- 标题
- 摘要
- 关键词
- 实验方案
- 产品
-
Significantly enhanced room temperature electrocaloric response with superior thermal stability in sodium niobate-based bulk ceramics
摘要： Converting electrical into thermal energy in ferroelectrics path the way for a novel cooling technology, be able to open up new fields of applications. For electrocaloric refrigeration, large temperature change (ΔT) and excellent temperature stability are highly desired. Unfortunately, a large room temperature ΔT in lead free bulk ceramics was usually obtained at the expense of temperature stability, and vice versa, limiting their practical applications. In this work, composition engineering is carried out as an important strategy to tune phase transition to room temperature and simultaneously induce diffuse phase transition to achieve excellent temperature stability. A large room temperature ΔT is realized by the application of large electric fields, possibly due to the optimization of the sintering process in sodium niobate based ceramics. The 0.78NaNbO3-0.22BaTiO3 ceramic is found to exhibit both large room temperature ΔT (~ 0.70 K) and superior temperature stability (±1.4% variation in ΔT from 300 K to 380 K). Those properties are superior to previously reported lead-free bulk ceramics. This work provides a guideline for the development of high-performance ceramic materials such as NaNbO3-ABO3 (A=Ba, Sr and Ca; and B=Ti and Zr) for electrocaloric refrigeration. Most importantly, this work expands the applications of NN-based ceramics from electric energy storage, electrostrictive and piezoelectric applications, to a new field, i.e. solid-state refrigeration. This makes NN-based ceramics very promising multifunctional materials for device integration.
关键词： Sodium niobate,relaxor ferroelectrics,electrocaloric effect,adiabatic temperature change,diffuse phase transitions
更新于2025-11-14 17:28:48
-
Influence of aging on electrocaloric effect in Li+ doped BaTiO3 ceramics
摘要： 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 BaTiO3 ceramics. We observe that aging induced defect polarization (PD) reduces the saturation polarization of the doped samples until Tc=115 oC. Above that temperature PD loses its effectiveness and material behaves like a fresh sample. Suppression of polarization below TC 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 BaTiO3 ceramics up to 23 % at TC. Above a critical Li doping amount, both negative and positive electrocaloric effect are observed in the same sample.
关键词： Aging,BaTiO3,Li-doping,Electrocaloric effect,Defect dipoles
更新于2025-11-14 17:28:48
-
Phase-transition induced giant negative electrocaloric effect in a lead-free relaxor ferroelectric thin film
摘要： Ferroelectric/antiferroelectric thin/thick films with large positive or negative electrocaloric (EC) effects could be very useful in designing commercial refrigeration devices. Here, a giant negative EC effect (maximum ΔT ≈ ?42.5 K with ΔS ≈ ?29.3 J K?1 kg?1) comparable to the best positive EC effects reported so far is demonstrated for 0.5(Ba0.8Ca0.2)TiO3–0.5Bi(Mg0.5Ti0.5)O3 (BCT–BMT) lead-free relaxor ferroelectric thin films prepared on Pt(111)/TiOx/SiO2/Si substrates using a sol–gel method. An electric-field induced structural phase transition (nanoscale tetragonal and orthorhombic to rhombohedral) along the out-of-plane [111] direction plays a very key role in developing the giant negative EC effect. This breakthrough will pave the way for practical applications of next-generation refrigeration devices with high cooling efficiency in one cycle by ingeniously utilizing and combining both the giant negative and positive EC effects. Moreover, a large energy density of 51.7 J cm?3 with a high power density of 1.15 × 1010 W kg?1 at room temperature is also achieved in the thin film, indicating that it is also an attractive multifunctional material for energy storage.
关键词： lead-free,energy storage,electrocaloric effect,phase transition,thin film,relaxor ferroelectric
更新于2025-11-14 17:28:48
-
Designing soft pyroelectric and electrocaloric materials using electrets
摘要： A temperature variation can electrically polarize a pyroelectric material. In its converse manifestation, the electrocaloric effect entails a change in temperature due to the application of an electric field. These phenomena have wide applications ranging from infrared detection sensors and solid-state refrigeration to energy harvesting. However, the pyroelectric–electrocaloric effect is typically observed in certain classes of hard, brittle crystalline materials that must satisfy a stringent set of lattice symmetry conditions. Some limited experiments have however demonstrated that embedding immobile charges and dipoles in soft foams (thus creating an electret state) may lead to a pyroelectric-like response as well as large deformations desired from soft matter. In this work, we develop a systematic theory for coupled electrical, thermal and mechanical responses of soft electrets. Using simple illustrative examples, we derive closed-form explicit expressions for the pyroelectric and electrocaloric coefficients of electrets. While pyroelectricity in electrets has been noted before, our derived expressions provide a clear quantitative basis to interpret (and eventually design) this effect as well as insights into how the geometrically nonlinear deformation and Maxwell stress give rise to its emergence. We present conditions to obtain a larger pyroelectric and electrocaloric response. In particular, the electrocaloric effect is predicted for the first time in such materials and we show that a proper design and a reasonable choice of materials can lead to a temperature reduction of as much as 1.5 K under the application of electrical fields of 10 MV cm?1.
关键词： material design,soft matter,theoretical framework,electrets,pyroelectricity,electrocaloric effect
更新于2025-09-23 15:23:52
-
Effect of an electric field on the electrocaloric response of ferroelectrics
摘要： The electrocaloric effect of the model ferroelectric BaTiO3 was investigated using phenomenological theory. The results indicate that the applied electric field strength is a key factor for the induced electrocaloric response and there are two distinguishing electrocaloric responses. When a moderate electric field is applied, the electrocaloric temperature variation is small but the electrocaloric strength is high. In contrast, the electrocaloric temperature variation is large but electrocaloric strength is low when a very high electric field is applied. These results are consistent with the experimental observations on BaTiO3 based bulk and thin film ferroelectric materials.
关键词： BaTiO3,ferroelectrics,electrocaloric effect
更新于2025-09-23 15:23:52
-
Nanoconfinement-Induced Giant Electrocaloric Effect in Ferroelectric Polymer Nanowire Array Integrated with Aluminum Oxide Membrane to Exhibit Record Cooling Power Density
摘要： The electrocaloric effect (ECE) offers a unique mechanism to realize environmentally friendly and highly efficient solid-state cooling that completely differs from the conventional vapor-compression refrigeration. Here a new class of hybrid films composed of ferroelectric polymer nanowire array and anodic aluminum oxide (AAO) membrane is reported, which displays pronounced ECE driven by relatively low electric fields. Under confinement and orientation of AAO channels on the crystallization of the polymer, the polymer nanowire array shows substantially enhanced ECE that is about three times that of the corresponding thin films. Simultaneously, the integrated AAO membrane forms thermally conducting channels for the polymer nanowires, enabling the efficient transfer of cooling energy and operation of the EC materials under high frequencies, which are unattainable based on the currently available EC structures. Consequently, the integrated polymer nanowire–AAO hybrid film exhibits the state-of-the-art cooling power density, outperforming the current ferroelectric polymers, ceramics, and composites. This work opens a new route for the development of scalable, high-performance EC materials for next-generation refrigeration.
关键词： electrocaloric effect,nanoconfinement,cooling power density,heat transfer,ferroelectric polymer
更新于2025-09-23 15:22:29
-
Understanding the Role of Ferroelastic Domains on the Pyroelectric and Electrocaloric Effects in Ferroelectric Thin Films
摘要： Temperature- and electric-field-induced structural transitions in a polydomain ferroelectric can have profound effects on its electrothermal susceptibilities. Here, the role of such ferroelastic domains on the pyroelectric and electrocaloric response is experimentally investigated in thin films of the tetragonal ferroelectric PbZr0.2Ti0.8O3. By utilizing epitaxial strain, a rich set of ferroelastic polydomain states spanning a broad thermodynamic phase space are stabilized. Using temperature-dependent scanning-probe microscopy, X-ray diffraction, and high-frequency phase-sensitive pyroelectric measurements, the propensity of domains to reconfigure under a temperature perturbation is quantitatively studied. In turn, the “extrinsic” contributions to pyroelectricity exclusively due to changes between the ferroelastic domain population is elucidated as a function of epitaxial strain. Further, using highly sensitive thin-film resistive thermometry, direct electrocaloric temperature changes are measured on these polydomain thin films for the first time. The results demonstrate that temperature- and electric-field-driven domain interconversion under compressive strain diminish both the pyroelectric and the electrocaloric effects, while both these susceptibilities are enhanced due to the exact-opposite effect from the extrinsic contributions under tensile strain.
关键词： electrocaloric effect,ferroelastic domains,ferroelectricity,pyroelectric effect,entropy
更新于2025-09-10 09:29:36
-
Large electrocaloric effect in tetragonal perovskite 0.03Bi(Mg1/2Ti1/2)O3–0.97(0.875Bi1/2Na1/2TiO3–0.125BaTiO3) lead-free ferroelectric ceramics
摘要： In this work, we reported a large electrocaloric effect (ECE) in tetragonal perovskite 0.03 Bi(Mg1/2Ti1/2)O3–0.97 (0.875Bi1/2Na1/2TiO3–0.125BaTiO3) ceramic. It was found that the composition demonstrates a coexisting state of the ferroelectric P4mm and relaxor P4bm. Due to the ?eld-induced phase transition from relaxor with P4bm symmetry to ferroelectric with P4mm symmetry, a positive ECE is observed in the temperature range of 25–130 °C. Under an electric ?eld of 4 kV/mm, a large temperature change ΔT of 0.75 °C was achieved at 80 °C, and the EC responsivity ΔTmax/ΔE of 0.19 K·cm/kV, indicating a promising lead-free material for potential application in solid-state refrigerators.
关键词： Sodium bismuth titanate,Tetragonal perovskite,Lead-free ceramics,Electrocaloric effect
更新于2025-09-09 09:28:46