A giant electrocaloric effect (ECE) near room temperature is reported in a lead‐free bulk inorganic material. By tuning Ba(ZrxTi1–x)O3 compositions which also exhibit relaxor ferroelectric response ...to near the invariant critical point, the Ba(ZrxTi1–x)O3 bulk ceramics at x ∼ 0.2 exhibit a large adiabatic temperature drop of 4.5 K, a large isothermal entropy change of 8 J kg−1 K−1, and a large EC coefficient (|ΔTc/ΔE| = 0.52 × 10−6 KmV−1 and ΔS/ΔE = 0.93 × 10−6 J m kg−1 K−1 V−1) over a 30 K temperature range. These properties added together indicate a general solution of the electrocaloric materials with high performance for practical cooling applications.
A giant electrocaloric effect (ECE), i.e., a large adiabatic temperature drop (ΔTc) with a high electrocaloric coefficient (ΔTc/ΔE), is demonstrated in a modified lead‐free ferroelectric ceramic, BaTiO3, over a broad temperature range near the invariant critical point (ICP). Multiphase coexistence near ICP provides a larger entropy change compared with that of a pure ferroelectric–paraelectric transition. When coupled with the relaxor behavior, this leads to the observed giant ECE in BZT (x = 0.2) over a broad temperature range
•Tailoring the first-order O-T phase transition strategy was adopted in this work.•The large ΔT of 0.3 K is attained in 0.6BST-0.4BZT ceramic at room temperature.•The ΔT of 0.53 K is achieved at ...342 K due to the quadruple point coexistence.
The development of refrigeration technology has burgeoned in response to the challenges posed by global warming. Notably, electrocaloric materials have garnered significant attention for their potential in miniaturization and high efficiency. However, investigations into the electrocaloric response in proximity to orthorhombic-tetragonal phase transition in BaTiO3-based ferroelectric ceramics remain scarce. In this study, we employ a lead-free x(Ba0.7Sr0.3)TiO3-(1-x)Ba(Zr0.2Ti0.8)O3 polycrystalline ceramics fabricated through the solid-state reaction method. The comprehensive analysis includes elucidation of the phase structure, surface morphologies, dielectric properties, domain switching behavior, and the electrocaloric effect. Integrating these findings with the phase diagram unveils optimal adiabatic temperature change (ΔT) achieved within the quadruple point coexistence region. That is, the highest ΔT of 0.53 K is achieved for x = 0.4 ceramic, which is attributed to the increased entropy resulting from multiple polar phases. Remarkably, the highest ΔT of 0.3 K is attained in x = 0.6 ceramic under a low driving electric field of 30 kV/cm at room temperature, precisely within the orthorhombic-tetragonal transition temperature. The investigation underscores the efficacy of regulating the first-order orthorhombic-tetragonal phase transition to achieve exceptional electrocaloric responses at room temperature.
The development of high-performance electrocaloric (EC) materials is crucial for solid-state refrigeration applied in micro-electromechanical systems. Herein, a large room-temperature EC response is ...realized in (1 – x)(K0.49Na0.49Li0.02)(Nb0.8Ta0.2)O3–xCaZrO3 (KNLNT–xCZ) benefiting from a relaxor enhancement effect and multilayer ceramic construct. The relaxor enhancement effect is because the long-range order is broken by adding CaZrO3, which is in favor of enhancing the temperature change (ΔT) and broadening the temperature span (T span) at room temperature. A ΔT of 0.48 K in the KNLNT–12CZ ceramic is ∼5 times higher than that in the KNLNT–8CZ ceramic at 30 °C. KNLNT–12CZ also exhibits good temperature stability, and the T span is up to 65 K. In addition, the multilayer ceramic construct improves the breakdown electric field (E b) through diminishing defects, leading to a booming ΔT of 3.2 K at 30 °C under 250 kV cm–1 via a direct measurement. The work proposes an avenue for developing high-performance EC materials with a large EC response and broad T span in solid-state refrigeration.
Although the solid-state cooling technology based on electrocaloric response has been considered a promising refrigeration solution for microdevices, the mediocre dipolar entropy change ΔS impedes ...its practical applications. In this work, ΔS of a conventional ferroelectric thin film, namely, 0.94(Bi0.5Na0.5)TiO3-0.06BaTiO3 (BNBT), was greatly improved through engineering the nanodomain structures. The number of zero-field polar states and saturation polarization were greatly increased concomitant with a weakened strength of polar correlation in the thin films, owing to the local stabilization of strongly tetragonally distorted nanoclusters (tetragonality of ∼1.25) by modulating the growth conditions during the thin film deposition process. Consequently, a giant ΔS value of ∼ –48.5 J K–1 kg–1 (corresponding to ΔT = ∼27.3 K) and a wide window of operating temperature (>70 °C) were obtained near room temperature under a moderate electric field of 1330 kV cm–1. Moreover, our engineered BNBT thin film exhibits decent fatigue endurance; i.e., a substantial electrocaloric effect over a broad span of temperature can be sustained after 5 × 107 cyclic loading of the electric field. This work provides a universal design strategy for significantly improving the close-to-room-temperature electrocaloric performance of Bi-based ferroelectric thin films without the need of compositional or architectural complexity.
On page 1300, by modifying BaTiO3 ceramics to their invariant critical points, Ba(ZrxTi1−x)O3 bulk ceramics exhibit a large electrocaloric effect (ECE). Q. M. Zhang and co‐workers show tetragonal, ...orthorhombic, and rhombohedral structures behind a larger cubic structure, with dipoles inside. A flat‐panel cooling device is schematically drawn as a 3D multi‐layered ECE cooling device. The temperature gradient is shown by rainbow color, in which blue indicates the cold end and the other warmer colors indicate higher temperatures.
We investigate the influence of grain size on the electrocaloric properties of ferroelectric systems using Landau theory. We study how the phase transformation temperature and electrocaloric property ...can be tuned by changing the grain size close to the critical size. Our results show that the electrocaloric coefficient at room temperature can be greatly enhanced by controlling the grain size. In particular, we calculate the adiabatic temperature change, ΔT to be ≈2 K with an electric field difference ΔE = 50 kV cm−1 at room temperature in a model for PbTiO3 ceramics. The results provide an approach to improving the electrocaloric properties at room temperature in experiments by engineering the grain size.
Could ferroelectric nanoparticles potentially be a means for large temperature changes important in solid‐state refrigeration? By controlling particle size, the ferroelectric‐to‐paraelectric phase transformation temperature can be tuned to room temperature and gives rise to a high electrocaloric coefficient. This provides a large enhancement in the electrocaloric response and adiabatic temperature change at room temperature.
The determination of the breakdown voltage and the diagnostics of the prebreakdown state of a material is a topical problem of studying characteristics of insulating materials and structures based on ...them when applying an external electric field. The new effective method of the diagnostics of the prebreakdown state of multilayer structures (MLC) based on the ferroelectric–relaxor 0.55Pb–Mg
1/3
Nb
2/3
O
3
–0.45-PbSc
1/2
Nb
1/2
O
3
(PMN–PSN) is considered. The method is based on an analysis of the dynamics of changing the MLC surface temperature during applying an external electric field. A series of the MLC samples has been tested under action of electric field
E
= 10–120 kV/cm and the ambient temperature from room temperature to 80°C. The critical electric field that characterizes the prebreakdown state of the PMN–PSN multilayer structures and, correspondingly, restricts the upper limit of operating voltages for the electrocaloric applications has been determined.
Despite the challenges of practical implementation, electrocaloric (EC) cooling remains a promising technology because of its good scalability and high efficiency. Here, we investigate the ...feasibility of an EC cooling device that couples the EC and electromechanical (EM) responses of a highly functionally, efficient, lead magnesium niobate ceramic material. We fabricated multifunctional cantilevers from this material and characterized their electrical, EM and EC properties. Two active cantilevers were stacked in a cascade structure, forming a proof-of-concept device, which was then analyzed in detail. The cooling effect was lower than the EC effect of the material itself, mainly due to the poor solid-to-solid heat transfer. However, we show that the use of ethylene glycol in the thermal contact area can significantly reduce the contact resistance, thereby improving the heat transfer. Although this solution is most likely impractical from the design point of view, the results clearly show that in this and similar cooling devices, a non-destructive, surface-modification method, with the same effectiveness as that of ethylene glycol, will have to be developed to reduce the thermal contact resistance. We hope this study will motivate the further development of multifunctional cooling devices.
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