Electrocaloric characterization of samarium doped barium titanate ceramics synthesized by sol-gel process

In this work, the effect of Sm ionic doping in BaTiO3 for electrocaloric effect has been studied. Ba1-xSmxTiO3 (x = 0, 0.02, 0.04, 0.06) ceramics were made via sol-gel method. All samples, according to XRD analysis, have a tetragonal symmetry that decreases with increasing Sm concentration. SEM micrographs revealed that, with the exception of the pure BaTiO3, all samples exhibited a dense microstructure. Compared to pure BaTiO3, thermal analysis using DSC measurement showed that as samarium content increases, the phase transition temperature decreases and the endothermic peak flattens. Dielectric measurements showed that the value of the loss tangent decreased and the value of the dielectric constant increased as the samarium doping concentration increased. Ferroelectric experiments highlighted that all samples were in the ferroelectric phase at room temperature. The remnant polarization increased with increasing Sm concentration. For Sm-doped ceramics the maximum value was Pr = 5.2 μC/cm2 for x = 6 %, under a maximum applied field of 25 kV/cm. An original customized pASC calorimeter was used in a direct method to study isothermal heat production resulting from the electrocaloric effect (ECE). According to the ECE results, the partial substitution of barium by samarium lowers the Curie temperature, which in turn lowers the temperature at which the electrocaloric effect is strongest. This extends the temperature range at which ECE can be used. For the sample Ba0.96Sm0.04TiO3, the maximum electrocaloric effect recorded is reached with a ΔT/ΔE = 0.343 K.m/MV.