In this study, NaNbO3 (NN) was introduced into Ba(Zr0.15Ti0.85)O3 (BZT) to form a solid solution with relaxor ferroelectric characteristics. The dielectric breakdown strength (BDS) of the specimen ...with 6 mol.% NN reached 680 kV/cm, the corresponding recoverable energy storage density (Wrec) was 5.15 J/cm3, and the energy storage efficiency (η) was 77%. The dissolution of Na + ions at the A position and Nb5+ ions at the B position of the perovskite structure reduced the concentration of oxygen vacancies in the lattice and compensated for defects. The doped ceramics exhibited lower dielectric loss and better thermal stability: the Wrec value was 2 ± 1% J/cm3 at 30–120 °C. In particular, in the 0.02NN ceramics, a ΔT of 1.81 K was achieved at 130 kV/cm, and the operating temperature zone expanded with the increase in doping concentration. The introduction of NN resulted in BZT ceramics that possess excellent energy storage performance and electrocaloric effect properties.
•Inducing relaxor evolution by adjusting intrinsic A-site Na+/K+ ratio.•Achieving large combined electromechanical and electrocaloric responses.•Realizing a larger electrocaloric endothermic peak at ...a low electric field.•Obtaining high electrocaloric strength and large electrostrictive coefficient.•Broadening the operating-temperature span.
Self-actuating cooling materials based on synergistic electromechanical (EM) and electrocaloric (EC) responses are expected to lead next-generation of intelligent cooling devices. However, most current materials with the two responses present poor performance, narrow operation-temperature span and high driving electric field, and even contain toxic lead. Here, environmentally benign lead-free Bi0.5Na0.5TiO3-based (BNT) system was designed to achieve large combined response of two effects in a large temperature span by adjusting intrinsic A-site Na+/K+ ratio to induce relaxor evolution. Simultaneously, high EC strength and large electrostrictive coefficient over a wide temperature range were obtained to resolve these challenges. The local-structural evolution is studied in detail to provide a theoretical basis for future application of this intelligent material. A novel asymmetric EC response presenting a larger endothermic peak was realized at a low electric field (<3 kV mm−1), which can provide a guideline for the development of low-driving-field EC materials to a certain extent. The phase-field simulation was performed to predict this unique behavior by describing the corresponding dipole coupling states under various electric fields.
Electrocaloric refrigeration based on electrocaloric effect (ECE) is a promising high efficiency and eco-friendly way to replace gas compression refrigeration. Herein, we have systematically ...investigated the electrocaloric effect in lead-free Bi0·5Na0·5TiO3 (BNT) ferroelectric ceramics synthesized via a conventional solid-state route. The high electric breakdown strength of the samples aided in measuring ΔT at higher applied electric fields. A large ECE (ΔT) of 3.2 K@ 65 kV/cm and a wide temperature span from 340 to 380 K with high ΔT was obtained for double-calcined BNT ceramics near the depolarization temperature (362 K). The outstanding ECE response can be attributed to the evolution of polar nano regions (PNRs). Our work suggests that this material is a promising electrocaloric material for applications in solid-state refrigeration systems with a broad range of operating temperatures.
Display omitted
•Bi0.5Na0.5TiO3 (BNT) ceramics were synthesized by the solid-state method.•Porosity-free and compact grains were obtained in doubly calcined BNT ceramics.•Presence of polar nano regions gave rise to relaxor behavior.•Large ECE (ΔT = 3.2 K) and EC efficiency (ΔT/ΔE = 0.61 K-mm/kV) were obtained near Td.•Large ΔT maintained in a wide temperature span from 340 to 380 K.
A small electrocaloric effect (ECE) is usually observed in aliovalent doped ferroelectric ceramics since decreased polarization is usually present. In this work, the high ECE is achieved in a barium ...titanate BaTiO3 (BT)-based ceramic by introducing defect polarization to enhance the ferroelectric polarization and polarization change. The defect dipoles consisting of donor ion and barium vacancy, or barium and oxygen vacancies were formed in samarium-doped (Ba1−1.5xSmx)TiO3 ceramics. The phase and defect structures, and dielectric and ferroelectric properties are analyzed to confirm the evolution of charge compensation states and defect structures, and the influences of defects on polarization rotation and ECE. An enhanced ferroelectric polarization and high internal bias field are present in the ceramic with a suitable defect dipole effect, leading to a high polarization change before/after applying an electric field, causing an enhanced ECE. Finally, a high electrocaloric temperature change of ∼1.11 K and a large electrocaloric strength of ∼0.037 K·cm kV−1 were achieved under a low electric field of 30 kV/cm, indicating that forming suitable defect dipoles can optimize the ECE. This work provides a significant paradigm for tuning ECE in ferroelectric materials via defect regulation.
•Enhanced ECE is achieved via introducing defect dipoles/polarization into BT-based ceramics.•Different charge compensation states and defect structures are shown by changing Sm3+ doped content.•High polarization change consisting of spontaneous & defect polarization change contributes to the high ECE.•High ΔT of ∼1.11 K and large ΔT/ΔE of ∼0.037 K·cm kV−1 are obtained under a low electric field.
Secondary electrocaloric effect (ECE) arising from piezoelectricity combined with crystal thermal expansion was often overlooked in ECE studies of ferroelectric ceramics. This work mainly evaluated ...the primary ECE (ΔTECE) and secondary ECE (∆T2) of eco-friendly BaSnxTi1-xO3 (BSnT100x, 0 < x < 12%) ceramics near the tetragonal (T)-orthorhombic (O) transition. Intriguingly, a maximum overall ΔT ~ 0.85 K was obtained at the T-O transition (~300 K) of BSnT2 under an electric field of 2 kV/mm, with ∆TECE and ∆T2 amounting to ~0.75 K, ~0.1 K, respectively. This ECE result is ~40% superior than the larger ECE reported previously for BSnT system.
Display omitted
The ferroelectric refrigeration technology based on electrocaloric effect (ECE) is a promising environmental way to replace the gas compression refrigeration. Lead-free bismuth sodium titanate ...(NBT)-based relaxor ferroelectric ceramics have advantages of a large ECE within a wide temperature range around the depolarization temperature (Td), but the Td of pure NBT is too high to meet the application requirements. Here, we systematically studied the electrocaloric effect in (0.95-x)(Na0.5Bi0.5)TiO3-0.05SrTiO3-x(K0.5Na0.5)NbO3 ((0.95-x)NBT-0.05ST-xKNN) ceramics and its relation with the relaxor behavior. The addition of KNN enhances the relaxor character, and shifts the Td from 120 °C to a low temperature even below 0 °C. The directly measured ECE shows a peak of high ∆Tmax = 0.88 K (@ 60 °C) for x = 0.05 under an electric field of 40 kV/cm and a wide temperature span of 79 °C (≥ 80% of ∆Tmax). The x = 0.07 sample exhibits the optimal room-temperature ECE performance with a high ∆T30 °C = 0.71 K because the non-ergodic – ergodic phase transition occurs near room temperature. The electric field–temperature phase diagram reveals the origin of the enhanced ECE as the electric-field-induced transition between polar nanoregions (PNRs) and long-range ferroelectric domain.
The very sharp first‐order phase transition in single‐crystal BaTiO3 permits thermal changes to be driven by very small electric fields. The resulting giant electrocaloric strength could be exploited ...in future cooling devices that operate at high frequency.
The electrocaloric effect (ECE) in gadolinium and tin ions doped lead lanthanum zirconate titanate ceramics was investigated. Five samples with different compositions and hence different relaxor ...behaviors and polarization properties were prepared via a conventional solid-state reaction process. The ECE was measured directly by a high resolution thermometer from 293 K to 423 K. The results show that the ECE is mainly determined by the number of polarization states and polar-correlation strength. Furthermore, the results reveal that the temperature variation of ECE around Curie temperature is associated with the generation rate, activation energy, size and freezing temperature of polar nanoregions. As a result, Sn doped PLZT composition exhibits the best ECE, i.e., a peak ΔT > 2 K obtained at 5 MV/m, and ΔT > 1.78 K achieved in the whole temperature range measured at the same field, which are very attractive for high performance ECE devices.
The electrocaloric effect (ECE) offers a pathway to environmentally sustainable and easily miniaturized refrigeration technology, positioning it as a front-runner for the next generation of ...solid-state cooling solutions. This research unveils a remarkable ECE in a finely tuned (Ba0.86Ca0.14)0.98La0.02Ti0.92Sn0.08O3 ceramic, exhibiting a temperature shift (ΔT) of 1.6 K across more than 85% of the maximum ΔT (ΔTmax) and spanning an exceptionally wide operational range of 92 K. Our investigation on dielectric responses and ferroelectric polarization-electric field (P–E) loops suggests that the broad operational scope results from the fragmentation of extended ferroelectric domains into smaller domains and polar nano-regions (PNRs) supported by PFM analysis. Furthermore, the introduction of La enhances spontaneous polarization by significantly extending the maximum electric field that can be applied, facilitating high-performance ECE at ambient temperature. This study positions BaTiO3-based lead-free ceramic as a sustainable alternative for addressing the cooling demands of modern electronic components, marking a significant stride toward next-generation solid-state refrigeration.
Display omitted
•An ECE of 1.6 K, exceeding 85% of ΔTmax over a 92 K range, was achieved in (Ba₀.₈₆Ca₀.₁₄)₀.₉₈La₀.₀₂Ti₀.₉₂Sn₀.₀₈O₃ ceramic.•Approach in this study offers a viable pathway for other lead-free materials to achieve high-performance ECE.
Electric-field-driven polarization in ferroelectrics delivers extraordinary electro-caloric, electro-optic, and electromechanical properties, etc. However, the controllable multifunctional ...ferroelectric switching between different electro-related performances still faces great challenges and deserves study. Herein, multifunctional BaTiO3 (BT)-based ferroelectrics are conceived tuning electrocaloric and electrostrictive properties by controlling doping site of dopants, namely site selective doping strategy. The well-concerned Ce is selected for its multivalent trait (Ce3+/Ce4+) and effective adjustment of Curie temperature (TC) in BT. Guided by the distinguished dielectric characteristics via doping Ce3+ in Ba site or Ce4+ in Ti site, BT-based ferroelectrics can direct at different applications. For Ba-site doping, in conjunction with ion-size mismatch effect and defect engineering, manipulating TC to room temperature (RT) and driving second-order-like phase transition are obtained simultaneously. Then, large electrocaloric temperature change (∆Tmax=1.3 K) over a broad temperature span (∆T>1 K, 37~70 ℃) is achieved, which is crucial in developing zero-global-warming-potential refrigeration near RT. For Ti-site doping, unique diffuse phase transition is observed without sacrificing TC, leading to multiphase structures and the formation of nanosize domains, hence facilitating polarization rotation. Therefore, an enhanced electrostrictive strain (S>0.17%) with ultra-low hysteresis (Hhyst<5%) among a wide temperature range is obtained, which challenges toxic lead-contained counterparts in actuators.
Display omitted
