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Abstract 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 low-temperature 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 properties due to an enhancement of densification. This work may provide a new strategy to design ferroelectric materials with enhanced properties. Graphical abstract Image Highlights • Novel way for the synthesis of lead-free BCZT ferroelectric relaxors with different grain size and grain size distribution. • Unfolding the effects of grain size and grain size distribution on the dielectric properties of lead-free BCZT ferroelectric ceramics. • Design of highly dense BCZT with improved dielectric properties. [ABSTRACT FROM AUTHOR]

Highlights: [•] Lead free Ba0.8Ca0.2Ti0.8Ge0.2O3 ceramics. [•] Dielectric and ferroelectric properties. [•] Low coercive field for polarization switching. [•] Change of the nature of BaTiO3 phase transition by co-doping. [Copyright &y& Elsevier]

Lanthanum (La) incorporation in the (Ba 0.8 Ca 0.2 )TiO 3 (BCT) matrix induces enhancement of electrocaloric effect, decrease of Curie temperature and increase of dielectric permittivity. We studied the influence of La substitution ceramics on grain size and electrocaloric effect (ECE) in BCT matrix using both indirect and direct methods. From ferroelectric polarization and pyroelectric measurements, we calculate ECE response versus temperature for all the (Ba 0.8 Ca 0.2 ) 1-x La 2x/3 TiO 3 (xBCTL) ceramics compositions ranging from x = 0 to 0.05. The results showed good agreement between the two methods at the same applied electric field. A maximal value of electrocaloric (EC) temperature change ΔT = 0.30 K was obtained at 25 kV/cm corresponding to an EC responsivity ξ = 0.120 × 10 −6 K m/V, in a wide temperature region in the vicinity of the ferroelectric phase transition temperature (250 K–400 K) for x = 0.05 that places this family as very promising materials for electrocaloric applications near room temperature. [ABSTRACT FROM AUTHOR]

Over the past decades, there has been significant interest in new cooling technology based on the large electrocaloric effect observed in polymeric and inorganic ferroelectric materials. We report a dramatic impact of annealing on the electrocaloric effect observed by direct measurements in Pb 0.88 La 0.12 (Zr 0.65 Ti 0.35) 0.97 O 3 bulk ceramics (12/65/35 PLZT). In addition, the EC response was measured deep in a relaxor part of the PLZT composition phase diagram. After additional one-hour sample annealing at 600 °C, the EC response increased by about six times. Electrocaloric results confirm the existence of the significant electrocaloric response with the EC temperature change (Δ T EC) of 4.5 K at 360 K and 90 kV/cm in an annealed sample. This value exceeds previously obtained maximum Δ T EC values at the same field in perovskite relaxor ferroelectrics such as Pb(Mg1/3Nb2/3)O 3 -PbTiO 3 (PMN-PT) and 8/65/35 PLZT ceramics. The electrocaloric responsivity Δ T /Δ E = 5.09 × 10−7 Km/V determined at 360 K is among the highest observed in bulk perovskite ferroelectrics at a relatively high electric field of 90 kV/cm. • Relaxor ferroelectrics exhibit mostly an electrocaloric effect (ECE) of about 3 K. • The stress field makes the ferroelectric state more supercritical with smaller ECE. • The annealing enhances the ECE in 12/65/35 PLZT ceramics by about six times. • ECE of 4.5 K exceeds previously obtained values in bulk relaxor ferroelectrics. • The ECE responsivity is the highest observed at a relatively high electric field. [ABSTRACT FROM AUTHOR]

The Ba 0.85 Ca 0.15 Zr 0.1 Ti 0.9 O 3 (BCZT) ceramics were successfully prepared by the sol-gel process and sintered at 1420 °C. The effect of sintering times (2, 4 and 6 h) on structural, microstructural, electric properties, energy storage, and electrocaloric effect was systematically examined. X-ray diffraction (XRD) results show that all the samples crystallize in the pure perovskite structure. The morphotropic phase transition from the tetragonal to the orthorhombic phase (T-O) was identified and confirmed by Rietveld refinement. The BCZT ceramic sintered at 1420 °C for 4 h possesses a good relative density of 98% and exhibits optimal properties with a high dielectric permittivity (ε r,max) ~16310, a large electrocaloric effect coefficient (ξ) ~ 0.244Kmm/kV and a high energy storage efficiency of 63.65%. [ABSTRACT FROM AUTHOR]