Conventional refrigeration methods based on compression–expansion cycles of greenhouse gases are environmentally threatening and cannot be miniaturized. Electrocaloric effects driven by electric fi...

Interface-Charge Induced Giant Electrocaloric Effect in Lead Free Ferroelectric Thin-Film Bilayers

Study of the effect of La3+ doping on the properties of ceramics based on BaTiOx

Electrocaloric (EC) refrigeration, an EC effect based technology has been accepted as an auspicious way in the development of next generation refrigeration due to high efficiency and compact size. Here, we report the results of our experimental investigations on electrocaloric response and electrical energy storage properties in lead-free nanocrystalline (1 − x)K0.5Na0.5NbO3-xLiSbO3 (KNN-xLS) ceramics in the range of 0.015 ≤ x ≤ 0.06 by the indirect EC measurements. Doping of LiSbO3 has lowered both the transitions (T
 C
 and TO–T) of KNN to the room temperature side effectively. A maximal value of EC temperature change, ΔT = 3.33 K was obtained for the composition with x = 0.03 at 345 K under an external electric field of 40 kV/cm. The higher value of EC responsivity, ζ = 8.32 × 10−7 K.m/V is found with COP of 8.14 and recoverable energy storage of 0.128 J/cm3 with 46% efficiency for the composition of x = 0.03. Our investigations show that this material is a very promising candidate for electrocaloric refrigeration and energy storage near room temperature.

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Giant electrocaloric and energy storage performance of [(K0.5Na0.5)NbO3](1-x)-[LiSbO3] x nanocrystalline ceramics.

Temperature induced phase transitions and electrocaloric effect (ECE) of (Pb,La)(Zr,Sn,Ti)O3 (PLZST) single crystals have been comprehensively studied. Based on the in situ evolution of domain structures and dielectric properties of the PLZST crystals, the phase transitions during heating are in the sequence of orthorhombic antiferroelectric → rhombohedral ferroelectric → cubic paraelectric. Coexistence of the negative and positive ECEs has been achieved in the PLZST single crystals. A negative ECE value of −1.26 °C and enhanced electrocaloric strength of −0.21 K mm/kV near the Curie temperature have been obtained. A modified Landau model gives a satisfactory description of the experimentally observed unusual ECE. Moreover, a temperature–electric field phase diagram is also established based on theoretical analysis. Our results will help people understand better the electrocaloric family, particularly on the negative and/or positive effect in antiferroelectrics and ferroelectrics.

Temperature induced phase transformations and negative electrocaloric effect in (Pb,La)(Zr,Sn,Ti)O3 antiferroelectric single crystal

(Ba1−xSrx)(MnyTi1−y)O3 (BSMT) ceramics with x = 35, 40 mol% and y = 0, 0.1, 0.2, 0.3, 0.4, 0.5 mol% were prepared using a conventional solid-state reaction approach. The dielectric and ferroelectric properties were characterized using impedance analysis and polarization-electric field (P–E) hysteresis loop measurements, respectively. The adiabatic temperature drop was directly measured using a thermocouple when the applied electric field was removed. The results indicate that high permittivity and low dielectric losses were obtained by doping 0.1–0.4 mol% of manganese ions in (BaSr)TiO3 (BST) specimens. A maximum electrocaloric effect (ECE) of 2.75 K in temperature change with electrocaloric strength of 0.55 K·(MV/m)−1 was directly obtained at ∼21 °C and 50 kV/cm in Ba0.6Sr0.4Mn0.001Ti0.999O3 sample, offering a promising ECE material for practical refrigeration devices working at room temperature.

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Enhanced electrocaloric effect at room temperature in Mn2+ doped lead-free (BaSr)TiO3 ceramics via a direct measurement

Dielectric permittivity enhancement and large electrocaloric effect in the lead free (Ba0.8Ca0.2)1-xLa2x/3TiO3 ferroelectric ceramics

Direct and indirect electrocaloric measurements were performed on the new Tellurium (Te) doped Ba0.8Ca0.2TiO3 (BCT) ceramics. The effects of Te addition on structural, electrical, and electrocaloric properties of BCT ceramics were investigated. The incorporation of the Te element in the BCT induced the decrease of the Curie temperature and the enhancement of the electrocaloric effect. The significant electrocaloric temperature change ΔT = 1.237 K determined by the direct method was obtained at the relatively moderate field of ∼25 kV/cm in Ba0.8Ca0.2Ti(1−x)TexO3 with x = 0.02. The corresponding electrocaloric responsivity ΔT/ΔE = 0.495 × 10−6 K m V−1 is higher than that observed in pure BCT ceramics and is one of the highest reported so far in lead-free ferroelectric materials. The material's coefficient of performance was determined at the phase transition with a maximal value of 14.7.

M. Trček

Papers

Dielectric permittivity enhancement and large electrocaloric effect in the lead free (Ba0.8Ca0.2)1-xLa2x/3TiO3 ferroelectric ceramics

Lead free Ba0.8Ca0.2TexTi1-xO3 ferroelectric ceramics exhibiting high electrocaloric properties