Tuning ferroelectricity by manipulating the global and local structure in a lead-free Sr-doped Ba(Ti_1-x Sn_x)O₃ceramics

Abstract

The effect of 5% Sr substitution at the Ba site in Ba(Ti1-x Snx )O3 (BTSnx ) system is investigated for x =0.05, 0.075, and 0.12 compositions. The phase transition studies were carried out using dielectric, high-resolution X-ray diffraction, and PE hysteresis loop measurements. Rietveld refinements, along with dielectric studies on strontium-doped BTSnx reveal that the inter-ferroelectric phase boundaries observed in pure BaTiO3 approach the Tc line, with morphotropic phase boundary like behaviour. The PE hysteresis loops show enhanced polarization (≈ 190%) in Sr-doped BTSn5, which is attributed to the inter-ferroelectric phase instability (which facilitates polarization rotation, phase boundary motion, and domain wall motion), enhanced tetragonality (c/a), and increased unit-cell polarization evident from the amplitude of frozen phonon mode GM4 − corresponding to the zone center of the cubic Brillouin zone. The ferroelectric polarization observed in the average-cubic-structure state of Sr-doped BTSn12 is attributed to the cooperative polar off-centre displacements of A (Ba2+ /Sr2+ ) and B (Ti4+ /Sn4+ ) site cations along 〈100〉 and 〈111〉 directions, respectively. Further, Sr-doped BTSn12 has high dielectric constant and low loss which makes this material an important composition for various technological applications.