The improvement of the electrocaloric effect (ECE) in (1−x)(Na0.5Bi0.5)TiO3−xSrTiO3 (NBT-ST) lead-free relaxor ferroelectric ceramics was determined by indirect measurements method and is reported ...here. The phase transition temperature can be reduced to room temperature by tuning the compositions of the (1−x)NBT-xST material. A large ECE (ΔTmax=1.64K, ΔSmax=2.52K and ΔT/ΔE=0.33KmmkV−1 at 50kVcm−1) was obtained at 60°C when x=0.25. A suitable response over a broad temperature range from 30°C to 70°C can be obtained with x=0.26 with very high cooling values (ΔT>1K). In addition, the 0.7NBT-0.3ST AFE-like bulk ceramic exhibited excellent temperature stability in its energy-storage properties from room temperature to 120°C. The maximum value of the recoverable energy density was 0.65J/cm3 obtained at 65kV/cm. Taken together, these properties signified that (1−x)NBT-xST is a promising material for applications in cooling systems and energy-storage in the room temperature range.
The microstructure, dielectric property and electrocaloric effect were investigated in the lead-free (1-x)BaTiO3–x (BiMg1/2Ti1/2)O3 ((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.
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•The electrocaloric effect was first investigated in the BT-BMT ceramics.•The negative electrocaloric effect was first reported in the BT-BMT ceramics.•The negative electrocaloric effect was related to the field induced phase transition.•The giant electrocaloric value of 1.21 K was observed in 0.98BT–0.02BMT ceramic.
This study reports on the electrocaloric effect in lead-free Ba1-xLn2x/3Ti0.925(Yb0.5Nb0.5)0.075O3 ceramics (where Ln = Eu3+, Nd3+, Pr3+), which was evaluated by an indirect method. The ...electrocaloric temperature change (ΔT) was estimated from the Maxwell relation based on measured P-E hysteresis loops recorded at different temperatures. For x = 0, the electrocaloric temperature change (ΔT) was about 0.052 K (7.95 kV/cm, 326 K), while they were 0.011 K (3.97 kV/cm and 338 K), 0.019 K (3.97 kV/cm and 332.5 K), and 0.622 K (28 kV/cm and 360 K) for the Eu 3+, Nd3+, and Pr3+ doped BaTi0.925(Yb0.5Nb0.5)0.075O3 (x = 0.005), respectively. The electrocaloric responsivity ξ = ΔT/ΔE, as calculated, reveals that the Ba0.995Pr0.005Ti0.925(Yb0.5Nb0.5)0.075O3 (BTYN: Pr3+) ceramic exhibits the largest value, of about 0.222 Kmm/kV, reported so far in the BTYN-based lead-free ceramics. As a result of this finding, the lead-free BTYN: Pr3+ system seems to be one of the best options for future electrocaloric applications as a lead-free alternative to lead-based materials.
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 (Wrec) and a large reversible adiabatic temperature change (ΔT) were obtained simultaneously in PLZS thick film ceramics (TFCs). A maximum Wrec 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 Pb0.97La0.02(Zr0.50Sn0.50)O3 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 Pb0.97La0.02(Zr0.50Sn0.50)O3.•A large negative electrocaloric effect, ∆Tmax 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.
The electrocaloric effect of ferroelectric ceramics has been studied extensively for solid-state caloric cooling. Generally, most ferroelectric ceramics are poor thermal conductors. In this work, the ...possibility of enhancing the thermal conduction of ferroelectric ceramics through the electrocaloric effect is studied. A multilayer ceramic structure is proposed and the proper sequential electric field is applied to each ceramic layer. The result shows that the thermal conduction of the multilayer structure is significantly enhanced because of the electrocaloric effect of the ferroelectric ceramics. As a result, the work finds an alternatively way of applying the electrocaloric effect, prompting thermal conduction.
Lead-free ferroelectric electrocaloric (EC) materials are promising candidates for the next generation of cooling materials. Bi0.5Na0.5TiO3 (BNT)-based relaxor ferroelectrics, one of the most ...representative EC materials, exhibit a superior electrocaloric effect (ECE) near the depolarization temperature (Td). However, there are more and more concerns over the reliability of the widely used indirect measurement method. Here, to comprehend the difference between indirectly and directly obtained ECE results in BNT-based system, the applicability of indirect measurement (based on Maxwell equation) was critically analyzed with respect to the reliable direct measurement (based on heat flow). As evidenced in prototypical BNT-based compositions with different Td values, the dynamic behaviors of local polar structures including ferroelectric domains and polar nano-sized regions (PNRs), can largely affect the measured polarization and thus affect the reliability of indirect measurement. After systematically comparing and analyzing the composition-, temperature-, electric field (E-field)-dependent ECE results obtained from indirect and direct ways, the applicable working regions for the indirect method were determined. This work reveals the underlying mechanism behind direct and indirect ECE measurements, providing the “indirect + direct” experimental strategy for effectively evaluating the ECE performance in BNT-based relaxor ferroelectrics.
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The giant electrocaloric effect (ECE) in ferroelectrics arouses enthusiasm on the electrocaloric refrigeration for its zero global-warming-potential. Previous studies have observed that large ECE ...response occurs around ferroelectric-paraelectric phase transition in BaTiO3-based ferroelectrics. However, few attention is paid to the effect of phase fraction on ECE performance. In this work, Ba1-xSrxTi0.95Sn0.05O3 ceramics which display varied phase fraction of orthorhombic and tetragonal (O and T) phase at room temperature, are developed to reveal the influence of phase fraction on the electric properties, especially ECE performance. The electrocaloric temperature change (ΔT) is enhanced in composition with equal phase fraction of O and T, which also shows excellent piezoelectric property. Intrinsically, a number of nanodomains are formed due to the incorporation of Sr2+, greatly benefiting the invertibility of domains under the electric field. It is believed that this study opens a new way for designing and understanding of ECE in BT-based ceramics.
Antiferroelectric materials are demanded in energy storage and solid-state cooling devices due to their distinct hysteresis loops and phase transition behaviors. In this work, ...(Pb0.98La0.02)(ZrxSn1-x)0.995O3 (PLZSx) antiferroelectric bulk ceramics with x = 0.45–0.60 were prepared via the conventional solid-state reaction approach. The recoverable energy storage density of 4.8 J cm−3 and energy storage efficiency of 82.5% were procured in PLZS0.6 ceramics. In addition, the hysteresis loops were measured over a broad range of temperature/electric field and the electrocaloric effects were calculated using the Maxwell relation. The linear parts occurred in the polarization – electric field (P-E) hysteresis loop were fitted, and a power function of Em with m>2 for antiferroelectrics, while m<2 for normal ferroelectrics and relaxor ferroelectrics were procured. A giant negative electrocaloric effect (ΔT=-10.2 K) was also obtained at an operating temperature of 383 K and 20 MV m − 1.
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The electrocaloric (EC) effect in ferroelectric materials has been studied extensively to develop materials for solid-state cooling applications. The Na0.5Bi0.5TiO3-based ferroelectric material is ...selected for this particular application. The Ti4+ of the lead-free Na0.5Bi0.5TiO3 is completely replaced by (Mg1/3Nb2/3)4+ to enhance the dielectric breakdown strength and to observe the EC effect. The lead-free Na0.5Bi0.5(Mg1/3Nb2/3)O3 is synthesized via the columbite route with optimized processing conditions. The material shows a frequency-independent high ferroelectric–paraelectric transition temperature (460 °C) with a slim polarization vs electric field loop. The adiabatic temperature change (ΔT) of the compound is evaluated from the temperature-dependent polarization behavior, and calculated ΔT is ≈ 0.135 K at room temperature. The room-temperature EC strength and leakage current of the material are examined to check its suitability for solid-state refrigeration.
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•Na0.5Bi0.5(Mg1/3Nb2/3)O3 shows enhanced breakdown voltage and reduced leakage current.•Polarization property of Na0.5Bi0.5TiO3 and Na0.5Bi0.5(Mg1/3Nb2/3)O3 differs significantly.•This Pb-free ceramic is suitable for solid-state cooling.
