Ferroelectric ceramic with a large electrocaloric (EC) effect at a very low electric field is very attractive in the next solid state refrigeration technology. In this work, two ...Pb(Sc0.25In0.25Nb0.25Ta0.25)O3 (PSINT) medium-entropy ceramics were successfully synthesized by a spark plasma sintering (SPS) technology, including one-step-SPS processed and two-step-SPS processed samples. A large EC effect (△T ∼ 0.85 K) with a high EC strength (△T/△E ∼ 0.021 K cm/kV) around room temperature are obtained at a very low electric field (∼40 kV/cm) in the two-step-SPS processed sample. Moreover, the working temperature range is very broad (∼120 K), which can be responsible for the high relaxation degree of the dielectric peak. It can be believed that the PSINT medium-entropy ceramics can be promising candidates for application in the next-generation EC cooling devices.
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) (K0.5Na0.5)NbO3 - ...xSrZrO3 (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 (Wrec) were calculated to be 0.62 and 0.20 J/cm3, 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.
Display omitted
•First report on electrocaloric effect in (1-x)(K0.5Na0.5)NbO3-xSrZrO3.•Large ΔT values are achieved in a wide temperature range near room temperature.•Electrocaloric responsivity is larger than the pristine KNN based ceramics.•Huge potential for electrocaloric refrigeration as a micro-cooler for devices.
Fluorite-structure antiferroelectrics Park, Min Hyuk; Hwang, Cheol Seong
Reports on progress in physics,
12/2019, Letnik:
82, Številka:
12
Journal Article
Recenzirano
Ferroelectricity in fluorite-structure oxides like hafnia and zirconia have attracted increasing interest since 2011. Two spontaneous polarizations of the fluorite-structure ferroelectrics are ...considered highly promising for nonvolatile memory applications, with their superior scalability and Si compatibility compared to the conventional perovskite-structure ferroelectrics. Besides, antiferroelectricity originating from a field-induced phase transition between the paraelectric and ferroelectric phases in fluorite-structure oxides is another highly interesting matter. It was suggested that the field-induced phase transition could be utilized for energy conversions between thermal and electrical energy, as well as for energy storage. The important energy-related applications of antiferroelectric fluorite-structure oxides, however, have not been systematically reviewed to date. Thus, in this work, the fluorite-structure antiferroelectrics are reviewed from their fundamentals to their applications based on pyroelectricity as well as antiferroelectricity. Another important application field of the fluorite-structure antiferroelectrics is the semiconductor memory devices. The fluorite-structure antiferroelectrics can be utilized for antiferroelectric random-access-memories, negative capacitance field-effect-transistors, and flash memories. Moreover, the recently reported morphotropic phase boundary (MPB) between the ferroelectric and antiferroelectric phases in this material system marks another significant progress in this material system, and thus, the fundamentals and applications of the MPB phase are also reviewed.
Ferroelectric/antiferroelectric materials are demanded for the development of future eco-friendly high-efficient electrocaloric refrigeration technology and energy-storage devices. Here, we report ...the electrocaloric effect (ECE) and an energy storage response in lead-free (1-x)K0.5Na0.5NbO3-xBaTiO3 (KNN-xBT) ferroelectric solid solution ceramics with x = 0.04, 0.06, 0.08, and 0.10 synthesized via the traditional solid-state route. The XRD and Raman spectroscopy investigations confirmed the coexistence of orthorhombic and tetragonal phases. The BT substitution has shifted the phase transitions of KNN towards the lower temperature side and also helped to diffuse the phase transitions. The maximum value of the ECE (ΔTmax), electrocaloric responsivity (ΔT/ΔE) and the recoverable energy density (Wrec) were evaluated to be around 0.70 K, 1.75 × 10−7 KmV−1 and 0.22 Jcm−3, respectively in KNN–xBT ceramics for x = 0.08 at an applied electric field of 40 kVcm−1. This study suggested that KNN-xBT material is an attractive ferroelectric material for potential applications in the design of ozone-friendly solid-state freezing technology and energy-storage devices.
The electrocaloric effect (ECE) of intrinsic-acceptor-doped ferroelectric system (1-x)Ba(Ti0.9Ce0.1)O3-x(Ba0.7Ca0.3)TiO3 (x = 0.3,0.5) has been studied by indirect and direct approaches. It was found ...that the indirect approach based on Maxwell equation is not appropriate for measuring the ECE of this acceptor-doped system. More importantly, a relatively large electrocaloric response is obtained at temperatures far below TC (maximum difference ~75 °C), which can reach 75%~90% of the maximum electrocaloric effect near TC. The unique characteristics of this acceptor-doped system have been explained by the existence of orientable defect dipoles. Our work could stimulate the design of temperature-stable electrocaloric effect through acceptor-doping.
Display omitted
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.
It is shown that a substantial enhancement of the electrocaloric (EC) effect can be achieved with a properly engineered, ceramic microstructure. In particular, a significant impact of the grain size ...on the EC effect in 0.9Pb(Mg1/3Nb2/3)O3–0.1PbTiO3 ceramics is demonstrated. The single-phase perovskite ceramics with grain sizes ranging from 2.8 to 9.4mm were prepared. The largest EC coefficient ΔTEC/ΔE is obtained for the ceramic with 5.8-μm grains, as a consequence of its larger saturation polarization.
The EC response is limited by the breakdown strength of the material, which is higher than 160kVcm−1 for the fine-grained ceramics. For the material with a ∼98% relative density and 3.6-μm grains, the large EC temperature change (ΔTEC) of 3.45°C is achieved. This value is the highest reported so far for Pb-based perovskites and is comparable to best results obtained by multi-critical-point enhancement.
The coexistence of negative and positive electrocaloric effect have been experimentally demonstrated in lead-free 0.9(K0.5Na0.5)NbO3 - 0.1SrTiO3 nanocrystalline ceramics using an indirect ...thermodynamic method. The electrocaloric response of −0.85K at 276K and 0.43K at 330K were calculated at 40kV/cm. The corresponding electrocaloric coefficient were estimated to be −0.24×10−7K·mV−1 and 0.7×10−7K·mV−1 at 273K and 333K, respectively. A large electrical storage energy density 1.46J/cm3 were achieved. The results indicate that materials possess a huge potential for electrocaloric refrigeration as a micro-cooler and energy storage capacity for electronic devices.
Display omitted
•Room temperature electrocaloric effect.•Bi0.5Na0.5TiO3-BaTiO3-based lead-free ceramics.•Relaxor PVDF-TrFE-CFE terpolymer-based nanocomposites.•PMMA coating on ceramic nanoparticles.•Reducing Joule ...heat in electrocaloric effect.
Recently, electrocaloric effect (ECE)-based cooling technology has attracted a great deal of research attention. With a relatively high energy conversion efficiency (∼70 %) and no generating greenhouse gases, ECE-based cooling technology is suitable for use in the next generation of solid-state cooling devices. In this investigation, the PMMA layer was coated on the surface of (Bi0.5Na0.5)TiO3-6BaTiO3-1.5 %BiCoO3 (BNBT-BCO) nanofillers to reduce the Joule heat of BNBT-BCO/terpolymer (P(VDF-TrFE-CFE)) nanocomposite. From the ECE measurement result, the adiabatic temperature change (ΔT) of the BNBT-BCO@P/T-15 nanocomposite film reached 10.33 °C under 90 MV/m, which is 25 % higher than that of the BNBT-BCO/T-15 nanocomposite film (no PMMA coating, ∼8.29 °C) under the same electric field. In addition, the ΔT of the BNBT-BCO@P/T-15 nanocomposite film reached 17.52 °C under 150 MV/m at room temperature. This value is approximately 60 % higher than that of the pristine terpolymer films (ΔT ∼ 10.84 °C) and 17.4 % higher than that of BNBT-BCO@P/T-20 nanocomposite film (ΔT ∼ 14.92 °C). This work creates a new approach to using the surface coating on ceramic nanoparticles to reduce the Joule heat of the nanocomposites and improving the adiabatic temperature change (ΔT) and efficiency of ECE devices.
Ba(Hf x Ti1–x )O3 ferroelectric ceramics were prepared by a conventional solid-state reaction process, and the correlation of structure, dielectric, ferroelectric, and electrocaloric properties ...were studied. The consequences indicated that the T C of Ba(Hf x Ti1–x )O3 ceramics decreased, while T T–O and T O–R increased with the increase of hafnium content. Large electrocaloric effect values of 1.64 K (117 °C) and 1.21 K (76 °C) were observed for Ba(Hf x Ti1–x )O3 with x = 0.05 compositions. And, corresponding electrocaloric coefficients respectively were 0.33 and 0.24 K·mm·kV–1. In addition, compared with the second-order phase transition region, larger electrocaloric coefficients (ΔT f /ΔE ≥ 0.19 K·mm·kV–1) were obtained in the first-order phase transition region for all compositions. Meanwhile, the maximum values of electrocaloric coefficients ΔT f /ΔE = 0.38 K·mm·kV–1 was achieved in a smaller electric field for Ba (Hf x Ti1–x )O3 with x = 0.03 compositions.
