Direct electrocaloric, structural, dielectric, and electric properties of lead-free ferroelectric material Ba0.9Sr0.1Ti1-xSnxO3 synthesized by semi-wet method
Résumé
By using the semi-wet synthesis method, lead-free ferroelectric materials Ba0.9Sr0.1Ti1-xSnxO3 with x = 0, 0.02, 0.05, and 0.10 (abbreviated as BSTS) were prepared and their structural, electric and electrocaloric properties were investigated. The X-ray diffraction (XRD) patterns show that the samples calcined at 950 degrees C have well crystallized into perovskite structure suggesting the substitution of Ti4+ by Sn4+ in BST lattice. With increasing content of Sn, the enhancement of the dielectric permittivity was observed for (0 <= x <= 0.05) and the ferroelectric transition temperature (T-c) was found to shift towards the room temperature (T-c = 20 degrees C for x = 0.10). Direct measurements of the electrocaloric effect (ECE) were performed on all samples by using the high-resolution calorimeter. It is found that Ba0.9Sr0.1Ti0.95Sn0.05O3 exhibits a high ECE temperature change of Delta T-EC = 0.188 K at an applied electric field of only 7 kV/cm. Impedance spectrum analysis of all the samples performed in the temperature range of 300-360 degrees C reveals the existence of two relaxation contributions related to the grain and grain boundaries that are well separated in frequency. Activation energies of conduction and relaxation processes were deduced for both contributions in order to determine the conduction mechanism of the studied compositions.