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The development of lead-free ferroelectric materials is highly desired for next-generation energy storage and superior electrocaloric effect (ECE) applications. However, one of the significant challenges in lead-free dielectric materials is to obtain enhanced ECE and energy storage density at lower applied electric fields, needed for realization of sustainable and efficient energy solutions. Herein, the sol-gel elaborated lead-free Ba 0.95 Ca 0.05 Sn 0.09 Ti 0.91 O 3 ceramics have been synthesized and sintered at temperatures 1100 and 1200 ˚C. The sample sintered at 1200 ˚C exhibits low field assisted improved ∆T ∼ 0.42 K and ∆S ∼ 0.52 J/kg/K values and are closely associated with presence of MPB and relaxor characteristics. The enhanced recoverable energy density (W rec) and total energy density (W tot) are also obtained as 79 mJ/cm3 and 87 mJ/cm3 for the same sample sintered at 1200 ˚C with excellent conversion efficiency of 91 % under a very low applied electric field of 30 kV/cm. The results demonstrate that the optimization of sintering temperature significantly affects the MPB evolution, microstructure and emergence of relaxor characteristics owing to vibrant polar-nano regions that result in enhanced ECE and energy storage characteristics. The present work would be beneficial for advancement of lead-free ferroelectric materials as an efficient electrocaloric cooling and sustainable green energy solutions. • Effect of sintering temperature on microstructure and MPB evolution. • Enhanced EC and energy storage responses owing to MPB evolution and improved microstructure. • Vibrant polar nano regions lead to the emergence of relaxor characteristics. • Enhanced EC temperature change ∆T ∼ 0.42 K at very low applied electric field. [ABSTRACT FROM AUTHOR]

Antiferroelectric materials are highly desired for high energy-storage density capacitors and electrocaloric refrigerator in the future due to their excellent energy storage properties and giant negative electrocaloric effect, which have attracted great attention in recent years. In the present work, a highly recoverable energy density (W rec) and a large reversible adiabatic temperature change (ΔT) were obtained simultaneously in PLZS thick film ceramics (TFCs). A maximum W rec of 9.84 J·cm−3 with an efficiency of 85.2 % at 440 kV·cm−1, and a negative ΔT of −9.50 °C at 280 kV·cm−1 were obtained. Moreover, the maximum value of electrocaloric strength of 0.98 K·m·MV−1 was achieved for Pb 0.97 La 0.02 (Zr 0.50 Sn 0.50)O 3 TFCs. These results demonstrate that the PLZS TFCs can be applied potentially for high energy-storage density capacitors and refrigerators. • A energy-storage density of 9.84 J cm-3 with a efficiency of 85.2 % at 440 kV cm-1 was obtained in Pb 0.97 La 0.02 (Zr 0.50 Sn 0.50)O 3. • A large negative electrocaloric effect, ∆T max of -9.50 °C at 280 kV cm-1, was observed. • An electrocaloric strength (dT/dE) max of 0.98 K/(MV m-1) was procured, which is consistent with the formula proposed by Lu et al. • AFE-FE (I)--FE (II) phase transitions were observed with the increasing electric field in the temperature range of -50 ~ 82 °C. [ABSTRACT FROM AUTHOR]

La and Nb codoping of ferroelectric five-layer Aurivillius phase Sr 2 Bi 4 Ti 5 O 18 (T C ∼ 560 K), induces compositional disorder and diffuse relaxor transitions at much lower temperatures than the parent compound, while preserving the orthorhombic structure. For moderate La and Nb concentrations, the ferroelectric properties are enhanced in the vicinity of room temperature, and so is the electrocaloric effect as measured directly with a homemade quasi-adiabatic calorimeter. The adiabatic temperature change reaches, e.g., in Sr 2 Bi 3.44 La 0.5 Ti 4.8 Nb 0.2 O 18 , Δ T ⁓ 0.3 K at 355 K with a temperature span ⁓ 15 K, under Δ E = 37 kV/cm. Besides, a large field dispersion of the electrocaloric effect is found, ascribed to field-induced transitions from short-range-ordered relaxor to long-range-ordered ferroelectric states. Indirect estimations of the electrocaloric effect from electric polarization data are not able to quantitatively predict the direct results and emphasize the need of applying direct measurement methods, especially for relaxor ferroelectrics. [Display omitted] • New lead-free Aurivillius oxides based on La/Nb codoped Sr 2 Bi 4 Ti 5 O 18 show a significant and tunable electrocaloric effect • Largest electrocaloric response of ΔT ⁓ 0.3 K at 355 K under ΔE = 37 kV/cm • Direct electrocaloric effect measurements reveal an important dispersion with the electric field • Indirect derivations based on commonly applied thermodynamic formulations do not agree with direct results quantitatively [ABSTRACT FROM AUTHOR]

We have synthesized a ceramic sample 0.85Pb(Sc0.5Ta0.5)O 3 -0.15PbTiO 3 [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 (W energy ∼ 0.638 J/cm3) and energy loss (W loss ∼ 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. • 0.85PST-0.15PT ceramics with large electrocaloric effect near room temperature were successfully prepared. • Systematic impact of annealing time (AT) on 0.85PST-0.15PT ceramics is studied to comprehend the comprehensive performance. • After 40 h of annealing, the 0.85PST-0.15PT ceramics exhibited significant improvements in various performance aspects. • Investigations provide valuable insights into optimizing the performance of PST-PT ceramic systems through annealing. [ABSTRACT FROM AUTHOR]

With industrializations speeding up, the need for materials with multiple functions are growing because of ever-increasing complexity of electronic devices. The BiFeO 3 - based ferroelectric relaxor ceramic as a multifunctional material has been ignored thus far. This work innovatively investigates the multifunctionality in a novel lead-free BiFeO 3 -BaTiO 3 -(Sr 0.7 Bi 0.2)TiO 3 relaxor ferroelectric ceramics since a high energy storage performance and electrocaloric effect are simultaneously obtained. Results show that a large adiabatic temperature change ΔT∼1.44 K is achieved. The total energy storage density (W S) reaches to ∼2.34 J/cm3, recoverable energy storage density (W R) are ∼1.74 J/cm3, accompanied by a high efficiency η∼74%. The charge- discharge characterizations indicate that this ceramic possesses an ultrahigh current density of 1184.7 A/cm2 and power density of 59.2 MW/cm3. In particular, the discharging speed is ultra-fast and the discharging period τ is in range of 25–30 ns at room temperature. This work strongly indicates that the studied ceramic is a promising candidate in multifunctional applications such as cooling devices and pulsed power electronics and also enrich the species of the lead-free materials in multifunctionality. • A large adiabatic temperature change ΔT ∼1.44 K is achieved. • High recoverable energy storage density ∼1.74 J/cm3 and efficiency ∼74% are gained. • High current density of 1184.7 A/cm2 and power density of 59.2 MW/cm3 are obtained. • The discharging speed is ultra-fast and its period τ is in range of 25–30 ns. [ABSTRACT FROM AUTHOR]

Sr x Ba 1- x Nb 2 O 6 ceramics were prepared via the high-temperature solid-state reaction method. Structural, ferroelectric, electrocaloric effect and pyroelectric energy harvesting capabilities of Sr x Ba 1- x Nb 2 O 6 ceramics were reported. The main structural phase of tetragonal tungsten bronze with Sr-doped was detected by X–ray diffraction. It was found that the ferroelectric hysteresis loops became slimmer after the temperature higher than Curie temperature of Sr x Ba 1- x Nb 2 O 6 ceramics, which was a representative feature of relaxor ferroelectric. In addition, we presented the positive peak values of electrocaloric at vicinity of Curie temperature which was affected by the applied electric field for all samples. It is worth noting that the pyroelectric energy harvesting property is the first time investigated by using Olsen cycle for Sr x Ba 1- x Nb 2 O 6 ceramic. The maximum pyroelectric energy harvesting density was 170 kJ m−3 for x = 0.6 in Sr x Ba 1- x Nb 2 O 6 with the temperature range from 293 to 433 K. The experimental results indicated that better pyroelectric energy harvesting property and larger electrocaloric effect of Sr x Ba 1- x Nb 2 O 6 ceramic benefited from the higher Sr/Ba ratio. Finally, energy-storage capacity for Sr x Ba 1- x Nb 2 O 6 ceramic was obtained from the ferroelectric hysteresis loop and the maximum room-temperature energy-storage efficiency was 86.37% with x = 0.6 under 60 kV cm−1. Image 1 • The pyroelectric energy harvesting property was first studied in Sr x Ba 1- x Nb 2 O 6 ceramics. • Positive electrocaloric effect in Sr x Ba 1- x Nb 2 O 6 ceramics were demonstrated. • The maximum energy-storage efficiency is 87.94% for Sr 0.6 Ba 0.4 Nb 2 O 6 ceramics. [ABSTRACT FROM AUTHOR]

Aging creates significant changes in the properties of the ferroelectric materials such as dielectric and piezoelectric properties. However, the influence of aging on the electrocaloric effect (ECE) has not yet been investigated. In this work, we investigate the effect of the aging on the ECE in acceptor (Li+) doped BaTiO 3 ceramics. We observe that aging induced defect polarization (P D) reduces the saturation polarization of the doped samples until T c = 115 °C. Above that temperature P D loses its effectiveness and material behaves like a fresh sample. Suppression of polarization below T C due to aging effect results in a sharper slope change in the temperature dependence of electrical polarization in aged samples which causes an increase in the electrocaloric temperature change of Li+ doped BaTiO 3 ceramics up to 23% at T C. Above a critical Li doping amount, both negative and positive electrocaloric effect are observed in the same sample. • Li+ as acceptor dopant in BaTiO 3 results in the formation of defect polarization. • Defect polarization suppresses electrical polarization in aged samples. • ΔT of aged BaTiO 3 increases up to 23% at T C compared to its fresh counterpart. [ABSTRACT FROM AUTHOR]

Abstract Motivated by a broad temperature span, we performed a strain-induced broadening temperature range of electrocaloric effects in PbZr 0.6 Ti 0.4 O 3 /PbTiO 3 ferroelectric superlattices based on phenomenological Landau-Devonshire thermodynamic theory. The results indicated that interlayer misfit strain and substrate misfit strain in superlattices modulate the Curie temperature. Considering two types of strains coexist in ferroelectric superlattices, there exist a balance between interlayer misfit strain and substrate misfit strain to broaden temperature range (281 K) of electrocaloric effects. The present study therefore contributes to the understanding of strain effects of electrocaloric cooling and provides guidance towards experimental design of high efficiency cooling devices. Highlights • Strain can induce a broadening temperature range of EC effects in ferroelectric superlattices. • Utilize Landau-Devonshire thermodynamic theory to investigate the effects of strain on ECE in PZT/PTO superlattices. • A balance between interlayer misfit strain and substrate misfit strain can broaden temperature range of EC effects. [ABSTRACT FROM AUTHOR]

Electrocaloric (EC) refrigeration materials have seen significant progress recently, with efficient Barium titanate-based (BT-based) lead-free materials particularly promising for microelectronics applications. However, their performance still lags behind their lead-based counterparts, highlighting the need for further improvements. This study employs a novel density adjustment strategy (DAS) to enhance the EC performance of (0.5- x)BCT-BTZ- x BST ceramics by carefully balancing the relationships among density, dielectric breakdown strength (BDS), and Δ T. Although Δ T intuitively decreases with increasing density, enhanced BDS can partially compensate for this decrease. An excellent EC performance with Δ T of 2.21 K and Δ T /Δ E of 0.471 K mm kV−1 is obtained in x = 0.5, together with a broader temperature span of 50.3 °C near room temperature, which surpasses or is comparable to other lead-free or lead-based ones. The results suggest that the DAS provides a promising approach for developing efficient EC, making speediness of application in EC devices. [Display omitted] • Developed innovative density adjustment strategy (DAS) for (0.5- x)BCT-BTZ- x BST ceramics to reconcile ρ and Δ T relationship. • Excellent EC properties (Δ T = 2.21 K, Δ T /Δ E = 0.471 K mm kV−1, T span =50.3 ℃) achieved by balancing ρ, BDS, and Δ T. • Identified physical mechanisms responsible for enhanced EC properties. [ABSTRACT FROM AUTHOR]

The electrocaloric (EC) cooling and energy storage capabilities of Pb-free ferroelectrics are thought to be a promising technology for developing environmentally friendly refrigeration and energy storage systems. The EC performance, energy storage and pyroelectric response of sol-gel derived Ba 0.85 Ca 0.15 Hf 0.10 Ti 0.90 O 3 (BCHT) ferroelectrics sintered at various temperatures are investigated here. It is thoroughly explored how sintering temperature affects the structural and electrical characteristics of BCHT ceramics. According to structural analysis by X-ray diffraction, the morphotropic phase boundary (MPB) of tetragonal and orthorhombic phases is evolved in BCHT ceramics sintered at higher temperatures of 1250 and 1350 °C. The density, grain size, and dielectric constant of BCHT ceramics increase when the sintering temperature rises from 1150 to 1350 °C. The BCHT ceramic sintered at 1250 °C exhibits the highest room temperature pyroelectric coefficient p ∼ 15.21 10−4 C/m2K and the various pyroelectric figure of merits calculated are F i = 7.46 10−10 m/V, F v = 0.033 m2/C, F D = 31.82 10−6 Pa−1/2, F e = 103.44 J/m3K2, and F e * = 24.85 10−12 m3/J respectively. At the ambient temperature, BCHT ceramic sintered at 1250 °C with MPB displayed a high EC temperature change ΔT ∼ 0.56 K and EC efficiency ΔT/ΔE ∼ 0.28 Kmm/kV under relatively low field ΔE ∼ 20 kV/cm. The highest EC temperature change ΔT ∼ 1.01 K is also observed in BCHT ceramics sintered at 1250 °C with corresponding ΔT/ΔE ∼ 0.50 Kmm/kV at 87 °C. The observed values are higher than the value reported for other lead-free materials. The maximum recoverable energy density J rec ∼ 116.18 10−3 J/cm3 and corresponding efficiency η ∼ 71.34 % has been observed in BCHT ceramics sintered at 1250 °C. These findings indicate that BCHT ceramics offer a promising way to develop high-performance pyroelectric sensors, electrocaloric refrigeration, and energy storage materials. • The sintering temperature greatly influences the microstructural and electrical properties of BCHT ceramics. • The ceramics with denser microstructure, larger grain size, and MPB evolution led to enhanced electrocaloric, and energy storage performance. • The giant ΔT ∼ 1.01 °C was observed under a lower electric field in BCHT ceramics with a high efficiency of 0.50 K.mm/kV. • The highest J rec of 116.18 10−3 J/cm3 with corresponding efficiency of 71.34 % is obtained in BCHT ceramics. [ABSTRACT FROM AUTHOR]

Recently electrocaloric effect in lead-free environmental friendly ferroelectrics is in its peak research. The feasible and existed electrocaloric response in lead-free (1-x) (K 0.5 Na 0.5 )NbO 3 - xSrZrO 3 (KNN-xSZ) nanocrystalline ceramics is demonstrated using Maxwell's thermodynamic approach. The maximum electrocaloric response of 1.19 K at 367 K was observed under the electric field of 35 kV/cm, and the corresponding electrocaloric responsivity value was found to be 3.40 × 10 −7  K m/V at 367 K for x = 0.10. A significant coefficient of performance (COP) and electrical energy storage density (W rec ) were calculated to be 0.62 and 0.20 J/cm 3 , respectively. The atomistic mechanism of the electrocaloric effect is discussed. The results indicate that KNN-xSZ is a favourable material in the cooling system applications and energy-storage for electronic devices. The material allows electrocaloric cooling mode with versatile properties for the cooling operation by an external electric field and operating temperature. [ABSTRACT FROM AUTHOR]

Lead-free based Bi 0.5 (K 0.15 Na 0.85 ) 0.5 TiO 3 (BKNT15) films were deposited on Pt/Ti/SiO 2 /Si(100) substrates using a sol–gel technique. The microstructure, electric domain, dielectric relaxation, ferroelectric properties, and electrocaloric effect were investigated. The giant negative electrocaloric effect (ECE) was obtained over a broad temperature range with the maximum temperature change (Δ T ) values reaching −16.55 K at working temperature of 303 K. So strong ECE is mainly attributed to high breakdown electric field and the large entropy change caused by the structural phase transition. As typical relaxation ferroelectric films, the giant negative electrocaloric effect enriches family of the electrocaloric effect, which is helpful to achieve good cooling effect in solid-state refrigeration at room temperature. [ABSTRACT FROM AUTHOR]

The microstructure, dielectric property and electrocaloric effect were investigated in the lead-free (1- x )BaTiO 3 – x (BiMg 1/2 Ti 1/2 )O 3 ((1- x ) BT– x BMT, x  = 0.0–0.05) ferroelectric ceramics. Under the low electric field (E ≤ 20 kV cm −1 ), the coexistence of a positive and negative electrocaloric effect was obtained in (1- x )BT– x BMT ( x  ≤ 0.04) ceramics system using the Maxwell relation. Negative electrocaloric behavior disappears and the positive electrocaloric effect was only observed at high electric field (E ≥ 25 kV cm −1 ). Firstly, the values of both negative electrocaloric effect under low electric field of E ≤ 20 kV cm −1 (NECE) and positive electrocaloric effect in the high electric field of E ≥ 25 kV cm −1 (PECE) increase, then decrease with increasing BMT content in the ceramics. The 0.98BT-0.02BMT ceramic shows the excellent PECE and NECE capabilities. The corresponding giant electrocaloric effect values of −0.37 K (42 °C) at 20 kV cm −1 and 1.21 K (143 °C) at 55 kV cm −1 were observed. These results show great potential in achieving large cooling power as refrigerants. [ABSTRACT FROM AUTHOR]

This paper demonstrated the thickness dependence of electrocaloric effect (ECE) in Ba 0.8 Sr 0.2 TiO 3 ferroelectric ceramics. The high-temperature sintered sample has inhomogeneous properties along the thickness direction although the microstructure has uniform features throughout. The core zone exhibits a much lower resistivity than that of the whole sample because of more ions' valence variation. Under a same electric field of 30 kV/cm, the ECE ΔT drops from 1.35 K to 1.12 K by reducing the thickness step by step. But the thinnest core sample can sustain much higher electric fields (>50 kV/cm) and exhibits a larger ΔT of 1.67 K, i.e. it has a high ECE value despite a low ECE strength. [ABSTRACT FROM AUTHOR]

The multiphase coexisting of compositionally graded PbZr x Ti 1- x O 3 multilayer thin films were fabricated using sol-gel method. The giant electrocaloric effect (ECE) has been obtained through regulating the growth sequence of the multilayer thin films. At room temperature (at 298 K), Δ T values of up graded multilayer and down multilayer thin films are 9.1 K (applied electric field E = 755 kV/cm) and 7.3 K ( E = 930 kV/cm), respectively. In addition, both of the films exhibit outstanding ECE at higher temperature, Δ T values of 17.9 K (at 453 K) and 26.8 K (at 393 K) are also obtained for up graded multilayer and down multilayer thin films. The results indicate that the compositionally graded multilayer thin films with a giant ECE could be a potential candidate for the application in cooling devices. [ABSTRACT FROM AUTHOR]

Crystal structures, dielectric, ferroelectric properties and electrocaloric effects of hetero-valent substituted Ba(Ti 1- x Y x )O 3- x /2 ceramics were studied in the present work. The polar space group of P 4 mm was adopted based on the Rietveld refinement at room temperature. The diffusivity of phase transition and relaxor behavior are both strengthened by the yttrium substitution. The maximal pyroelectric coefficient decreases, and the extent of corresponding temperature deviated from the dielectric peak temperature to higher temperature increases with increasing the yttrium content. The adiabatic temperature changes and isothermal entropy changes display the same tendencies as those of the pyroelectric coefficients. The Ba(Ti 0.944 Y 0.056 )O 2.972 ceramic shows the largest adiabatic temperature change and largest isothermal entropy change among all compositions over a broad temperature range of 50 K. For individual composition, the value of pyroelectric coefficient decreases with increasing the magnitude of applied electric field, and the temperature of maximal pyroelectric coefficient deviates from the dielectric peak temperature to higher temperature. Therefore, the optimal electrocaloric temperature can be adjusted by the magnitude of electric field in relaxor ferroelectricity. [ABSTRACT FROM AUTHOR]

The temperature and electric field dependences of electrocaloric effect (ECE) of 0.5 mol.% La–doped 0.88Pb(Mg 1/3 Nb 2/3 )O 3 –0.12PbTiO 3 (La–doped 0.88PMN–0.12PT) relaxor ferroelectric ceramic were investigated by direct measurement method using a home–made adiabatic calorimeter. Direct and indirect ECE were compared and large discrepancy was observed not only in a magnitude but also in the changing trend. Dual–peak effect was observed in the ΔT ECE –T curves, which can be ascribed to the evolution of polar nanoregions (PNRs). The first ECE peak appears near the depolarization temperature (T d ) of 40 °C at low electric field, and the second ECE maxima with ΔT ECE of 0.44 °C at E = 4 kV/mm occurs at a higher temperature around 70 °C corresponding to the temperature with the maximum dielectric constant (T m ). In addition, the ECE was found to insignificantly change well above the T m . The wide temperature range accompanied by high ΔT ECE in La–doped PMN–0.12PT ferroelectric ceramic indicates the promising candidate for applications in cooling technologies. [ABSTRACT FROM AUTHOR]

In this work, the (100-x)Ba(Hf 0.2 Ti 0.8 )O 3 -x(Ba 0.7 Ca 0.3 )TiO 3 (BHT–xBCT) ferroelectric ceramics were fabricated by a conventional solid-state reaction method. The electrocaloric effect (ECE) of these ceramics was studied by both indirect and direct methods over a wide temperature range with the composition changing from x = 20 to 50. The most excellent direct ECE occurs in the BHT–50BCT with a good direct ΔT EC = 0.27 K (at 92 °C) under the electric field of 10 kV/cm. What's more, the direct EC effect peaks not only locates at near the Curie temperature, but also at the phase-transition temperatures corresponding to the transitions between different ferroelectric phases. In particular, it is found that BHT–50BCT exhibits a direct ECE anomaly ΔT EC = 0.1 K at 30 °C under an electric field of 10 kV/cm, which can be ascribed to the orthorhombic to tetragonal phase transition, proposing that one can achieve a broad temperature window by tuning the temperature gap between ferroelectric (FE) to paraelectric (PE) boundary and FE-FE boundary. In addition, BHT–30BCT shows good stability of indirect ΔT EC,max /ΔE and a broad ECE peak at a higher electric field, indicating that it is possible for electrocaloric temperature ΔT EC to be tuned linearly by electric field. Overall, our results imply that the BHT– xBCT ceramics are promising candidates for lead-free cooling refrigeration applications. [ABSTRACT FROM AUTHOR]

The tunable electrocaloric effect (ECE) is reported in BaZr 0.2 Ti 0.8 O 3 homogeneous bilayer thick films through a minor modification during fabrication process. Two types of sintering aids, LiBiO 2 and the mixture of PbO and B 2 O 3 , were used to lower the sintering temperature, improving the sintering condition. Compared with the mixture of PbO and B 2 O 3, the LiBiO 2 is demonstrated to be more effective in inducing ECE enhancement in the BaZr 0.2 Ti 0.8 O 3 bilayer thick films, where a large electrocaloric temperature change of −3.9 K under 10 MV m −1 around room temperature can be observed. The result reveals the potential of fine tuning additives in improving the electrocaloric effect, providing an effective and affordable route to realize large ECE under low electric fields. [ABSTRACT FROM AUTHOR]

This paper demonstrated the electrocaloric effect (ECE) in BaTiO 3 ceramics with Ce doping in either A or B sites, which were prepared by the solid-state reaction method. All sintered samples have pure perovsikte phase, whether Ce doping in A or B sites, but the properties are different from each other. For A-site doping of Ba 1-x Ce x TiO 3 , the Curie temperature gradually shifts to lower temperature because the doped Ce ion have smaller radius than Ba ion, while the phase transition is diffused and the latent heat drops. Then the ECE ΔT peak shifts accordingly and ΔT max reduces gradually except small Ce doping. For B-site doping of BaCe x Ti 1 -x O 3 , the phase transition is diffused more significantly but the Curie temperature hardly moves, so that the ECE peak is depressed but does not shift. [ABSTRACT FROM AUTHOR]

The environmentally friendly and low-cost ferroelectric refrigeration based on the electrocaloric effect (ECE) has attracted considerable attention to replace the conventional vapor compression cooling technology. The ECE has been experimentally demonstrated in lead-free 0.9(K 0.5 Na 0.5 )NbO 3 0.1Sr(Sc 0.5 Nb 0.5 )O 3 (KNN-0.1SSN) polycrystalline ferroelectric ceramics using an indirect thermodynamic method. A large electrocaloric effect (adiabatic temperature change) of 0.28 K was observed near the transition temperature of 357 K for electric field 25 kV/cm, and that corresponds to an electrocaloric responsivity of ΔT/ΔE = 0.27 × 10 −7 K mV −1 , significantly larger than the pristine KNN based ceramics. A concurrent increment in specific entropy change of the material was also observed. The results indicate that ferroelectric KNN-0.1SSN materials possess a huge potential for electrocaloric refrigeration as a micro-cooler for electronic devices. [ABSTRACT FROM AUTHOR]

The influence of the incorporation of Calcium in lead-free ferroelectric Ba(Zr 0.1 Ti 0.9 )O 3 perovskite on its structural phase transition, dielectric, pyroelectric, ferroelectric, and electrocaloric effect was investigated. Room temperature X-ray diffraction study allowed the identification of a continuous solid solution in the composition range 0 ≤ x ≤ 20 mol% with a rhombohedral to orthorhombic structural transition beyond 15mol%.Structural investigation of X-ray diffraction as a function of temperature reveals four different structural regions for the compositions with low content of Ca and three regions for the compositions with high Ca-content. Using heat flow measurements and dielectric investigations, two sequences of structural phase transitions were elucidated. The tetragonal-to-orthorhombic and orthorhombic-to-rhombohedral phase transitions induced by temperature variation were found to decrease with the increase of the Ca 2+ content, while the cubic-to-tetragonal phase transition temperature remained almost unchanged and exhibited a dielectric permittivity maximum observed around the composition of x = 15mol%.The electrocaloric temperature change ΔT was calculated from two methods: the thermal variation of P–E hysteresis loops and pyroelectric current. The highest electrocaloric ΔT/ΔE = 0 .24 K mm/kV was found for the composition x = 0.05. The largest electrocaloric responsivity around 0.30 K mm/kV was observed for this composition at Curie temperature using direct method. [ABSTRACT FROM AUTHOR]

With the increased concerns on the toxicity of lead, the barium titanate (BT) has developed a vital lead-free ferroelectric material to replace lead-based one due to the extraordinary multi-functionality. However, to date the deep understanding on evolution mechanisms of multiple electro-related performances in single BT based ceramics is still limited, and the simultaneous enhancement or balanced development of comprehensive performance in BT ceramics face challenges. Here, a new lead-free ceramic system of Ba 0.9+ x Sr 0.1- x Ti 0.91 Sn 0.09 O 3 (BSTS, 0 ≤ x ≤ 0.1) was successfully prepared by the conventional solid-state reaction method, and the dopant tuned multi-functionality and underlying physical mechanism of performance evolutions were revealed in detail. The BSTS ceramics present R-O-T-C multiphase coexistence at a wider temperature range near room temperature, along with the structural features with flattened thermodynamic energy landscape and flexible polarization rotation. Accordingly, the enhanced piezoelectric coefficient (d 33 = 600 pC/N), large electrostrictive coefficient (Q 33 = 0.0405 m4/C2, E = 30 kV/cm), superior electrocaloric effect (Δ T = 0.77 K, E = 30 kV/cm) with a wider temperature span of 49 °C (Δ T > 0.5 K), and strong electrocaloric strength (Δ T /Δ E = 0.3857 K mm/kV, E = 5 kV/cm) are simultaneously attained under smaller electric field for BSTS ceramics. It exhibits a superior comprehensive performance than many reported BT based ceramics, which is suitable for more potential applications in the emerging fields of advanced functional devices, such as high precision displacement or strain actuators and zero-global-warming-potential refrigeration with larger capacity near room temperature. This work sheds insight into simultaneously optimizing different electro-related performances, and stimulates future studies on dopant tuned multi-functionality in BT based ceramics. • A new BT based material system with R-O-T-R multiphase boundary is designed. • Enhanced d 33 , large Q 33 , and high Δ T with a wider temperature span are simultaneously achieved. • The physical origin of enhanced performance is revealed. [ABSTRACT FROM AUTHOR]

Electrocaloric effect in lead-free (Ba 1− x Ca x ) (Zr 0.1 Ti 0.9 )O 3 ceramics (with x = 0.05 and x = 0.20) has been investigated by using two different indirect methods. In the first classic approach, the electrocaloric temperature change ( ΔT ) was calculated from the Maxwell relation based on measured P – E hysteresis loops recorded at different temperatures. In the second approach, the ΔT was calculated from the Maxwell relation based on pyroelectric current measurements. The advantage of such approach is that it enables direct determination of the pyroelectric coefficient, which should be otherwise calculated from the hysteresis loops in the classic approach. Direct method was finally used for verification of the obtained results. Good agreement between methods was found near the cubic-to-tetragonal phase transition temperature with a significant electrocaloric responsivity of ΔT/ Δ E = 0.30 K mm/kV for the composition x = 0.05 obtained by direct method. [ABSTRACT FROM AUTHOR]

In this work, 1.5-μm Pb 0.97 La 0.02 (Zr 0.57 Sn 0.38 Ti 0.05 )O 3 antiferroelectric thick films with and without a ZrO 2 thin layer were deposited on LaNiO 3 (100)/Si(100) substrates. The effects of ZrO 2 thin layer on the microstructure, electrical properties, and especial electrocaloric effect of the antiferroelectric films were studied in detail. Although the films both with and without ZrO 2 buffer layer displayed (100)-preferred orientation, possessed dense and uniform surface microstructure, the ZrO 2 -buffered films have an enlarged grain size by 27%, compared with the thick films without the buffer layer. Accordingly, the dielectric constant and saturate polarization of this antiferroelectric thick films was improved by the insertion of ZrO 2 thin layer, and simultaneously its leakage current was slightly reduced. As a result, a great improvement in cooling character caused by ferroelectric–antiferroelectric phase switching, was realized in the ZrO 2 -buffered films. [ABSTRACT FROM AUTHOR]

A phenomenological thermodynamic model is employed to investigate electrocaloric effect in EuTiO 3 nanowires, in which the effects of surface tension, gradient, external stress, nanowires radius and so on are considered. We are surprised that the decrease in size and the increase in external tensile stress can significantly enhance the electrocaloric effect of EuTiO 3 nanowires under the same applied electric filed. Giant adiabatic temperature changes ( ΔT = 15–20 K) are achieved near room temperature by controlling the radius of EuTiO 3 nanowires and applied external electric fields, which is much higher than the previous results obtained in many other isomorphic electrocaloric materials. The large electrocaloric effects suggest the potential application for micro-nanodevice in refrigeration. [ABSTRACT FROM AUTHOR]

• The relation between the hexagonal, rhombohedral and pseudo cubic settings of R3c space group. • The study of valence states using X-Ray Photoluminescence and its correlation with structural parameters. • A detailed analysis of AC Conductivity, Modulus spectra, and Impedance spectra to study the relaxation and conduction mechanism. • The study of the presence of defect dipoles and its implications on the electrical properties. The Rietveld refinement of the polycrystalline powders of 1% Fe and Mn-doped (Na 0.5 Bi 0.5) 0.94 Ba 0.06 Ti 0.98 V 0.02 O 3 at the Ti-site confirmed a single rhombohedral (R3c) phase. The bandgap, (E g) was affected by the anti-phase octahedral tilt angle and the spin-orbit splitting energy of Ti4+2 p 3/2 and Ti4+2 p 1/2 states. The decrease in Bi loss and increase in the binding energy of Ba due to Fe/Mn doping has been correlated to the strengthening of Bi-O and Ba-O bonds which was revealed from the XPS studies thereby further related to the average A-O bond length from structural studies. Hence, a reduction of oxygen vacancy (V O) for the doped samples has been justified. A significant improvement of the dielectric constant, relaxation time (τ 0), and the decrease in conductivity due to doping was revealed from the frequency-dependent (10 Hz-1 MHz) dielectric measurement study. The conduction and relaxation process are dominated by the short-range movement of defects. The activation energy (E a ~ 1 eV) revealed that there is a presence of double-ionized V O s. The ECE study showed a significant enhancement of the changes in entropy, ΔS, and the adiabatic temperature difference, ΔT, due to doping, with ΔT being highest in the Fe-doped sample. Such improvement of dielectric and ECE properties was confirmed due to the reduction of the mobility of oxygen vacancy because of the formation (Mn Ti ′ ′ − V o • •) / (Mn Ti ′ − V o • •) • and Fe Ti ′ ′ − V o • • / (Fe Ti ′ − V o • •) • defect dipoles. [ABSTRACT FROM AUTHOR]

• The existence of O phase of the Fe-doped thin films is observed at room temperature. • T, R, and O phases coexist in all Fe-doped thin films, and the relative content of O phase depends on Fe-doped content. • The BZT-0.32BCT-xFe thin film shows a large ΔT = 22.99 K at x = 0.0075 due to multiphase coexistence and a prominent O phase. In this study, the electrocaloric (EC) effect was enhanced at room temperature for (Ba 0.904 Ca 0.096)(Zr 0.136 Ti 0.864−x Fe x)O 3 (BZT-0.32BCT-xFe 0 ≤ x ≤ 0.015) thin films prepared on Pt/Ti/SiO 2 /(100)Si substrates. The existence of an orthorhombic phase in the Fe-doped thin films at room temperature was confirmed by X-ray diffraction and Raman spectra. Tetragonal, orthorhombic, and rhombohedral phases coexist in all the investigated Fe-doped thin films. The relative content of the orthorhombic phase is most prominent at x = 0.0075. The BZT-0.32BCT-xFe thin film exhibits excellent properties with a giant EC effect (ΔT = 22.99 K, E = 1050 kV/cm, and T = 307 K) at x = 0.0075 compared to the undoped thin film, stemming from multiphase coexistence and a larger orthorhombic phase. The results of this study are useful for developing lead-free electrocaloric materials with superior properties. [ABSTRACT FROM AUTHOR]

Solid-state refrigeration based on electrocaloric effect (ECE) is a high efficiency and eco-friendly refrigeration technique, which has attracted increasing attention. However, it is still a challenge to realize a large adiabatic temperature change (∆ T) accompanied by wide operating temperature range (T span). Herein, enhanced room temperature ECE was realized in lead-free (1-x)Na 0.5 Bi 0.5 TiO 3 -xSr 0.85 Bi 0.10 TiO 3 (NBT-xSBT) by a synergistic effect of forming relaxor ferroelectric and constructing multilayer ceramic capacitor (MLCC). It is found that the maximum ∆ T of NBT-0.50SBT ceramic is 0.31 K at 80 kV/cm, and T span is up to 60 K. To further improve the breakdown strength (BDS), NBT-0.50SBT MLCC was fabricated by a tape-casting method. A large ECE of MLCC reached 2.59 K at 60 °C with excellent temperature stability from 35 °C to 95 °C. These results indicate that NBT-based material is a promising electrocaloric material for solid-state cooling applications. [ABSTRACT FROM AUTHOR]

• First direct measurements of the electrocaloric effect in a ferrielectric (NH 4) 2 SO 4. • Small effect of the electric field on the temperature and entropy of the transition. • High extensive and low intensive electrocaloric efficiency. • No conversion between conventional and inverse electrocaloric effects. • Contribution of Joule heat to the temperature change under the electric field. [Display omitted] The influence of an electric field on the phase transition parameters and the electrocaloric response in ferrielectric (NH 4) 2 SO 4 was studied using a universal multifunctional adiabatic calorimeter. The very low sensitivity of the phase transition temperature to the electric field, dT 0 /dE ≈ 5·10-3 K/(kV/cm), was shown to be the reason for the low maximum value of the intensive electrocaloric effect, ΔT AD , at E = 11 kV/cm: direct and indirect measurements gave the values of 0.01 K and 0.05 K, respectively. However, the extensive electrocaloric response revealed by an analysis of the entropy–temperature–electric field phase diagram was relatively large, with a value of ΔS ECE ≈ − 19 J/kg K, due to the significant contribution of a jump in the excess entropy to the total value, δS 0 /ΔS 0 ~ 0.37. An additional irreversible increase in temperature under the electric field was associated with the Joule effect and indicated a significant electrical conductivity of ammonium sulphate. [ABSTRACT FROM AUTHOR]

• 2.5 mol.% Bi(Mg 0.5 Ti 0.5)O 3 sets as a bridge between nonergodic and ergodic relaxors in tetragonal Bi 0.5 Na 0.5 TiO 3 -12.5BaTiO 3. • A microstructure existing P4mm ferroelectric nanodomains in weakly-polar P4bm matrix was constructed. • 2.5 mol.% Bi(Mg 0.5 Ti 0.5)O 3 -modified Bi 0.5 Na 0.5 TiO 3 -12.5BaTiO 3 shows aΔ T of 0.80 K @ 4 kV/mm a Δ T /Δ E of 0.020 K∙cm/kV. [Display omitted] Taking the advantage of the low transition barrier between P4bm and P4mm distortions, tetragonal structured 0.875Bi 0.5 Na 0.5 TiO 3 –0.125BaTiO 3 was designed to construct an electrocaloric ceramics with large electrocaloric strength by adding the third compound Bi(Mg 0.5 Ti 0.5)O 3 (BMT). The experiments show that, through adding 2.5 mol.% BMT, a large Δ T of 0.80 K was directly observed under 4 kV/mm; especially, a high Δ T /Δ E of 0.020–0.023 K cm/kV was achieved, approximate to BaTiO 3 -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. [ABSTRACT FROM AUTHOR]

• Temperature coefficient (Tcc) is above 10%. • The value of tanδ is very small all over the temperature range. • The tetragonality decreases with Sm3+ and Fe3+ substitution. • Room temperature dielectric constant increases. Polycrystalline ferroelectric ceramics with compositional formula Ba 0.70−x Ca 0.30 Sm x Ti 1−x Fe x O 3 (BCSTF) with (0, 0.005, 0.010, 0.015 and 0.020) were prepared by solid state reaction route and sintered at 1325 °C for 4 h. Single perovskite phase with tetragonal structure was confirmed from X-ray diffraction (XRD) analysis. The dielectric constant 'ε' and tangent loss 'tanδ' were studied for all the samples as a function of frequency (100 Hz to 100 kHz) and temperature (30–200 °C). A very small low 'tanδ' (0.9% at 100 kHz) was observed. The high value of temperature coefficient of capacitance 'Tcc' (~10%) was observed for all the BCSTF samples. P-E hysteresis loops were recorded for sample with x = 0.020 at different temperature. Electrocaloric effect 'ECE' was investigated and the temperature change 'ΔT' was found to be 0.53 K at 35 kV/cm with a high value of electrocaloric coefficient (0.15 K m/MV). The results show that the prepared ceramics can be useful in applications such as capacitor, dielectric bolometers, electrocaloric applications. [ABSTRACT FROM AUTHOR]

• Electrocaloric effects in (SrBa)(SnTi)O 3 ceramics were investigated using direct and indirect approaches. • The largest electrocaloric strength obtained is 0.52 × 10−6 K m/V at T = 56 °C and E = 2 MV/m. • An analytic formula of electrocaloric strength (dT/dE) was firstly deduced via a thermodynamic theory. • The electrocaloric strength mainly depends on the large permittivity peak, phenomenological coefficient and polarization. The electrocaloric effect (ECE) in lead-free (Ba 1−x Sr x)(Sn 0.05 Ti 0.95)O 3 (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. [ABSTRACT FROM AUTHOR]

A systematic investigation of both electrocaloric effect (ECE) and energy storage properties is presented in the Pb 0.88 La 0.08 (Zr 0.60 Ti 0.40)O 3 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 (T f), 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 (J r) 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. • A ΔT value around 1.6 K, at room temperature, was obtained. • ΔT displayed its maximum value around the freezing temperature (T f). • An important contribution of the polar nanoregions to the ECE is suggested. • A J r value around 0.43 J/cm3 remains almost constant up to around T f. • The studied PLZT is a promising material for application in multifunctional devices. [ABSTRACT FROM AUTHOR]

For several decades, ferroelectrics with enhanced electrocaloric (EC) effect have served as competitive alternatives for solid-state cooling devices. In order to enhance the EC effect, there has been increasing research interest on exploring novel systems of EC materials and efficient cooling cycles. In contrast, optimizing intrinsic properties through doping effect has been relatively ignored. In this work, we introduce the binary compound CuO as an additive into the conventional lead-free BaSn 0·11 Ti 0·89 O 3 (BST) ferroelectric ceramic. This leads to a remarkably large adiabatic temperature change of Δ T = −0.33 °C under a relatively low electric field (10 kV/cm). This is higher than the ΔT of pure BST (Δ T = −0.15 °C, under 10 kV/cm). The largest of Δ T = −0.48 °C was achieved under 20 kV/cm. We assume that the large temperature change was achieved due to the addition of CuO additive, which improves the ferroelectric properties (e.g., a higher polarization and a lower coercive field). In addition, by introducing CuO additives, the breakdown electric field of the ceramics was also enhanced at high temperatures (above the Curie temperature, T C) and the working temperature range was greatly broadened (30 °C–60 °C) under a slightly high electric field. Our findings present a promising approach to enhance the EC effect by tuning the intrinsic properties of EC materials. We expect that our work emphasizes the importance of additives in enhancing the EC properties. • CuO was added into BaSn/TiO 3 as an additive for optimizing ferroelectric and electrocaloric effect (EC) properties. • EC temperature change was increased from −0.15°C to −0.33°C at the electric field of 10kV/cm after adding 2 mol%CuO. • A relatively large EC temperature change of −0.48°C at the electric field of 20kV/cm was achieved. • The relationship between the EC effect and intrinsic properties was explained based on Landau-Devonshire theory. [ABSTRACT FROM AUTHOR]

We have investigated the electrocaloric properties of K+ and Na+ co-substituted Sr 0.6 Ba 0.4 Nb 2 O 6 (SBN) ceramics using the indirect method. Tetragonal tungsten bronze (K 0.5 Na 0.5) 2 x (Sr 0.6 Ba 0.4) 5- x Nb 10 O 30 (KNSBN) with x = 0.24 was synthesized using dual-step sintering. Despite the low amount, K+ and Na+ co-substitution resulted in normal ferroelectric behaviour, showing no significant shift in the dielectric maximum temperature of 111 °C with increasing frequency. Maximum electrocaloric temperature change (ΔT) of 0.3 K was observed at an electric field of 30 kV/cm (ΔE) yielding the largest electrocaloric responsivity (ΔT/ΔE) among SBN based ceramics. This relatively large value is in agreement with the larger pyroelectric coefficient of KNSBN compared to SBN based ceramics. • Alkali doping results in normal ferroelectric behaviour. • Largest electrocaloric temperature change among SBN based ceramics is obtained. • Observed effects are related with the stabilization of the ferroelectricity upon doping. [ABSTRACT FROM AUTHOR]

This work directly tests electrocaloric effect (ECE) of (0.94- x)Bi 0.5 Na 0.5 TiO 3 –0.06BaTiO 3 – x SrZrO 3 (BNBTSZ x) with x = 0 (SZ0), x = 0.01 (SZ0.01), x = 0.02 (SZ0.02) and x = 0.03 (SZ0.03) at different temperature points. The Sr2+ and Zr4+ are introduced into 0.94Bi 0.5 Na 0.5 TiO 3 –0.06BaTiO 3 to convert nonergodic relaxor phase into ergodic relaxor phase and form new morphotropic phase boundary (MPBⅡ) at room temperature. A temperature change of 0.37 K and electrocaloric strength of 6.17 × 10−3 K cm/kV are obtained at room temperature. According to the temperature dependence of Δ T and the electric-field dependence of electrocaloric strength, this work focus on the mechanism about higher electrocaloric effect at over-MPBⅡ temperature point. Electrical performances, microstructure and piezoelectric properties are investigated in detail to analyze the local-area phase transformation causing the high electrocaloric effect. The electrocaloric strength of ergodic relaxor phase shows stronger dependence on the electric field than that of nonergodic relaxor phase. • Local-structure evolution gradually emerges by introducing Sr2+ and Zr4+. • Highest electrocaloric effect appears at the MPBⅡ content point or over-MPBⅡ temperature point. • Highest electrocaloric effect at over-MPBⅡ temperature point originates from phase transformation. • Electrocaloric strength of ergodic relaxor phase performs stronger dependence on the electric field than that of nonergodic relaxor phase. [ABSTRACT FROM AUTHOR]