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The solid-state refrigeration technique based on the electrocaloric effect (ECE) of ferroelectric materials has been regarded as a promising alternative to vapor compression systems due to its advantages of high efficiency and easy miniaturization. However, the small adiabatic temperature change (ATC) and narrow operating temperature range of ferroelectric materials are key obstacles for their practical applications of ECE refrigeration. To improve the ECE performance of ferroelectric polymer poly(vinylidene fluoride) [P(VDF-TrFE)], PbZr1−xTixO3 (PZT) nanoparticles with larger polarization is herein introduced to form ferroelectric nanocomposites. The phase-field simulation is employed to investigate the dynamic hysteresis loops and corresponding domain evolution of the ferroelectric nanocomposites. The temperature-dependent ATC values are calculated using the indirect method based on the Maxwell relation. The appearance of the double hysteresis loop is observed in P(VDF-TrFE) nanocomposite filled with PbZr0.1Ti0.9O3 nanoparticles [P(VDF-TrFE)–PZT0.9], which is mainly caused by a microscopic domain transition from single domain to polar vortex. Compared to the P(VDF-TrFE), enhanced ATC values associated with the domain transition are unveiled in P(VDF-TrFE)–PZT0.9, and the temperature range of excellent ECE is also effectively broadened. In addition, as the component x of filled PZT nanoparticles increases to cross the morphotropic phase boundary (MPB), the maximum ATC value shows a significant increase. The results presented in this work not only explain the mechanism of domain transition induced excellent ECE in the P(VDF-TrFE)–PZT nanocomposite, but also stimulate future studies on enhancing ECE of P(VDF-TrFE) by introducing ferroelectric nanofillers. [ABSTRACT FROM AUTHOR]

The electric field dependence of the electrocaloric effect is investigated in BaTiO 3 and Ba(Zr 0.12 Ti 0.88 )O 3 by a direct method with sub-mK temperature resolution. The field dependence of the caloric temperature change Δ T (E) shows a pronounced change within a few Kelvin around the Curie temperature for the first-order phase transition in BaTiO 3. The transition from a linear field dependence in the ferroelectric phase over a butterfly-shaped to a quadratic field dependence in the paraelectric phase is compared to predictions of Landau–Devonshire theory. The simultaneous measurement of caloric and dielectric properties further allows for the investigation of the polarization dependence Δ T (P) of the electrocaloric effect. We find clear deviations from the predicted quadratic polarization dependence for temperatures close to the Curie temperature. Ba(Zr 0.12 Ti 0.88 )O 3 shows in contrast only a slow and gradual change of the field dependence over a broad temperature range as a consequence of its diffuse phase transition. [ABSTRACT FROM AUTHOR]

Ferroelectric (FE) electrocaloric materials research has been blossoming worldwide for solid-state refrigeration and potential cooling systems replacing thermoelectric Peltier coolers in microelectronics. In this work, we report the outcomes from a systematic study of combined phase transition (thermodynamics) based on the phenomenological Landau theory and distributed electric field (electrostatics of thin film interfaces) in FE bilayer films. Specifically, the compositional variation of ferroelectric bilayers results in broken spatial inversion symmetry leading to asymmetric thermodynamic potentials due to a combination of normal (first- and second-order phase transition) and relaxor (dispersive dielectric constant) ferroelectric behaviors devised for efficient electrocaloric cooling effects. Extensive theoretical analyses conducted for bilayers consisting of insulating materials highlight modified phase transition temperature behavior and self-poling by effective electric field amplification arising due to bilayers' electrostatic coupling yielding significant changes in isothermal entropy (ΔS) and adiabatic temperature (ΔT). The theoretical calculation insights supported with experimental results signify, through case studies for a combination of materials experimental parameters, that amplification of the local electric field and materials engineering maximize the number of coexisting phases at or away from the morphotropic phase boundary of constituent layers in bilayer thin film architectures, which can be applicable toward other classes of materials and multilayer systems. These are effective ways for efficient cooling, in general, and for microelectronics thermal management either directly or by developing a thermal switch with phase change materials integrated with thermoelectric coolers for residual heat dissipation, both at the system and on-chip levels. [ABSTRACT FROM AUTHOR]

Morphotropic phase boundary of ferroelectric solid solutions attracts interest with respect to not only improved piezoelectric properties but also the electrocaloric effect, which is attractive to build new-generation cooling devices. In the present study, the electrocaloric effect in (1 − x − y)Na0.5Bi0.5TiO3–xBaTiO3–yNaNbO3 near its morphotropic phase boundary is studied by direct measurements of temperature change ΔT. ΔT maximum is observed in the region of depolarization temperature, where the major contribution comes from an entropy jump at the electric field-induced phase transition. Differences between ΔT values measured when an electric field pulse is applied and removed are explained by slow domain rearrangement in the ferroelectric phase and metastability of phases close to the depolarization temperature. Among studied compositions, the highest value of ΔT is obtained for the compositions 0.94Na0.5Bi0.5TiO3–0.06BaTiO3 and 0.93Na0.5Bi0.5TiO3–0.06BaTiO3–0.01NaNbO3 in the region of depolarization temperature. Examples of the comparison of the directly measured values of ΔT and the values calculated using the Maxwell relation revealing inconsistency between the two methods in the ferroelectric and the nonferroelectric phase are presented. [ABSTRACT FROM AUTHOR]

Polar 2D materials hold the emerging functionalities such as ferro‐, piezo‐, and pyro‐electric properties. On account of infrared‐active low bandgap and polar nature at reduced dimensionality, they served as an ideal choice of pyroelectric material. It can cover up a diverse range of applications, such as waste thermal energy harvesting, IR imaging, photodetector, temperature sensors, and several catalytic processes due to the abundance of dynamic thermal fluxes. Recently, 2D pyroelectric materials have manifested a substantial role in thermal energy harvesting. Consequently, it is realized that there are plenty of scopes available to diversify its applicability. Thus, the challenges are spotlighted in this perspective to envision the desired 2D pyroelectric materials to achieve the effective thermal energy harvesting, sensing, and catalytic efficacy. Particularly, the emphasis is given to elucidate the role of spontaneous polarization in 2D materials to ascertain the giant pyroelectricity. [ABSTRACT FROM AUTHOR]

Solid-state cooling, represented by the electrocaloric effect (ECE) in (anti)ferroelectric materials, has emerged as an alternative green refrigeration technology by virtue of its high efficiency and miniaturization and is expected to substitute conventional vapor-compression. Significant progress has been made in developing high-performance EC materials since its revival. However, anomalous EC behaviors are frequently observed, including asymmetric and negative EC profiles, and the physical mechanism behind this is still under debate. Its rationalization is of great importance since full utilization of anomalous EC behaviors could enhance EC strength and/or cooling capacity. This mini-review gives a brief overview of research advances in EC anomalies in (anti)ferroelectrics with the hope of provoking thought on the design of reconstructed refrigeration cycles and superior EC materials for application in solid-state cooling devices. [ABSTRACT FROM AUTHOR]

We report the effects of B-site cationic size disorder ( σ 2 ) and configurational entropy (CE) on the crystal structure and electrocaloric (EC) effect of BaTi1−x−ySnxZryO3 (BTSZ) (0.01 ≤ x ≤ 0.06) ceramics. The samples were designed to show decreased σ 2 and increased CE but the same B-site cation average radius and tolerance factor with increasing x. The tetragonal lattice distortion c/a and piezoelectricity showed a minimum and maximum, respectively, near x = 0.04. The ferroelectric Curie temperature decreased overall from ∼358 to ∼332 K with x increasing from 0.01 to 0.06. The EC effects measured by the direct method showed a maximum with an adiabatic temperature change of ∼0.80 K at 60 kV/cm near x = 0.04. The large EC effect in x = 0.04 is attributed to the small tetragonal distortion and low energy barrier for E-induced phase transformation due to the combined disorder effects of cationic size and configuration. Our results suggest a close correlation between the lattice distortion and EC effects and an effective route to improve the EC effects. [ABSTRACT FROM AUTHOR]

In order to obtain large room-temperature electrocaloric effect (ECE) and wide operation temperature range simultaneously in lead-free ceramics, we proposed designing a relaxor ferroelectric with a Tm (the temperature at which the maximum dielectric permittivity is achieved) near-room temperature and glass addition. Based on this strategy, we designed and fabricated lead-free 0.76NaNbO3–0.24BaTiO3 (NN-24BT) ceramics with 1wt.% BaO–B2O3–SiO2 glass addition, which showed distinct relaxor ferroelectric characteristics with strongly diffused phase transition and a Tm near-room temperature. Based on a direct measurement method, a large ΔT (adiabatic temperature change) of 1.3 K was obtained at room temperature under a high field of 11.0 kV mm−1. Additionally, large ECE can be maintained (>0.6 K@6.1 kV mm−1) over a broad temperature range from 23 °C to 69 °C. Moreover, the ECE displayed excellent cyclic stability with a variation in ΔT below ±7% within 100 test cycles. The comprehensive ECE performance is significantly better than other lead-free ceramics. Our work provides a general and effective approach to designing lead-free, high-performance ECE ceramics, and the approach possesses the potential to be utilized to improve the ECE performance of other lead-free ferroelectric ceramic systems. [ABSTRACT FROM AUTHOR]

Struvite (MgNH4PO4·6H2O) is a mineral first identified in 1845. It is being tested for several reasons: (1) it is a problem in liquid wastewater treatment plants; (2) on the other hand, it is recovered from these wastewaters for its phosphorus, magnesium and nitrogen; (3) is the main component of microbial-induced urinary stones. We have recently shown that struvite is ferroelectric and piezoelectric. In this paper, we present the first experimental evidence of the pyroelectric nature of struvite. Using a single-diffusion gel growth technique, we grew struvite crystals as flat, parallel plates. We performed measurements of pyroelectric currents on struvite of this shape, using it as a dielectric of a plate capacitor. The occurrence of pyroelectric effects in struvite was investigated by measuring depolarization currents as a function of temperature. This technique allows the disclosure of ferroelectric/pyroelectric transitions as well as the reconstruction of the ferroelectric loop. We found that the value of the pyroelectric coefficient p attains a maximum of 22 × 10−6 C m−2 K−1 slightly below room temperature, going down to p ≅ 10 × 10−6 C m−2 K−1 at room temperature. This value is comparable to values for other minerals. For example, the pyroelectric polarization coefficient of tourmaline, the mineral for which the pyroelectric effect was first discovered, is 4 × 10−6 C m−2 K−1. This value is 2.5 times lower than that measured for struvite, illustrating struvite's fairly strong pyroelectricity. [ABSTRACT FROM AUTHOR]

A key challenge currently for the new ferroelectric refrigeration with high efficiency and environmental friendliness lies in the urgent demand for ferroelectric materials with huge electrocaloric effects (ECE). Ferroelectric polycrystalline ceramics with high ECE stand out as one of the most promising candidates for electrocaloric cooling applications. However, the grain boundary network, as a barrier for the cross‐transmission of charged carriers, widely exists in electrocaloric polycrystalline ceramics and is often neglected in favor of focusing more on composition regulation and structural design. Herein, a grain boundary barrier engineering is proposed that regulates the Schottky barrier at the grain boundary network in the Ba0.8Zr0.2TiO3 ceramics by a maneuverable annealing process and clarifies its critical role in enhancing the ECE of polycrystalline ceramics. As a result, a substantial enhancement of the EC performance (from 0.68 to 1.63 K at 50 °C and 80 kV cm−1, ≈2.4 times) has been achieved in the annealed Ba0.8Zr0.2TiO3 ceramics with a lower Schottky barrier. The microstructural and electrical characterization reveals that the lower Schottky barrier in the grain boundary network facilitates the domain switching and electronic transition, hence resulting in enhanced polarization response and EC performance. [ABSTRACT FROM AUTHOR]

Polyvinylidene fluoride (PVDF) with pyroelectric properties has demonstrated great potential in sensors, actuators and structural health monitoring. However, the low content of β phase and the secondary pyroelectricity induced by thermal expansion limit its pyroelectric performances for a broader range of applications. In this work, graphene nanoplatelets (GNP) that have excellent physical properties are added to PVDF to improve the matrix's pyroelectric properties. To fully take advantage of the reinforcements, PVDF composite films with functionally graded (FG) distribution of GNP fillers are prepared. The pyroelectric properties of the FG films that are subjected to different scenarios are experimentally tested and analyzed. Combining experiments and finite element simulation, the secondary pyroelectricity of the multi‐layered FG films is particularly investigated for the first time. Compared to uniform dispersion, FG distribution of the GNP has an obvious effect on the pyroelectric performances of the PVDF composites. The increase in the number of layers and the thickness of the outer layers is beneficial for the improvement of the pyroelectric performances. The FG films with higher GNP concentration in the outer layer exhibit more favorable pyroelectricity. The parametric study is envisaged to provide guidelines for the design and optimization of the FG‐GNP/PVDF composites with improved pyroelectric performances. Highlights: FG‐GNP is favorable for pyroelectricity and stability of PVDF composite films.GNP/PVDF composite films with more layers demonstrate superior pyroelectricity.Attributes of layers have significant effects on pyroelectric responses.Effects of factors associated with secondary pyroelectricity are quantitatively identified. [ABSTRACT FROM AUTHOR]

The pursuit of high-efficiency and zero-emission refrigeration technologies has spurred interest in electrocaloric (EC) refrigeration utilizing ferroelectric (FE) materials, where accurate characterization of the EC effect is crucial for comprehending its underlying physical mechanisms and for developing high-performance EC materials. In this study, we investigate the influence of unsaturated vs saturated FE polarization characteristics on EC effects using Pb0.99Nb0.02[(Zr0.6Sn0.4)0.85Ti0.15]0.98O3 ceramics. Direct EC measurement reveals that unsaturated loops can introduce substantial errors and even fake negative EC effects when employing the Maxwell approach for indirect EC measurement. In contrast, relatively accurate indirect EC results can be obtained using saturated FE hysteresis loops. Furthermore, it also highlights the necessity for saturated polarization conditions to achieve optimal EC performance in FEs. This work not only emphasizes the importance of carefully selecting polarization data for indirect EC measurements, but also presents a universal strategy to enhance EC effects in various materials. [ABSTRACT FROM AUTHOR]

Employing piezoelectrically activated beam-like structures is extending in numerous applications for instance energy harvesters and sensors. On the other hand, advanced materials such as carbon nanotube-reinforced nanocomposites are widely implemented in making passive structures with the aim of using their advantages. For the first time, a study is established on the critical temperature of a piezoelectric sandwich aggregated CNTRC beam regarding the pyroelectricity. The stabilization contribution of pyroelectricity against the thermal buckling incidence of sandwich beams has been demonstrated specifically. It is found that the pyroelectricity develops the critical point for the temperature of a clamped-clamped piezoelectric sandwich non-reinforced beam. [ABSTRACT FROM AUTHOR]

Materials with electrocaloric effect (ECE) and/or thermal switching ratio λ are desirable for developing various heat management devices, but developing high-performance candidates, especially those that simultaneously possess large near room-temperature ECE and λ is actually absent. The Zr-rich PbZr1−xTixO3 (PZT) displays a composition-induced antiferroelectric-ferroelectric (AFE-FE) phase boundary, where an unusual negative ECE is expected. Meanwhile, the electric field-sensitive dipole orientation during the AFE-FE phase transition can be employed to modulate λ. In this work, the Zr-rich PZT with coexisting AFE and FE phases was developed and the AFE-FE phase transition temperature is tuned toward room temperature by changing the Ti content to achieve large negative ECE and λ. A large adiabatic temperature change ΔT of −3.3 K accompanied by a giant λ of 1.84 near 60 °C is captured in optimal PbZr0.95Ti0.05O3 ceramics, demonstrating a prominent application prospect in solid-state refrigeration. [ABSTRACT FROM AUTHOR]

They found that metal contacts can facilitate the stabilization of the ferroelectric phase, enabling aggressive scaling of 2D ferroelectrics.[13] As a recently discovered vdW ferroelectric, -In SB 2 sb Se SB 3 sb exhibits inter-correlated in-plane and out-of-plane polarization.[[17]] Unlike traditional ferroelectric materials, which are usually insulators, -In SB 2 sb Se SB 3 sb is a semiconductor with a band gap of 1.36 eV (bulk). In recent years, a range of two-dimensional (2D) layered materials have been experimentally confirmed or theoretically predicted to be piezoelectric, pyroelectric, or ferroelectric.[[1], [3], [5], [7], [9]] Compared to their bulk counterparts, 2D piezoelectric, pyroelectric, and ferroelectric materials exhibit many intriguing properties, such as excellent size scaling, tunable bandgap, negative piezoelectric coefficient, and high mechanical flexibility.[[1], [3], [5], [7], [9]] Furthermore, the stackable nature of 2D layered materials makes them promising building blocks for designing functional heterostructures, where the 2D layers can be integrated with conventional piezoelectric, pyroelectric, and ferroelectric oxides and polymers. Piezoelectric, pyroelectric, and ferroelectric materials have attracted tremendous attention owing to their potential applications in nonvolatile memories, logic devices, photodetectors, sensors, actuators, transducers, and energy harvesting devices. 10.1063/5.0116445 40 X. Hong, A. Posadas, K. Zou, C. H. Ahn, and J. Zhu, "High mobility few layer graphene field effect transistors fabricated on epitaxial ferroelectric gate oxides", Phys. [Extracted from the article]

Using the previously developed model, we study the electrocaloric effect (ECE) in antiferroelectric crystals of squaric acid, where the low-temperature polarization reorientation by the external electric field has been earlier predicted to be a two-stage process with the intermediate ferrielectric phase. The T - E landscape of the model entropy is explored. The ECE, characterized by the electric Grüneisen parameter, is found to be negative in the antiferroelectric phase. In the ferrielectric phase, it is positive at low fields but becomes slightly negative below the transition to the ferroelectric phase. In the ferroelectric phase, the ECE is positive at all temperatures and fields. The negative EC temperature shift Δ T of the largest magnitude is predicted to be around − 2.7 K at 200 kV/cm. The supercritical behavior of the Grüneisen parameter in the crossover region between two bicritical end points is studied. [ABSTRACT FROM AUTHOR]

Negative charge card refrigeration, as a new solid-state refrigeration technology, has garnered much interest with its broad application potential in the area of temperature control for sensors and electronic devices. In this study, antiferroelectric thin films of Pb1−xMnxZrO3 (x = 0.0%, 0.5%, 1.0%, 2.0%, abbreviated as PMZ-100x) were prepared on tin oxide doped with fluorine/glass substrates by the sol-gel method. When the variable temperature P–E loops under various applied electric fields are compared, the P–E loops gradually change from linear to typical double P–E loops. This result implies that temperature and electric field work together to induce the phase change. The negative electrocaloric effect of the PMZ-0.5 film is greatly enhanced at 50 °C, 444 kV/cm, ΔS = 16.75 J·K−1·kg−1, ΔT = −16.39 K, in comparison to the PbZrO3 film (ΔS = 11.84 J·K−1·kg−1, ΔT = −12.48 K at 75 °C, 421 kV/cm). The great cooling performance indicates that PMZ-100x films have excellent potential for use in integrated circuit solid-state cooling. [ABSTRACT FROM AUTHOR]

Pyroelectric materials, with piezoelectricity and pyroelectricity, have been widely used in infrared thermal detectors. In this paper, a modified first-order plate theory is extended to analyze a pyroelectric sensitive element structure. The displacement, temperature, and electric potential expand along the thickness direction. The governing equation of the pyroelectric plate is built up. The potential distributions with upper and lower electrodes are obtained under different supported boundary conditions. The corresponding numerical results of electric potential are consistent with those obtained by the three-dimensional finite element method. Meanwhile, the theoretical results of electric potential are close to that of experiments. The influence of supported boundary conditions, piezoelectric effect, and plate thickness are analyzed. Numerical results show that the piezoelectric effect reduces the electric potential. The thickness of the pyroelectric plate enhances the electric potential but reduces the response speed of the detector. It is anticipated that the pyroelectric plate theory can provide a theoretical approach for the structural design of pyroelectric sensitive elements. [ABSTRACT FROM AUTHOR]

Lead‐free electrocaloric (EC) materials have attracted considerable attention due to their potential applications in environmentally friendly solid‐state cooling devices. Achieving a large adiabatic temperature change (ΔTEC$\Delta T_{\text{EC}}$) at low applied voltage and good temperature stability is crucial and closely related to the phase structure and ferroelectric properties. In this study, 0.2Ba(Ti0.9Sn0.1)O3–0.8Ba(Zr0.18Ti0.82)O3 (BZSnT20) multilayer electrocaloric ceramics (MLEC) are synthesized and characterized for their phase structure and dielectric properties using X‐ray diffraction and dielectric testing. The ferroelectric performance of BZSnT20 is assessed by analyzing their polarization–electric field loops, and the ΔTEC$\Delta T_{\text{EC}}$ is measured using a heat‐flow measurement system. By investigating the mechanisms, structure–activity relationship between the BaO–CaO–SiO2 (BCS) glass sintering aid and the ΔTEC$\Delta T_{\text{EC}}$, the optimal content of BCS glass sintering aid is obtained. In the case of BZSnT20 MLEC, a positive relationship between effective volume and ΔTEC$\Delta T_{\text{EC}}$ is observed, consistent with theoretical calculations. Additionally, the ceramic layer is found to have no significant influence on the EC properties of the sample. In this study, valuable insights into modifying the dielectric and adiabatic temperature change performance in lead‐free MLEC are provided and a potential pathway for the development of low‐voltage EC cooling devices is suggested. [ABSTRACT FROM AUTHOR]

Measuring contact angles (CAs) on super-hydrophobic surfaces (CA ≥ 150 °) can be challenging using traditional methods. In this work, we develop an alternative technique to measure CAs indirectly by measuring the minimum of the dimensionless hydrostatic pressure of a droplet as it de-wets a surface. This technique does not require measuring the slope of the profile close to the three-phase contact line and is devoid of any external pressure or force gauges. An experimental proof of principle is presented. Our results suggest that this technique may become a viable alternative for measuring the CA on super-hydrophobic and liquid repellent surfaces with relatively low uncertainty. [ABSTRACT FROM AUTHOR]

Electrocaloric refrigeration which is environmentally benign has attracted considerable attention. In distinction to ferroelectric materials, which exhibit an extremely high positive electrocaloric effect near the Curie temperature, antiferroelectric materials represented by PbZrO3 have a specific negative electrocaloric effect, i.e., electric field decreases the temperature of the materials. However, the explanation of the microscopic mechanism of the negative electrocaloric effect is still unclear, and further research is still needed to provide a theoretical basis for the negative electrocaloric effect enhancement. Herein, the antiferroelectric phase-field model has been proposed to design polar boundaries enhancing antiferroelectric negative electrocaloric performance in PbZrO3-based materials. Based on this, we have simulated the polarization response and domain switching process of the temperature and electric field-induced antiferroelectric—ferroelectric phase transition. It is shown that the temperature range tends to increase as the density of polar boundaries increases from the antiferroelectric stripe domain, polymorphic domain to the nanodomain. Among them, the peak adiabatic temperature change of antiferroelectric nanodomains can reach −13.05 K at 84 kV/cm, and a wide temperature range of about 75 K can be realized at 42 kV/cm. We expect these discoveries to spur further interest in the potential applications of antiferroelectric materials for next-generation refrigeration devices. [ABSTRACT FROM AUTHOR]

A large adiabatic temperature change along with a wide operating temperature region is usually required for the electrocaloric materials to fulfill their refrigeration function. In general, doping foreign ions into BaTiO3 is the frequently utilized strategy in order to obtain excellent electrocaloric materials for the practical application. In the current paper, BaTiO3 lead‐free ferroelectric ceramics were doped by Ca2+ and Sn4+ simultaneously in order to generate a coexistence state at room temperature, where ferroelectric domains and nanodomains exit. As a result, a large polarization and a wide operating temperature range were finally induced. It is found that Ba0.9Ca0.1Ti0.85Sn0.15O3 has a maximum adiabatic temperature change of 0.85 K and an excellent working temperature region (65 K, ∆T > 90% Tmax) was achieved under an electric field of 50 kV/cm. The above phenomenon indicates that the modified BaTiO3 ceramics can be a good potential electrocaloric material in the state of cross‐existence of ferroelectric domains and nanodomains. [ABSTRACT FROM AUTHOR]

Lithium tantalate crystals, as a type of pyroelectric material, stand out from many other pyroelectric materials due to the advantages of high Curie temperature, large pyroelectric coefficient, high figure of merits, and environmental friendliness. Due to the pyroelectric effect caused by their spontaneous polarization, lithium tantalate crystals have broad application prospects in wide spectral bandwidth and uncooled pyroelectric detectors. This article reviews the pyroelectric properties of lithium tantalate crystals and evaluates methods for pyroelectric properties, methods for modulating pyroelectric properties, and pyroelectric detectors and their applications. The prospects of lithium tantalate thin films, doped lithium tantalate crystals, and near stoichiometric lithium tantalate crystals as response components for pyroelectric detectors are also discussed. [ABSTRACT FROM AUTHOR]

In this work, the electrocaloric effect (ECE) and electrocaloric strength (ΔT/E) were measured and thermal and dielectric studies were performed on Pb-modified BaTiO3 (BPT). The saturated hysteresis loops and normal ferroelectric behavior of the ferroelectric ceramics allow the utilization of the indirect method to estimate the electrocaloric properties. The electrocaloric measurements were performed under high (18 kV/cm) versus low (8 kV/cm) electric field conditions. These conditions were chosen to notice and then eliminate an artificial negative electrocaloric effect in the tested ceramics. At the same time, relatively high values of positive electrocaloric temperature change ΔT ( ~   2.19   K ) and electrocaloric strength ΔT/E ( ~ 0.27–0.11 K · cm/kV) were obtained. [ABSTRACT FROM AUTHOR]

Relaxor ferroelectric polymers exhibiting a giant electrocaloric effect (ECE) can potentially be used to create next‐generation solid‐state coolers. Under an electric field, poly(vinylidene fluoride‐trifluoroethylene‐chlorofluoroethylene) terpolymer goes through a large dipolar entropy change producing a high adiabatic temperature change (ΔTECE). This work resolves the molecular origins of the large entropy change behind the electric field‐induced dipole switching. A Fourier transform infrared spectroscopy equipped with a high voltage source is used to operandoly observe the characteristic molecular vibrational modes. A short‐range trans (T) conformation of the CF2‐CH2 dyads interrupted by a gauche (G) conformation, e.g., TTTG in the terpolymer chain, undergoes a dynamic transformation that leads to a corresponding ΔTECE whenever an electric field is applied. The molecular dynamics simulation also proves that the energy barrier that the transformation from TTTGs into a long T sequence overcomes is smaller than that for all other conformations. A mixed solvent system is used to obtain T3G‐enriched terpolymer films exhibiting a 4.02 K ΔTECE at 60 MV m−1 and these films are employed to manufacture a 2‐layer‐cascaded cooling device that achieves a 6.7 K temperature lift, the highest reported value for a 2‐layer cascaded device made of fluoropolymers. [ABSTRACT FROM AUTHOR]

Pyroelectric materials hold significant potential for energy harvesting, sensing, and imaging applications. However, achieving high‐performance pyroelectricity across a wide temperature range near room temperature remains a significant challenge. Herein, we demonstrate a single crystal of Fe(II) spin‐crossover compound shows remarkable pyroelectric properties accompanied by a thermally controlled spin transition. In this material, the uniaxial alignment of polar molecules results in a polarization of the lattice. As the molecular geometry is modulated during a gradual spin transition, the polar axis experiences a colossal thermal expansion with a coefficient of 796×10−6 K−1. Consequently, the material's polarization undergoes significant modulation as a secondary pyroelectric effect. The considerable shift in polarization (pyroelectric coefficient, p=3.7–22 nC K−1cm−2), coupled with a low dielectric constant (ϵ′=4.4–5.4) over a remarkably wide temperature range of 298 to 400 K, suggests this material is a high‐performance pyroelectric. The demonstration of pyroelectricity combined with magnetic switching in this study will inspire further investigations in the field of molecular electronics and magnetism. [ABSTRACT FROM AUTHOR]

This study describes the synthesis and characterization of the lead-free organic ferroelectric perovskite N-methyl-N'-diazabicyclo [2.2.2]octonium)-ammonium trichloride (MDABCO-NH4Cl3). The electrospinning technique was employed to obtain nanofibers embedded with this perovskite in a PVC polymer for hybrid fiber production. The dielectric, piezoelectric, and pyroelectric properties of these fibers were carefully examined. Based on measurements of the dielectric permittivity temperature and frequency dependence, together with the pyroelectric results, a transition from a high temperature paraelectric to a ferroelectric phase that persisted at room temperature was found to occur at 438 K. The measured pyroelectric coefficient yielded values as high as 290 μC K−1 m−2, which is in between the values reported for MDABCO-NH4I3 and the semiorganic ferroelectric triglycine sulfate (TGS). The hybrid nanofibers exhibited good morphological characteristics and demonstrated very good piezoelectric properties. Specifically, a piezoelectric coefficient of 42 pC/N was obtained when applying a periodical force of 3 N and a piezoelectric voltage coefficient of geff = 0.65 V mN−1. The performance of these fibers is on par with that of materials discussed in the existing literature for the fabrication of nano energy-harvesting generators. Importantly, the perovskite nanocrystals within the fibers are protected from degradation by the surrounding polymer, making them a promising environmentally friendly platform for flexible mechanical energy harvesting. [ABSTRACT FROM AUTHOR]

We propose a characterization method based on modulated thermoreflectance technique for measuring directly the electrocaloric (EC) effect. First, the EC response in BaTiO3-based multilayer capacitors (MLC) with Y5V specification was measured using thermoreflectance set-up. Further, the direct measurement method was implemented on P(VDF-TrFE) 55/45 thin films deposited on flexible PET substrate, where the frequency dependence of the EC response in these films was investigated. It was noted that the P(VDF-TrFE) EC temperature responses depend on the operation voltage frequency, thus we considered three frequency ranges using square voltage waveform. Three distinct types of EC temperature variation responses were observed depending on the waveform frequency range. In addition, the EC temperature variation of the thin film with a thickness of 1.4 µm was measured via thermoreflectance. The data reveal a large EC effect occurring at room temperature where a temperature change ΔT = 1.14°C was induced under a field of 82 MV/m. [ABSTRACT FROM AUTHOR]

Lead-free ferroelectric materials are essential for environment-friendly solid-state cooling technology. In this respect, the electrocaloric effect of lead-free Ba0.8−xSr0.2SmxTiO3 (x = 0.01–0.05) ceramics has been investigated. The Rietveld refinement reveals that all the ceramics exhibit tetragonal symmetry and the tetragonality decreases for x > 0.03, which is the major reason behind the decrease in both isothermal entropy change and adiabatic temperature change. The degree of diffuseness parameter is enhanced by doping of Sm3+, which confirms the formation of polar nanoregion and the enhancement of the electrocaloric effect parameter by adding extra entropy. The relaxor behavior of the prepared samples is also confirmed by estimating the degree of deviation parameter (Δ T m = 77 K ) from the 1 ε r vs. T curve. So, the temperature stability of the prepared ceramics is improved in a broad temperature window. The highest isothermal entropy change (Δ S) , adiabatic temperature change (Δ T) , and electrocaloric strength ( Δ T Δ E ) are found to be 1.230 Jkg−1 K−1, 0.862 K, and 0.028 73 K cm/kV at 316 K, respectively, for Ba0.77Sr0.2Sm0.03TiO3. [ABSTRACT FROM AUTHOR]

More than a decade of active electrocaloric (EC) material research has produced several EC materials that exhibit a giant electrocaloric effect (ECE) at high electric fields, which is assured by direct measurement. These EC materials have enabled the demonstration of EC cooling devices, which exhibit temperature lifts of more than 10 K. These research and development efforts have revealed the critical importance of electrical breakdown, which is common in all electric and dielectric materials and devices under high voltages and electric fields. In general, the electric field for reliable device operation of dielectrics has to be less than 25% of the typical electric breakdown strength. To realize EC cooling devices with competitive performance requires advanced EC materials that generate large ECE (ΔT > 5 K) under these low electric fields. Double-bond (DB) defect modified P(VDF-TrFE-CFE) relaxor polymers, as reported recently, generate large ECE under low electric fields without any fatigue effects even after 1 × 106 field cycles. These relaxor ferroelectrics promise to meet the application challenge. A closely coupled experimental and theoretical study of EC materials will undoubtedly lead to advanced EC materials that generate large ECE at low electric fields beyond the DB modified relaxor polymers. This will result in practical and high-performance EC coolers, which are environmentally benign, compressor-free, and highly efficient. [ABSTRACT FROM AUTHOR]

This study describes the synthesis and characterization of the lead-free organic ferroelectric perovskite N-methyl-N’-diazabicyclo [2.2.2]octonium)-ammonium trichloride (MDABCO-NH4Cl3). The electrospinning technique was employed to obtain nanofibers embedded with this perovskite in a PVC polymer for hybrid fiber production. The dielectric, piezoelectric, and pyroelectric properties of these fibers were carefully examined. Based on measurements of the dielectric permittivity temperature and frequency dependence, together with the pyroelectric results, a transition from a high temperature paraelectric to a ferroelectric phase that persisted at room temperature was found to occur at 438 K. The measured pyroelectric coefficient yielded values as high as 290 μC K−1 m−2, which is in between the values reported for MDABCO-NH4I3 and the semiorganic ferroelectric triglycine sulfate (TGS). The hybrid nanofibers exhibited good morphological characteristics and demonstrated very good piezoelectric properties. Specifically, a piezoelectric coefficient of 42 pC/N was obtained when applying a periodical force of 3 N and a piezoelectric voltage coefficient of geff = 0.65 V mN−1. The performance of these fibers is on par with that of materials discussed in the existing literature for the fabrication of nano energy-harvesting generators. Importantly, the perovskite nanocrystals within the fibers are protected from degradation by the surrounding polymer, making them a promising environmentally friendly platform for flexible mechanical energy harvesting.

The energy conversion potential of ferroelectric materials originating from their phase transitions, in particular temperature ranges and electric field values, is very promising. Pyroelectric energy harvesting consists of directly converting thermal energy into electrical energy. Due to its high energy conversion potential, the Olsen cycle is the most favorable for pyroelectric energy harvesting. This cycle includes two isothermal and two constant electric field branches. In this study, the Olsen cycle was modeled, then varying temperatures and applied electric field directions for different crystal orientations were simulated. Polarization responses were obtained via the Landau–Devonshire theory. Then, an innovative way to model the electrocaloric effect was proposed; experimental results and first-principle calculations confirmed the simulation results. The resulting negative electrocaloric effect due to crystal orientation, previously reported in the literature, has been successfully simulated through a phenomenological approach. Finally, we identified which phase transitions are interesting for pyroelectric energy harvesting applications depending on crystal orientations while obtaining an energy density in the order of ≈ 10 2 mJ / cm 3. This value corresponds to previous results in the literature. [ABSTRACT FROM AUTHOR]

The switching behavior of the novel hybrid material (FA)Na[Fe(CN)5(NO)].H2O (1) in response to temperature (T), light irradiation and electric field (E) is studied using in situ X‐ray diffraction (XRD). Crystals of 1 display piezoelectricity, pyroelectricity, second and third harmonic generation. XRD shows that the FA+ are disordered at room‐temperature, but stepwise cooling from 273–100 K induces gradual ordering, while cooling under an applied field (E=+40 kVcm−1) induces a sudden phase change at 140 K. Structural‐dynamics calculations suggest the field pushes the system into a region of the structural potential‐energy surface that is otherwise inaccessible, demonstrating that application of T and E offers an effective route to manipulating the crystal chemistry of these materials. Photocrystallography also reveals photoinduced linkage isomerism, which coexists with but is not correlated to other switching behaviors. These experiments highlight a new approach to in situ studies of hybrid materials, providing insight into the structure–property relationships that underpin their functionality. [ABSTRACT FROM AUTHOR]

Ferroelectrics exhibiting both positive and negative electrocaloric effects stand out as promising materials for achieving high-efficiency solid-state refrigeration. The phase transition is acknowledged as a crucial factor in designing such materials. This study investigates the electrocaloric behavior and its correlation with phase transitions in Rochelle salt single crystal using Landau thermodynamic theory. Analysis of free energy density, ferroelectric, and dielectric data uncovers a complex temperature-dependent phase transition sequence of paraelectric–ferroelectric–paraelectric. This imparts Rochelle salt single crystal with intriguing field-induced phase transition behaviors and electrocaloric responses. Pronounced positive and negative electrocaloric effects are, respectively, observed near the high-temperature and low-temperature Curie point. The opposite sign of entropy differences between the ferroelectric and the two paraelectric phases is identified as the origin of the difference in electrocaloric response. These findings not only enhance our understanding of the electrocaloric effect but also provide a design solution for materials with the coexistence of positive and negative electrocaloric effects. [ABSTRACT FROM AUTHOR]

Electrocaloric effect and loss-induced self-heating are simultaneously investigated in single-crystalline relaxor 0.9Pb(Mg1/3Nb2/3)O3-0.1PbTiO3 by a direct, high-resolution method. Transients of the total temperature change for few-cycle electric field pulses allow to distinguish and individually determine the contributions from electrocaloric effect and self-heating with millikelvin temperature and submillisecond temporal resolution. Simultaneous dielectric measurements make the comparison of observed self-heating to hysteresis losses possible, where very good agreement is found. The loss factor as a figure of merit for electrocaloric materials is directly obtained from the combined determination of caloric temperature change and losses. [ABSTRACT FROM AUTHOR]

Polarization‐sensitive and self‐driven pyroelectric‐based photodetectors have recently gained interest due to their potential application in artificial electronic eyes, biomedical imaging, and optical switches. Here, a photodetector based on light modulation‐induced polarization and depolarization of water molecules on the surface of a 2D MoS2 crystal is reported. The MoS2‐water heterostructure photodetector serves as a self‐driven pyro‐phototronic device that converts light‐induced thermal energy to electrical signals, leading to a transient photoresponsivity as high as 24.6 mA W−1 and a specific detectivity of 2.85 × 108 Jones under 470 nm wavelength at zero bias. Due to the formation of a built‐in electric field at the MoS2‐water interface, this structure also has a high steady–state responsivity of 3.62 A W−1 and detectivity of 9.18 × 108 Jones at 3 V bias, along with a fast response time of ≈0.74 ms. Moreover, due to the rearrangement of the hydrogen bond network in the liquid water upon visible light illumination, the MoS2‐water photodetector is light polarization‐sensitive. The simple fabrication process, low cost, polarization sensitivity, and high performance of the MoS2‐water structure make it an excellent candidate for liquid‐compatible photodetectors. [ABSTRACT FROM AUTHOR]

Ceramic samples of new compositions (1−x)(0.9NaNbO3 − 0.1BaTiO3) − xBaZrO3 (x = 0 ÷ 0.05) modified by SiO2 oxide additive were prepared; their phase composition, structure parameters, microstructure, dielectric and ferroelectric properties were studied. Formation of a phase with a perovskite structure with a tetragonal unit cell was established, which volume increased due to partial replacement of A and B cations by Ba2+ and Zr4+ ones with large ionic radii. Decrease in the temperature of ferroelectric phase transitions and corresponding increase in polarization and electrocaloric effect indicates a positive effect of doping on the functional properties of sodium niobate-based ceramics. [ABSTRACT FROM AUTHOR]

Temperature stability of electrocaloric effect (ECE) is a thorny problem in ferroelectrics (FE). A general method is to design ferroelectric-to-relaxor phase transition at a sacrifice of electrocaloric (EC) strength. The Pb(Yb1/2Nb1/2)O3 antiferroelectrics (AFE) + Pb(Mg1/3Nb2/3)O3 relaxors strategy designed in this work is effective to tackle this dilemma [(1 -- x)PYN--xPMN, x = 0.08-0.36]. PMN addition induces a successive phase transition and dual phase boundaries of ferrielectric (FIE)-nonergodic relaxor (NER) and NER-ergodic relaxor (ER), where ferroelectric polarization/strain and ECE reach a localmaximum. Thermally stable ΔT is unexpectedly achieved in FIE (x = 0.14) and NER (x = 0.24), except for a generality for ER state (x = 0.30). A dome-like variation trend is observed in x = 0.14 and 0.24 with a wide temperature span of ~60 and ~55 K (±15%ΔTmax). Notably, x = 0.24 NER possesses a large directlymeasured ΔTmax ~0.64 K simultaneously. Dielectric/ferroelectric properties clarify that two-stage transition of AFE rigid-order de-texture and dissociation of de-textured AFE domains into polar nano-entities accounts for thermal stability of ΔT as the alternation of ordered antipolar domains to disorder relaxors serves as a buffer to compensate for the thermal-shock enhanced random field. This work not only accounts for the underlying mechanism for thermal stability of ΔT at FIE and NER side for the first time in physics but also provides an exotic approach to seek for high-performance EC materials in practical applications. [ABSTRACT FROM AUTHOR]

This work reports the dielectric behavior of the biopolymer ethyl cellulose (EC) observed from transient currents experiments under the action of a direct current (DC) electric field (~107 V/m) under vacuum conditions. The viscoelastic response of the EC was evaluated using dynamic mechanical analysis (DMA), observing a mechanical relaxation related to glass transition of around ~402 K. Furthermore, we propose a mathematical framework that describes the transient current in EC using a fractional differential equation, whose solution involves the Mittag–Leffler function. The fractional order, between 0 and 1, is related to the energy dissipation rate and the molecular mobility of the polymer. Subsequently, the conduction mechanisms are considered, on the one hand, the phenomena that occur through the polymer–electrode interface and, on the other hand, those which manifest themselves in the bulk material. Finally, alternating current (AC) conductivity measurements above the glass transition temperature (~402 K) and in a frequency domain from 20 Hz to 2 MHz were carried out, observing electrical conduction described by the segmental movements of the polymeric chains. Its electrical properties also position EC as a potential candidate for electrical, electronics, and mechatronics applications. [ABSTRACT FROM AUTHOR]

One of the negative effects of ferroelectric applications, particularly for electrocaloric effect (ECE) applications, is temperature hysteresis (ΔTHyst). Temperature hysteresis is the difference between the temperatures corresponding to the maximum dielectric permittivity in heating and cooling modes. The value of ΔTHyst is commensurate with the value of the ECE temperature change. The ECE is a phenomenon in which a material shows a reversible temperature change under an applied electric field. The aim of this work is to study the possibilities of temperature hysteresis reduction by varying the ceramic sintering temperature, changing the stoichiometry of BaxSr1-xTiO3 solid solutions, and changing the rate of the heating-cooling cycle. [ABSTRACT FROM AUTHOR]

The ferroelectric‐semiconductor behavior of antimony sulfoiodide (SbSI) has opened up the material as a base for energy‐harvesting devices. Specifically, SbSI has drawn much attention for pyroelectric energy harvesting and thermal sensing with outstanding electrothermal properties. This work investigates the thermistor properties of an SbSI material and presents the development of an SbSI nanorod/Kapton‐based triboelectric nanogenerator (TENG) for effective energy harvesting and temperature sensing. The TENG based on SbSI/ Kapton operating in vertical contact separation mode delivers a peak‐to‐peak voltage of 90 V and a current of 1510 nA, respectively. Introducing SbSI nanorods for TENG opens the possibility of extending the conventional triboelectric series. The electrical and dielectric properties of the SbSI nanorods are investigated. SbSI exhibits a highly linear temperature coefficient of resistance (TCR) of −0.026 °C−1, making it an excellent candidate material for a thermistor. In addition, the material exhibits an excellent thermal sensitivity (β20/80 = 1612.1 K). For demonstration, the SbSI thermistor is connected with TENG, and the outputs at various temperatures are analyzed for self‐powered temperature sensing. This capability allows for efficient temperature monitoring without relying on external power sources, advancing remote, and autonomous sensing applications. [ABSTRACT FROM AUTHOR]

In the current study, an improved method of adding Zn ion doping to the 0.5BZT–0.5BCT–based films with high pyroelectric properties was designed. Under different Zn ion doping ratios, the structure, dielectric constant, phase transition relationship and other characteristics of the test product were analyzed experimentally to obtain the optimal ratio parameters. The experimental results demonstrate that the dielectric properties of the 0.5BZT–0.5BCT–xZn–based films proposed in this study can be far superior to those of other films under the optimal preparation process. The optimal dielectric properties and ferroelectric properties are obtained when the doped data are 0.008. Considering the comprehensive dielectric and energy storage capacity, the optimal doping ratio is 0.01, which can take into account dielectric data and energy storage performance. The energy storage density is 1.842 J/cm3, and the energy storage efficiency exceeds 30%. From 0 to 0.02, the properties of the material, such as the hysteresis loop and phase transition relationship are excellent. The properties of the materials studied in this study are excellent, and they are excellent candidate materials for the future application of ferroelectric materials, and provide ideas for related work.

The method of generating x-rays using the pyroelectric effect has garnered interest for applications that desire portability and low power consumption, particularly for real-time in-field and on-line analyses. However, the x-ray intensity produced by this type of x-ray generator is low and inconsistent compared to conventional x-ray tubes. The properties of several pyroelectric materials, including LiTaO3, LiNbO3, and PMN-xPT, were studied and subsequently tested on an in-house developed x-ray generator to explore their suitability for the application. The production of electrons to subsequently generate x-ray relies on the process of ferroelectric electron emission and field ionization to be dominant over charge compensation via the DC conductivity of the pyroelectric material. Given that the time of temperature change occurs faster than the material's charge relaxation time, it was found that the ratio of the pyroelectric coefficient to relative permittivity determined the performance of the x-ray generator. Thus, the x-ray count rates and end-point energies produced by LiTaO3 showed that it continues to be a strong candidate for such x-ray generation applications. [ABSTRACT FROM AUTHOR]

Pyroelectric properties of dielectrics have been occupying the agenda of relevant scientific research groups owing to a number of device designs tailoring this effect, such as energy harvesting and caloric devices. Ferroelectrics come forward probably as the most important class of dielectrics in this regard due to their spontaneous polarization that is strongly dependent on temperature as well as strain and electric field. Here, we rigorously formulate and identify the connection between the experimentally accessible pyroelectric coefficient of a perovskite type ferroelectric and contributions arising from strain and clamping conditions. Secondary pyroelectric coefficient under partial clamping reminiscing a thin film is formulated so as to separate it from the primary coefficient that is conventionally defined at constant volume. The formulation is then applied to a number of ferroelectric compositions to reveal the extent of the variations in the secondary pyroelectric effect. The secondary effect reinforces the primary pyroelectric coefficient for the PMN-PT system, whereas it diminishes the total coefficient for PbZr0.4Ti0.6O3 and BaTiO3 systems. The role of thermal expansion coefficients in these variations is discussed. [ABSTRACT FROM AUTHOR]

Pyroelectric materials are naturally electrically polarized and exhibits a built-in spontaneous polarization in their unit cell structure even in the absence of any externally applied electric field. These materials are regarded as one of the ideal detector elements for infrared applications because they have a fast response time and uniform sensitivity at room temperature across all wavelengths. Crystals of the perovskite lead titanate (PbTi O 3 ) family show pyroelectric characteristics and undergo structural phase transitions. They have a high Curie temperature (the temperature at which the material changes from the ferroelectric (polar) to the paraelectric (nonpolar) phase), high pyroelectric coefficient, high spontaneous polarization, low dielectric constant, and constitute important component materials not only useful for infrared detection, but also with vast applications in electronic, optic, and MEMS devices. However, the preparation of large perfect and pure single crystals PbTi O 3 is challenging. Additionally, difficulties arise in the application of such bulk crystals in terms of connection to processing circuits, large size, and high voltages required for their operation. In this part of the review paper, we explain the electrical behavior and characterization techniques commonly utilized to unravel the pyroelectric properties of lead titanate and its derivatives. Further, it explains how the material preparation techniques affect the electrical characteristics of resulting thin films. It also provides an in-depth discussion of the measurement of pyroelectric coefficients using different techniques. [ABSTRACT FROM AUTHOR]

This work highlights the influence of dysprosium (Dy) doping on structural, dielectric, ferroelectric, energy storage density (ESD) and the electro-caloric(EC) response of solid state synthesized Ba1−xDyxTiO3 (BDT) ceramics with a composition of x varying from 0 to 0.05. The X-ray diffraction and Raman studies suggest that BDT ceramics exhibited pure perovskite tetragonal phase. Scanning electron microscopy (SEM) analysis evidences that Dy doping causes a significant reduction in grain size. The Ba0.99Dy0.01TiO3 ceramics exhibited enhanced dielectric constant and ferroelectric polarization due to the optimum mobility of domains. The temperature-dependent dielectric studies depict that the tetragonal ferroelectric—cubic paraelectric phase transition temperature (Tc) is shifted from 140 to 80 °C as x varies from 0 to 0.05. Further, BDT ceramics are found to be normal ferroelectric at low composition and is of relaxor type at x = 0.05. The Ba0.99Dy0.01TiO3 ceramics exhibited optimum recoverable ESD of 278 mJ/cm3 and an efficiency (η) of 67% at an electric field of 50 kV/cm. Moreover, the values of ESD and η are stable up to 107 cycles and at different operating temperatures ranging from RT to 70 °C. Besides, the Ba0.99Dy0.01TiO3 ceramics demonstrated an enhanced EC effect with an adiabatic temperature change (ΔT) ≈ 1.92 K in the vicinity of Tc at a field of 50 kV/cm and an EC responsivity (ΔT/E) ≈ 0.38 K m/MV compared to other BT based ceramics. [ABSTRACT FROM AUTHOR]

Ferroelectric polymer-based electrocaloric effect may lead to sustainable heat pumps and refrigeration owing to the large electrocaloric-induced entropy changes, flexible, lightweight and zero-global warming potential. Herein, low-k nanodiamonds are served as extrinsic dielectric fillers to fabricate polymeric nanocomposites for electrocaloric refrigeration. As low-k nanofillers are naturally polar-inactive, hence they have been widely applied for consolidate electrical stability in dielectrics. Interestingly, we observe that the nanodiamonds markedly enhances the electrocaloric effect in relaxor ferroelectrics. Compared with their high-k counterparts that have been extensively studied in the field of electrocaloric nanocomposites, the nanodiamonds introduces the highest volumetric electrocaloric enhancement (~23%/vol%). The resulting polymeric nanocomposite exhibits concurrently improved electrocaloric effect (160%), thermal conductivity (175%) and electrical stability (125%), which allow a fluid-solid coupling-based electrocaloric refrigerator to exhibit an improved coefficient of performance from 0.8 to 5.3 (660%) while maintaining high cooling power (over 240 W) at a temperature span of 10 K. Low-k nanodiamonds are discovered to possess the ability to concurrently enhance the electrocaloric effect, thermal conductivity, and electrical stability of polymeric nanocomposites, providing support for electrocaloric refrigeration. [ABSTRACT FROM AUTHOR]

In this work, the evolution behavior of electrocaloric effect in BaTiO3‐based ceramics with different phase structures and phase transitions was compared. A paradigmatic system of (Ba0.85Ca0.15)(Ti1−xHfx)O3 ceramics was selected. Diffuseness exponent γ increases linearly with rising x. Electrocaloric temperature change (ΔT) shows an opposite variation, whereas temperature span (Tspan) displays the same tendency with γ changing. The degeneration of maximum polarization and polarization change rate contributes to the decrease in ΔT due to the diffusion phase transition, whereas the diffusion can lead to a large Tspan. The ceramic with a single ferroelectric or paraelectric phase shows a small ΔT but a high variation rate with elevating electric field (E), whereas a small variation rate is present in the phase‐transition region that shows a high ΔT. Besides, small electrocaloric strength (ΔT/ΔE) is obtained in the single‐phase region and increases with elevating E. A high ΔT/ΔE is present in the phase‐transition region but decreases with elevating E. When phase transition becomes diffusion, ΔT variation with E becomes obvious, whereas ΔT/ΔE dependence will decrease. These phenomena result from the difficult polarization orientation in single ferroelectric phase or weak polarization in paraelectric phase, and the easy polarization orientation in the phase‐transition region. [ABSTRACT FROM AUTHOR]