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International audience; Ba0.85Ca0.15Zr0.10Ti0.90O3 (BCZT) relaxor ferroelectric ceramics exhibit enhanced energy storage and electrocaloric performances due to their excellent dielectric and ferroelectric properties. In this study, the temperature-dependence of the structural and dielectric properties, as well as the field and temperature-dependence of the energy storage and the electrocaloric properties in BCZT ceramics elaborated at low-temperature hydrothermal processing are investigated. X-ray diffraction and Raman spectroscopy results confirmed the ferroelectric–paraelectric phase transition in the BCZT ceramic. At room temperature and 1 kHz, the dielectric constant and dielectric loss reached 5000 and 0.029, respectively. The BCZT ceramic showed a large recovered energy density (Wrec) of 414.1 mJ cm−3 at 380 K, with an energy efficiency of 78.6%, and high thermal-stability of Wrec of 3.9% in the temperature range of 340–400 K. The electrocaloric effect in BCZT was explored via an indirect approach following the Maxwell relation at 60 kV cm−1. The significant electrocaloric temperature change of 1.479 K at 367 K, a broad temperature span of 87 K, an enhanced refrigerant capacity of 140.33 J kg−1, and a high coefficient of performance of 6.12 obtained at 60 kV cm−1 make BCZT ceramics potentially useful coolant materials in the development of future eco-friendly solid-state refrigeration technology.

Lead-free BaTi0.89Sn0.11O3 (BTSn) ceramic was elaborated via a solid-state reaction method and its dielectric, ferroelectric, energy storage, electromechanical as well as electrocaloric properties were investigated at 25 kV/cm. Pure perovskite structure was confirmed by X-ray diffraction analysis. The maximum of the dielectric constant was found to be 17390 at 41 °C. The enhanced total energy density, the recovered energy density, and the energy storage efficiency of 92.7 mJ/cm3, 84.4 mJ/cm3, and 91.04 %, respectively, were observed at 60 °C. In contrast, the highest energy storage efficiency of 95.87 % was obtained at 100 °C. At room temperature, the electromechanical strain and the large-signal piezoelectric coefficient reached a maximum of 0.07 % and 280 pm/V. The large electrocaloric effect of 0.71 K and the electrocaloric responsivity of 0.28 × 10-6 K mm/kV at 49 °C under 25 kV/cm were indirectly determined via Maxwell approach and the measured ferroelectric polarization P(T,E). The electrocaloric response was also modelled by exploiting the Landau-Ginzburg-Devonshire (LGD) phenomenological theory. The modelling result of 0.61 K at 50 °C under 25 kV/cm supports the experimental findings. We conclude that BTSn lead-free ceramic is a promising candidate for potential applications in high-efficiency energy storage devices and solid-state refrigeration technology.

The lead-free Ba0.85Ca0.15Zr0.10Ti0.90O3 (BCZT) relaxor ferroelectric ceramic has aroused much attention due to its enhanced piezoelectric, energy storage and electrocaloric properties. In this study, the BCZT ceramic was elaborated by the solid-state reaction route, and the temperature-dependence of the structural, electrical, piezoelectric, energy storage and electrocaloric properties was investigated. X-ray diffraction analysis revealed a pure perovskite phase, and the temperature-dependence of Raman spectroscopy, dielectric and ferroelectric measurements revealed the phase transitions in the BCZT ceramic. At room temperature, the strain and the large-signal piezoelectric coefficient reached a maximum of 0.062% and 234 pm V−1, respectively. Furthermore, enhanced recovered energy density (Wrec = 62 mJ cm−3) and high-energy storage efficiency (η) of 72.9% at 130 °C were found. The BCZT ceramic demonstrated excellent thermal stability of the energy storage variation (ESV), less than ±5.5% in the temperature range of 30–100 °C compared to other lead-free ceramics. The electrocaloric response in the BCZT ceramic was explored via the indirect approach by using the Maxwell relation. Significant electrocaloric temperature change (ΔT) of 0.57 K over a broad temperature span (Tspan = 70 °C) and enhanced coefficient of performance (COP = 11) were obtained under 25 kV cm−1. The obtained results make the BCZT ceramic a suitable eco-friendly material for energy storage and solid-state electrocaloric cooling devices.

Ba0.85Ca0.15Zr0.10Ti0.90O3 (BCZT) lead-free ceramics demonstrated excellent dielectric, ferroelectric, and piezoelectric properties at the morphotropic phase boundary (MPB). So far, to study the effect of morphological changes on dielectric and ferroelectric properties in lead-free BCZT ceramics, researchers have mostly focused on the influence of spherical grain shape change. In this study, BCZT ceramics with rod-like grains and aspect ratio of about 10 were synthesized by surfactant-assisted solvothermal route. X-ray diffraction (XRD) and selected area electron diffraction (SAED) performed at room temperature confirm the crystallization of pure perovskite with tetragonal symmetry. Scanning electron microscopy (SEM) image showed that BCZT ceramics have kept the 1D rod-like grains with an average aspect ratio of about 4. Rod-like BCZT ceramics exhibit enhanced dielectric ferroelectric (ɛr = 11,906, tanδ = 0.014, Pr = 6.01 μgC/cm2, and Ec = 2.46 kV/cm), and electrocaloric properties (ΔT = 0.492 K and gZ = 0.289 (K·mm)/kV at 17 kV/cm) with respect to spherical BCZT ceramics. Therefore, rod-like BCZT lead-free ceramics have good potential to be used in solid-state refrigeration technology.

International audience; The effects of 2% Zr introduction in Ba0.8Ca0.2TiO3 (BCT) system on its electrical and electrocaloric properties was investigated. BCT and Ba0.8Ca0.2Zr0.02Ti0.98O3 (BCZT) ceramics synthesized by solid-state processing were crystallized in a pure perovskite phase with a group space P4mm. After Zr insertion, the enhanced dielectric constant was obtained around the Curie temperature (Tc) in BCZT ceramic (εr = 6330 at Tc = 388 K) compared to BCT ceramic (εr = 5080 at Tc = 388.6 K). Moreover, the large-signal piezoelectric coefficient (d∗33) was improved from 270 to 310 pm/V in BCT and BCZT ceramics, respectively, under a moderate electric field of 25 kV/cm. The electrocaloric effect was determined via indirect and direct methods. In the indirect approach, the electrocaloric temperature change (ΔT) was calculated via Maxwell relation, and the measured ferroelectric polarization P (E, T) extracted from the P–E curves recorded at 24 kV/cm. The maximum values of ΔT = 0.68 K and the electrocaloric responsivity ζ = 0.283 K mm/kV obtained at 385 K in BCZT ceramic were found to be higher than those observed in BCT ceramic (ΔT = 0.37 K and ζ = 0.154 K mm/kV at 387 K). In the direct approach, ΔT was measured utilizing a modified high-resolution calorimeter at 14 kV/cm. As the direct method is more sensitive to the latent heat, it provided larger values for smaller applied field, i.e., ΔT = 0.474 and 0.668 K for BCT and BCZT ceramics, respectively. A significant ζ of 0.477 K mm/kV was obtained in BCZT at 385 K and 14 kV/cm that matches the values found in lead-based materials. These results suggest that BCZT lead-free ceramics could have an excellent potential to be used in solid-state refrigeration applications.