Large Electrocaloric Effect Research Articles

Directly measured electrocaloric heat in multilayer capacitors of lead scandium tantalate

Isothermal electrocaloric (EC) heat is a key—but rarely reported—parameter for cooling applications. Here, we employ calorimetry with large-area Peltiers (10 × 10 mm2) to study a multilayer capacitor (MLC) of well-ordered PbSc0.5Ta0.5O3 (PST) with a first-order ferroelectric phase transition. Our direct measurements of isothermal EC heat are consistent with complementary EC measurements of similar MLCs that display large EC effects, i.e., indirect EC measurements and direct measurements of adiabatic EC temperature change [Nair et al., Nature 575, 468 (2019)]. Using a field of 7.9 V μm−1, the EC heat associated with the electrically active PST peaks at 11 MJ m−3 near 300 K. At higher temperatures, as one approaches the critical point, the transition is seen to become less first order. Separately, we find that the inactive PST compromises quasi-direct EC measurements. In the future, isothermal EC heat should be directly measured as a matter of routine.

Large Room-Temperature Electrocaloric Effect in Lead-Free Relaxor Ferroelectric Ceramics with Wide Operation Temperature Range.

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.

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

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

Wide working temperature range and large electrocaloric effect in BaTiO3 based ceramics achieved by regulating phase boundaries through a compensatory ion co-doping strategy

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 (Tspan) 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 (ΔTmax) of 1.14 K was obtained, and the temperature span (Tspan) reached 45 °C (Tspan is defined as ΔT ≥ 80 % ΔTmax). This work proposes a high-performance environmentally friendly electrocaloric effect (ECE) material suitable for solid-state cooling applications.

Simultaneous achievement of large electrocaloric effect and ultra-wide operating temperature range in BaTiO 3-based lead-free ceramic

Simultaneous achievement of large electrocaloric effect and ultra-wide operating temperature range in BaTiO ₃-based lead-free ceramic

Large electrocaloric effect across the non-hysteretic electrostructural phase transition in lead-free (Ba0.88Ca0.12)(Ti0.94Sn0.06)O3 ceramics

Structural, dielectric, and electrocaloric properties were investigated in Pb-free ceramic (Ba0.88Ca0.12)(Ti0.94Sn0.06)O3 (BCST), synthesized using solid-state sintering method. Rietveld refinement of room temperature XRD data revealed the existence of pure perovskite tetragonal (P4mm) phase. Temperature-dependent XRD analyses confirmed a structural transition from tetragonal to cubic phase near 380 K. Temperature-dependent dielectric constant (εr) and specific heat capacity (Cp) confirmed the presence of thermal hysteresis in two phase transitions near 233 ± 10 K and 254 ± 10 K, and a non-hysteretic behavior at the Curie temperature (TC∼373 ± 10 K). A comprehensive Raman study corroborated the existence of phase transitions. Electrocaloric properties were determined using indirect method utilizing the non-hysteretic nature across TC. A large adiabatic temperature change of |∆T| = 0.52 K, isotropic entropy change |∆S| = 0.68 J/kg.K, electrocaloric coefficients, |∆T/∆E |= 0.311 K.mm/kV and |∆S/∆E| = 0.41 J.mm/K.kg.kV were obtained at 380 K for an electric field of 16.7 kV/cm. Obtained value of |∆T/∆E| is relatively good, reported among other BaTiO3-based ceramics.

Achieving large negative electrocaloric effect in AgNbO3-based antiferroelectric ceramics based on dipole disordering

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(Nb1-0.8xHfx)O3 (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 M1 - M2 toward room temperature (RT), and a large negative ECE (ΔT = −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 AgNbO3-based AFE ceramics could be used in the refrigeration devices as an electrocaloric material.

Large electrocaloric effect near room temperature induced by domain switching in ferroelectric nanocomposites

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.

Simultaneously achieved large electrocaloric effect and broad working temperature range in transparent Sm-doped 0.88 Pb(Mg1/3Nb2/3)O3-0.12PbTiO3 ceramics at low electric field

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(Mg1/3Nb2/3)O3-0.12PbTiO3-xSm(0.88PMN-0.12 PT-xSm) 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.

Large electrocaloric effect and wide working area in the transition from ferroelectric to nanodomains

AbstractA 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.

Multifunctional Flexible Ferroelectric Thin Films with Large Electrocaloric Effect and High Energy Storage Performance.

Flexible ferroelectric films with high polarization hold great promise for energy storage and electrocaloric (EC) refrigeration. Herein, we fabricate a lead-free Mn-modified 0.75 Bi(Mg0.5Ti0.5)O3-0.25 BaTiO3 (BMT-BTO) thin film based on a flexible mica substrate. Excellent EC performance with maximum adiabatic temperature change (ΔT ∼23.5 K) and isothermal entropy change (ΔS ∼33.1 J K-1 kg-1) is achieved in the flexible BMT-BTO film, which is attributed to the local structural transition and lattice disorder near 90 °C. Meanwhile, a good energy storage density of ∼70.6 J cm-3 and a quite high efficiency of ∼82% are realized in the same ferroelectric film, accompanied by excellent stability of frequency and electric fatigue (500-10 kHz and 108 cycles). Furthermore, there is no apparent variation in performance under different bending strains. These prominent properties indicate that the multifunctional BMT-BTO ferroelectric film is a promising candidate for applications of flexible energy storage and EC refrigeration.

Impact of annealing process on the properties of 0.85Pb(Sc0.5Ta0.5)O3-0.15PbTiO3 ceramics

We have synthesized a ceramic sample 0.85Pb(Sc0.5Ta0.5)O3-0.15PbTiO3 [0.85PST-0.15PT] of perovskite structure by using a conventional solid-state reaction method. Systematic impact of annealing time (AT) is studied methodically for comprehending the ferroelectric and dielectric properties, as well as electrocaloric effect and energy harvesting performance. After 40 h of AT and using the electric field of 40 kV/cm on 0.85PST-0.15PT, we have achieved maximum ferroelectric polarization (P = 46.9 μC/cm2), energy capture performance (W = 0.542 J/cm3), and large positive electrocaloric effect (ΔT ∼ 1.63 K and ΔS ∼ 1.23 J/(K.kg)). Additionally, we also achieved high dielectric constant (ε = 23,350) and low dielectric loss (tanδ = 0.039) at the frequency of 1 Hz. As compared to an unannealed situation, the results on ceramic sample with 40 h of AT have revealed increase in P, ε, ΔT, ΔS, and W by 36%, 27%, 37%, 12% and 14%, respectively. Optimal values of AT differed radically for achieving the highest performance in each category. The best performance of energy storage (Wenergy ∼ 0.638 J/cm3) and energy loss (Wloss ∼ 0.498 J/cm3) densities are achieved with the AT of 30 h. The performance of 0.85PST-0.15PT sample increased gradually with the increase of AT until it attained the highest value and then decreased by further increasing AT – exhibiting a peak distribution. Our investigations have provided valuable insights of optimizing the performance of 0.85PST-0.15PT ceramic system through annealing.

Enhanced electrocaloric effect in KNN-based ceramic via polymorphic phase transition

A large adiabatic temperature change (ΔT) in lead-free ceramics is highly desired to develop eco-friendly and high efficiency solid-state refrigeration device based on electrocaloric effect (ECE). However, a large ΔT is often obtained near high Curie temperature (Tc > 100 °C), which impedes the practical applications for electrocaloric refrigeration technology. Herein, the lead-free (1-x)(K0.48Na0.535)0.03Li0.07(Nb0.99Sb0.01)O3-xBaZrO3 (x = 0, 0.02, 0.04 and 0.06) ceramics were synthesized through a conventional solid-state sintering method. A polymorphic phase transition (PPT) region is constructed by composition engineering to achieve large ECE near the ambient temperature. A ΔT of 0.48 K under 50 kV/cm is obtained at 60 °C by using the direct measurement in KNLNS-0.02BZ ceramic with coexistence of R-O-T phase. This work suggests that building multi-phase coexistence is a feasible design scheme in order to achieve ECE near the room temperature.

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

Flexible solid-state cooling devices with high efficiency are attracted to ferroelectric polymers with excellent negative electrocaloric (EC) effects. It is challenging to obtain a large negative EC effect in ferroelectric polymers due to the lack of tunable techniques. A giant negative EC response was obtained in the poly(vinylidene fluoride-trifluoroethylene) copolymers (P(VDF-TrFE), 70/30, in mole ratio) irradiated with high-energy X-ray. The irradiated P(VDF-TrFE) films showed an adiabatic temperature change of −13.5 K at 40 MV/m under a dose of 5 Mrad (1 Mrad=104 J/kg) obtained by the indirect method. This significant negative EC effect is attributed to the enhancement of crystalline due to the entry of polymer molecules into the amorphous to crystalline structure and the reduction of heat capacity due to the increase of crosslinking. In addition, X-ray irradiation improves the dielectric coefficient from 15 to 22. This research indicates that irradiation can modify the negative EC properties of ferroelectric polymers for solid-state cooling.

Multicaloric Effect in 0–3-Type MnAs/PMN–PT Composites

The new xMnAs/(1 − x)PMN–PT (x = 0.2, 0.3) multicaloric composites, consisting of the modified PMN–PT-based relaxor-type ferroelectric ceramics and ferromagnetic compound of MnAs were fabricated, and their structure, magnetic, dielectric properties, and caloric effects were studied. Both components of the multicaloric composite have phase transition temperatures around 315 K, and large electrocaloric (~0.27 K at 20 kV/cm) and magnetocaloric (~13 K at 5 T) effects around this temperature were observed. As expected, composite samples exhibit a decrease in magnetocaloric effect (<1.4 K at 4 T) in comparison with an initial MnAs magnetic component (6.7 K at 4 T), but some interesting phenomena associated with magnetoelectric interaction between ferromagnetic and ferroelectric components were observed. Thus, a composite with x = 0.2 exhibits a double maximum in isothermal magnetic entropy changes, while a composite with x = 0.3 demonstrates behavior more similar to MnAs. Based on the results of experiments, the model of the multicaloric effect in an MnAs/PMN–PT composite was developed and different scenario observations of multicaloric response were modeled. In the framework of the proposed model, it was shown that boosting of caloric effect could be achieved by (1) compilation of ferromagnetic and ferroelectric components with large caloric effects in selected mass ratio and phase transition temperature; and (2) choosing of magnetic and electric field coapplying protocol. The 0.3MnAs/0.7PMN–PT composite was concluded to be the optimal multicaloric composite and a phase shift ∆φ = −π/4 between applied manetic fields can provide a synergetic caloric effect at a working point of 316 K.

Large electrocaloric effects induced by multidomain-to-monodomain transition in ferroelectrics with electrical inclusions

The electrocaloric effect (ECE) depends on the sudden change of the polarization field during ferroelectric phase transition near the Curie temperature. Similarly, giant ECE can be found enormously during the domain structure transition from multidomain to monodomain process in ferroelectrics. To reveal the mechanism with the effects of the electric inclusions, the ECE of PbTiO3 (PTO) ferroelectric solids under electric loads is investigated by phase-field simulation. The giant ECEs of ferroelectric materials containing three kinds of electric inclusions, namely, air, silicone oil, and water, are discussed in detail under applied electric fields. The results suggest that an unusual ultrahigh negative ECE (−9.30 K) and a large EC strength (∆T/∆E=0.237 KmMV−1 are achieved near room temperature (about 50°C) in ferroelectrics containing water inclusion. The results indicate that electric inclusions generate high electrostatic energy under electric loads to break through the energy barrier and play an importation role in the ECE. In summary, the works may provide a better way to obtain the giant ECE and large EC strength close to room temperature by effectively regulating the dielectric constant of the electric inclusion and the increment of the applied electric field.

Large conventional and inverse electrocaloric effects in PbMg0.5W0.5O3 multilayer capacitors above and below the Néel temperature

Bulk PbMg0.5W0.5O3 (PMW) is an antiferroelectric in which an electric field of 12 V μm−1 is sufficient to initiate a nominally reversible transition to a dipole-aligned (ferroelectric) phase if operating just below the Néel temperature T N, near room temperature (Li et al 2021 Adv. Funct. Mater. 31 2101176). Here we describe multilayer capacitors (MLCs) of PMW that permit 27 V µm−1 to be applied without breakdown. Below T N, nominally reversible driving of the partial (full) antiferroelectric–ferroelectric (AF–FE) transition over a wide (narrow) range of temperatures yields large inverse electrocaloric (EC) effects that peak at ΔTj ∼ –2.6 K when applying 25 V μm−1 at 293 K (ΔTj denotes directly measured temperature jumps). Above T N, nominally reversible driving of the partial (full) paraelectric–ferroelectric (PE–FE) transition yields large conventional EC effects that peak at ΔTj ∼ +5.2 K when applying 25 V μm−1 at 302 K. This good EC performance near room temperature implies that MLCs of PMW could be exploited in prototype EC coolers.

Large room temperature electrocaloric effect in PbZrO3/Ca3Mn2O7 heterostructure

Electrocaloric effects of antiferroelectric and ferroelectric films have been intensively studied for the applications in refrigeration. However, achieving high electrocaloric performance near room temperature is still very difficult in films. Herein, we report that large and regulable electrocaloric effects at room temperature are achieved in PbZrO3/Ca3Mn2O7 bilayer films based on PbZrO3 phase transition, and the sign of adiabatic temperature change, ΔT, is determined by Ca3Mn2O7 thickness. The PbZrO3-Ca3Mn2O7 heterojunction formed by carrier diffusions reduces the carrier concentration of the film and establishes a built-in electric field in the junction region, and withstanding voltages of the bilayer films are enhanced greatly. The maximum positive ΔT of 66.5 K was obtained in the bilayer film with a thin Ca3Mn2O7 layer, but a negative ΔT of -9.9 K with a thick Ca3Mn2O7 layer, near room temperature. This work presents a simple and effective approach to designing huge electrocaloric based on antiferroelectric-containing multilayers near room temperature.

Measurement of the dynamic temperature response of electrocaloric effect in solid ferroelectric materials via thermoreflectance

ABSTRACT 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.

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

Ferroelectric (FE) phase transition with a large polarization change benefits to generate large electrocaloric (EC) effect for solid-sate and zero-carbon cooling application. However, most EC studies only focus on the single-physical factor associated phase transition. Herein, we initiated a comprehensive discussion on phase transition in Pb_0.99Nb_0.02[(Zr_0.6Sn_0.4)_1−<i>x</i>Ti_<i>x</i>]_0.98O₃ (PNZST100<i>x</i>) antiferroelectric (AFE) ceramic system under the joint action of multi-physical factors, including composition, temperature, and electric field. Due to low energy barrier and enhanced zero-field entropy, the multi-phase coexistence point (<i>x</i> = 0.12) in the composition–temperature phase diagram yields a large positive EC peak of maximum temperature change (Δ<i>T</i>_max) = 2.44 K (at 40 kV/cm). Moreover, the electric field–temperature phase diagrams for four representative ceramics provide a more explicit guidance for EC evolution behavior. Besides the positive EC peaks near various phase transition temperatures, giant positive EC effects are also brought out by the electric field-induced phase transition from tetragonal AFE (AFE_T) to low-temperature rhombohedral FE (FE_R), which is reflected by a positive-slope boundary in the electric field–temperature phase diagram, while significant negative EC responses are generated by the phase transition from AFE_T to high-temperature multi-cell cubic paraelectric (PE_MCC) with a negative-slope phase boundary. This work emphasizes the importance of phase diagram covering multi-physical factors for high-performance EC material design.