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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]

This paper reports an extensive investigation on the structural, dielectric, ferroelectric and pyroelectric properties of 0.7Ba 1-x Sr x TiO 3 – 0.3Bi 0.5 Na 0.5 TiO 3 (x = 0.0, 0.5, 0.6, 0.7) ceramics synthesized via conventional solid-state reaction (SSR) technique. X-ray diffraction data confirms the presence of pure perovskite phase. The variation of lattice parameters with strontium concentration in 0.7Ba 1-x Sr x TiO 3 – 0.3Bi 0.5 Na 0.5 TiO 3 ceramics were evaluated using the Rietveld refinement of the XRD data. The variation of dielectric permittivity with temperature (ε' ∼ T) shows the diffused phase transition and all the parameters related to the relaxor ferroelectrics (relaxation coefficient, activation energy and freezing temperature) were evaluated. The energy storage properties of the as-prepared ceramics were evaluated using the room temperature PE loop. Amongst the as-prepared ceramics, the composition with x = 0.5 possesses the highest energy storage density of 0.46 J/cm3 with an efficiency of 90 %. The temperature dependent P-E loops were used to study the electrocaloric effect (ECE). The ECE calculations were performed using in-direct method based on Maxwell's thermodynamic relations. A maximum adiabatic temperature change of 0.32 K is achieved at 268 K under a small applied electric field of 25 kV/cm for the ceramic with Sr content x = 0.5. Additionally, electrocaloric responsivity ξ max = 0.13 K mm/kV was also found for the studied ceramics. The above results show that the ceramic 0.7Ba 1-x Sr x TiO 3 – 0.3Bi 0.5 Na 0.5 TiO 3 with the composition x = 0.5 is a viable lead-free option for application in solid state refrigeration. [ABSTRACT FROM AUTHOR]

In the present work, flexible Potassium Sodium Niobate - Polyvinyledene Fluoride (KNN-PVDF) composite sheets have been developed and utilized for the realization of a highly efficient pyroelectric energy harvester. KNN-PVDF composite sheets with varying the weight % of KNN (10–50 %) have been synthesized using solution casting method. The influence of KNN (Potassium Sodium Niobate) on the structural, morphological, and dielectric properties of PVDF has been investigated. The highest value of pyroelectric coefficient of 14.7 x 10 −4 Cm −2K−1 has been obtained for the flexible sheets of 30 % KNN-PVDF composite with change in temperature. It has been also observed from the ferroelectric studies that a high value of saturation polarization of 1.44 μC/cm2 is obtained at the applied bias of 5 V and 50 Hz frequency due to the presence of 30 % KNN in the KNN-PVDF composite sheets. The obtained results show the potential application of non-toxic, lead free KNN-PVDF composite sheets for thermal energy harvesting applications utilizing pyroelectric effect. [ABSTRACT FROM AUTHOR]

Ba 0.87 Ca 0.13 (Ti 0.9 Zr 0.1) 0.98 (Zn 1/3 Nb 2/3) 0.02 O 3 ceramic was prepared using a solid-state reaction method. This work investigates their dielectric, ferroelectric, energy storage, and electrocaloric properties. X-ray diffraction analysis confirms a pure perovskite structure. The dielectric constant reaches a maximum of 9364 at 326 K. Enhanced total energy density, recovered energy density, and energy storage efficiency are observed between 303 K and 363 K. Artificial neural networks (ANNs) are employed for the indirect determination of large ECE and responsivity based solely on measured ferroelectric polarization (P(E,T)). This approach offers rapid and accurate predictions with minimal experimental data, significantly accelerating the characterization of novel electrocaloric materials. The maximum ECE occurs above the Curie temperature (T C) and increases with higher electric fields. The ceramic exhibits significant ECE parameters around TC with a broad electrocaloric temperature span. Various figures of merit, including relative cooling power, refrigerant capacity, and temperature-averaged entropy change, are explored under different electric fields, demonstrating the material's potential for green cooling devices. These figures improve monotonically with increasing field strength. A comprehensive analysis of the field dependence of ΔS (entropy change) confirms the second-order nature of the electric phase transition through master curve analysis. In conclusion, these lead-free ceramics exhibit promising applications in high-performance energy storage devices and solid-state refrigeration technology. [ABSTRACT FROM AUTHOR]

The concept of multisource energy harvesting has attracted attention in order to harvest multiple types of energy in a single material. In this work, Pb‐free (Ba,Ca)(Zr,Ti)O3 (BCZT) ceramics were used to investigate a combination of piezoelectric and pyroelectric energy harvesting behavior. The temperature dependence of the permittivity and the pyroelectric coefficient was measured, and the pyroelectric properties of BCZT were expected to improve near its orthorhombic–tetragonal phase transition temperature TO–T (∼40°C). The output voltage and current were measured using a BCZT plate, where the BCZT was oscillated under a temperature gradient to apply mechanical stress and temperature fluctuation simultaneously. The measured output voltage from the combined piezo‐ and pyroelectric contributions at a frequency of 2 Hz and with a load resistance of 10 MΩ was 1.4 times higher than the sole piezoelectric output voltage. The resulting combined output voltage was confirmed by finite element simulation. [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]

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]

Polymer‐based pyroelectric thin films are crucial functional materials at the core of flexible and lightweight electronic devices, such as wearable monitoring sensors, energy harvesters, and infrared detectors. Nevertheless, the pyroelectric properties of the polymer films, such as poly(vinylidene fluoride‐trifluoroethylene) (P(VDF‐TrFE)), vanish when the surrounding temperature exceeds the ferroelectric‐to‐paraelectric transition temperature, and thus limits their pyroelectric performance to a low‐temperature range. Herein, to mitigate this issue by employing a new class of P(VDF‐TrFE) copolymer which has a low TrFE molar content is proposed. Fine‐tuning of the structure through thermal annealing in a vacuum environment significantly favors robust and highly polarized polymer films with a large area. Electric poling combined with an optimal annealing temperature (110–120 °C) gives highly ordered ferroelectric crystalline domains in the polymer films. Consequently, this remarkably broadens the temperature range (roughly up to 140 °C) for which the polymer film still presents high pyroelectric properties (pyroelectric coefficient 50 µC (m2K)−1). This study provides an alternative choice for pyroelectric polymer films with enhanced pyroelectricity in applications that require wider temperature ranges. [ABSTRACT FROM AUTHOR]

The electrocaloric effect (ECE) refers to the isothermal entropy or adiabatic temperature change of polar crystals when an electric field is applied or removed. This effect is a promising approach for the development of compact solid state coolers. Among the promising materials are environmentally friendly lead-free relaxors of the (Na 0.5 Bi 0.5)TiO 3 –BaTiO 3 (NBT-BT) family showing a large ECE in a wide temperature range. Intriguingly, some groups have reported negative ECE in these materials and attributed this to the antiferroelectric features of NBT. Both relaxor and antiferroelectric properties of NBT can be enhanced by doping, e.g., by adding bismuth magnesium titanate (BMT). In this study, the effect of the incorporation of BMT on the structural, electrical, and electrocaloric properties of lead-free ceramics (1- x)[0.95(Na 0.5 Bi 0.5)TiO 3 -0.05BaTiO 3 ]-(x)Bi(Mg 0.5 Ti 0.5)O 3 , where x = 0, 0.1, and 0.2, was investigated. The temperature dependences of the dielectric permittivity exhibit behavior characteristic of relaxors. With increasing BMT content, the maximum polarization value decreases from 23 to 8.5 μC/cm2, and the depolarization temperature shifts from 322 to 254 K, which points out an enhancement in relaxor properties. We have shown that double hysteresis loops observed in the studied materials are not caused by the antiferroelectric nature of the compositions, but by the pinning effect by point defects. Furthermore, the negative ECE estimated from the indirect measurements using Maxwell's relation was not confirmed by the direct measurements using a quasi-adiabatic calorimeter. The interplay between defect dipoles and the role of BMT in stabilization of ergodic relaxor behavior at lower temperatures and electrocaloric effects are discussed. The study also shows that the NBT-5BT-10BMT composition is promising for energy storage applications. [ABSTRACT FROM AUTHOR]

Influences of calcination temperature (T cal) on discontinuous grain growth (DGG), and related grain size effect on structure/ferroelectric/electrocaloric properties were studied and compared in fine-/large-grain Ba(Ti 0.85 Zr 0.15)O 3 ceramics. DGG phenomena from several to >100 μm are all observed with rising sintering temperature (T S). Increasing T cal (1200–1320 °C) can cause larger powders but decrease the sintering activity, leading to a higher critical T S (1320–1360 °C) of DGG. Relatively high T cal (larger powder size) will lead to smaller ceramic grains and density before DGG, while being prone to obtain larger grains and stronger ferroelectric correlations, but lower density after DGG. The over-sized powders and smaller grains/density will present in ceramics if T cal closes to critical T S. In fine- and large-grain ceramics, grain size variation is similar to the evolution of dielectric, ferroelectric polarization, and electrocaloric properties, but shows an opposite variation trend with coercive field and relaxor phase transition. Electrocaloric strength of fine-grain ceramics increases with a rising electric field due to their difficult domain switching, while an opposite trend shows in large-grain ceramics. Finally, higher electrocaloric properties are obtained in ceramics with relatively big grains because of easier polarization rotation, higher polarization, and polarization change rate. [ABSTRACT FROM AUTHOR]

Electrocaloric refrigeration shows the merits of environmental safeguarding, large efficiency, easy combination, and miniaturization as a novel solid-state refrigeration technique. In this paper, Sn4+ is doped into the B site of BLNT ceramics. By adjusting the doping content, the T-C phase transition peak was successfully shifted to room temperature and promoted the formation of relaxor ferroelectrics, resulting in a wider operating temperature range (T span) and improved adiabatic temperature change (ΔT). A comprehensive study was conducted on the crystal structure, surface morphology, dielectric properties, ferroelectricity, and electrical properties of BLNTS ceramics with varying levels of Sn4+ doping. Wherein, when the doping amount is 5Sn, a maximum adiabatic temperature change value (ΔT max) of 1.14 K was obtained, and the temperature span (T span) reached 45 °C (T span is defined as ΔT ≥ 80 % ΔT max). This work proposes a high-performance environmentally friendly electrocaloric effect (ECE) material suitable for solid-state cooling applications. [ABSTRACT FROM AUTHOR]

In this study, lead-free Ba 0.85 Ca 0.15 Ti 0.95 (Nb 0.5 Yb 0.5) 0.05 O 3 (BC15TYN5) ceramic has been successfully obtained through the conventional solid-state reaction. It has been found the multifunctionality of the BC15TYN5 ceramic. It exhibits ferroelectric properties, with a significant remanent polarization value of about P r = 9.36 μC/cm2, and a recoverable energy storage density value of about W rec = 42.21 mJ/cm3. Additionally, it displays a dielectric permittivity of about ε ′ r = 7230 around T C = 80 °C, and an electro-caloric strength value of about ξ = 0.12 K mm/kV. It's worth noting that these values surpass those typically found in BaTiO 3 ceramics elaborated with similar experimental conditions. Electrical study (impedance, modulus, and conductivity characteristics) is essential for characterizing the BC15TYN5 material, determining its suitability for various technological applications, and optimizing manufacturing processes. The Cole-Cole plots exhibited two relaxations associated with the contribution of the grains and grain boundaries. The relaxation times for both grains and grain boundaries showed temperature-dependent variation following Arrhenius relation. The measured AC conductivity was evaluated by applying the Jonsher power law. Based on the thermal evolution of the exponent S , it was confirmed that the conduction mechanism follows the Correlated Barrier Hopping (CBH) model. These properties make BC15TYN5 ceramic suitable for applications such as dielectric capacitors, ferroelectric random-access memories, electrical energy storage units, and electro-caloric refrigeration systems. [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]

The electrocaloric effect (ECE) capabilities of environmentally sustainable BaTiO 3 systems have garnered extensive scrutiny for their potential applications, owing to their intricate phase transition characteristics, facile miniaturization, heightened efficacy, and low cost. Nevertheless, persistent challenges loom in the quest for a substantial trade-off between significant temperature change (Δ T) and a wide operating temperature range (T span). In this study, we synthesized the Ba (1–1.5 x) La x Ti 0.9 Zr 0. 1 O 3 (abbreviated as BLZT100 x , x = 0, 0.005, 0.01, and 0.015) ferroelectric system and conducted thorough characterizations encompassing phase structure, electrical attributes, and electrocaloric properties. The results reveal a reduction in the phase transition temperature to lower regimes and an augmentation in the diffuse phase transition characteristics upon the incorporation of La3+ into the Ba(Zr, Ti)O 3 matrix. This enhancement significantly bolsters the electrocaloric performance while expanding the viable operating temperature ranges. Notably, in the BLZT0.5 sample, an exceptional Δ T of 1.22 K under a moderate electric field of 50 kV/cm is observed, accompanied by an extraordinarily broad T span of 80 °C spanning from 60 °C to 140 °C, as determined through direct measurement method. These findings impeccably align with the prerequisites of practical refrigeration applications. [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]

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]

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]

The electrocaloric effect (ECE) is considered as an environmentally friendly refrigeration technology, which can be used to replace vapor compression refrigeration. Lead-free antiferroelectric (AFE) ceramics are promising electrocaloric materials because of large saturation polarization and polarization change with temperature, which can generate large positive or negative ECE. In this work, the lead-free Ag(Nb 1-0.8x Hf x)O 3 (x = 0, 0.001 and 0.003) AFE ceramics are fabricated through a conventional solid-state reaction method which shows a decreased the phase transition temperature of M 1 - M 2 toward room temperature (RT), and a large negative ECE (Δ T = −2.3 K under 130 kV cm−1) is obtained near the ambient temperature by using an indirect measurement in ANH0.001 AFE ceramic. The large negative ECE behavior is ascribed to dipole disordering (i.e. the anti-parallel dipoles are broken and gradually becomes disordered under an external electric field) resulting from the field-induced phase transition under a modest electric field. This work shows that AgNbO 3 -based AFE ceramics could be used in the refrigeration devices as an electrocaloric material. [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]

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]

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]

Minuscule pressure/stress detection with high sensitivity can recognize and deal with potential hazards timely, which is crucial for guaranteeing the security of human and stability of social functioning. Lithium niobate (LiNbO 3) single crystal possessing excellent piezoelectric and ferroelectric properties is suitable for fabricating piezoelectric pressure sensors. Therefore, in this paper, the pressure sensors based on LiNbO 3 single crystals with parallel connected structure were researched. Sensors with parallel connected structure can improve the sensitivity from 4.86 V/N of single sheet structure to 8.71 V/N under the stress between 0.01 N and 0.2 N at 30 °C. Both types of the sensors can detect the minuscule stress low to 0.01 N and minuscule pressure generated by balloon pump, blowing largely or slowly. The influence of temperature on sensors was also researched, and the results exhibited that sensors performed well from 30 °C to 60 °C and still sustained high sensitivity of 5.26 V/N of parallel connected structure and 3.71 V/N of single sheet structure at 60 °C. Besides, the response time of sensors to the pressure of balloon pump is 60 ms under different temperature. These excellent properties indicate the great potential applications of fabricated sensors in practical minuscule pressure/stress detection. [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]

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]

We report the effect of configurational entropy (CE) on the electrocaloric (EC) effect of Ba x Sr y Ca z (Bi 0.5 Li 0.5) 1- x - y - z TiO 3 (BSCBLT) (0.627≤ x ≤ 0.66, 0.0716≤ y ≤ 0.1993, 0.0145≤ z ≤ 0.1758) ceramics. All samples were designed to show different CE but the same A-site cation average radius, tolerance factor and cationic size disorder. The samples with x ≤ 0.64 show ferroelectric (FE) relaxor behavior, while x ≥ 0.65 are normal FEs. x = 0.65 shows the maximum EC effects among all samples. Both maximum adiabatic temperature change (ΔT m) and CE vary almost in the same way with increasing x. The anomalous enhancement of ΔT m in x = 0.65 with relatively lower CE compared with that in x = 0.64 can be ascribed to an additional contribution of Ba concentration induced FE to relaxor FE transition in BSCBLT. Our results reveal important evidences of enhanced EC effects by CE and suggest that designing FEs or relaxor FEs with high CE might be an effective route to achieve high EC effects. [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]

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]

Electrocaloric refrigeration technology has garnered significant attention due to its potential for next-generation solid-state cooling, which is miniaturized and efficient. However, achieving a substantial electrocaloric effect (ECE) and a wide working temperature range at low electric fields remains a challenge. In this study, a synergistic approach combining domain and defect engineering was used in transparent 0.88 Pb(Mg 1/3 Nb 2/3)O 3 -0.12PbTiO 3 - x Sm(0.88PMN-0.12 PT- x Sm) ceramics to improve ECE and temperature stability. Finally, a notable adiabatic temperature change (ΔT) of 2.07 K in the x = 0.01 ceramic, with ΔT exceeding 1.0 K across a broad temperature range from 30 to 180 °C was achieved. Piezoresponse force microscopy (PFM) and X-ray photoelectron spectroscopy revealed the presence of small domains and appropriate oxygen vacancies as contributors to the enhanced ECE and broad operation temperature range. This work introduces a promising candidate material for electrocaloric refrigeration. [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]

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]

In this work, the effect of Sm ionic doping in BaTiO 3 for electrocaloric effect has been studied. Ba 1-x Sm x TiO 3 (x = 0, 0.02, 0.04, 0.06) ceramics were made via sol-gel method. All samples, according to XRD analysis, have a tetragonal symmetry that decreases with increasing Sm concentration. SEM micrographs revealed that, with the exception of the pure BaTiO 3 , all samples exhibited a dense microstructure. Compared to pure BaTiO 3 , thermal analysis using DSC measurement showed that as samarium content increases, the phase transition temperature decreases and the endothermic peak flattens. Dielectric measurements showed that the value of the loss tangent decreased and the value of the dielectric constant increased as the samarium doping concentration increased. Ferroelectric experiments highlighted that all samples were in the ferroelectric phase at room temperature. The remnant polarization increased with increasing Sm concentration. For Sm-doped ceramics the maximum value was Pr = 5.2 μC/cm2 for x = 6 %, under a maximum applied field of 25 kV/cm. An original customized pASC calorimeter was used in a direct method to study isothermal heat production resulting from the electrocaloric effect (ECE). According to the ECE results, the partial substitution of barium by samarium lowers the Curie temperature, which in turn lowers the temperature at which the electrocaloric effect is strongest. This extends the temperature range at which ECE can be used. For the sample Ba 0.96 Sm 0.04 TiO 3 , the maximum electrocaloric effect recorded is reached with a ΔT/ΔE = 0.343 K m/MV. [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]