Articles you may be interested inElectro-caloric effect in (Ba1−xCax)(Zr0.05Ti0.95)O3: A lead-free ferroelectric material

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Thermally-stable recovered energy density and significant electrocaloric temperature change over a broad temperature span in BCZT ceramic elaborated by low-temperature hydrothermal processing.

Lead-free Ba 0.85 Ca 0.15 Ti 0.9 Zr 0.1 O 3 (BCZT) ceramics had attracted much attention for the fabrication of microelectronic devices by virtue of their excellent dielectric, ferroelectric and piezoelectric properties. To understand the effects of both mean grain size and grain size distribution on the dielectric properties of lead-free Ba 0.85 Ca 0.15 Ti 0.9 Zr 0.1 O 3 (BCZT) ferroelectric relaxors, an original method was proposed. It is based on the surfactant-assisted solvothermal processing coupled with lowtemperature conventional sintering at 1250 °C. In this way, three highly dense BCZT with different mean grain size and dissimilar grain size distribution were designed. A significant increase of dielectric properties was obtained by a control of grain size and densification process. The dielectric constants measured were ranged from 5370 to 9646 and the dielectric loss was enhanced by 70%. Surprisingly, it was evidenced that there is unequivocal link between mean grain size with dielectric properties. Indeed, it was found that the presence of high density of refined grains leads to an improvement of dielectric 2 properties due to an enhancement of densification. This work may provide a new strategy to design ferroelectric materials with enhanced properties.

Lead-free Ba0.85Ca0.15Zr0.10Ti0.90O3 (BCZT) ceramic exhibits excellent dielectric, ferroelectric and piezoelectric properties at the Morphotropic Phase Boundary (MPB). Previously, we demonstrated that the use of the anionic surfactant Sodium Dodecyl Sulfate (SDS, NaC12H25SO4) could enhance the dielectric properties of BCZT ceramic using surfactant-assisted solvothermal processing [1]. In the present study, structural, dielectric, ferroelectric properties, as well as electrocaloric effect and energy storage performances of this BCZT ceramic were thoroughly investigated. X-ray diffraction (XRD) measurements revealed the presence of single perovskite phase at room temperature with the coexistence of orthorhombic and tetragonal symmetries. In-situ Raman spectroscopy results confirmed the existence of all phase transitions from rhombohedral through orthorhombic and tetragonal to cubic symmetries when the temperature varies as reported in undoped-BaTiO3. Evolution of energy storage performances with temperature have been investigated. BCZT ceramic exhibits a high energy storage efficiency of ~80% at 120 °C. In addition, the electrocaloric responsivity was found to be 0.164×10 -6 K.m/V at 360 K.

Ba 0.85 Ca 0.15 Zr 0.10 Ti 0.90 O 3 (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 (ε r = 11,906, tanδ = 0.014, P r = 6.01 µC/cm², and E c = 2.46 kV/cm), and electrocaloric properties (ΔT = 0.492 K and  = 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. Keywords: lead-free Ba 0.85 Ca 0.15 Zr 0.10 Ti 0.90 O 3 (BCZT); rod-like Ba 0.85 Ca 0.15 Zr 0.10 Ti 0.90 O 3 (BCZT); dielectric; ferroelectric; electrocaloric effect

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