Electrocaloric Strength Research Articles

Large energy-storage density and positive electrocaloric effect in xBiFeO3–(1 − x)BaTiO3 relaxor ferroelectric ceramics

Large energy storage density and big electrocaloric strength in the BiFeO3–BaTiO3 system.

Large energy storage density and electrocaloric strength of Pb0.97La0.02(Zr0.46-xSn0.54Tix)O3 antiferroelectric thick film ceramics

Pb0.97La0.02(Zr0.46-xSn0.54Tix)O3 (PLZST, x = 0.04, 0.06, 0.08, 0.15, and 0.18) antiferroelectric thick film ceramics were fabricated via a tape-casting approach. The energy storage performance and electrocaloric effect (ECE) were investigated in terms of the measurements on the hysteresis loops and Maxwell relation. The maximum value of energy storage density of 5.2 J/cm3 and efficiency of 78.2% were procured at 600 kV/cm in Pb0.97La0.02(Zr0.42Sn0.54Ti0.04)O3 thick film ceramics at room temperature. In addition, the ECE was indirectly calculated using the Maxwell relation and the polarizations extracted from the P-E loops as a function of temperature and electric field, an adiabatic temperature change of ΔT = 2.47 °C was procured in Pb0.97La0.02(Zr0.42Sn0.54Ti0.04)O3 thick film ceramics at 500 kV/cm, corresponding to the calculated electrocaloric strength of 0.48 K(MV/m)−1. These results indicate that the PLZST thick film ceramics are promising for practical applications in high-power energy storage capacitors and solid-state refrigeration devices.

Abnormal electrocaloric effect near ambient temperature in MgO modified NBT-KBT

Present work proposes the advancement in the field of modern refrigeration based upon electrocaloric effect. The values of electrocaloric effect near ambient temperature is demonstrated in (Na0.41K0.09Bi0.50)(Ti1-xMgx)O3 where x = 0, 0.025 and 0.050. The MgO modified NBT-KBT sold solution has exhibited abnormal electrocaloric effect with ΔT ~ − 2.03 K and electrocaloric strength ΔT/ΔE = 0.033 K cm kV−1 at 60 °C for highest doping. Moreover, a broad operating time range Tspan = 50–80 °C has achieved which allow this material to be useful for potential cooling application and provide new horizons in this field.

Coexistence of giant positive and large negative electrocaloric effects in lead-free ferroelectric thin film for continuous solid-state refrigeration

The solid-state cooling technique utilizing electrocaloric (EC) materials is an alternative approach to tackle the greenhouse effect caused by traditional vapor-compression refrigeration. However, such a promising technique is severely hampered by the lack of proper materials considering that most existing EC materials with a single positive/negative EC effect exhibit a limited cooling effect. Here, the coexistence of a positive and negative EC effects has been achieved in a lead-free Na0.5Bi0.5(Ti0.97W0.01Fe0.02)O3 ferroelectric film. A state-of-the-art positive adiabatic temperature change (ΔT) of ~56 K accompanied by an isothermal entropy change (ΔS) of ~64 J K−1 kg−1 at 143 °C and a large negative ΔT of ~ − 17 K with a ΔS of ~ − 24 J K−1 kg−1 at 55 °C are obtained under a strong electric field strength of 2692 kV cm−1. Oxygen vacancy-related defect dipoles play a critical role in the negative EC effect at lower temperatures, while the phase transition is responsible for the positive EC effect at higher temperatures. Meanwhile, the film exhibits a high EC strength with a maximum ΔT/ΔE of 0.021 K cm kV−1, together with a ΔS/ΔE of 0.024 J cm K−1 kg−1 kV−1. This work ensures a giant total temperature change by utilizing and combining both the negative and positive EC effects in a dual cooling process.

Large electrocaloric strength in Bi(Mg0.5Ti0.5)O3-modified tetragonal-structured Bi0.5Na0.5TiO3–12.5BaTiO3 ceramics

Taking the advantage of the low transition barrier between P4bm and P4mm distortions, tetragonal structured 0.875Bi0.5Na0.5TiO3–0.125BaTiO3 was designed to construct an electrocaloric ceramics with large electrocaloric strength by adding the third compound Bi(Mg0.5Ti0.5)O3 (BMT). The experiments show that, through adding 2.5 mol.% BMT, a large ΔT of 0.80 K was directly observed under 4 kV/mm; especially, a high ΔT/ΔE of 0.020–0.023 K cm/kV was achieved, approximate to BaTiO3-based and some lead-based relaxors. The high electrocaloric effect is attributed to that the 2.5 mol.% BMT added sample bridges the nonergodic ferroelectric and ergodic relaxor states, and exhibits a microstructure coexisting P4bm and P4mm symmetries. Our design provides a new route in probing lead-free BNT-based electrocaloric materials apart from the MPB.

Multifunctionality in (K,Na)NbO3-based ceramic near polymorphic phase boundary

The 0.95K0.42Na0.58Nb0.96Sb0.04O3–0.02BaZrO3–0.03Bi0.5K0.5HfO3 ceramic was fabricated via a conventional solid-state reaction. This ceramic exhibits the diffuse polymorphic phase boundary (PPB) near room temperature. The dielectric, ferroelectric, electromechanical, electrocaloric, and dielectric energy storage properties were studied systemically. The normalized large signal d33* values are approximately 400–600 pm/V at measured temperatures and electric fields, which are larger than or comparable with the values reported in other lead-free compositions. The electrocaloric strength is enhanced at the broad region of PPB provided by the indirect and direct measurements. At low field of 30 kV/cm, the dielectric energy storage is ∼0.12–018 J/cm3 at relative broad temperature range due to the diffuse nature of polymorphic phase boundary. Theoretical simulations reveal that multi-element dopants, such as Sb5+, Hf4+, Zr4+, and Bi3+ ions, could induce the breaking of local structure symmetry in the orthorhombic phase to form the PPB. In addition, the charge distribution may also break the long-range ferroelectric order through the analysis of Bader charge. Our study suggests that the K0.5Na0.5NbO3-based ceramic exhibits improved performance and good thermal stability in piezoelectric, electrocaloric, and dielectric energy storage characteristics in terms of the design of multi-element dopants to form the PPB and it will benefit the promising applications in electronic devices.

Near‐Room‐Temperature Large Electrocaloric Effect in Barium Titanate Single Crystal Based on the Electric Field–Temperature Phase Diagram

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

Designed Giant Room‐Temperature Electrocaloric Effects in Metal‐Free Organic Perovskite [MDABCO](NH4)I3 by Phase–Field Simulations

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

Large electrocaloric effect of BCTZ/P(VDF-TrFE) 0–3 composites

0–3 type composites of lead-free 0.3(Ba0.7Ca0.3)TiO3–0.7Ba(Zr0.2Ti0.8)O3 (BCTZ) ceramic filler and polyvinylidene difluoride trifluoroethylene [P(VDF-TrFE) (55/45)] polymer matrix were fabricated. With a fixed BCTZ filler volume fraction at 30 vol%, the ceramic/polymer composites exhibited the largest temperature change (ΔT = 9.1 K) and electrocaloric strength (ΔT/ΔE = 0.18 µKm/V) under a low electric field of 500 kV/cm. Microstructure and dielectric/ferroelectric characterizations attributed the main reason to a well dispersion of ceramic filler together with few pores, where sufficient and appropriate electric fields were applied not to pores but mainly to higher dielectric BCTZ fillers inside the matrix polymer.

Halide-modulated self-assembly of metal-free perovskite single crystals for bio-friendly X-ray detection

Halide-modulated self-assembly of metal-free perovskite single crystals for bio-friendly X-ray detection

Giant caloric effects close to any critical end point

The electrocaloric (EC) effect, i.e., the reversible temperature change due to adiabatic variations of the electric field, is of great interest due to its potential technological applications in refrigeration. Based on entropy arguments, we present a new framework to attain giant EC effects. Our findings are fourfold: (i) we employ the recently-proposed electric Grüneisen parameter ΓE to quantify the EC effect and discuss its advantages over the existing so-called electrocaloric strength; (ii) prediction of giant caloric effects close to any critical end point; (iii) proposal of potential key-ingredients to enhance the EC effect; (iv) demonstration of ΓE as a proper parameter to probe quantum ferroelectricity in connection with the celebrated Barrett's formula. Our findings enable us to interpret the recently-reported large EC effect at room-temperature in oxide multilayer capacitors [5], paving thus the way for new venues in the field.

Large Room Temperature Negative Electrocaloric Effect in Novel Antiferroelectric PbHfO3 Films.

Extremely high temperature in a chip will severely affect the normal operation of electronic equipment; however, the traditional air conditioning cooling technology is unsuitable for integrated circuit cooling. It is necessary to develop convenient and high-efficiency cooling techniques. In this paper, PbHfO3 antiferroelectric (PHO AFE) film was fabricated by a sol-gel method and was first found to be a promising electrocaloric (EC) material with high temperature change (ΔT ∼ -7.7 K) and acceptable EC strength (|ΔT/ΔE| ∼ 0.023 K cm kV-1) at room temperature. In addition to the negative EC effect (ECE), a large positive ECE can be observed at high temperature. The outstanding ECEs and their combination will make the PHO film one of the potential candidates for next-generation solid-state refrigeration. To understand the underlying physical mechanism for positive and negative ECEs in the PHO AFE film, a modified Ginzburg-Landau-Devonshire free-energy theory is adopted.

Enhanced electrocaloric effect at room temperature in Mn2+ doped lead-free (BaSr)TiO3 ceramics via a direct measurement

(Ba1−xSrx)(MnyTi1−y)O3 (BSMT) ceramics with x = 35, 40 mol% and y = 0, 0.1, 0.2, 0.3, 0.4, 0.5 mol% were prepared using a conventional solid-state reaction approach. The dielectric and ferroelectric properties were characterized using impedance analysis and polarization-electric field (P–E) hysteresis loop measurements, respectively. The adiabatic temperature drop was directly measured using a thermocouple when the applied electric field was removed. The results indicate that high permittivity and low dielectric losses were obtained by doping 0.1–0.4 mol% of manganese ions in (BaSr)TiO3 (BST) specimens. A maximum electrocaloric effect (ECE) of 2.75 K in temperature change with electrocaloric strength of 0.55 K·(MV/m)−1 was directly obtained at ∼21 °C and 50 kV/cm in Ba0.6Sr0.4Mn0.001Ti0.999O3 sample, offering a promising ECE material for practical refrigeration devices working at room temperature.

Enhanced electrocaloric strengths at room temperature in (SrxBa1−x)(Sn0.05Ti0.95)O3 lead-free ceramics

The electrocaloric effect (ECE) in lead-free (Ba1−xSrx)(Sn0.05Ti0.95)O3 (BSSnT) (x = 0.05, 0.10, 0.15, 0.20) ceramics were investigated around room temperature using direct and indirect approaches. Results indicate that the maximum ECE occurs near the Curie temperature and slightly shifts towards high temperatures with the increasing applied electric field. The directly measured ECE is larger than that calculated using the Maxwell relation. The maximum electrocaloric strength ΔT/ΔE = 0.52 × 10−6 K m/V was obtained at T = 36 °C, with an adiabatic ΔT of 1.05 °C at 2 MV m−1. An analytic formula of electrocaloric strength (dT/dE) was deduced, via which the maximum dT/dE was estimated. The factors affecting the electrocaloric strength were discussed, and the experimental results were compared with those derived from the formula.

Electric field induced phase transitions and electrocaloric effect of La3+ doped Pb(Zr,Sn,Ti)O3 ceramics

Electrocaloric effect (ECE) is considered well applicable in the field of next generation solid state refrigeration technology. In this article, the structural properties and ECE response were altered and optimized by tailoring the Zr/Ti molar ratio in (Pb0.94La0.04)(ZrxSn0.30Ti0.70-x)O3 (x = 0.54, 0.52, 0.50 and 0.48) polycrystalline ceramics. Multiple phase transition behaviors including antiferroelectric (AFE) state to ferroelectric (FE) state transition under applied electric field, depolarization phase change behavior and AFE state to paraelectric state (PE) transition were observed, and their effects on the ECE response were investigated in detail. Significant improvement of ECE adiabatic temperature change of 1.04 K at room temperature (30 °C) was obtained by Maxwell method in (Pb0.94La0.04)(Zr0.52Sn0.30Ti0.18)O3 bulk ceramic through AFE→FE phase transition, while the highest ΔT of 2.73 K with electrocaloric strength (ΔT·ΔE−1) of 0.039 K cm kV−1 were observed in (Pb0.94La0.04)(Zr0.50Sn0.30Ti0.20)O3 bulk ceramic at temperature close to its Curie peak. The high ECE temperature change and ECE strength make them to be candidates for using in next generation solid-state refrigeration device.

Decoding the relationship between the electrocaloric strength and phase structure in perovskite ferroelectrics towards high performance

The adverse variation of electrocaloric coefficient ΔT/ΔE versusthe electric field at different phase structures was first noticed and reported, and it was employed to explore the optimization of both electrocaloric temperature change ΔTand ΔT/ΔE.

Large Energy Storage Density and Electrocaloric Strength of Pb <sub>0.97</sub>La <sub>0.02</sub>(Zr <sub>0.46-x</sub>Sn <sub>0.54</sub>Ti <sub>x</sub>)O <sub>3</sub> Antiferroelectric Thick Film Ceramics

Pb0.97La0.02(Zr0.46-xSn0.54Tix)O3 (PLZST, x=0.04, 0.06, 0.08, 0.15, and 0.18) antiferroelectric thick film ceramics were fabricated via a tape-casting approach. The energy storage performance and electrocaloric effect were investigated in terms of the measurements on the hysteresis loops and Maxwell relation. The maximum value of energy storage density of 5.2 J/cm3 and efficiency of 78.2 % were procured at 600 kV/cm in Pb0.97La0.02(Zr0.42-xSn0.54Ti0.04)O3 thick film ceramics at room temperature. In addition, the ECE was indirectly calculated using the Maxwell relation and the P-E loops as a function of temperature and electric field, a reversible adiabatic temperature change of ΔT=2.47 °C was presented in Pb0.97La0.02(Zr0.42-xSn0.54Ti0.04)O3 thick film ceramics at 500 kV/cm, corresponding to the calculated electrocaloric strength of 0.48 K(MV/m)-1. These results indicate that the PLZST thick film ceramics are promising for practical applications in high-power energy storage capacitors and solid-state refrigeration devices.

Soft Perovskite-Type Antiferroelectric with Giant Electrocaloric Strength near Room Temperature.

Antiferroelectric materials, characterized by an antiparallel array of adjacent dipoles, are holding a bright future for solid-state refrigeration based on their electrocaloric (EC) effects. Despite great advances of inorganic oxides and some organic soft polymers, their EC effects are achieved under quite high electric fields that result in too low EC strengths for practical application. Currently, it is a challenge to exploit soft antiferroelectric with strong EC strengths. Here, by the mixed-cation alloying, we present a new perovskite-type soft antiferroelectric, (isopentylammonium)2CsPb2Br7 (1), which incorporates both an organic spacing cation and an inorganic perovskitizer Cs+ moiety. Remarkably, the synergic cooperativity between the reorientation of the organic spacer and atomic displacement of Cs+ cation triggers its multiple ferroelectric-antiferroelectric-paraelectric phase transitions at 321 and 350 K. Their natural polarization vs electric field hysteresis loops are characterized to confirm ferroelectric and antiferroelectric orders of 1, respectively. It is emphasized that, under a low electric field of 13 kV/cm, the antipolar dipole realignment in 1 endows a giant near-room-temperature EC strength (ΔTEC/ΔE) of 15.4 K m MV-1 at antiferroelectric phase. This merit is on par with the record-high value of BaTiO3 (∼16 K m/MV) but far beyond the state-of-the-art soft polymers. The underlying EC mechanism for 1 is ascribed to the extremely low critical field to switch dipoles, involving the reorientation of the organic spacer and the shift of the Cs+ cation. Besides, notable EC entropy change (∼4.1 J K-1 kg-1) and temperature change (∼2 K) reveal potentials of 1 for solid-state refrigeration. As far as we know, this discovery of near-room-temperature EC strengths is unprecedented in the hybrid perovskite family, which sheds light on the exploration of new soft antiferroelectrics toward high-efficiency refrigeration devices.

Multifunctional response of lanthanum-modified PZT relaxor ferroelectric system with improved electrocaloric effect and energy storage performance

A systematic investigation of both electrocaloric effect (ECE) and energy storage properties is presented in the Pb0.88La0.08(Zr0.60Ti0.40)O3 relaxor system. The ECE, studied from direct and indirect methods, revealed an electrocaloric temperature change (ΔT) around 1.6 K, under an applied electric field of 60 kV/cm at room temperature, with a corresponding electrocaloric strength (ΔT/ΔE) around 0.03 K cm/kV. The temperature dependence of ΔT displayed its maximum value (∼2.32 K) around the freezing temperature (Tf), which is known as a critical temperature for relaxor ferroelectrics, thus suggesting an important contribution of the polar nanoregions to the electrocaloric properties. This result, together with the observed recoverable energy density (Jr) value around 0.43 J/cm3 and a relatively high discharge energy efficiency, reveals the studied system as a promising material for application in multifunctional devices based on high ECE materials combined with excellent energy storage performance.

Giant Electrocaloric Effect and Ultrahigh Refrigeration Efficiency in Antiferroelectric Ceramics by Morphotropic Phase Boundary Design.

Electrocaloric effect (ECE) in ferroelectric (FE)/antiferroelectric (AFE) materials offers a promising high-efficient and zero-emission solid-state cooling technology, whose materials design is usually focused on the morphotropic phase boundary (MPB) between two FE phases. This work constructs an MPB between an orthorhombic AFE and a rhombohedral FE phase in Pb0.97-xBaxLa0.02Zr0.95Ti0.05O3 (PBLZT100x, x = 0-0.08) ceramics and achieves a superior ECE performance. An unprecedented high electrocaloric strength of 1.52 K·mm/kV and an ultrahigh refrigeration efficiency (coefficient of performance = 16) are obtained in PBLZT4, in the MPB near AFE end. Moreover, a large negative ECE, with the highest strength up to -0.41 K·mm/kV, is also realized due to the electric field-induced AFE-FE transition. The coexistence of giant positive and negative ECEs at adjacent temperatures can further improve the cooling capacity (∼17%) of solid-state refrigeration in a well-designed cooling cycle. This work provides a brand new materials design strategy to achieve giant positive and negative ECEs simultaneously and a novel cooling cycle to efficiently utilize the two effects.