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

¹ Department of Physics, Indian Institute of Technology (BHU) - Varanasi, 221005, India
² Laser and Functional Materials Division, Raja Ramanna Centre for Advanced Technology - Indore, 452013, India

^(a) stripathi.phy@itbhu.ac.in

Received: 7 January 2020
Accepted: 28 April 2020

Abstract

The effect of 5% Sr substitution at the Ba site in Ba(Ti_1-x Sn_x)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.