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A synergistic realization of high electrocaloric effect (ECE) and excellent temperature stability in ferroelectrics are foundation for practical applications, which is, however, a major challenge in ferroelectric cooling community thus far. In confront with this long‐standing issue, an emergent monomorphic ferrodistortion strategy in NaNbO3‐based relaxor is proposed with flexible tetragonal polar nanoregions immersing in short‐range oxygen octahedral tilt. This not only contributes to large quantities of polar entities to increase entropy change but also produces highly robust oxygen octahedral tilt to persist ferroelectricity and obstruct thermal agitations. Therefore, a high ΔT of 0.96 K and an ultrawide temperature span ΔTspan of 110 K with a record‐high figure of merit of 4.74 is achieved in Ta‐doped NaNbO3‐BaTiO3 ceramics and these superior EC performances present a remarkable breakthrough in ferroelectric bulks cooling. This work thus provides an innovative way of utilizing ferrodistortive relaxor feature with polar nanoregions immersing in oxygen octahedral tilt to simultaneously boost EC value and temperature stability and thus monomorphic ferrodistortion is proposed as an effective strategy to develop high‐performance entropy‐change materials. [ABSTRACT FROM AUTHOR]

Electrocaloric (EC) refrigeration offers superior energy-conversion efficiency, miniaturization, and environmental benefits compared to compression refrigeration. However, its practical application is limited by the challenge of aligning the adiabatic temperature change (Δ T) with the operational temperature range. In this study, we have tailored the EC characteristics of BaTiO 3 (BT)-based Ba(Ti 0.9 Sn 0.1)O 3 (BTS) ferroelectric ceramics using Bi(Mg 0.5 Ti 0.5)O 3 (BMT). We provide a comprehensive analysis of the microstructure, electrical properties, and EC behavior of the (1– x)BTS- x BMT system. Our results indicate that the incorporation of BMT establishes a broad platform in the dielectric spectrum while maintaining high polarization. This improvement potentially increases the electrocaloric effect (ECE) and expands the operating temperature range. Direct heat flux measurements reveal that the x = 0.02 composition achieves a maximum Δ T (Δ T max) of 0.41 K with a temperature span (T span) of 68 °C under an intermediate electric field of 50 kV/cm. Moreover, the x = 0.01 sample exhibits a room-temperature Δ T of 0.33 K and relatively good temperature stability within 30–130 °C. These findings indicate that chemical modification methods have the potential to optimize the cooling capacity of refrigerants. [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]

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]

Environment-friendly Ba0.95Ca0.05Ti0.91Sn0.09-xZrxO3 ceramics, with x = 0.00 and 0.01 (BCTSZx) were prepared through a standard solid-state sintering process. The diffusion coefficient estimated from the Santos-Eiras fit of ε r -T plot implies that the ferroelectric-paraelectric transition is a diffuse type. Well-saturated and fatigue resistant P-E hysteresis loops were obtained at room temperature (RT). The energy-storage density (Wrec) and the associated efficiency (η) were obtained from P-E loops data. When applying a relatively losw electric field of 30 kV/cm, a large value of adiabatic temperature change (∆T = 0.73 K), high values of electrocaloric responsivity (ξ = 0.247*10−6 K·m·V−1) and coefficient of performance (COP = 12.26) were obtained in BCTSZ ceramic. In addition, the pyroelectric figures of merit (FOMs) were calculated. The density of pyroelectric energy harvesting increased from 206 to 237 kJ/m3 when the Olsen cycle was operated at temperatures between 25 and 100 °C and an electric field between 0 and 30 kV/cm. The results indicate that the increase in the grain size significantly enhances the dielectric, electrocaloric and pyroelectric properties. This research not only presents a novel technique for generating high-performance ceramic for refrigeration devices, but also expands the field of applications for BaTiO3-based lead-free ferroelectrics for energy storage applications. [ABSTRACT FROM AUTHOR]

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

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]

Ferroelectric phase transition has been identified as a promising avenue for designing high-performance electrocaloric materials for zero-emission and solid-state refrigeration. However, extensive research has been limited to developing ferroelectric materials with large electrocaloric effects near room temperature, preventing them from meeting diverse refrigeration requirements. In this study, by leveraging the room-temperature phase diagram of the (PbLa)(ZrTi)O3 solution, we prepared a series of Pb0.775La0.15ZrxTi1−xO3 bulk ceramics spanning the ferroelectric and relaxor ferroelectric phase regions. This enabled the attainment of various phase transition features and temperatures. Finally, large electrocaloric effects, coupled with adjustable operation temperatures ranging from 150 to −45 °C, are successfully achieved through manipulation of the Zr/Ti ratio. This comprehensive range of operation temperatures effectively addresses diverse refrigeration application requirements, ranging from industrial equipment to freezer cabinets. This work not only underscores the expansion of the electrocaloric refrigeration application domain but also proposes a material design strategy tailored to meet these evolving demands.

The electrocaloric effect (ECE), known for its environmentally friendly characteristics, holds significant promise for advancing next-generation solid-state refrigeration technologies. Achieving a large ECE along with a wide working temperature range near room temperature remains a key developmental goal. In this study, we successfully obtained a substantial ECE of 1.78 K and an extensive working temperature range of 103 K (ΔT > 1.52 K) near room temperature in CaZrO3-modified BaTiO3 lead-free ferroelectric ceramics. Furthermore, this achievement was verified using direct methods. The piezoresponse force microscopy (PFM) results suggest that the broad temperature range is attributed to the formation of ferroelectric microdomains and polar nanoregions (PNRs). Furthermore, X-ray photoelectron spectroscopy (XPS) and ultraviolet‒visible (UV‒Vis) spectroscopy reveal a decrease in the oxygen vacancy concentration and an increase in the bandgap for higher CaZrO3 doping levels. These changes synergistically enhance the maximum applied electric field, helping to achieve a high-performance ECE near room temperature. This research presents a straightforward and effective approach for achieving high-performance ECEs in BaTiO3 lead-free ceramics, offering promising prospects for application in next-generation solid-state refrigeration technologies.

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]

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]

Copyright of Journal of Refrigeration is the property of Journal of Refrigeration Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

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]

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.

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]

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]

This study highlights the effect of copper oxide (CuO) doping on electrocaloric (EC) and energy storage (ES) properties of solid state synthesised 1-x(0.6[Ba(Zr0.2Ti0.8)O3]-0.4[(Ba0.7Ca0.3)TiO3])-xCuO (1-xBZCT-xCuO) ceramics with x = 0.005 to 0.05. The x-ray diffraction (XRD) analysis evidences the formation of impurity free 1-xBZCT-xCuO ceramics. Further, XRD, Raman and temperature dependent dielectric studies reveal that the inclusion of CuO into the BZCT lattice suppresses the morphotropic phase boundary (MPB) and reduces the tetragonality (c/a ratio) and consequently enhances the diffused phase transition (DPT) behaviour. The Curie temperature (Tc) shifted towards lower temperature, as the CuO content increases in 1-xBZCT-xCuO ceramics. Significantly, 0.995BZCT-0.005CuO ceramics demonstrated a maximum recoverable energy density (Wr) of 398 mJ/cm3 with an efficiency of 90 % under electric field of 100 kV/cm with an excellent heat stability. Moreover, EC effect exhibited a temperature change of 1.02 K at 30 kV/cm and a responsivity of 0.03 Kcm/kV near Tc. [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]

Here the BaTiO3 nanoceramics (BTNs), with 15 nm grain size, have giant electrocaloric effect. Most importantly, BTNs have the cooling per unit field about 3.95 at Tc =114°C under ∆E = 100 kV/cm. Moreover, the adiabatic temperature change of BTNs with 15 nm grain size under electric field shifts of 10, 50, 100 kV/cm are larger than one of BaTiO3 bulk and BaTiO3 thin film (T = 1.3 K). [ABSTRACT FROM AUTHOR]

The versatile electrocaloric (EC) behaviors of the (1-x)Pb(Mg1/3Nb2/3)O3-xPT (PMN-100xPT) single crystal are closely related to the multiple phase transitions under the multiple fields of electric field and temperature. In this work, the EC effect of <001>-oriented PMN-30PT single crystals with chemical composition at morphotropic phase boundary has been studied during the phase transformation process from the ferroelectric rhombohedral (R) phase to the tetragonal (T) phase. Two consecutive negative EC peaks have been achieved for the first time. Based on the projection of the EC effect in the electric field-temperature phase diagram, the relationship between the EC behaviors and the phase transitions is further established. It was found that the monoclinic (M) phase actually existed during the transformation from the R phase to the T phase, and the related R-M phase transition and M-T phase transition could both induce negative EC peaks. Under the electric field of E = 10 kV/cm, the first negative EC peaks induced by the R-M phase transition is at 57 °C with ΔTmax = −0.11 K. And the M-T phase transition can produce a higher negative EC peak, and its value can reach −0.22 K at 68 °C. Based on thermodynamic calculations, the relationship between the entropy change in different phase transitions and the EC behaviors has been further elucidated. The negative EC effect originates from the structural entropy increase in the electric field-induced phase transition process. This work not only advances the research on the electrical properties of relaxor ferroelectric single crystals but also provides a new insight into high-performance ferroelectric materials design. [ABSTRACT FROM AUTHOR]

Electrocaloric effect (ECE) refrigeration stands out as a promising alternative to conventional compression refrigeration owing to its potential for miniaturization, high energy conversion efficiency, cost-effectiveness, and environmental friendliness. However, the practical applications of ECE refrigeration in lead-free ceramics face limitations due to the challenge of achieving a substantial adiabatic temperature change (Δ T) and a wide operating temperature span (T span). In this study, we tackle this challenge by introducing rare-earth Sm3+ ions into Ba(Ti 0 · 90 Sn 0.10)O 3 (BTSn) ceramics to enhance their ECE stability. We comprehensively investigate the structural, dielectric, and ECE properties of (Ba 1−3 x /2 Sm x) (Ti 0 · 9 Sn 0.1)O 3 (BSmTSn, x = 0−0.03) ceramics. Our findings reveal that the incorporation of Sm3+ ions leads to a reduction in the temperature at which the permittivity reaches its maximum, accompanied by an increased dispersion compared to undoped BTSn ceramics. Particularly noteworthy is the achievement of a Δ T of 0.9 K with a T span of 55.5 °C in the x = 0.005 composition. Furthermore, increasing x to 0.01 enables the realization of a wide T span of 70 °C, starting from 30 °C. These significant enhancements in the T span across all BSmTSn ceramics, facilitated by the introduction of Sm3+ ions, present a promising strategy for optimizing the ECE performance of BaTiO 3 -based ceramics. [ABSTRACT FROM AUTHOR]

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

Herein, the internal stress is regulated to enhance the electrocaloric effect (ECE) of the BaZr 0.2 Ti 0.8 O 3 -2 wt% LiCO 3 (2BLZT) thick films. The internal stress in 2BLZT thick films is inversely proportional to increased grain size. XRD Rietveld refinements reveal an increased fraction of ferroelectric R 3 m phase with the enlarged grain size, resulting in larger polarization and EC strength. A maximum Δ T of 1.88 K is achieved at 150 kV/cm. Furthermore, the 2BLZT ceramics with multilayer structure (2BLZT MLCs) are prepared, which can withstand a high field of 250 kV/cm and achieve a Δ T of 1.2 K. These performances are higher than that of 2BLZT bulks with the same effective working medium. Moreover, the required voltage to produce the same Δ T of 0.6 K is reduced from 1920 V for the bulks to 440 V for the MLCs. This work provides a strategy for designing high-ECE lead-free thick films and MLCs. [ABSTRACT FROM AUTHOR]

We have investigated the effects of grain orientation and tape casting process on the electrocaloric properties of 0.82Na 0.5 Bi 0.5 TiO 3 -0.18 K 0.5 Bi 0.5 TiO 3 (0.82NBT-0.18KBT) ceramics at the Morphotropic Phase Boundary (MPB), using direct and indirect measurements. We observe a larger electrocaloric response for the template-free ceramics compared to 7 and 10 wt% template containing ones, suggesting that grain orientation along rhombohedral < 100 > does not improve the electrocaloric response. Indirect measurements yielded a large adiabatic temperature change of around 3 K under an electric field of 50 kV/cm, which is significantly higher than 0.9 K reached at a lower electric field of 40 kV/cm using the direct measurement. [ABSTRACT FROM AUTHOR]

Copyright of Chinese Journal of Refrigeration Technology is the property of Shanghai Society of Refrigeration and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

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

This work highlights the electrocaloric (EC) and energy storage (ES) properties of 1-x(0.6Ba(Zr0.2Ti0.8)O3-0.4(Ba0.7Ca0.3)TiO3)-x(BiTa0.5La0.5)O3 (1-xBZCT-xBTL) ceramics with x = 0 to 0.05. The XRD studies revealed that inclusion of BTL content in BZCT does not induce any impurity phase. The peak splitting of BZCT near 2θ = 45 ∘ and 66 ∘ confirms the presence of morphotropic phase boundary corresponding to tetragonal and rhombohedral phases. Further, the solid solution formation of BZCT-BTL has suppressed its morphotropic phase boundary behaviour. The XRD, Raman and temperature dependent dielectric studies suggest the presence of pseudocubic phase in 1-xBZCT-xBTL at higher values of x = 0.025 and 0.05. Moreover, the inclusion of BTL boosts the diffused phase transition behaviour of BZCT ceramics. Further, BTL strengthened its relaxor nature due to a reduction in grain size as evidenced from SEM analysis. It is observed that the 0.99BZCT-0.01BTL ceramics show 95% efficiency and a maximum recoverable energy density of 479 mJ/cm3 at 100 kV/cm. Moreover, the electrocaloric temperature change and responsivity are found to be 1.06 K and 0.01 Kcm/kV near the transition temperature. [ABSTRACT FROM AUTHOR]

Point defects play a versatile role in modulating ferroelectricity and piezoelectricity, however, the decisive role of point-defect concentration/species in controlling macroscopic performance remains unknown. In this work, defects are implanted by reduced atmosphere annealing and/or Mn doping in Pb 0.7 Ba 0.3 ZrO 3 ceramics. i) defects induce lattice distortion, internal lattice strain and accordingly, phase structure is changed (Williamson-Hall analysis and Rietveld refinement); ii) ferroelectricity is enhanced for 0 MN and 1 MA sample with contribution of defect polarization (first-order reversal curves). iii) Joule heat is depressed as an enhanced resistivity by carrier annihilation/forming defect complex; iv) ECE behaves distinctly among 0 MN, 1 MA and 1 MH, respectively. 0 MN sample exhibits a ΔT max of 0.39 K and 1 MA possesses a ΔT max of 0.34 K. Interestingly, a broad temperature span with a low instability of ∼20 % within 288 K–423 K is obtained in 1 MH sample. This work not only provides a guideline for defects enhancing ferroelectricity and ECE, but also clarifies the reduction-resistant properties of (Pb, Ba)ZrO 3 system that are suitable for constructing base-metal multilayer ceramic capacitors in solid-state cooling devices. [ABSTRACT FROM AUTHOR]

A large adiabatic temperature change (Δ T) 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 Δ T is often obtained near high Curie temperature (T c > 100 °C), which impedes the practical applications for electrocaloric refrigeration technology. Herein, the lead-free (1-x)(K 0.48 Na 0.535) 0.03 Li 0.07 (Nb 0.99 Sb 0.01)O 3 -xBaZrO 3 (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 Δ T 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. [ABSTRACT FROM AUTHOR]

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

In this current study, comprehensive investigations were carried out to examine the pyroelectric energy storage, electrocaloric performance, and temperature-sensitive scaling behavior of Ba0.85Ca0.15Zr0.10Ti0.9O3 ceramics synthesized by mixed oxide route. Tetragonal and orthorhombic symmetries were concurrently present with the presence of a single perovskite material under ambient conditions, according to X-ray diffraction (XRD) and Rietveld refinement investigations. The scanning electron micrograph reveals distinct, pore-free grain structures. The dielectric performance shows a temperature-dependent characteristic with a diffuse phase transition. The temperature-sensitive behavior of ferroelectric hysteresis was analyzed with a variety of applied electric fields. The pyroelectric energy storage capabilities were assessed using the Olsen cycle for calculation. Furthermore, figures of merit (FoMs) for pyroelectric properties, including responsivity (Fv), current responsivity (Fi), energy harvesting (Fe), new energy harvesting (Fe*), and detectivity (Fd), were computed. An indirect method based on the thermodynamic Maxwell's relation was employed to analyze the changes in adiabatic temperature, isothermal entropy, and electrocaloric strength. The scaling relationships for ferroelectric hysteresis, specifically about the coercive field (EC), remnant polarization (Pr), and hysteresis area (), were methodically explored across varying temperatures (T). The power-law temperature exponents were found for all the associated hysteresis parameters.

Introduction. Ferroelectric films are widely used for radiotechnical, microwave microelectronic, sensoric, and energy conversion purposes. Such a diverse application range demands film materials with specific electrophysical properties. For instance, while energy storage applications require materials with a high dielectric constant, energy conversion devices largely use those with a low dielectric constant. The necessary physical properties can be achieved using multicomponent ferroelectric structures, such as solid solutions, composites, and multilayer film structures. Mechanical stresses between the substrate and ferroelectric layers play an extremely important role in dielectric properties of multilayer structures.Aim. Development of a mathematical model quantifying the ferroelectric polarization, static dielectric constant, as well as pyroelectric and electrocaloric properties of multilayered ferroelectric film structures.Materials and methods. The presented model is based on the Landau–Ginzburg–Devonshire model (LGD) considering elasticity equations and using electric induction as the order parameter.Results. The developed mathematical model based on LGD provides for a quantifiable description of dielectric, pyroelectric, and electrocaloric properties of layered ferroelectric structures. This model displays the effect of the thickness ratio of polycrystalline layers and grain size distribution on the dielectric properties of films.Conclusion. The developed quantitative model demonstrates the dependence of the thickness, grain size, and stacking order of ferroelectric layers on the dielectric constant and pyroelectric coefficient of multilayered polycrystalline film structures. The presented model can be applied when optimizing the parameters of multilayer structures with respect to their application area.

In the present work, we investigated the effect of BiZn0.5Ti0.5O3 composition on energy storage and electrocaloric properties of lead free (1-x)(0.6Ba(Zr0.2Ti0.8)O3‐0.4(Ba0.7Ca0.3)TiO3)–xBiZn0.5Ti0.5O3 [BZCT-BZ] ceramics by varying the x from 0 to 10%. The x-ray diffraction (XRD) analysis evidences the formation of BZCT-BZ solid solution without any secondary or impurity phase. The peaks splitting at 2θ = ∼ 45° and 66° suggested the co-existence of rhombohedral (R) and tetragonal (T) phases (morphotropic phase boundary) at room temperature for x ≤ 1%. Further, BZCT-BZ ceramics with x > 1% exhibited pseudocubic nature. The ferroelectric hysteresis loop confirms relaxor behavior and the decrease in remanent polarization with increase of BZ content is explained based on the back switching calculations. The BZCT-BZ ceramics as function of BZ composition gave the optimum recoverable energy density of 197 mJ/cm3 and an efficiency of 92% at an applied field of 45 kVcm−1. Such an exceptionally high energy storage efficiency is attributed to the enhanced relaxor behavior and superior back switching capability. Further, the values of electrocaloric temperature change and responsivity are found to be 0.67 K at 45 kV/cm and 0.014 Kcm/kV respectively in 0.98BZCT-0.02BZ ceramics. Thus, BZCT-BZ ceramics are appealing candidates for energy storage and electrocaloric application. [ABSTRACT FROM AUTHOR]

Temperature response of a material to an external electric field is the main method for electrocaloric effect study in ferroelectrics. In this work, for 0.65PbFe2/3W1/3O3–0.35PbTiO3 solid solution as a model object, it is shown that with an increase in the electric field strength, current fomentation effect can occur. It leads to formation of local regions of increased conductivity in the sample. The associated thermal effect have short characteristic times, due to the small volume of the filament. They are comparable to the times of the electrocaloric response of the material, and can lead to significant errors in the detection of the electrocaloric effect. [ABSTRACT FROM AUTHOR]

The electrocaloric properties of commercially modified Pb(Zr,Ti)O 3 - (PZT)-based soft and hard ceramics were investigated by the indirect estimation via measurement of temperature–electric field P (T,E) hysteresis loops. The adiabatic temperature change ΔT due to electrocaloric effects was estimated from the polarization change of these samples. Both positive and negative electrocaloric temperature change was obtained for all ceramics. The existence of the negative electrocaloric effect was related to the FE-FE field-induced phase transition, between rhombohedral and monoclinic phases that occur in PZT ceramics synthesized near the morphotropic phase boundary. The resulting negative electrocaloric temperature change reveals higher values for the hard-type ceramics (∼-1.5 K for PIC 300) than for the soft-type. Insignificant positive effect values were achieved for all ceramics. The highest values of positive ECE were recorded for PIC 155 (soft) and PIC 181 (hard) and are of the order of ΔT = 0.67 K. In this case, no correlation was observed between the type of PZT ceramics soft or hard. [ABSTRACT FROM AUTHOR]

A comparative study on the influence of different 3d transition metal ions (Cr3+, Fe3+ and Ni2+) on the structural, dielectric, ferroelectric and electrocaloric response of BST ceramics is reported in the present work. Conventional solid-state reaction method was adopted for preparing the samples. A pure perovskite phase with tetragonal structure was confirmed by X-ray diffraction (XRD) analysis. Tetragonality was found to be decreased with the substitution of transition metal ions except in Cr3+ substituted sample. The dielectric behavior was investigated as a function of temperature (30 °C–150 °C) at different frequencies. Dielectric constant (ε) data was fitted with Power Law above T c and diffused phase behavior was observed in the samples. P-E loops were recorded at different applied electric fields and temperatures. Improvement in ferroelectric properties (P r = 10.56 μC/cm2, E c = 2.40 kV/cm and P r/ P max = 0.53) was observed for Cr-substituted sample. Indirect method based on Maxwell's entropy-polarization relationship was employed to evaluate the electrocaloric effect (ECE) for all the samples. The value of ΔT max was found to be maximum for (1.113K) for Cr substituted samples. The results show that Cr substituted BST are suitable for use in capacitor, memory devices and new generation solid-state cooling devices. [ABSTRACT FROM AUTHOR]

Electrocaloric (EC) refrigeration is a new type of solid-state refrigeration technology based on the electrocaloric effect (ECE), which has the advantages of environmental protection, high efficiency, easy integration and miniaturization. In this paper, Sr2+ and Hf4+ are doped into the A and B sites of BaTiO 3 (BT), respectively. By adjusting the proportional composition, the multicritical point is constructed to improve the adiabatic temperature change (Δ T), and the relaxor ferroelectrics are formed to broaden the working temperature span (T span). The effect of doping content on the crystal structure, surface morphology, dielectric, ferroelectric and electrocaloric properties of ceramics is studied systematically. The phase diagram of (Ba 1- x Sr x)(Hf x Ti 1- x)O 3 (BSHT) ceramics is established, and (Ba 0.9 Sr 0.1)(Hf 0.1 Ti 0.9)O 3 (BSHT10) is at the multicritical point. It has the most excellent comprehensive electrocaloric performance, with Δ T max obtained 1.2 K and T span (Δ T ≥ 0.9 Δ T max) reached 45 °C under 50 kV/cm, indicating its potential as a lead-free bulk ceramic material for EC refrigeration applications. [ABSTRACT FROM AUTHOR]

The order-degree-modulated ferroic response and electrocaloric effect (ECE) in Pb(B1,B2)O3-type B-site complex antiferroelectrics (AFEs) are explored in this work. The results show that local/phase structure and dielectric/ferroic properties are strikingly dependent on the degree of order (high, intermediate and low for samples S1, S2 and S3, respectively). A decrease in the content of the AFE orthorhombic phase and an increase in the weakly polar disorder phase is observed from S1 to S3, accompanied by an enhanced relaxation behavior with a smearing of the AFE-to-paraelectric phase transition. Ferroic and EC responses in the three samples present distinct features. Antiferroelectricity wakes-up significantly in sample S1, which boosts the ECE to ∼0.95 K and is almost three times that of S3 (∼0.23 K). An abnormal ECE [negative ECE with a hop–hop character and asymmetrical electrocaloric (EC) response] is unexpectedly found in sample S1. The underlying mechanism is unveiled by dipolar relaxation and phenomenology analysis, which states that the AFE coupling strength dominates the EC performance in this AFE. This work not only presents a refreshing method for order-degree regulation of the ECE in B-site complex AFEs, but also clarifies the possibility that AFEs with robust dipolar coupling strength have an unconventional ECE. [ABSTRACT FROM AUTHOR]

Our societies are highly dependent on reliable cooling for air conditioning (AC) and refrigeration. Currently, modern cooling is supported by a 19th century technology: vapor compression cycle (VCC)-based cooling. Refrigerants used in the VCC cooling are strong greenhouse gases and thus are among the leading causes of global warming. The electrocaloric (EC) cooling is attractive as an alternative to the VCC cooling. EC cooling is environmentally benign, compressor-free, highly scalable, and has the potential of achieving higher efficiency than VCC cooling. The active EC materials research since the late 2000s has created several EC materials that exhibit giant electrocaloric effect (ECE) (by direct measurement). These EC materials have enabled the demonstration of EC cooling devices that exhibit temperature lifts of more than 8 K. These EC materials and device research reveals the promise of ferroelectric materials in generating giant ECE at low electric fields and EC cooling devices achieving high performance. This review highlights these advances and offers perspectives of the EC cooling technologies.

The versatile electrocaloric (EC) behaviors of the (1-x)Pb(Mg1/3Nb2/3)O3-xPT (PMN-100xPT) single crystal are closely related to the multiple phase transitions under the multiple fields of electric field and temperature. In this work, the EC effect of -oriented PMN-30PT single crystals with chemical composition at morphotropic phase boundary has been studied during the phase transformation process from the ferroelectric rhombohedral (R) phase to the tetragonal (T) phase. Two consecutive negative EC peaks have been achieved for the first time. Based on the projection of the EC effect in the electric field-temperature phase diagram, the relationship between the EC behaviors and the phase transitions is further established. It was found that the monoclinic (M) phase actually existed during the transformation from the R phase to the T phase, and the related R-M phase transition and M-T phase transition could both induce negative EC peaks. Under the electric field of E = 10 kV/cm, the first negative EC peaks induced by the R-M phase transition is at 57 °C with ΔTmax = −0.11 K. And the M-T phase transition can produce a higher negative EC peak, and its value can reach −0.22 K at 68 °C. Based on thermodynamic calculations, the relationship between the entropy change in different phase transitions and the EC behaviors has been further elucidated. The negative EC effect originates from the structural entropy increase in the electric field-induced phase transition process. This work not only advances the research on the electrical properties of relaxor ferroelectric single crystals but also provides a new insight into high-performance ferroelectric materials design.

To investigate the effect of A‐site substitution on phase‐structure evolution and electrocaloric effect (ECE) in filled tungsten bronze ceramics, Sr2–3x/2LaxNaNb4.3Ta0.7O15 (x = 0, 0.02, 0.04, and 0.06) ceramics are prepared through a two‐step solid‐state reaction method. Rietveld refinement shows that La2O3 addition achieves a partial transition from orthorhombic (Im2a) to tetragonal phase (P4bm). A decrease in phase transition temperature, enhancement in distortion degree, and relaxation behavior are observed with increasing La2O3 content, as demonstrated by dielectric, in situ Raman spectra, and ferroelectric properties. The indirectly measured ECE shows a non‐monotonic variation, with room‐temperature ECE ranging from 0.19, 0.15, 0.23 to finally 0.19 K for x = 0, 0.02, 0.04, and 0.06 compositions, respectively. This evolution trend is explained by an interplay of relaxation and multiphase coexistence. Directly measured ECE is also performed and a positive ECE character with a good temperature stability is observed. This work not only establishes relationships between phase‐structure evolution and ECE in filled Sr2NaNb4.3Ta0.7O15 tungsten bronze ceramics, but also presents its possibility in applications of thermally stable EC devices. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The performance parameters for characterizing the electrocaloric effect are isothermal entropy change and the adiabatic temperature change, respectively. This paper reviews the electrocaloric effect of ferroelectric materials based on different theoretical models. First, it provides four different calculation scales (the first-principle-based effective Hamiltonian, the Landau-Devonshire thermodynamic theory, phase-field simulation, and finite element analysis) to explain the basic theory of calculating the electrocaloric effect. Then, it comprehensively reviews the recent progress of these methods in regulating the electrocaloric effect and the generation mechanism of the electrocaloric effect. Finally, it summarizes and anticipates the exploration of more novel electrocaloric materials based on the framework constructed by the different computational methods. [ABSTRACT FROM AUTHOR]

Ba0.7Sr0.3TiO3 added with 1 mol% B3+ and x mol% Mn2+ (BSTBM) ceramics were synthesized using citrate combustion technique. An enhanced electrocaloric effect has been reported in BSTBM ceramic. The addition of B3+ and Mn2+ ions lowers the sintering temperature of BSTBM ceramics to 1200 °C. The ceramic sample with x = 0.5 exhibits homogeneous grain size, low dielectric loss and large polarization. More importantly, the ceramic sample with x = 0.5 shows the excellent electrocaloric properties (adiabatic temperature change, ΔT = 0.86 K, and electrocaloric responsivity, ΔT/ΔE = 0.43 K m MV−1) under electric field of 20 kV/cm and room temperature. Moreover, a high ΔT of 3.08 K and ΔT/ΔE of 0.31 K m MV−1 are obtained under electric field of 100 kV/cm near room temperature for this composition. Highlights: The addition of B3+ and Mn2+ lowers the sintering temperature of BSTBM ceramic. Improved microstructure and enhanced electrocaloric properties are realized. Large adiabatic temperature change ΔT = 3.08 K is obtained at 100 kV/cm. ΔT = 0.86 K and ΔT/ΔE = 0.43 K m MV−1 are realized at 37.5 °C and 20 kV/cm. [ABSTRACT FROM AUTHOR]

The use of refrigeration technology is widespread in national security, industrial and agricultural production, biomedicine, and everyday life. High efficiency, environmental friendliness, and low cost make solid-state refrigeration based on electrocaloric effect (ECE) a promising refrigeration technology. Lead-free ferroelectric ceramics (1–x)Ba(Zr0.2Ti0.8)O3–x(Ba0.7Ca0.3)TiO3 (BZT–BCT) are promising materials for electrocaloric refrigeration in the field. In this paper, Sm-doped 0.5BZT–0.5BCT ceramic was fabricated by the conventional solid-state reaction method. The effect of Sm-doping contents (0, 1.0, 2.0, 2.5, and 3.0 mol.%) on the phase structures, dielectric properties, ferroelectricity, and electrocaloric properties of 0.5BZT–0.5BCT ceramics was systematically examined. The results indicate that all ceramics have a pure perovskite structure with no other secondary phase available. High relative densities are observed in all lead-free ferroelectric ceramics and all of the samples show transgranular fracture with no clear grain boundaries seen. The ceramics' ferroelectric hysteresis loops become thinner as the Sm doping content increases. At that, remanent polarization Pr decreases, indicating that more polar nanoregions (PNRs) are formed in BZT–BCT lead-free ceramics through Sm doping. The increase in Sm doping content resulted in a change in the dielectric permittivity and electrocaloric temperature that first increased and then decreased. The maximum dielectric permittivity is 5,518 when the doping content of Sm is 2.5 mol.% and the maximum electrocaloric temperature change ΔTmax of 0.109 K at 4 kV/mm was obtained when Sm doping content was 2 mol.%. The results show that an appropriate Sm doping is favorable for improving the dielectric, ferroelectric, and electrothermal properties of lead-free ceramics 0.5BZT–0.5BCT. [ABSTRACT FROM AUTHOR]

For efficient solid-state refrigeration technologies based on electrocaloric effect (ECE), it is a great challenge of simultaneously obtaining a large adiabatic temperature change (ΔT) within a wide temperature span (Tspan) in lead-free ferroelectric ceramics. Here, we studied the electrocaloric effect (ECE) in (1-x)(Na0.5Bi0.5)TiO3-xCaTiO3 ((1-x)NBT-xCT) and explored the combining effect of morphotropic phase boundary (MPB) and relaxor feature. The addition of CT not only constructs a MPB region with the coexistence of rhombohedral and orthorhombic phases, but also enhances the relaxor feature. The ECE peak appears around the freezing temperature (Tf), and shifts toward to lower temperature with the increasing CT amount. The directly measured ECE result shows that the ceramic of x = 0.10, which is in the MPB region, has an optimal ECE property of ΔTmax = 1.28 K @ 60 °C under 60 kV/cm with a wide Tspan of 65 °C. The enhanced ECE originates from the electric-field-induced transition between more types of polar nanoregions and long-range ferroelectric macrodomains. For the composition with more relaxor feature in the MPB region, such as x = 0.12, the ECE is relatively weak under low electric fields but it exhibits a sharp increment under a sufficiently high electric field. This work provides a guideline to develop the solid–state cooling devices for electronic components.