)I3 are obtained by using a combination of thermodynamic calculations and phase–field simulations. Under the hydrostatic pressure of 1 GPa, there emerges excellent room‐temperature (300 K) electrocaloric performance with the temperature change (ΔT) of 8.41 K at 30 MV m−1 and electrocaloric strength (ΔT/ΔE) of 0.63 K m MV−1 at 10 MV m−1, respectively. The prominent electrocaloric effects of MDABCO(NH4)I3 may be related to its rapid change rates of free energy barrier height. Additionally, it can be found that some stripe domains and non‐180° domain walls form in the [MDABCO](NH4)I3 bulk, which is consistent with the experimental results. This work not only provides new insights into organic perovskite [MDABCO](NH4)I3, but also guides for further developing to realize remarkable room‐temperature electrocaloric cooling. [ABSTRACT FROM AUTHOR]

A comparative study is reported on the ferroelectric ceramics with compostional formula Ba 0 · 98 La 0 · 02 Ti 0 · 98 Fe 0 · 02 O 3 (BLTF1) and Ba 0 · 97 La 0 · 02 Ti 0 · 98 Fe 0 · 02 O 3 (BLTF2; valency compensated). The samples were prepared by solid state route and sintered in air at 1325 °C for 4 h. The X-ray diffraction analysis confirmed the formation of tetragonal perovskite phase. The prepared samples were characterized for their dielectric and ferroelectric properties at different temperatures at 1, 5, 10 and 100 kHz. Enhancement in ferroelectric properties (P r = 11.25 μC/cm2, E c = 9.05 kV/cm) was observed in BLTF2 ceramics as compared to BLTF1 ceramics (P r = 6.53 μC/cm2, E c = 9.35 kV/cm) along with the observation of electrocaloric effect. The value of piezoelectric coefficient 'd 33 ' was found to be 140 pC/N and 163 pC/N for BLTF1 and BLTF2 samples respectively. The present investigations show that the valency compensation method can improve the ferroelectric properties of the ferroelectric ceramics thereby making them more suitable for different applications. [ABSTRACT FROM AUTHOR]

As an emerging solid‐state refrigeration technology with zero‐emission and high energy conversion efficiency, there is a compelling need for ferroelectric materials with giant electrocaloric effects (ECEs) at room temperature suitable for refrigeration applications. The complex perovskite antiferroelectric (AFE), PbMg0.5W0.5O3, containing non‐equivalent B‐site ions with a symmetric giant positive and negative ECE near room temperature is presented. At the Curie temperature of 36 °C, the first‐order AFE–paraelectric phase transition gives rise to a large enthalpy change of 3.92 J g−1, more than four times that of BaTiO3. This leads to a significant ECE under the influence of an electric field. The direct electrocaloric characterization shows that the adiabatic temperature change, ΔT, exhibits symmetric peaks with a giant positive maximum of 1.79 K (ΔS = 1.68 J kg−1 K−1) at 36 °C and a negative maximum of −2.02 K (ΔS = −1.93 J kg−1 K−1) at 34 °C. The ultrahigh magnitude of ΔT near room temperature makes PbMg0.5W0.5O3 a superior electrocaloric material far beyond traditional PbZrO3‐based AFEs. The coexistence of symmetric giant positive and negative ΔT to further improve cooling efficiency is expected. In addition, the good reversibility and negligible leakage current should pave the way for practical applications. [ABSTRACT FROM AUTHOR]

BaSnxTi1–xO3 + 0.5 mol% Y ceramics (x = 0.06, 0.08, 0.11, and 0.13) are synthesized using citrate combustion technique and the electrocaloric effect (ECE) is investigated. Dense microstructures with fine grain are observed as increasing Sn contents. The dielectric results reveal that TO–T (tetragonal‐to‐orthorhombic phase) shifts toward higher temperature, whereas TC (cubic‐to‐tetragonal phase) shifts toward lower temperature as increasing Sn, and TO–T merges with TC at x = 0.11. An improving EC temperature change accompanying with large electrocaloric efficiency (ΔT/ΔE) of 0.28 × 10−6 K mV−1 over a wide temperature span is obtained at x = 0.11 under electric field of 50 kV cm−1. The enhanced ECE is mainly attributed to the multiphase coexistence. The dielectric properties and the grain boundary resistance are enhanced by optimizing Sn doping contents. [ABSTRACT FROM AUTHOR]

Phase transition plays a key role in the electrocaloric effect, but the first‐order ferroelectric–paraelectric phase transition always occurs far above room temperature, which heavily limits the practical application. Herein, the focus is on the orthorhombic–tetragonal first‐order ferroelectric–ferroelectric phase transition (@288 K) in <011>‐oriented barium titanate single crystal. Ferroelectric properties under a high electric field indicate a reversible field‐induced tetragonal–orthorhombic phase transition, based on which the electric field–temperature phase diagram is established. It is strongly related to the enhanced electrocaloric effect, and a large adiabatic temperature change of 1.33 K is obtained at 288 K under 15 kV cm−1, that is, a high electrocaloric strength of 88.7 mK cm kV−1. The large electrocaloric effect near room temperature makes lead‐free BaTiO3 a promising candidate for next‐generation solid‐state refrigeration. [ABSTRACT FROM AUTHOR]

Ferroelectric materials have emerged as intriguing contenders for a variety of applications in the ongoing effort to look for sustainable energy solutions, including energy storage and solid-state cooling systems. In this work, a systematic investigation has been conducted on the microstructural, dielectric, electrocaloric, and energy storage characteristics of sol-gel elaborated BaHf 0.20 Ti 0.80 O3 (BHT) ferroelectric ceramics. The structural investigation by Raman and X-ray diffraction indicated that when the sintering temperature increases, the tetragonality of BHT ceramics reduces, and the evolution of the cubic phase increases. The evolution of the microstructure in BHT ceramics is found to be significantly reliant on the sintering temperature. With increasing temperature of sintering, the bulk density of BHT ceramics increases. The improved dielectric and ferroelectric properties were attained in BHT ceramics at higher sintering temperatures. The BHT ceramic sintered at 1350 °C exhibited a maximum electrocaloric temperature change of ΔT ∼0.6 °C with a corresponding efficiency ΔT/ΔE of 0.3 K mm/kV near ambient temperature under a low electric field of 20 kV/cm. The BHT ceramic sintered at 1450 °C exhibited excellent room temperature recoverable energy density of J Rec ∼67.84 10−3J/cm3 and high energy storage efficiency of η ∼75.13 % under a low electric field of 20 kV/cm. The highest J Rec ∼73.22 10−3J/cm3 with corresponding η of 64.60 % were obtained in BHT ceramic sintered at temperature 1350 °C. These findings broaden the possibility of exploring BHT-based systems as efficient lead-free ferroelectrics for both solid-state refrigeration and energy storage applications. • The microstructural and electrical properties influenced by sintering temperature. • The density and grain size increases with increasing sintering temperature. • Enhanced electrocaloric and energy storage response at higher sintering temperatures. • The maximum ΔT of 0.6 °C was obtained under a low electric field of 20 kV/cm. • The small grain size is useful in achieving improved energy storage density. [ABSTRACT FROM AUTHOR]

La and Nb codoping of ferroelectric five-layer Aurivillius phase Sr 2 Bi 4 Ti 5 O 18 (T C ∼ 560 K), induces compositional disorder and diffuse relaxor transitions at much lower temperatures than the parent compound, while preserving the orthorhombic structure. For moderate La and Nb concentrations, the ferroelectric properties are enhanced in the vicinity of room temperature, and so is the electrocaloric effect as measured directly with a homemade quasi-adiabatic calorimeter. The adiabatic temperature change reaches, e.g., in Sr 2 Bi 3.44 La 0.5 Ti 4.8 Nb 0.2 O 18 , Δ T ⁓ 0.3 K at 355 K with a temperature span ⁓ 15 K, under Δ E = 37 kV/cm. Besides, a large field dispersion of the electrocaloric effect is found, ascribed to field-induced transitions from short-range-ordered relaxor to long-range-ordered ferroelectric states. Indirect estimations of the electrocaloric effect from electric polarization data are not able to quantitatively predict the direct results and emphasize the need of applying direct measurement methods, especially for relaxor ferroelectrics. [Display omitted] • New lead-free Aurivillius oxides based on La/Nb codoped Sr 2 Bi 4 Ti 5 O 18 show a significant and tunable electrocaloric effect • Largest electrocaloric response of ΔT ⁓ 0.3 K at 355 K under ΔE = 37 kV/cm • Direct electrocaloric effect measurements reveal an important dispersion with the electric field • Indirect derivations based on commonly applied thermodynamic formulations do not agree with direct results quantitatively [ABSTRACT FROM AUTHOR]

0.9KNbO3-0.1BaTiO3 ceramics, with a bimodal grain size distribution and typical tetragonal perovskite structure at room temperature, were prepared by using an induced abnormal grain growth (IAGG) method at a relatively low sintering temperature. In this bimodal grain size distribution structure, the extra-large grains (~10–50 μm) were evolved from the micron-sized filler powders, and the fine grains (~0.05–0.35 μm) were derived from the sol precursor matrix. The 0.9KNbO3-0.1BaTiO3 ceramics exhibit relaxor-like behavior with a diffused phase transition near room temperature, as confirmed by the presence of the polar nanodomain regions revealed through high resolution transmission electron microscope analyses. A large room-temperature electrocaloric effect (ECE) was observed, with an adiabatic temperature drop (ΔT) of 1.5 K, an isothermal entropy change (ΔS) of 2.48 J·kg−1·K−1, and high ECE strengths of |ΔT/ΔE| = 1.50 × 10−6 K·m·V−1 and ΔS/ΔE = 2.48 × 10−6 J·m·kg−1·K−1·V−1 (directly measured at E = 1.0 MV·m−1). These greatly enhanced ECEs demonstrate that our simple IAGG method is highly appreciated for synthesizing high-performance electrocaloric materials for efficient cooling devices.

Nowadays, much attention is paid for developing lead-free ceramics, which can be utilized in the refrigeration domain. This communication provides a detailed description of the synthesis and characterization of a lead-free solid solution of BaTi0.91Sn0.09O3. The X-ray diffraction analysis showed that the compound exhibits a single phase of tetragonal symmetry (P4mm (99)). The average crystallite size estimated using Scherrer's technique was found to be 122 nm. The microstructure or surface morphology of the sintered sample was investigated by using scanning electron microscopy. Based on mapping image, the sensitivity and spatial resolution of the different elements in our sample were improved. Analytical and simulation data for the electrocaloric effect in our sample were reported. A good electrocaloric strength (ξ = ΔT/ΔE) of ξ = 0.171 K mm/kV near the ferroelectric-paraelectric phase transition temperature was obtained. These values are very interesting when compared to those for other materials and show the possibility of using such lead-free ceramics for refrigeration domain. [ABSTRACT FROM AUTHOR]

Electrocaloric effect (ECE) is considered well applicable in the field of next generation solid state refrigeration technology. In this article, the structural properties and ECE response were altered and optimized by tailoring the Zr/Ti molar ratio in (Pb 0.94 La 0.04)(Zr x Sn 0.30 Ti 0.70-x)O 3 (x = 0.54, 0.52, 0.50 and 0.48) polycrystalline ceramics. Multiple phase transition behaviors including antiferroelectric (AFE) state to ferroelectric (FE) state transition under applied electric field, depolarization phase change behavior and AFE state to paraelectric state (PE) transition were observed, and their effects on the ECE response were investigated in detail. Significant improvement of ECE adiabatic temperature change of 1.04 K at room temperature (30 °C) was obtained by Maxwell method in (Pb 0.94 La 0.04)(Zr 0.52 Sn 0.30 Ti 0.18)O 3 bulk ceramic through AFE→FE phase transition, while the highest Δ T of 2.73 K with electrocaloric strength (Δ T· Δ E −1) of 0.039 K cm kV−1 were observed in (Pb 0.94 La 0.04)(Zr 0.50 Sn 0.30 Ti 0.20)O 3 bulk ceramic at temperature close to its Curie peak. The high ECE temperature change and ECE strength make them to be candidates for using in next generation solid-state refrigeration device. [ABSTRACT FROM AUTHOR]

The electrocaloric (EC) effect in dielectrics has shown great potential in the next-generation solid-state refrigeration; however, most dielectrics cannot satisfy the requirement for refrigeration at various temperatures. How to control large EC response to various temperatures is a critical problem for practical cooling applications. In this work, based on entropy analysis, a nonlinear thermodynamic approach considering mechanical loading has been generalized to demonstrate mechanical control of EC response in epitaxial ferroelectric Ba x Sr 1− x TiO 3 (BST) thin films. The effects of chemical composition x , in-plane misfit strain u m , and out-of-plane external uniaxial stress σ 3 on the phase diagrams, phase transition temperatures, and EC response of BST thin films have been studied. The results reveal that a large EC temperature change Δ T appears in the vicinity of c -PE and r-aa phase boundaries, because the polarization component P 3 becomes zero across both phase boundaries, leading to a large change of order in dipoles. It is found that the phase structures and the transition temperatures are sensitive to misfit strain and stress. Large EC response in BST thin films can be controlled and shifted to various temperatures over a wide temperature range for practical applications. It also indicates that the peak of Δ T can be shifted to higher temperature under in-plane compressive strain u m , while it is shifted to lower temperature under tensile strain u m or compressive stress σ 3. Furthermore, the optimal combination of misfit strain and stress for the EC temperature change are identified, which further enhances EC response. These insights offer an alternative pathway to control and implement EC refrigeration over a wide range of temperature. [ABSTRACT FROM AUTHOR]

Compact solid‐state refrigeration systems that offer a high specific cooling power and a high coefficient of performance (COP) are desirable in a wide range of applications where efficient and localized heat transfer is required. Here, a double‐unit electrocaloric (EC) polymer‐based refrigeration device with high intrinsic thermodynamic efficiency is demonstrated using a flexible EC polymer film with improved performance by doping plasticizer and an electrostatic actuation mechanism. The double‐unit refrigeration device achieves a large temperature span of 4.8 K, which is 71% higher than that of the single‐unit device. A specific cooling power of 3.6 W g−1 and a maximum COP of 8.3 for the cooling device are produced. The surface temperature of a central processing unit (CPU) cooled by an active EC device is 22.4 K lower than that of the CPU cooled in air. The highly efficient and compact EC cooling device demonstrated here not only leapfrogs the performance of existing solid‐state cooling technologies, but also brings solid state cooling closer to reality for a variety of practical applications that require compact or mechanically flexible refrigeration. [ABSTRACT FROM AUTHOR]

The 1980s saw the development of ferroelectric chiral smectic C (SmC*) liquid crystals (FLCs) with a clear focus on their application in fast electro-optic devices. However, as the only known fluid ferroelectric materials, they also have potential in other applications, one of which is in heat-exchange devices based on the electrocaloric effect. In particular, ferroelectric liquid crystals can be both the electrocaloric material and the heat exchanging fluid in an electrocaloric device, significantly simplifying some of the design constraints associated with solid dielectrics. In this paper, we consider the electrocaloric potential of three SmC* ferroelectric liquid crystal systems, two of which are pure materials that exhibit ferroelectric, antiferroelectric, and intermediate phases and one that was developed as a room-temperature SmC* material for electro-optic applications. We report the field-induced temperature changes of these selected materials, measured indirectly using the Maxwell method. The maximum induced temperature change determined, 0.37 K, is currently record-breaking for an FLC and is sufficiently large to make these materials interesting candidates for the development for electrocaloric applications. Using the electrocaloric temperature change normalised as a function of electric field strength, as a function of merit, the performances of FLCs are compared with ferroelectric ceramics and polymers.

A thermodynamic model is established to investigate the effects of internal stress in PbZrO3 (PZ) antiferroelectric (AFE) film on the barocaloric effect (BCE), electrocaloric effect (ECE), and energy storage properties. It is found that the internal stress can change the phase transition behaviors and free energy barriers among AFE, ferroelectric (FE), and paraelectric (PE) phases. For the BCE, it occurs only in the FE phase induced by stress or temperature. Under a certain temperature, the optimized negative and positive ECE can be obtained by controlling the internal stress and electric field. In addition, the switching electric field of the AFE→FE phase transition increases and causes a larger recoverable energy density with decreasing tensile stress. These results are analyzed and explained by tricritical points (3 cp) with different stresses, temperatures, and electric fields. Therefore, this thermodynamic model provides an effective route to optimize the BCE, ECE, and energy storage properties of PZ films. [ABSTRACT FROM AUTHOR]

The electrocaloric effect (ECE) was investigated in BaTiO3 ceramics, pure and doped with 2% of Eu3+ ions. The temperature and electric field dependences of ECE were investigated by the indirect method. Based on Maxwell relations, the ECE was characterized via P–T curves under different electric fields. The ECE experiments have been carried out from room temperature through the phase transition region and in the paraelectric phase. A normal positive ECE was found around the phase transition point and is of the order of 0.6 K for pure BaTiO3 and 0.15 K for the BT doped with Eu ions. The abnormal negative ECE was detected for the BaTiO3 ceramic doped with Eu ions above the temperature of the phase transition. This phenomenon was related to the existence of defects that originates from the fixed local polarization of defect dipoles. [ABSTRACT FROM AUTHOR]

Herein, 0.9(K 0.49 Na 0.49 Li 0.02)(Nb 0.8 Ta 0.2)O 3 –0.1CaZrO 3 (KNLNT–0.1CZ) relaxor system in multilayer ceramic capacitor (MLCC) are designed to attain elevated electrocaloric effect (ECE). Based on direct measurement, a large ∆ T of 2.45 K is achieved in KNLNT–0.1CZ MLCC, which is nearly 10 times higher than that of ceramic counterpart. The temperature span (T span) on a benchmark of ∆T above 1.5 K come up to 65 °C. Such excellent ECE benefits by synergistic effect of relaxor phase transition and high electric field. This study shed light a strategy on designing new ECE materials with large ∆T and wide T span for solid-state cooling. Image, graphical abstract [ABSTRACT FROM AUTHOR]

Image, graphical abstract Barium strontium titanate (Ba 0.65 Sr 0.35 TiO 3 -BST) added with a 0.5 wt% of B 2 O 3 -ZnO glass phase was prepared via a solid-state reaction approach. The lattice structures and morphologies of the ceramics were analyzed using X-ray diffraction and scanning electron microscopy technologies. The dielectric and ferroelectric properties of the glass added BST ceramics were characterized using a precision impedance analyzer and a ferroelectric polarization-electric field (P-E) hysteresis loop tester, respectively. The electrocaloric effect (ECE) was directly measured by a computer controlled thermocouple and high-voltage power supply, and also indirectly calculated using the Maxwell relation and the polarization extracted from the P-E loops as a function of temperature and electric field. The results indicate that when added with 0.5 wt% of B 2 O 3 -ZnO glass phase, the breakdown electric field of BST ceramic can be increased, and the adiabatic temperature change ΔT was enhanced from 1.70 K to 2.29 K. [ABSTRACT FROM AUTHOR]

The impact of the differing phase change characteristics on the electrocaloric effect (ECE) and thermophysical properties of Ba(Zr x Ti 1- x)O 3 (BZT) were investigated. It is demonstrated that the ECE reduces strongly with increasing Zr concentration, from 1.25 K to 0.10 K. The strong reduction of ECE is associated with the vanishing of the latent heat as the nature of paraelectric to ferroelectric phase transition changes. Despite the second order nature of the phase transition, an enhanced electrocaloric responsivity, 0.225 × 10−6 Km V-1, occurs at the triple point composition (x = 0.13), where the stability fields of ferroelectric phases converge. The decreasing ECE and thermophysical properties with increasing Zr concentration result in a more than one order of magnitude reduction in a caloric figure of merit, from ∼3500 J m−1s−1/2 to ∼200 J m−1s−1/2. The caloric figure of merit was used to compare the performance of other representative electrocaloric, magnetocaloric and mechanocaloric materials. [ABSTRACT FROM AUTHOR]

Electrocaloric refrigeration is one of the most promising environmentally‐friendly technologies to replace current cooling platforms—if a notable electrocaloric effect (ECE) is realized around room temperature where the highest need is. Here, a straight‐forward, one‐pot chemical modification of P(VDF‐ter‐TrFE‐ter‐CTFE) is reported through the controlled introduction of small fractions of double bonds within the backbone that, very uniquely, decreases the lamellar crystalline thickness while, simultaneously, enlarging the crystalline coherence along the a‐b plane. This increases the polarizability and polarization without affecting the degree of crystallinity or amending the crystal unit cell—undesirable effects observed with other approaches. Specifically, the permittivity increases by >35%, from 52 to 71 at 1 kHz, and ECE improves by >60% at moderate electric fields. At 40 °C, an adiabatic temperature change >2 K is realized at 60 MV m−1 (>5.5 K at 192 MV m−1), compared to ≈1.3 K for pristine P(VDF‐ter‐TrFE‐ter‐CTFE), highlighting the promise of a simple, versatile approach that allows direct film deposition without requiring any post‐treatment such as mechanical stretching or high‐temperature annealing for achieving the desired performance. [ABSTRACT FROM AUTHOR]